tag:theconversation.com,2011:/fr/topics/kitchen-science-26291/articlesKitchen science – The Conversation2024-02-19T00:42:34Ztag:theconversation.com,2011:article/2020362024-02-19T00:42:34Z2024-02-19T00:42:34ZRun out of butter or eggs? Here’s the science behind substitute ingredients<figure><img src="https://images.theconversation.com/files/575492/original/file-20240213-28-yaukh5.jpg?ixlib=rb-1.1.0&rect=80%2C35%2C5784%2C3952&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://unsplash.com/photos/white-soup-on-brown-ceramic-bowl-wg5kaMtJ3Ts">Joanna Lopez/Unsplash</a></span></figcaption></figure><p>It’s an all too common situation – you’re busy cooking or baking to a recipe when you open the cupboard and suddenly realise you are missing an ingredient.</p>
<p>Unless you can immediately run to the shops, this can leave you scrambling for a substitute that can perform a similar function. Thankfully, such substitutes can be more successful than you’d expect.</p>
<p>There are a few reasons why certain ingredient substitutions work so well. This is usually to do with the chemistry and the physical features having enough similarity to the original ingredient to still do the job appropriately. </p>
<p>Let’s delve into some common ingredient substitutions and why they work – or need to be tweaked.</p>
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<h2>Oils versus butter</h2>
<p>Both butter and oils belong to a chemical class called <a href="https://chem.libretexts.org/Bookshelves/Introductory_Chemistry/Map%3A_Fundamentals_of_General_Organic_and_Biological_Chemistry_(McMurry_et_al.)/23%3A_Lipids/23.01%3A_Structure_and_Classification_of_Lipids">lipids</a>. It encompasses solid, semi-solid and liquid fats.</p>
<p>In a baked product the “job” of these ingredients is to provide flavour and influence the structure and texture of the finished item. In cake batters, lipids contribute to creating an emulsion structure – this means combining two liquids that wouldn’t usually mix. In the baking process, this helps to create a light, fluffy crumb.</p>
<p>One of the primary differences between butter and oil is that butter is only about 80% lipid (the rest being water), while <a href="https://www.nutritionadvance.com/types-of-cooking-fats-and-oils/">oil is almost 100% lipid</a>. Oil creates a softer crumb but is still a great fat to bake with.</p>
<p>You can use a wide range of oils from different sources, such as olive oil, rice bran, avocado, peanut, coconut, macadamia and many more. Each of these may impart different flavours.</p>
<p>Other “butters”, such as peanut and cashew butter, aren’t strictly butters but pastes. They impart different characteristics and can’t easily replace dairy butter, unless you also add extra oil.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/575161/original/file-20240213-30-j0czv9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A block of yellow butter in an open silver foil wrapper" src="https://images.theconversation.com/files/575161/original/file-20240213-30-j0czv9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/575161/original/file-20240213-30-j0czv9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=390&fit=crop&dpr=1 600w, https://images.theconversation.com/files/575161/original/file-20240213-30-j0czv9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=390&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/575161/original/file-20240213-30-j0czv9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=390&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/575161/original/file-20240213-30-j0czv9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=491&fit=crop&dpr=1 754w, https://images.theconversation.com/files/575161/original/file-20240213-30-j0czv9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=491&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/575161/original/file-20240213-30-j0czv9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=491&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Nut ‘butters’ can’t replace dairy butter because their composition is too different.</span>
<span class="attribution"><a class="source" href="https://pixabay.com/photos/butter-good-butter-fat-nourishment-3411126/">congerdesign/Pixabay</a></span>
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</figure>
<h2>Aquafaba or flaxseed versus eggs</h2>
<p>Aquafaba is the liquid you drain from a can of legumes – such as chickpeas or lentils. It contains proteins, kind of how egg white also contains proteins.</p>
<p>The proteins in egg white include albumins, and <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5912395/">aquafaba also contains albumins</a>. This is why it is possible to make meringue from egg whites, or from aquafaba if you’re after a vegan version.</p>
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Read more:
<a href="https://theconversation.com/how-to-make-the-perfect-pavlova-according-to-chemistry-experts-196485">How to make the perfect pavlova, according to chemistry experts</a>
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<p>The proteins act as a foam stabiliser – they hold the light, airy texture in the product. The concentration of protein in egg white is a bit higher, so it doesn’t take long to create a stable foam. Aquafaba requires more whipping to create a meringue-like foam, but it will bake in a similar way. </p>
<p>Another albumin-containing alternative for eggs is <a href="https://foodstruct.com/compare/seeds-flaxseed-vs-egg">flaxseed</a>. These seeds form a thick gel texture when mixed with a little water. The texture is similar to raw egg and can provide structure and emulsification in baked recipes that call for a small amount of egg white. </p>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/eggs-are-so-expensive-right-now-what-else-can-i-use-207837">Eggs are so expensive right now. What else can I use?</a>
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<h2>Lemon plus dairy versus buttermilk</h2>
<p>Buttermilk is the liquid left over after churning butter – it can be made from sweet cream, cultured/sour cream or whey-based cream. Buttermilk mostly <a href="https://www.journalofdairyscience.org/article/S0022-0302(06)72115-4/fulltext">contains proteins and fats</a>.</p>
<p>Cultured buttermilk has a somewhat tangy flavour. Slightly soured milk can be a good substitute as it contains similar components and isn’t too different from “real” buttermilk, chemically speaking.</p>
<p>One way to achieve slightly soured milk is by adding some lemon juice or cream of tartar to milk. Buttermilk is used in pancakes and baked goods to give extra height or volume. This is because the acidic (sour) components of buttermilk interact with baking soda, producing a light and airy texture. </p>
<p>Buttermilk can also influence flavour, imparting a slightly tangy taste to pancakes and baked goods. It can also be used in sauces and dressings if you’re looking for a lightly acidic touch. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/575163/original/file-20240213-16-ol6va7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A stack of fluffy pancakes dusted with sugar with a strawberry on top" src="https://images.theconversation.com/files/575163/original/file-20240213-16-ol6va7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/575163/original/file-20240213-16-ol6va7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/575163/original/file-20240213-16-ol6va7.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/575163/original/file-20240213-16-ol6va7.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/575163/original/file-20240213-16-ol6va7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=502&fit=crop&dpr=1 754w, https://images.theconversation.com/files/575163/original/file-20240213-16-ol6va7.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=502&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/575163/original/file-20240213-16-ol6va7.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=502&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Buttermilk is a common ingredient for making fluffy pancakes.</span>
<span class="attribution"><a class="source" href="https://pixabay.com/photos/pancakes-food-strawberry-plate-2801959/">Matthias_Groeneveld/Pixabay</a></span>
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<h2>Honey versus sugar</h2>
<p>Honey is a <a href="https://resources.perkinelmer.com/lab-solutions/resources/docs/APP_Analysis-of-Sugars-in-Honey-012101_01.pdf">complex sugar-based syrup</a> that includes floral or botanical flavours and aromas. Honey can be used in cooking and baking, adding both flavour and texture (viscosity, softness) to a wide range of products.</p>
<p>If you add honey instead of regular sugar in baked goods, keep in mind that honey imparts a softer, moister texture. This is because it contains more moisture and is a humectant (that is, it likes to hold on to water). It is also less crystalline than sugar, unless you leave it to crystallise.</p>
<p>The intensity of sweetness can also be different – some people find honey is sweeter than its granular counterpart, so you will want to adjust your recipes accordingly.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/575164/original/file-20240213-26-6c2r7t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Close-up of a slice of bread with golden honey pooling on top" src="https://images.theconversation.com/files/575164/original/file-20240213-26-6c2r7t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/575164/original/file-20240213-26-6c2r7t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/575164/original/file-20240213-26-6c2r7t.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/575164/original/file-20240213-26-6c2r7t.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/575164/original/file-20240213-26-6c2r7t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=502&fit=crop&dpr=1 754w, https://images.theconversation.com/files/575164/original/file-20240213-26-6c2r7t.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=502&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/575164/original/file-20240213-26-6c2r7t.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=502&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Honey has a complex flavour and can taste sweeter than regular sugar.</span>
<span class="attribution"><a class="source" href="https://pixabay.com/photos/honey-bread-spoon-bio-nature-752145/">estelheitz/Pixabay</a></span>
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<h2>Gluten-free versus regular flour</h2>
<p>Sometimes you need to make substitutions to avoid allergens, such as gluten – the protein found in cereal grains such as wheat, rye, barley and others. </p>
<p>Unfortunately, gluten is also the component that gives a nice, stretchy, squishy quality to bread.</p>
<p>To build this characteristic in a gluten-free product, it’s necessary to have a mixture of ingredients that work together to mimic this texture. Common ingredients used are corn or rice flour, xanthan gum, which acts as a binder and moisture holder, and tapioca starch, which is a good water absorbent and can aid with binding the dough. </p>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/thank-glutens-complex-chemistry-for-your-light-fluffy-baked-goods-216869">Thank gluten's complex chemistry for your light, fluffy baked goods</a>
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<img src="https://counter.theconversation.com/content/202036/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Paulomi (Polly) Burey does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>In a pinch, the water from a can of beans can replace eggs. But how does that work, exactly?Paulomi (Polly) Burey, Associate Professor (Food Science), University of Southern QueenslandLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2161592023-12-26T20:30:30Z2023-12-26T20:30:30ZThe science of the ideal salad dressing<figure><img src="https://images.theconversation.com/files/558179/original/file-20231107-19-8sujdg.jpg?ixlib=rb-1.1.0&rect=626%2C107%2C3159%2C2310&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/salad-dressing-ingredients-olive-oil-honey-1808249242">HannaTor/Shutterstock</a></span></figcaption></figure><p>Summer means salads. And salads are even more delicious with a good dressing.</p>
<p>Most salad dressings are temporarily stable mixtures of oil and water known as emulsions.</p>
<p>But how do salad dressing emulsions form? And how can we enhance our emulsions for better salads and more?</p>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/how-to-make-the-perfect-pavlova-according-to-chemistry-experts-196485">How to make the perfect pavlova, according to chemistry experts</a>
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<h2>Oil and water don’t mix</h2>
<p>It’s accepted wisdom that oil and water don’t mix. The water and oil molecules have distinct chemical properties that don’t interact well together. </p>
<p>You may have seen this if you’ve attempted to make a salad dressing by shaking together oil and vinegar (which is mostly water), which gives a temporary suspension that quickly separates.</p>
<p>There is a large energy cost to breaking apart and mixing the water and oil layers. The secret to blending them together is to add an extra ingredient known as a “surfactant” or emulsifier.</p>
<p>The name surfactant is derived from “surface active”. It highlights that these molecules work at the surface or interface to bridge the interactions between the oil and water. This is similar to how <a href="https://theconversation.com/what-is-sodium-lauryl-sulfate-and-is-it-safe-to-use-125129">detergents</a> are able to remove grease from your dishes.</p>
<p>Many vinaigrette recipes call for emulsifiers without specifically mentioning their crucial emulsifying role. </p>
<p>Key examples are mustard and garlic, which contain “mucilage” – a mix of carbohydrates – that can act as emulsifiers. </p>
<p>So if your vinegar/oil salad dressings are separating, make sure you’re adding enough of these ingredients (which also contain <a href="https://theconversation.com/hate-vegetables-you-might-have-super-taster-genes-74428">wonderful flavour chemicals</a>).</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/557661/original/file-20231106-21-zqku7t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Three salad dressings sit on a bench; one with chilli seeds, one creamy yoghurt-based dressing and one mustard and oil emulsion." src="https://images.theconversation.com/files/557661/original/file-20231106-21-zqku7t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/557661/original/file-20231106-21-zqku7t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/557661/original/file-20231106-21-zqku7t.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/557661/original/file-20231106-21-zqku7t.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/557661/original/file-20231106-21-zqku7t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/557661/original/file-20231106-21-zqku7t.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/557661/original/file-20231106-21-zqku7t.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Many vinaigrette recipes call for emulsifiers such as mustard.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/variety-homemade-sauces-salad-dressings-mason-571747333">Shutterstock</a></span>
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<p>Commercial salad dressings also contain naturally sourced emulsifying carbohydrates. These will often be listed on the ingredients as generic “vegetable gum” or similar, and you may need to <a href="https://theconversation.com/busting-the-myth-that-all-food-additives-are-bad-a-quick-guide-for-label-readers-82883">read the label</a> and delve a little deeper into the <a href="https://www.foodstandards.gov.au/consumer/additives/additiveoverview/Documents/Food%20Additive%20Code%20Numbers%20%28July%202014%29.pdf">food additive number</a> to find out the source. </p>
<p>Researchers have raised questions about <a href="https://theconversation.com/food-additives-and-chronic-disease-risk-what-role-do-emulsifiers-play-38492">synthetic emulsifiers used in processed food</a>, as studies in mice suggest they have health risks. It’s too early to say exactly what this means for humans. </p>
<h2>Shake it ‘til you make it</h2>
<p>Mixing is key to dispersing oil in water. While shaking a jar is convenient, a whisk or food processor will give a more complete emulsion. The white (or opaque) colour of many emulsions is due to the formation of microdroplets that scatter light. </p>
<p>These mechanical mixing methods are even more essential for the formation of so-called “permanent emulsions” such as mayonnaise. </p>
<p>Mayonnaise is an emulsion of oil in water, but egg yolk is the key emulsifier. Egg yolks contain long molecules called <a href="https://link.springer.com/referenceworkentry/10.1007/978-3-642-36605-5_28">phospholipids</a> that are able to interact with both the oil layer and the water. Mayonnaise is an impressively stable emulsion, which is why is can be sold in a shelf-stable form.</p>
<p>But it isn’t infinitely stable; heating the mayonnaise emulsion will cause it to split. Perhaps you’ve hurriedly prepared a potato salad and added a mayonnaise-based dressing before the potatoes have cooled down?</p>
<p>Or toasted a sandwich spread with mayonnaise? (Incidentally, adding mayonnaise to the <em>outside</em> of a toasted sandwich is an excellent path to some <a href="https://theconversation.com/kitchen-science-from-sizzling-brisket-to-fresh-baked-bread-the-chemical-reaction-that-makes-our-favourite-foods-taste-so-good-58577">delicious and crispy chemical reactions</a>.) </p>
<p>The heat destabilises the emulsion and the separate oil and water phases will reform. Depending on the mixture, split emulsions may be recovered by adding more emulsifier and re-whisking or re-mixing.</p>
<p>Hollandaise sauce is a notoriously difficult emulsion to prepare. The traditional hollandaise method involves whisking egg yolk, water, and lemon juice over a low heat, then slowly adding melted butter with further whisking. Not only can the emulsion split, but you can also overcook the added emulsifying egg yolk. </p>
<p>The key to a successful hollandaise emulsion is separating the butter into fine, dispersed droplets, giving a thick and opaque mixture, but without cooking the eggs. Adding the butter too quickly or without sufficient mixing can give a split sauce. </p>
<p>Using an <a href="https://www.seriouseats.com/foolproof-2-minute-hollandaise-recipe">immersion blender</a> can help, as can controlling the temperature of the melted butter. You might get a more consistently emulsified sauce with far less strain on your wrists. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/557663/original/file-20231106-28-8oczkp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A person makes mayonnaise using a mechanical stick blender." src="https://images.theconversation.com/files/557663/original/file-20231106-28-8oczkp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/557663/original/file-20231106-28-8oczkp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=371&fit=crop&dpr=1 600w, https://images.theconversation.com/files/557663/original/file-20231106-28-8oczkp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=371&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/557663/original/file-20231106-28-8oczkp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=371&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/557663/original/file-20231106-28-8oczkp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=466&fit=crop&dpr=1 754w, https://images.theconversation.com/files/557663/original/file-20231106-28-8oczkp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=466&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/557663/original/file-20231106-28-8oczkp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=466&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Mechanical mixing methods are even more essential for the formation of ‘permanent emulsions’ such as mayonnaise.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/concept-making-homemade-mayonnaise-natural-healthy-1829111036">Shutterstock</a></span>
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<h2>You’ve got me feeling emulsions</h2>
<p>Emulsions are used in many more places than salads and sauces. Most medicated creams, cosmetics and lotions are emulsions of oils and water, which is why they look white. </p>
<p>Gardeners might be familiar with a mixture known as “<a href="https://www.abc.net.au/gardening/how-to/horticultural-oils/9428876">white oil</a>” – a mixture of vegetable oil and detergent. This brew, when diluted in water, is an inexpensive, effective, yet mild insecticide. Commercial versions often contain other pesticides, so make sure you read the label.</p>
<p>Modern <a href="https://www.acs.org/education/whatischemistry/landmarks/acrylicemulsion.html">acrylic paints use emulsions</a> for both their manufacturing and application. The emulsions suspend the paint polymers in a water base.</p>
<p>The water from the paint evaporates, leaving a film of paint polymers that can’t be re-dispersed into water. This clever chemical trick has saved huge quantities of oil-derived solvents from being used, <a href="https://theconversation.com/why-solvents-can-affect-brain-health-even-at-low-levels-of-exposure-98081">inhaled</a>, and emitted into the environment from traditional oil-based paints.</p>
<p>Modern vaccines use <a href="https://theconversation.com/adjuvants-the-unsung-heroes-of-vaccines-156548">emulsions to increase the immune systems response</a>. Other common emulsions are inks, <a href="https://theconversation.com/how-does-ice-cream-work-a-chemist-explains-why-you-cant-just-freeze-cream-and-expect-results-205038">ice cream</a>, margarine and hair products, to name just a few.</p>
<p>So next time you’re making a salad, check your emulsions. Opposites don’t attract, but mixing them with the right chemistry can give a delicious result.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/kitchen-science-the-many-wonders-of-humble-flour-59310">Kitchen Science: the many wonders of humble flour</a>
</strong>
</em>
</p>
<hr>
<img src="https://counter.theconversation.com/content/216159/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Nathan Kilah does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>There is a large energy cost to breaking apart and mixing the water and oil layers. The secret to blending them is to add an extra ingredient known as a ‘surfactant’ or emulsifier, like mustard.Nathan Kilah, Senior Lecturer in Chemistry, University of TasmaniaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2195892023-12-20T22:11:26Z2023-12-20T22:11:26ZHow to make gravy (using chemistry)<figure><img src="https://images.theconversation.com/files/566166/original/file-20231217-26-g6qyx4.jpg?ixlib=rb-1.1.0&rect=0%2C8%2C5472%2C3628&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/caucasian-male-hand-pouring-gravy-on-1256033632">OKMG/Shutterstock</a></span></figcaption></figure><p>“Gravy Day” is a relatively new date in the Australian calendar. Paul Kelly’s song <a href="https://theconversation.com/humbug-tinsel-and-gravy-in-search-of-the-perfect-christmas-pop-song-88924">How to Make Gravy</a> tells the story of a prisoner (Joe) writing to his brother on December 21. Joe laments missing the family Christmas celebrations and asks who will make gravy for the roast lunch in his absence.</p>
<p>While a roast may not be everyone’s idea of the perfect <a href="https://theconversation.com/a-festive-feast-of-fish-and-fruit-the-creation-of-the-australian-christmas-dinner-151201">Christmas feast</a>, “Gravy Day” does give the opportunity to discuss the chemistry involved in making gravy – a thickened sauce made from drippings collected from roasted meats.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/FozoWgvh-m4?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Paul Kelly performs his song How To Make Gravy.</span></figcaption>
</figure>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/how-does-ice-cream-work-a-chemist-explains-why-you-cant-just-freeze-cream-and-expect-results-205038">How does ice cream work? A chemist explains why you can't just freeze cream and expect results</a>
</strong>
</em>
</p>
<hr>
<h2>Give my love to Angus (beef?)</h2>
<p>Roasting meat sets off a cascade of chemical reactions, producing myriad new flavour chemicals. More than <a href="https://link.springer.com/chapter/10.1007/978-1-4615-2143-3_10#:%7E:text=This%20has%20resulted%20in%20the,and%20lean%20components%20of%20meat.">1,000</a> flavour compounds have been identified in roasted meats.</p>
<p>Each chemical gives its unique characteristics to the taste and smell of the finished roast. The chemical <a href="https://www.sciencedirect.com/science/article/pii/S0308814698000764">12-methyltridecanal</a> helps give roast beef its “beefy” flavour, while the sulfur-containing compound <a href="https://www.sciencedirect.com/science/article/pii/S0963996922004422">2-methyl-3-furanthiol</a> is more often found in roast chicken.</p>
<p>There are three main types of chemical reactions taking place when roasting meats that produce flavour chemicals. </p>
<p>The <a href="https://theconversation.com/kitchen-science-from-sizzling-brisket-to-fresh-baked-bread-the-chemical-reaction-that-makes-our-favourite-foods-taste-so-good-58577">Maillard reaction</a> is responsible for both colour and flavour. This broad reaction type takes place between amino acids from the protein and sugars and simple carbohydrates found in the meat. </p>
<p>The Maillard reaction is also the chemistry responsible for many favourite flavours, including roasted coffee, chocolate, steak, toast and more. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/566164/original/file-20231217-27-m8n75f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A roast chicken is displayed on a table." src="https://images.theconversation.com/files/566164/original/file-20231217-27-m8n75f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/566164/original/file-20231217-27-m8n75f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/566164/original/file-20231217-27-m8n75f.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/566164/original/file-20231217-27-m8n75f.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/566164/original/file-20231217-27-m8n75f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/566164/original/file-20231217-27-m8n75f.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/566164/original/file-20231217-27-m8n75f.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The sulfur-containing compound 2-methyl-3-furanthiol is often found in roast chicken.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/homemade-chicken-rotisserie-thyme-lemon-closeup-1574170006">AS Foodstudio/Shutterstock</a></span>
</figcaption>
</figure>
<h2>A hundred degrees, even more maybe</h2>
<p>The other main type of reaction occurring in a hot oven is the breakdown of fats by “<a href="https://doi.org/10.1016/j.foodres.2022.111385">lipid degradation</a>”. This can form hundreds of different chemical compounds. Many of these chemicals are described as “fatty”, “tallowy”, or smell like fried foods. </p>
<p>The unique fat profiles found in different animals translate to the profile of flavour chemicals that form from lipid degradation when roasted. Further flavour compounds can arise through the third type of reactions combining products of Maillard reactions and lipid degradation.</p>
<p>One specific flavour compound identified as having a “gravy aroma” is known as <a href="https://pubs.acs.org/doi/10.1021/jf9023189">3-mercapto-2-methylpentan-1-ol</a>. This compound comes from roasted vegetables, so including some veggies in your roasting pan will give you more depth of gravy flavour. Also, “cutting onions” is a useful excuse if listening to How to Make Gravy gets you feeling emotional.</p>
<h2>The treasure and the trash</h2>
<p>Roasting meats causes the fats to “render” and separate from the meat as a liquid. The fat pools in the tray with flavour-rich meat juices.</p>
<p>While the fat and the water both carry flavour compounds, too much fat can give the finished gravy an unpleasant mouth feel, or can separate into layers when served.</p>
<p>It’s worth pouring off the pan juices into a jug to allow the fat to separate from the liquid so you can control how much fat you’re adding. Be sure to dispose of the excess fat responsibly – <a href="https://theconversation.com/why-shouldnt-i-pour-oil-or-paint-down-the-sink-and-what-should-i-do-instead-206604">don’t pour it down the drain</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/566165/original/file-20231217-19-yw2q11.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Meat juices drip off a spoon into a tray of roasted meats." src="https://images.theconversation.com/files/566165/original/file-20231217-19-yw2q11.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/566165/original/file-20231217-19-yw2q11.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=401&fit=crop&dpr=1 600w, https://images.theconversation.com/files/566165/original/file-20231217-19-yw2q11.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=401&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/566165/original/file-20231217-19-yw2q11.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=401&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/566165/original/file-20231217-19-yw2q11.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=504&fit=crop&dpr=1 754w, https://images.theconversation.com/files/566165/original/file-20231217-19-yw2q11.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=504&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/566165/original/file-20231217-19-yw2q11.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=504&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Roasting meats causes the fats to ‘render’ and separate from the meat as a liquid.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/closeup-spoon-juice-sauce-over-cooked-1005879244">Jevanto Productions/Shutterstock</a></span>
</figcaption>
</figure>
<h2>Just add flour…</h2>
<p>Flour (or, more specifically, starch) is the secret ingredient of a good gravy. Starches are <a href="https://www.sciencedirect.com/science/article/pii/S0168945222000474">large complex chemicals</a> that are made up of lots of sugars joined together. </p>
<p>Starch granules are tightly packed and swell greatly when they absorb water. The swollen starch molecules forms a gel-like network that traps water and oil to give a thickened gravy.</p>
<p>Wheat flour is most often used as the starch source. Corn and arrowroot starch can also be used. They have a higher percentage of starch than flour and a more neutral flavour. </p>
<p>Wheat starch typically requires a larger quantity to be added and longer cooking to form a paste. Whichever starch you use, don’t add it too quickly or without mixing as you’ll form lumps.</p>
<h2>…salt, red wine, and a dollop of tomato sauce</h2>
<p>Salt is a common ingredient when preparing roast meats, both on the surface of the meat to draw out moisture and as a flavouring agent. The pan juices are typically concentrated as part of the gravy making process. </p>
<p>Make sure you taste the gravy before seasoning, as salt will be concentrated by heating. </p>
<p>Additional flavour components can be introduced by adding red wine, sherry, stock, or tomato sauce. These ingredients will broaden the flavour profile through sweetness (sugar), acidity (vinegar, citric and malic acids), and umami in the case of tomato sauce (natural glutamates, such as those found in MSG). Some folk even add Vegemite to their gravy for an extra umami boost.</p>
<h2>I bet it will taste the same</h2>
<p>If you happen to have screwed up your gravy this time, or are after convenience, then you can turn to an instant gravy powder. The main ingredient is typically maltodextrin or another corn-derived (and possibly chemically modified) starch.</p>
<p>Shelf-stable powdered fats, salt, colours, and a range of <a href="https://theconversation.com/busting-the-myth-that-all-food-additives-are-bad-a-quick-guide-for-label-readers-82883">flavour additives</a> will be present in varying amounts depending on the style and price point of the product.</p>
<p>The advantages of the instant version are speed and uniformity due to the carefully controlled commercial production.</p>
<p>So unlike Joe’s concerns for his family’s gravy, an instant gravy will be more likely to taste the same, regardless of who ends up making it.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/how-to-make-the-perfect-pavlova-according-to-chemistry-experts-196485">How to make the perfect pavlova, according to chemistry experts</a>
</strong>
</em>
</p>
<hr>
<img src="https://counter.theconversation.com/content/219589/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Nathan Kilah does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Roasting meat sets off a cascade of chemical reactions. With a bit of kitchen chemistry know-how, you can use these reactions to your advantage when you make gravy.Nathan Kilah, Senior Lecturer in Chemistry, University of TasmaniaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2050382023-07-24T04:17:13Z2023-07-24T04:17:13ZHow does ice cream work? A chemist explains why you can’t just freeze cream and expect results<figure><img src="https://images.theconversation.com/files/538876/original/file-20230724-79526-ui0tqq.jpg?ixlib=rb-1.1.0&rect=181%2C623%2C6237%2C3842&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/homemade-neopolitan-ice-cream-vanilla-chocolate-1093782722">Shutterstock</a></span></figcaption></figure><p>Ice cream seems like a simple concept. Take some dairy, add some sugar and flavours, and freeze.</p>
<p>But to get a perfectly creamy, smoothly textured frozen treat, we need more than just a low temperature – it takes a careful interplay of chemistry and three states of matter: solid, liquid and gas.</p>
<h2>What’s in the box?</h2>
<p>Commercial ice cream includes many ingredients: air, water, milk fat, so-called milk solids (mainly milk proteins and lactose), sweeteners, stabilisers, emulsifiers and flavours. The ingredients are mixed and <a href="https://theconversation.com/e-coli-in-milk-wont-necessarily-make-you-sick-but-it-signals-risks-from-other-bacteria-119229">pasteurised for food safety</a>.</p>
<p>Homemade ice creams tend to use milk, heavy cream, sugar and flavourings, such as fruit, berries, or chocolate. The exact quantities vary with the recipe, but the processing steps are similar.</p>
<p><a href="https://www.hsph.harvard.edu/nutritionsource/milk/">Milk is composed</a> of everything a young cow needs to grow and develop – water, fats, carbohydrates, proteins, minerals and vitamins. These components respond in different ways when they are frozen.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/crying-over-plant-based-milk-neither-science-nor-history-favours-a-dairy-monopoly-123852">Crying over plant-based milk: neither science nor history favours a dairy monopoly</a>
</strong>
</em>
</p>
<hr>
<h2>First, the crystals</h2>
<p>As the mixture of ice cream ingredients is cooled down, small clusters of water molecules assemble to form <a href="https://theconversation.com/how-do-snowflakes-form-is-each-snowflake-really-unique-why-is-some-snow-light-and-fluffy-or-heavy-the-amazing-science-of-snow-196269">tiny ice crystals</a>. The size of the ice crystals is responsible for the mouth feel of the ice cream – the <a href="https://ift.onlinelibrary.wiley.com/doi/full/10.1111/j.1541-4337.2009.00101.x">smaller the crystals, the smoother the feel</a>.</p>
<p>If the crystallisation is not well controlled, these crystals can get very large. Ice cream makers (commercial or for home use) ensure small ice crystals by agitating or beating the liquid as it freezes. This keeps the water molecules moving and prevents the crystals from growing larger.</p>
<p>The mixing process also incorporates air, which is the secret ingredient to give ice cream a lighter texture.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/526974/original/file-20230518-23-jkyrps.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Close up of ivory coloured ice cream being churned in a stainless steel container" src="https://images.theconversation.com/files/526974/original/file-20230518-23-jkyrps.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/526974/original/file-20230518-23-jkyrps.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/526974/original/file-20230518-23-jkyrps.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/526974/original/file-20230518-23-jkyrps.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/526974/original/file-20230518-23-jkyrps.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/526974/original/file-20230518-23-jkyrps.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/526974/original/file-20230518-23-jkyrps.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Without mixing during the freezing process, the ice crystals in the milk or cream will be too large to yield the texture that defines ice cream.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/close-on-industrial-ice-cream-mixing-1584957778">Shutterstock</a></span>
</figcaption>
</figure>
<h2>Next, the fat</h2>
<p>The fat in the milk exists as globules surrounded by proteins. These proteins bridge the fat and the water, helping to keep the fats suspended. (Milk looks white because light scatters off these fat globules.)</p>
<p>These dairy fat molecules have different properties at different temperatures. At room temperature they are semi-solids (like butter), and are about two-thirds solid when at 0°C. </p>
<p>The fat globules can stick together – that’s why you get a layer of cream on top of unprocessed milk. A process called <a href="https://iufost.org/iufostold/wp-content/uploads/2020/05/98-Milk-Homogenization.pdf">homogenisation</a> forces the milk through a small opening under very high pressure, breaking large fat globules down into smaller ones. This process makes many small fat globules – as many as a trillion per litre. Homogenised milk ensures the mixture will freeze evenly, and separated fats won’t get stuck to the mixing machinery.</p>
<p>Freezing the fat globules makes them clump together, with the surrounding proteins acting as bridges to other fat molecules and to the ice crystals. These fats melt in your mouth, giving a creamy feel and taste.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/slip-slop-slurp-the-surprising-science-of-sunscreen-sand-and-ice-cream-169155">Slip, slop, slurp! The surprising science of sunscreen, sand and ice cream</a>
</strong>
</em>
</p>
<hr>
<h2>Then, the sugar</h2>
<p>The sugar and other dissolved ingredients in milk are also essential to the final texture of ice cream. The presence of sugars in the water lowers the mixture’s freezing temperature to below 0°C. </p>
<p>Here’s why that’s important. As ice crystals start to form, the concentration of sugars and other dissolved materials in the <a href="https://www.tandfonline.com/doi/full/10.1081/FRI-100100289">unfrozen liquid increases</a>, which further <a href="https://theconversation.com/salt-doesnt-melt-ice-heres-how-it-actually-makes-winter-streets-safe-110870">lowers its freezing point</a>. By the time the majority of the ice crystals have formed, the resulting liquid is very concentrated in sugars. </p>
<p>This concentrated liquid, known as the “serum”, bridges <em>between</em> the ice crystals, solid fat globules and air bubbles. The serum remains a liquid well below 0°C and adds enough flexibility to the mixture so the ice cream can still be scooped or shaped.</p>
<p>In this way, the unique chemical properties of water, fats, proteins and sugars come together with air to give the solid, liquid and gas mixture we know and love.</p>
<h2>Not everything is ‘ice cream’</h2>
<p>What’s called “ice cream” is actually governed by a <a href="https://www.legislation.gov.au/Series/F2015L00424">food standards code</a>. That’s why not all frozen desserts can be legally called ice cream, because they don’t contain enough milk fat.</p>
<p>There are lots of variations on the standard ice cream recipe. Gelato uses more sugar, incorporates less air, and typically has less fats and other solids. Sorbets do away with the dairy and typically contain more sugar, but have historically used egg or gelatin as a protein source. </p>
<p>Regardless of the exact recipe, the fundamental ice crystal formation, fat solidification, and serum phase separation steps are the same.</p>
<p>Product names like “soft serve”, “dairy dessert”, or “ice confection” are often an indication the ingredient list includes vegetable fats rather than more expensive milk fats. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/526980/original/file-20230518-2311-9i1j4h.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A hand holding a waffle cone under the nozzle of a machine dispensing pink and white soft serve" src="https://images.theconversation.com/files/526980/original/file-20230518-2311-9i1j4h.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/526980/original/file-20230518-2311-9i1j4h.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/526980/original/file-20230518-2311-9i1j4h.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/526980/original/file-20230518-2311-9i1j4h.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/526980/original/file-20230518-2311-9i1j4h.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/526980/original/file-20230518-2311-9i1j4h.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/526980/original/file-20230518-2311-9i1j4h.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Technically, soft serve isn’t ice cream.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/soft-ice-cream-machine-1312164440">Shutterstock</a></span>
</figcaption>
</figure>
<p>Soft serve products are also formed by agitation as the mixture freezes, but tend to contain less air than ice cream you’d buy in a tub, due to the constant agitation inside the dispensing machine.</p>
<p>Icy poles, ice blocks, freezies, or freeze pops (depending on <a href="https://theconversation.com/togs-or-swimmers-why-australians-use-different-words-to-describe-the-same-things-52007">your local phraseology</a>) and other “water ices” are frozen inside a mould or plastic tubing. The shape of the mould limits the ability to stir the mixture, so the freezing process is typically done “quiescently”, meaning at rest. The crystallisation of the ice is not well controlled, and you may have experienced large crystals that have grown (technically “seeded”) from the popsicle stick.</p>
<p>Humanity has enjoyed ice cream for centuries. It’s a marvellously versatile food with endless variations of flavours, additives, and toppings coupled with memories of happiness, comfort, indulgence and nostalgia. And plenty of chemistry, too.</p><img src="https://counter.theconversation.com/content/205038/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Nathan Kilah does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>It might seem like a simple concept, but to get ice cream right, you need three states of matter and a delicate interplay of chemistry.Nathan Kilah, Senior Lecturer in Chemistry, University of TasmaniaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2046922023-06-12T20:00:49Z2023-06-12T20:00:49ZDo you need to wash rice before cooking? Here’s the science<figure><img src="https://images.theconversation.com/files/527941/original/file-20230524-21-2zy4a7.jpg?ixlib=rb-1.1.0&rect=242%2C44%2C5595%2C3943&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/jasmine-rice-cooking-electric-cooker-steam-1786700948">Shutterstock</a></span></figcaption></figure><p>Rice is a staple food for billions of people in Asia and Africa. It’s also a versatile ingredient for many iconic dishes from around the world, including dolmades from Greece, risottos from Italy, paella from Spain and rice puddings from the United Kingdom.</p>
<p>Despite its universal appeal, the question asked in every kitchen, be it a professional one or your own home, is whether you should pre-wash (or rinse) your rice before cooking.</p>
<h2>What do chefs and cooks say?</h2>
<p>Culinary experts claim pre-washing rice <a href="https://www.americastestkitchen.com/articles/3946-do-you-really-need-to-rinse-your-rice">reduces the amount of starch</a> coming from the rice grains. You can see this in the cloudy rinse water, which <a href="https://www.sciencedirect.com/science/article/pii/S0924224416300619">studies have shown</a> to be the free starch (amylose) on the surface of the rice grain produced by the milling process. </p>
<p>In culinary circles, washing is advocated for some dishes when a separated grain is sought after. Yet for other dishes such as risottos, paella and rice puddings (where you need a sticky, creamy effect), washing is avoided.</p>
<p>Other factors, such as the type of rice, family tradition, local health warnings and even the perceived time and effort required will influence whether people pre-wash their rice.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/527943/original/file-20230524-19-867jpc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Close-up of a golden mushroom risotto with flakes of parmesan on top" src="https://images.theconversation.com/files/527943/original/file-20230524-19-867jpc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/527943/original/file-20230524-19-867jpc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/527943/original/file-20230524-19-867jpc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/527943/original/file-20230524-19-867jpc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/527943/original/file-20230524-19-867jpc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/527943/original/file-20230524-19-867jpc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/527943/original/file-20230524-19-867jpc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">For risotto, traditionally cooked with arborio rice, rinsing the rice is not recommended, to help enhance the creamy texture of the dish.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/macro-close-small-portion-fungi-risotto-173037734">Shutterstock</a></span>
</figcaption>
</figure>
<h2>Is there evidence that washing rice makes it less sticky?</h2>
<p>A <a href="https://www.sciencedirect.com/science/article/pii/S0308814618313293#b0005">recent study</a> compared the effect of washing on the stickiness and hardness of three different types of rice from the same supplier. The three types were glutinous rice, medium grain rice and jasmine rice. These different rices were either not washed at all, washed three times with water, or washed ten times with water.</p>
<p>Contrary to what chefs will tell you, this study showed the washing process had no effect on the stickiness (or hardness) of the rice. </p>
<p>Instead, the researchers demonstrated the stickiness was not due to the surface starch (amylose), but rather a different starch called amylopectin that is leached out of the rice grain during the cooking process. The amount leached differed between the types of rice grains.</p>
<p>So, it’s the variety of rice – rather than washing – that’s critical to the stickiness. In this study, glutinous rice was the stickiest, while medium grain rice and jasmine rice were less sticky, and also harder as tested in the laboratory. (Hardness is representative of the textures associated with biting and chewing.)</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/527944/original/file-20230524-29-eqan30.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Close-up of a fried rice dish with chicken, vegetables and a sunny side egg on top" src="https://images.theconversation.com/files/527944/original/file-20230524-29-eqan30.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/527944/original/file-20230524-29-eqan30.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/527944/original/file-20230524-29-eqan30.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/527944/original/file-20230524-29-eqan30.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/527944/original/file-20230524-29-eqan30.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/527944/original/file-20230524-29-eqan30.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/527944/original/file-20230524-29-eqan30.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Fried rice dishes, such as nasi goreng, tend to use less sticky varieties of rice, leading to a more fluffy texture.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/fried-rice-nasi-goreng-chicken-egg-759039364">Shutterstock</a></span>
</figcaption>
</figure>
<h2>You may still want to wash your rice, though</h2>
<p>Traditionally rice was washed to rinse off dust, insects, little stones and bits of husk left from the rice hulling process. This may still be important for some regions of the world where the processing is not as meticulous, and may provide peace of mind for others. </p>
<p>More recently, with the heavy use of plastics in the food supply chain, microplastics have been found in our foods, including rice. The washing process has been shown to rinse up to 20% of the plastics <a href="https://www.sciencedirect.com/science/article/pii/S0304389421007421?via%3Dihub">from uncooked rice</a>.</p>
<p>This same study found that irrespective of the packaging (plastic or paper bags) you buy rice in, it contains the same level of microplastics. The researchers also showed plastics in (pre-cooked) instant rice have been found to be fourfold higher than in uncooked rice. If you pre-rinse instant rice, you could reduce plastics by 40%.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/youre-eating-microplastics-in-ways-you-dont-even-realise-97649">You're eating microplastics in ways you don't even realise</a>
</strong>
</em>
</p>
<hr>
<p>Rice is also known to contain relatively high levels of arsenic, due to the crop absorbing more arsenic as it grows. <a href="https://pubmed.ncbi.nlm.nih.gov/23245893/">Washing rice has been shown to remove</a> about 90% of bio-accessible arsenic, but it also rinses out a large amount of other nutrients important for our health, including copper, iron, zinc and vanadium.</p>
<p>For some people, rice offers a small percentage of their daily intake of these nutrients and hence will have a small impact on their health. But for populations that consume large amounts of heavily washed rice daily, it could impact their overall nutrition.</p>
<p><a href="https://pubmed.ncbi.nlm.nih.gov/29363749/">Another study</a> looked at other heavy metals, lead and cadmium, in addition to arsenic; it found that pre-washing decreased levels of all these from between 7–20%. The <a href="https://www.who.int/news-room/fact-sheets/detail/arsenic#:%7E:text=Long%2Dterm%20exposure%20to%20arsenic,increased%20deaths%20in%20young%20adults.">World Health Organization has warned </a> of the risk of arsenic exposure from water and food.</p>
<p>Arsenic levels in rice vary depending on where it’s grown, the cultivars of rice and the ways it is cooked. The best advice remains to pre-wash your rice and ensure you <a href="https://www.eatforhealth.gov.au/guidelines/australian-guide-healthy-eating">consume a variety of grains</a>. The most <a href="https://pubmed.ncbi.nlm.nih.gov/16124284/">recent study in 2005</a> found that the highest level of arsenic was in the United States. However it is important to keep in mind that arsenic is present in <a href="https://www.sciencedirect.com/science/article/pii/S0048969714010614">other foods</a> including products made from rice (cakes, crackers, biscuits and cereals), seaweed, seafood and vegetables.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/high-levels-of-cancer-causing-arsenic-in-rice-so-why-isnt-it-regulated-in-our-food-33691">High levels of cancer-causing arsenic in rice – so why isn’t it regulated in our food?</a>
</strong>
</em>
</p>
<hr>
<h2>Can washing rice prevent bacteria?</h2>
<p>In short, no. Washing rice will have no effect on the bacterial content of the cooked rice, as high cooking temperatures will kill all bacteria present.</p>
<p>What is more concerning is how long you store cooked rice or washed rice at room temperature. Cooking rice does not kill the bacterial spores from a pathogen called <em><a href="https://www.foodstandards.gov.au/consumer/safety/foodborne-illness/Pages/bacillus-cereus-.aspx">Bacillus cereus</a></em>.</p>
<p>If wet rice or cooked rice is kept at room temperature, this can activate the bacterial spores and they begin to grow. These bacteria then produce toxins which can not be deactivated by cooking or re-heating; these toxins can cause severe gastrointestinal disease. So, make sure you avoid keeping washed or cooked rice at room temperature for too long.</p><img src="https://counter.theconversation.com/content/204692/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Evangeline Mantzioris is affiliated with Alliance for Research in Nutrition, Exercise and Activity (ARENA) at the University of South Australia. Evangeline Mantzioris has received funding from the National Health and Medical Research Council, and has been appointed to the National Health and Medical Research Council Dietary Guideline Expert Committee.</span></em></p>Some people swear by it, while others don’t bother. But what does the evidence say about washing rice, and when should you do it?Evangeline Mantzioris, Program Director of Nutrition and Food Sciences, Accredited Practising Dietitian, University of South AustraliaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2030582023-05-02T03:43:47Z2023-05-02T03:43:47ZHere’s why your freezer smells so bad – and what you can do about it<figure><img src="https://images.theconversation.com/files/523344/original/file-20230427-28-gy0qd6.jpg?ixlib=rb-1.1.0&rect=206%2C35%2C2568%2C1742&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">TY Lim/Shutterstock</span></span></figcaption></figure><p>Most people would expect a freezer can keep perishable food fresh and safe from spoilage for many months. Unfortunately, this is not always the case.</p>
<p>Have you ever noticed a funky smell in your freezer? Where does it come from and what can be done to fix the problem?</p>
<h2>Hardy microbes and pungent chemicals</h2>
<p>There are several causes for bad smells coming from your freezer. Typically, the culprits are microbes – bacteria, yeasts and moulds.</p>
<p>Although a freezer dramatically slows down the growth of most common spoilage microbes, some can still thrive if the temperature rises above -18°C (<a href="https://www.foodsafety.asn.au/topic/fridge-freezer-foodsafety/">the recommended freezer temperature</a>). This can happen if there is a power outage for more than a few hours, or if you put something hot straight in the freezer.</p>
<p>Food spills and open containers provide an opportunity for microbes to get to work. It’s also worth noting that many microbes will <a href="https://www.safefood.qld.gov.au/newsroom/food-safety-myths-continued/?keyword=freezing">survive freezing</a> and start growing again once conditions are favourable – for example, if you remove the food, partially thaw it, and return it to the freezer.</p>
<p>Two things happen when food breaks down. First, as microbes start to grow, several pungent chemicals are produced. Second, the fats and flavours that are part of the food itself can and will be released.</p>
<p>These are generally referred to as volatile organic compounds (VOCs). They are the pleasant aromas that we sense when we eat, but VOCs can also be produced by bacteria.</p>
<p>For example, many of us would be familiar with the smells that come from fermentation – a microbial process. When fermenting a food, we intentionally contaminate it with microbes of known characteristics, or provide conditions that favour the growth of desirable microbes and subsequent production of aromatic compounds.</p>
<p>By contrast, uncontrolled food spoilage is problematic, especially when the contaminating microbes can cause disease.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/523356/original/file-20230428-28-iqy59g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Close-up of chopsticks picking up a piece of kimchi from a white bowl" src="https://images.theconversation.com/files/523356/original/file-20230428-28-iqy59g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/523356/original/file-20230428-28-iqy59g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=401&fit=crop&dpr=1 600w, https://images.theconversation.com/files/523356/original/file-20230428-28-iqy59g.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=401&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/523356/original/file-20230428-28-iqy59g.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=401&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/523356/original/file-20230428-28-iqy59g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=504&fit=crop&dpr=1 754w, https://images.theconversation.com/files/523356/original/file-20230428-28-iqy59g.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=504&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/523356/original/file-20230428-28-iqy59g.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=504&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Kimchi is one of the foods we deliberately allow to be ‘contaminated’ in order to produce the intense flavour.</span>
<span class="attribution"><span class="source">Nungning20/Shutterstock</span></span>
</figcaption>
</figure>
<h2>Freezing changes the food</h2>
<p>It is not only microbial growth that can lead to undesirable odours. There’s a suite of chemical processes happening in the freezer, too.</p>
<p>Freezing causes physical changes to foods, often enhancing their breakdown. Many of us would be familiar with “freezer burn” on meats and other foods, as well as ice crystals on frozen food.</p>
<p>This phenomenon is called “<a href="https://en.wikipedia.org/wiki/Brine_rejection">salt rejection</a>”. Depending on how rapidly something is frozen, salts can sometimes be concentrated, as pure water freezes at a higher temperature than water with things dissolved in it – like sugars and salts. On a large scale, this happens to icebergs in the ocean. As the sea water freezes, salt is removed. Thus, the iceberg is composed of fresh water, and the surrounding sea water becomes a saltier and denser brine.</p>
<p>In a similar way, as water in food freezes, organic molecules are concentrated and expelled. If these are volatile, they move about the freezer and stick to other things. Where they end up depends on what else is around.</p>
<p>Some of the volatiles like water. We call them “hydrophilic” or water loving; those are the ones that will make your food taste bad. Other are more water-hating or “hydrophobic” and they stick to things like silicone ice cube trays, <a href="https://www.nytimes.com/wirecutter/blog/how-to-get-smells-out-of-silicone-kitchenware/">making them go smelly</a>.</p>
<p>Domestic freezers are commonly attached to a refrigerator, and this provides another opportunity for smells to move through the systems. The two units share a single cooling source and airflow channel. If your fridge has foul odours from the food inside (natural or after microbial spoilage), it is very likely they will migrate to your freezer.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/how-colour-coding-your-fridge-can-stop-your-greens-going-to-waste-45703">How colour-coding your fridge can stop your greens going to waste</a>
</strong>
</em>
</p>
<hr>
<h2>Help, my freezer smells!</h2>
<p>There are some simple steps you can take to stop your freezer from smelling.</p>
<p>First, try to prevent odours from developing in the first place by covering the food. If you place food in an airtight container (glass is best), it will dramatically slow the release of any aromatic compounds produced by bacteria or the food itself. Covered food is also less likely to absorb smells and flavours from other foods around it.</p>
<p>If the smells have already developed, you can eliminate them by following a few simple steps, including a thorough clean.</p>
<ul>
<li><p>Remove all items from the freezer and inspect the foods for any spoilage, freezer burn or unpleasant odours. </p></li>
<li><p>Discard anything that has developed ice crystals and store the rest in a cooler box while attending to the freezer itself. You should also inspect the fridge and discard any bad-smelling foods. </p></li>
<li><p>Once you have removed all items, take out the shelves and clean up spills or crumbs. </p></li>
<li><p>Wipe down all surfaces using warm soapy water or a mix of two tablespoons of baking soda with warm water.</p></li>
<li><p>Wash all the shelves and ice compartments and let them dry completely. </p></li>
</ul>
<p>If the smells are not removed with these simple cleaning steps, the freezer may require a deep clean, which involves turning off the unit and letting it “breathe” for a few days.</p>
<p>Placing some baking soda inside the freezer before adding food can help to absorb any residual odours. For serious smells where crevices or insulation are contaminated, you may need a service technician.</p>
<p>In short, even though we think freezers keep things “fresh”, microbes can still proliferate in there. Make sure to clean your freezer now and then to keep your food safe and healthy.</p><img src="https://counter.theconversation.com/content/203058/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>The authors do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Do your ice taste funny? Is there ‘freezer burn’ on your meat? This is why your freezer probably isn’t as clean as you think – but it only takes a few simple steps to fix it.Enzo Palombo, Professor of Microbiology, Swinburne University of TechnologyRosalie Hocking, Swinburne University of TechnologyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1964852022-12-21T19:12:01Z2022-12-21T19:12:01ZHow to make the perfect pavlova, according to chemistry experts<figure><img src="https://images.theconversation.com/files/502052/original/file-20221220-16-21qe2q.jpeg?ixlib=rb-1.1.0&rect=0%2C9%2C6016%2C3998&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Shutterstock</span></span></figcaption></figure><p>The pavlova is a summer icon; just a few simple ingredients can be transformed into a beautifully flavoured and textured dessert. </p>
<p>But despite its simplicity, there’s a surprising amount of chemistry involved in making a pavlova. Knowing what’s happening in each step is a sure-fire way to make yours a success.</p>
<p>So exactly what does it take to make the perfect pavlova? Let us break it down for you.</p>
<h2>Egg whites</h2>
<p><a href="https://theconversation.com/eight-cracking-facts-about-eggs-150797">Egg white</a> is basically a mixture of proteins in water. Two of these proteins, ovalbumin and ovomucin, are the key to forming a perfect foamy meringue mixture.</p>
<p>Whipping the egg whites agitates the proteins and disrupts their structure, causing them to unfold so the protein’s interior surface is exposed, in a process <a href="https://theconversation.com/sunny-side-up-can-you-really-fry-an-egg-on-the-footpath-on-a-hot-day-172616">known as denaturing</a>. These surfaces then join with one another to trap air bubbles and turn into a stable foam.</p>
<p>Egg yolk must be completely removed for this process to work. Yolk is mostly made of fat molecules, which would destabilise the protein network and pop the air bubbles. It only takes a trace amount of fat, or even just a greasy bowl, to disrupt foam formation. </p>
<p>You should always whip your egg whites in a clean glass or metal bowl. Plastic bowls are more likely to hold leftover grease.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/502270/original/file-20221220-11-1epnaj.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Close-up view of someone separating egg white from yolks in two small glass bowls." src="https://images.theconversation.com/files/502270/original/file-20221220-11-1epnaj.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/502270/original/file-20221220-11-1epnaj.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/502270/original/file-20221220-11-1epnaj.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/502270/original/file-20221220-11-1epnaj.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/502270/original/file-20221220-11-1epnaj.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/502270/original/file-20221220-11-1epnaj.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/502270/original/file-20221220-11-1epnaj.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Having any trace of fat in your meringue will limit your ability to form a stable foam, so be careful when separating your eggs.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<h2>Sugar</h2>
<p>A traditional pavlova uses sugar – a lot of it – to provide texture and flavour. The ratio of sugar to egg white will differ between recipes. </p>
<p>The first thing to remember is that adding more sugar will give you a drier and crispier texture, whereas less sugar will lead to a softer and chewier pavlova that won’t keep as long.</p>
<p>The second thing is the size of the sugar crystals. The larger they are, the longer they’ll need to be whipped to dissolve, and the greater the chance you will overwork the proteins in your meringue. Powdered icing sugar (not icing mixture) is preferable to caster or granulated sugar. </p>
<p>If you do happen to overbeat your meringue (which may end up looking clumpy and watery) you can try to save it by adding another egg white. </p>
<h2>Acid</h2>
<p>Many pavlova recipes call for adding cream of tartar or vinegar. Cream of tartar is also known as potassium hydrogen tartrate, which you may have seen in the form of crystals at the <a href="https://theconversation.com/louis-pasteurs-scientific-discoveries-in-the-19th-century-revolutionized-medicine-and-continue-to-save-the-lives-of-millions-today-191395">bottom of a wine glass</a>. </p>
<p>These acids act as a stabilising agent for the meringue by aiding in the unfolding of the egg white proteins. More isn’t always better, though. Using too much stabiliser can affect the taste and texture, so use it sparingly. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/502276/original/file-20221221-25-ddkqk5.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Tiny clear crystals ar‹e seen forming at the bottom of a glass of white wine." src="https://images.theconversation.com/files/502276/original/file-20221221-25-ddkqk5.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/502276/original/file-20221221-25-ddkqk5.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/502276/original/file-20221221-25-ddkqk5.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/502276/original/file-20221221-25-ddkqk5.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/502276/original/file-20221221-25-ddkqk5.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/502276/original/file-20221221-25-ddkqk5.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/502276/original/file-20221221-25-ddkqk5.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Tartaric acid is the most abundant acid in grapes, so you might sometimes see crystals of potassium hydrogen tartrate at the bottom of a wine glass.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<h2>Heat</h2>
<p>Cooking a pavlova requires a very slow oven for specific chemical reasons. Namely, egg white proteins gel at temperatures above 60°C, setting the meringue.</p>
<p>At higher temperatures a chemical reaction known as the <a href="https://theconversation.com/kitchen-science-from-sizzling-brisket-to-fresh-baked-bread-the-chemical-reaction-that-makes-our-favourite-foods-taste-so-good-58577">Maillard reaction</a> takes place in which proteins and sugars react to form new flavourful compounds. We can thank the Maillard reaction for many delicious foods including <a href="https://theconversation.com/brewing-a-great-cup-of-coffee-depends-on-chemistry-and-physics-84473">roasted coffee</a>, toast and <a href="https://theconversation.com/what-makes-smoky-charred-barbecue-taste-so-good-the-chemistry-of-cooking-over-an-open-flame-184206">seared steak</a>. </p>
<p>However, excessive Maillard reactions are undesirable for a pavlova. An oven that’s too hot will turn your meringue brown and give it a “caramelised” flavour. Recipes calling for pavlova to be left in the oven overnight may actually overcook it.</p>
<p>At the same time, you don’t want to accidentally undercook your pavlova – especially since uncooked eggs are often responsible for <a href="https://theconversation.com/how-to-avoid-food-borne-illness-a-nutritionist-explains-153185">food poisoning</a>. To kill dangerous bacteria, including salmonella, the pavlova’s spongy centre must reach <a href="https://foodsafety.asn.au/eggs/">temperatures above 72°C</a>.</p>
<p>An alternative is to use pasteurised egg whites, which are briefly heated to a very high temperature to kill any pathogens. But this processing may also affect the egg white’s whippability.</p>
<h2>Substitute ingredients</h2>
<p>People love pavlova, and nobody should have to miss out. Luckily they don’t have to.</p>
<p>If you want to <a href="https://theconversation.com/a-taste-for-sweet-an-anthropologist-explains-the-evolutionary-origins-of-why-youre-programmed-to-love-sugar-173197">limit your sugar intake</a>, you can make your meringue using sweeteners such as <a href="https://theconversation.com/whats-the-difference-between-sugar-other-natural-sweeteners-and-artificial-sweeteners-a-food-chemist-explains-sweet-science-172571">powdered erythritol or monk fruit</a>. But, if you do, you may want to add some extra stabiliser such as cornflour, arrowroot starch, or a pinch of xanthan gum to maintain the classic texture.</p>
<p>Also, if you want a vegan pavlova, you can turn to the chickpea instead of the chicken! <a href="https://review.jove.com/t/56305/composition-properties-aquafaba-water-recovered-from-commercially">Aquafaba</a> – the water collected from tinned or soaked beans – contains proteins and carbohydrates that give it emulsifying, foaming and even thickening properties. Egg-free pavlova recipes typically replace one egg white with about two tablespoons of aquafaba. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/502279/original/file-20221221-11-slbol7.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Chickpeas in a jar, next to a bowl of soft white peaks whipped from aquafaba." src="https://images.theconversation.com/files/502279/original/file-20221221-11-slbol7.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/502279/original/file-20221221-11-slbol7.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=401&fit=crop&dpr=1 600w, https://images.theconversation.com/files/502279/original/file-20221221-11-slbol7.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=401&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/502279/original/file-20221221-11-slbol7.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=401&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/502279/original/file-20221221-11-slbol7.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/502279/original/file-20221221-11-slbol7.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/502279/original/file-20221221-11-slbol7.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Although chickpeas may not come to mind when you picture pavlova, their aquafaba can be used to replace egg white.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<p>And for those of you who don’t do gluten, pavlova can easily be made <a href="https://theconversation.com/gluten-free-diet-is-expensive-socially-challenging-for-those-with-celiac-disease-and-wheat-allergy-155861">gluten-free</a> by using certain stabilising agents. </p>
<p>All that’s left is to get creative with your toppings and decide what to do with those leftover yolks!</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/egg-shortage-a-nutritionist-on-the-best-egg-alternatives-195248">Egg shortage: a nutritionist on the best egg alternatives</a>
</strong>
</em>
</p>
<hr>
<img src="https://counter.theconversation.com/content/196485/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Nathan Kilah has previously received payment to write an article on the chemistry of eggs in COSMOS Magazine, published by the Royal Institution of Australia.</span></em></p><p class="fine-print"><em><span>Chloe Taylor does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Why should you not beat your eggs in a plastic bowl? Can you save an over-beaten meringue? And is there a specific sugar you should use?Nathan Kilah, Senior Lecturer in Chemistry, University of TasmaniaChloe Taylor, Research Fellow - PhD candidate, University of TasmaniaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1005642018-08-14T10:32:39Z2018-08-14T10:32:39ZFrom slag to swag: The story of Earl Tupper’s fantastic plastics<figure><img src="https://images.theconversation.com/files/231724/original/file-20180813-2891-ba9goj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A postcard from the 1950s advertises a variety Tupperware products.</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/thomashawk/24781416158/">Thomas Hawk</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc/4.0/">CC BY-NC</a></span></figcaption></figure><p>When “American Horror Story,” the Museum of Modern Art and “Napoleon Dynamite” pay homage to an invention, you know it’s made a cultural impact in a big way.</p>
<p>Tupperware has a staying power that most plastic products don’t. So far, it has evaded the anti-plastics movement, and it seems to survive most kitchen clean-outs. Its annual sales <a href="https://www.marketwatch.com/investing/stock/tup/financials">exceed US$2 billion</a>. </p>
<p>I’ve taught the story of Tupperware products in a course on the American 1950s. I’m also teaching it in the <a href="https://www.youtube.com/watch?v=rqURhLnn9yA&feature=youtu.be">polymers</a> unit of an <a href="https://www.mrs.org/impact-of-materials-on-society">interdisciplinary course</a> in materials science engineering. </p>
<p>Tupperware products’ ability to bridge the humanities and STEM fields speaks to their cultural and utilitarian value – evidence of how a compelling, innovative design can have mass appeal.</p>
<h2>Polyethylene – ‘Material of the Future’</h2>
<p>Our relationships with plastics can be as richly diverse as the shapes and colors these malleable materials can assume. </p>
<p>Technically speaking, plastics are pliable, ductile and flexible synthetic materials that are easily shaped through heat and other applications of force. The word “plastic” also has an aesthetic meaning: A plastic actor is more versatile before the camera, and a medium such as stone can become plastic in an artist’s hands.</p>
<p>Literary and cultural critic Roland Barthes saw modern plastics as a form of alchemy – a way to transmute matter in seemingly infinite ways. </p>
<p>“More than a substance,” <a href="https://www.newyorker.com/culture/richard-brody/the-uses-of-mythologies">he wrote in “Mythologies,”</a> “plastic is the very idea of its infinite transformation.” </p>
<p>Barthes imagined polystyrene, polyvinyl and polyethylene as Greek shepherds in a world of gods and monsters – magical materials alive with possibility. </p>
<p>Earl Tupper, inventor of Tupperware products, saw such promise in polyethylene – the plastic he used to craft his inventions – that he called it “Poly-T: Material of the Future,” as Alison J. Clarke notes in her book “<a href="https://www.smithsonianbooks.com/store/history/tupperware-promise-plastic-1950s-america/">Tupperware: The Promise of Plastic in 1950s America</a>.” </p>
<p>After failing at his first business as a tree surgeon, Tupper decided to try his hand at plastics production. In 1937, he got a gig as a sample maker at a Dupont-affiliated plastics factory. </p>
<p>At the time, DuPont employed amateur sample makers to further research and development. They could even take scrap materials home with them to work on new prototypes – a mutually beneficial arrangement, Clarke points out. </p>
<p>So when working with injection molding machines at the factory failed to yield the plastic Tupper envisioned, he turned to his home kitchen and tried the stovetop.</p>
<h2>It’s all about the lid</h2>
<p>The polyethylene that Tupper brought home from the factory was an industrial waste product – opaque, greasy, clumpy black slag. It was hardly the stuff that marketing dreams are made of. Tupper sought to overcome such material limitations by producing a plastic more durable than molded transparent <a href="https://www.google.com/search?q=styrene&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjI0uXx1-DcAhWqct8KHWeIBscQ_AUICigB&biw=1440&bih=673">styrene</a>; he wanted to create something that could flex without cracking or snapping.</p>
<p>He and his son boiled the scrap samples at home, eventually finding the right balance of pressure and temperature so the polyethylene flowed into the desired shapes and thickness. Tupper also fashioned a system for dyeing his containers in pastel colors. </p>
<p>Eventually, Tupper was able to create what author Bob Kealing <a href="https://books.google.com/books/about/Tupperware_Unsealed.html?id=7rkTAQAAIAAJ">referred to</a> as “a polished, waxy, upscale plastic.”</p>
<p>But he still needed the right lid – something that could both preserve food and prevent spills.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/231750/original/file-20180813-2894-azzsmx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/231750/original/file-20180813-2894-azzsmx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=382&fit=crop&dpr=1 600w, https://images.theconversation.com/files/231750/original/file-20180813-2894-azzsmx.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=382&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/231750/original/file-20180813-2894-azzsmx.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=382&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/231750/original/file-20180813-2894-azzsmx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=481&fit=crop&dpr=1 754w, https://images.theconversation.com/files/231750/original/file-20180813-2894-azzsmx.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=481&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/231750/original/file-20180813-2894-azzsmx.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=481&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Earl Tupper got the idea for his famous lid from paint cans.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/giuntinijonathan/4457615235/">Giuntini Jonathan</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span>
</figcaption>
</figure>
<p>Inspired by paint cans, Tupper fashioned a flexible polyethylene lid that, when snapped onto the container, created an airtight seal. As Kealing points out, this worked much better than tin foil or a shower cap – materials many American women had relied on to cover their leftovers. </p>
<p>In 1947, <a href="https://patents.google.com/patent/US2487400?oq=Tupper+nonsnap+1949">Tupper patented</a> the nonsnap lid for his first plastic container. </p>
<p>Legendary saleswoman <a href="https://www.pbs.org/wgbh/americanexperience/features/tupperware-wise/">Brownie Wise</a> – the first woman to appear on the cover of Business Week – would demonstrate how to “burp” the container by lifting part of the patented lid before sealing it. Her direct sales acumen made Tupper’s product come alive. At her iconic “Tupperware parties,” she would toss liquid-filled <a href="https://i.pinimg.com/736x/df/64/39/df6439845a60f0c2b42bb16083bb171b--tupperware-shop-perfect-wedding-gifts.jpg">Wonder Bowls</a> across American living rooms, astonishing housewives with the airtight seal that prevented spills.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/-Mm_z5xwwbs?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">A 1958 ad markets Tupperware parties and showcases the air-tight seal.</span></figcaption>
</figure>
<h2>From pantry shelf to gallery shelf</h2>
<p>In the 1972 film “<a href="http://www.eamesoffice.com/the-work/design-q-a/">Design Q&A</a>,” designer Ray Eames insists that design is fundamentally “a plan for arranging elements to accomplish a particular purpose,” although superior designs “may later be judged as art.” </p>
<p>Today, Tupper’s <a href="https://www.moma.org/learn/moma_learning/earl-s-tupper-pitcher-and-creamer-1946">polyethylene pitcher and creamer</a> reside in the Museum of Modern Art, along with his tumblers, bowls and ingenious popsicle molds, called “Ice Tups.” Curators have included Tupperware products in exhibitions on mid-century design and most recently in the 2011 exhibit “<a href="https://www.moma.org/calendar/exhibitions/957?locale=en">What was Good Design? MoMA’s Message, 1944-1956</a>.”</p>
<p>As Clarke explains, Tupper’s products embodied modernism’s “ideal of a tasteful, restrained and mass-produced artifact, free of inauthentic decoration and gratuitous ornament.” </p>
<p>With their clean lines and elegant curves, they fused form and function. The plastic used in Tupperware products is top-shelf – aesthetically pleasing, meaningful and durable. </p>
<p>In today’s Tupperware products, we also see a refined design. Take the Eco Water Bottle. Its sleek curves – together with its softly translucent pink, blue and turquoise variations – conjure glass. The concave center looks pretty and fits the hand.</p>
<h2>Tales from Tupper’s wares</h2>
<p>Tupperware products continue to play a role in our cultural conscious. A friend who lent me her Ice Tups told me that she’ll always associate it with early memories of her mother. </p>
<p>In one “Seinfeld” episode, Kramer frantically tries to recover his Tupperware container that he’d loaned to someone, while Jimmy of “American Horror Story” <a href="http://americanhorrorstory.wikia.com/wiki/Tupperware_Party_Massacre">causes mayhem at a Tupperware Party</a>. Meanwhile, the synthwave band <a href="https://twrp.bandcamp.com/">Tupper Ware Remix Party</a> spins 80s-inspired dance tracks. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/PfIJILHnpPU?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Can you relate to Kramer?</span></figcaption>
</figure>
<p>Non-biodegradable plastic like Tupperware containers will be part of Earth’s future for centuries. <a href="http://www.plasticfreejuly.org/">The Plastics Free July initiative</a> has advocated against single-use plastics, like bags and straws. Luckily, Tupperware products are reusable, and the stories we tell about them will continue to reinvent our relationships with a material we won’t – and can’t – let go of.</p><img src="https://counter.theconversation.com/content/100564/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Marsha Bryant does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>You know you’ve hit it big when your designs find their way into millions of kitchens – and the Museum of Modern Art.Marsha Bryant, Professor of English & Distinguished Teaching Scholar, University of FloridaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/913242018-03-28T01:08:45Z2018-03-28T01:08:45ZI’ve always wondered: why does lemon juice lighten the colour of tea?<figure><img src="https://images.theconversation.com/files/211649/original/file-20180323-54893-10jdeqq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Adding lemon makes your tea taste nice - and changes its colour. </span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/cut-into-pieces-lemon-tea-leaves-1051559990?src=I4QhI1t9hlyg0QXyYuff3A-1-6">from www.shutterstock.com </a></span></figcaption></figure><p><em>This is an article from I’ve Always Wondered, a series where readers send in questions they’d like an expert to answer. Send your question to alwayswondered@theconversation.edu.au</em></p>
<hr>
<p><strong>I’ve always wondered what happens when pouring a few drops of lemon juice into a cup of tea (no milk added). Why does it lighten the tea’s colour? – Michel, Paris</strong> </p>
<p>To answer this question, we need to think about the molecules that give a cup of tea its colour - and how lemon juice affects them. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/what-science-says-about-getting-the-most-out-of-your-tea-75767">What science says about getting the most out of your tea</a>
</strong>
</em>
</p>
<hr>
<p>Tea is typically made from the plant <em>Camellia sinensis</em>. </p>
<p>It is one of the most consumed beverages (second only to water) globally and is ranked as the <a href="http://www.fao.org/3/a-i4480e.pdf">most consumed manufactured drink</a>. The origins of its consumption were first recorded more than 5,000 years ago, so it is also one of the world’s oldest drinks. </p>
<p>Tea has been used for a variety of health conditions in China since ancient times, and it took time (around 1,000 years) to change from being seen as a medicine to today’s “every day drink”. Some of the health benefits of tea are now receiving <a href="https://theconversation.com/health-check-five-reasons-to-put-the-kettle-on-and-have-a-cup-of-tea-42419">renewed attention</a>. </p>
<h2>The colour of tea</h2>
<p>Today, tea varieties are heavily dependent on the processing techniques after harvest. These include oxidation and fermentation of tea leaves, which change their colour and flavour. Use of these manufacturing techniques provides six distinctive categories of tea, based primarily on colour: green, yellow, dark, white, oolong, and black. </p>
<p>Black tea and green tea are often (but not always) obtained from the same plant but their chemical makeup is vastly different. </p>
<p>The leaves used for green tea production are heated either by steam, pan frying, roasting or baking immediately after harvesting. This process stops chemical reactions driven by the enzyme polyphenol oxidase that would otherwise oxidise coloured chemicals such as polyphenols (catechins). </p>
<p>This results in tea keeping its familiar yellow-green colour. Once the leaves are “fixed” they are soft – and are then rolled and dried to become the product we see on supermarket shelves. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/211651/original/file-20180323-54863-8cch23.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/211651/original/file-20180323-54863-8cch23.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/211651/original/file-20180323-54863-8cch23.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/211651/original/file-20180323-54863-8cch23.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/211651/original/file-20180323-54863-8cch23.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/211651/original/file-20180323-54863-8cch23.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/211651/original/file-20180323-54863-8cch23.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Tea plantation in India.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/green-tea-plantations-munnar-kerala-india-1051735985">from www.shutterstock.com</a></span>
</figcaption>
</figure>
<p>The production of black tea depends on the enzymes being allowed to oxidise the catechins completely to form new chemicals – these are pigments (theaflavin and thearubigin) that provide the characteristic dark colour. </p>
<p>Although thearubigins are less common in your black teabag (around 10-20% of the dry weight), they are more soluble – so when you make a brew these compounds can account for up to <a href="https://www.sciencedirect.com/science/article/pii/B9780080453828001088">60% of the solids</a> suspended in the solution. </p>
<p>In broad terms, all other colour categories of tea fit between green and black. So categorisation of teas based simply on colour mostly depends on the type and amounts of these compounds found in the brewed product.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/what-is-kombucha-and-how-do-the-health-claims-stack-up-87180">What is kombucha and how do the health claims stack up?</a>
</strong>
</em>
</p>
<hr>
<h2>What happens when lemon juice is added?</h2>
<p>The thearubigins in brewed tea are highly coloured (red-brown) molecules that <a href="https://www.sciencedirect.com/science/article/pii/S030881460100108X">change according to the acidity of the liquid used</a>.</p>
<p>If the water used for the tea infusion is relatively alkaline (for example, due to limescale found in “hard” water), the colour of the tea will be darker and deeper. </p>
<p>However, once an acid such as a slice of lemon or lemon juice is added, tea changes colour because of an increase in acidity (reduction in pH) of the beverage itself. Lemon juice is quite strong as a food acid – a few drops are enough to alter the theaurbigins, resulting in a dramatic change in colour. Interestingly, theaflavins are not that affected by the change in acidity, and still retain their normal dark red colour. </p>
<p><img width="100%" src="https://media.giphy.com/media/dTkLBIzRggchi/giphy.gif"></p>
<p>In a case of green tea, the addition of lemon juice will also affect the colour through a similar process. This results in a much paler beverage - beyond the level that would occur just by initial tea suspension. </p>
<h2>Does lemon juice make your tea healthier?</h2>
<p>The beneficial health effects of tea are linked to its total polyphenol content, mainly the catechins. However, one of the problems with these compounds is that they are rather unstable. When alkaline (hard) water is used, they break down relatively quickly (<a href="https://www.sciencedirect.com/science/article/pii/S0308814603000621">within a few minutes of brewing</a>). </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/science-or-snake-oil-do-skinny-teas-boost-weight-loss-87353">Science or Snake Oil: do skinny teas boost weight loss?</a>
</strong>
</em>
</p>
<hr>
<p>Even if they do remain in solution, the absorption of these compounds is low (less than 2%), and can also be inhibited by the <a href="http://www.mdpi.com/2076-3921/4/2/373">food consumed with your cuppa</a>. </p>
<p>Increasing the acidity of drinks has been shown to improve the stability of catechins in beverages. This is one of the main reasons why drinks such as iced teas tend to be quite acidic. However, to make them more palatable, relatively high levels of sweeteners (mainly sugars) are also added. </p>
<p>So, all up, although the key compounds in your cup of tea tend to degrade quickly, the addition of lemon does protect them temporarily from this breakdown. But it’s not a huge effect. Adding lemon can enhance the flavour and enjoyment of tea, and change its colour, but its best not to expect any extra boosts to your health.</p><img src="https://counter.theconversation.com/content/91324/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Nenad Naumovski received a Australian Postgraduate Award (APA) for a completion of his PhD investigating the Cholesterol lowering properties of major green tea catechin. </span></em></p><p class="fine-print"><em><span>Duane Mellor is a director, council member and spokesperson of the British Dietetic Association</span></em></p>It’s all about the chemistry. Adding lemon can enhance the flavour and enjoyment of tea, and change its colour, but its best not to expect any extra boosts to your health.Nenad Naumovski, Asistant Professor in Food Science and Human Nutrition, University of CanberraDuane Mellor, Senior lecturer, Coventry UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/888842017-12-17T21:04:57Z2017-12-17T21:04:57ZScience in the kitchen: the fresher the flour, the softer the cake<figure><img src="https://images.theconversation.com/files/198297/original/file-20171208-27689-11hbpq7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">So how do you like my brioche?</span> <span class="attribution"><a class="source" href="https://unsplash.com/photos/h5rgWo1_F_U">Element5 Digital/Unsplash</a></span></figcaption></figure><p>From the most elaborate holiday cake to the humblest loaf of bread, one of the keys to success is the beautifully aerated structure within. Yet how many cakes and loaves have slumped despite untold care being taken in their preparation? And how many bakers have fallen into despair, not knowing why their creations never puffed to perfection? Science may have now found the answer.</p>
<p>A <a href="http://onlinelibrary.wiley.com/doi/10.1111/jtxs.12303/full">research paper</a> published in the <em>Journal of Texture Studies</em> brings to light a new element in the everlasting quest for perfect cake. It’s the result of work by a team of scientists from <a href="http://www.agroparistech.fr/Genial-Ingenierie-procedes.html">GENIAL</a>, a joint research unit of INRA and AgroParisTech, working in collaboration with the <a href="http://eu.mondelezinternational.com/">Mondelez</a> company. They found that the quality of a cake is strongly linked with the age of the flour used.</p>
<p>The softness of a cake is synonymous with its freshness. For it to be nicely soft, the walls of its cells must be regularly perforated, with small and consistently sized air chambers. The feeling of softness of a cake is influenced by the formation and distribution of bubbles in the dough rather than the firmness of the cell walls – they’re in fact secondary.</p>
<h2>Seven cakes to bake and compare</h2>
<p>Cakes are traditionally made with eggs, sugar, fat and flour, plus a small portion of baking powder. As the dough is being mixed, the bubbles within are stabilised by components from the eggs and flour. Flour proteins are also active during the baking itself, giving to cake its structure – ideally as smooth and consistent as possible. During the production process of large-scale bakeries, they can add <a href="https://en.wikipedia.org/wiki/Emulsion#Emulsifiers">emulsifiers</a>, substances that encourage the stable mixing of normally unblendable fluids – oil and water, in particular.</p>
<figure class="align-right ">
<img alt="" src="https://images.theconversation.com/files/197606/original/file-20171204-19588-xqomeu.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/197606/original/file-20171204-19588-xqomeu.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=394&fit=crop&dpr=1 600w, https://images.theconversation.com/files/197606/original/file-20171204-19588-xqomeu.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=394&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/197606/original/file-20171204-19588-xqomeu.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=394&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/197606/original/file-20171204-19588-xqomeu.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=495&fit=crop&dpr=1 754w, https://images.theconversation.com/files/197606/original/file-20171204-19588-xqomeu.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=495&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/197606/original/file-20171204-19588-xqomeu.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=495&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A cake that was part of the study.</span>
<span class="attribution"><span class="source">Journal of Texture Studies</span>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>In our study we used two different emulsifiers and flour aged at between 1 and 9 months to produce seven cakes. We then compared the cakes’ cellular structures and their softness. Afterwards, we observed the evolution of the cakes’ texture after 6, 13 and 32 weeks.</p>
<p>Scientific breakthroughs often involves years of research, but chance can also play a key role. Even if the subject study cannot be compared to, say, the <a href="https://en.wikipedia.org/wiki/Alexander_Fleming#Accidental_discovery">invention of penicillin</a> by Dr. Alexander Fleming, our discovery of the role of flour age in the cake texture was also discovered by chance. One flour sample was used both before and after summer, yet gave strikingly different results.</p>
<p>We were amazed to find that the age of flour had a significant impact on the cakes’ cellular structure. Indeed, during its unintended “ageing”, flour is enriched in free fatty acids that change the way air is stabilized in the form of bubbles in the batter and their behaviour during baking process. It leads to an increase in bubble size, heterogeneity and distribution, as well as cell-wall thickness. These and other changes affect a cake’s cellular structure and thus its softness.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/197599/original/file-20171204-4090-17isjmm.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/197599/original/file-20171204-4090-17isjmm.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=309&fit=crop&dpr=1 600w, https://images.theconversation.com/files/197599/original/file-20171204-4090-17isjmm.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=309&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/197599/original/file-20171204-4090-17isjmm.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=309&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/197599/original/file-20171204-4090-17isjmm.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=388&fit=crop&dpr=1 754w, https://images.theconversation.com/files/197599/original/file-20171204-4090-17isjmm.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=388&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/197599/original/file-20171204-4090-17isjmm.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=388&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A cross-sectional view of one of the cakes in the study.</span>
<span class="attribution"><span class="source">Journal of Texture Studies</span>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<h2>A quest for the ultimate recipe</h2>
<p>The emulsifying agents in a cake make its bubbles smaller and more regular, and these in turn make the cake softer. Without an emulsifier, the cake’s texture will become coarser, and with all the predicable consequences – in particular, disappointed looks on the faces of all the cake lovers at the ready.</p>
<p>When it comes to cake storage, it’s common sense that softness decreases over time. Nevertheless, if a cake is softer to start out with, we determined that it will remain so over time compared to those that are less so, even weeks or months later.</p>
<p>The result of our research highlight the fact that inside a cake, cell formation is strongly related to dough composition. In addition to using flour as fresh as possi ble, regular and rapid checking of the evolution of a cake’s structure can help produce consistently soft cakes. This is why we strongly believe that the new image-analysis technique, developed by INRA and AgroParisTech, can improve baking quality control, whether it’s in the production facilities of a multinational food giant or your family’s kitchen.</p><img src="https://counter.theconversation.com/content/88884/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Les auteurs ne travaillent pas, ne conseillent pas, ne possèdent pas de parts, ne reçoivent pas de fonds d'une organisation qui pourrait tirer profit de cet article, et n'ont déclaré aucune autre affiliation que leur organisme de recherche.</span></em></p>From the most elaborate cake to the humblest loaf, a key to success is the beautifully aerated structure within – but producing consistent results can be difficult. Now, science may have found out why.Camille Michon, Chercheuse en sciences alimentaire, présidente du centre de recherche Ile-de-France – Versailles-Grignon, InraeNicolas Plantey, Doctorant en épistémologie et chargé du projet DIM ASTREA, InraeLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/681682017-05-30T20:12:59Z2017-05-30T20:12:59ZThe science of taste, or why you choose fries over broccoli<figure><img src="https://images.theconversation.com/files/169413/original/file-20170515-6990-xxf5hq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">It's in the genes why some people find broccoli unpleasantly bitter, but others barely flinch when eating it. </span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/download/confirm/338976938?src=objvRyCLN1HcmlLsvaT23g-1-38&size=huge_jpg">from www.shutterstock.com </a></span></figcaption></figure><p>Most people say that if there is a healthy choice on a menu they will take it. But observations and <a href="http://link.springer.com/article/10.1007/s40547-014-0025-9">research</a> show this is generally not the case.</p>
<p>Instead, people tend to make choices based on how food tastes. Typically, the more sugar, salt and fat in the food, the more we will like it. Genetics, experience and environment also influence our perception of food and the consumption choices we make.</p>
<p>Australians are <a href="https://theconversation.com/food-as-medicine-why-do-we-need-to-eat-so-many-vegetables-and-what-does-a-serve-actually-look-like-76149">still not eating</a> as healthily as they should, despite years of programs and publicity warning of the health impacts of poor diets.</p>
<p>But what if we could make healthier foods taste better and thus improve eating patterns?</p>
<p>To examine questions of food taste, flavour and digestion under controlled conditions, we have developed a <a href="https://www.csiro.au/en/Research/AF/Areas/Food/Making-healthier-foods/Virtual-mouth">computational model</a> of food mastication (chewing) and digestion. </p>
<p>We have also developed a kit to map genes that predict flavour preferences, and are measuring how proteins in saliva affect food flavour. </p>
<h2>A model to chew on</h2>
<figure>
<iframe src="https://player.vimeo.com/video/116316268" width="500" height="281" frameborder="0" webkitallowfullscreen="" mozallowfullscreen="" allowfullscreen=""></iframe>
<figcaption><span class="caption">A less messy way to watch food being chewed - a computerised model.</span></figcaption>
</figure>
<p>How a person chews their food, mixes it with saliva and squeezes it with their tongue has a large impact on how it tastes. But eating is a complex process and is different for every person, and until recently was very difficult to measure and monitor. </p>
<p>Our model can simulate eating behaviour based on data from real people eating different foods. It shows how food products break down in the mouth and how components such as sugar and salt are transported to our taste receptors.</p>
<p>We are also modelling how food gets broken down in the stomach and what happens to it as it moves through the digestive tract. </p>
<p>This will help in the future development of food matched to an individual’s physiology, which can deliver nutrients at the ideal location and control the rate of digestion.</p>
<h2>Measuring genetic variation in taste</h2>
<p>It’s now clear that variation in genes influences whether people will like certain foods, and how much they will eat. </p>
<p>For example, the presence or absence of a particular form of a <a href="https://www.ncbi.nlm.nih.gov/pubmed/17873857">gene involved in smell</a> determines whether an individual is <a href="https://genepi.qimr.edu.au/contents/p/staff/Knaapila_ChemSenses_MarchEPUB2012.pdf">sensitive to androstenone</a>, a molecule that generates the unpleasant flavour found in pork from male pigs. Individuals with a variant of this particular gene <a href="https://doi.org/10.1371/journal.pone.0035259">can detect androstenone</a> by sniffing pork. Androstenone sensitivity is <a href="https://academic.oup.com/chemse/article/40/7/481/400181/Global-Survey-of-Variation-in-a-Human-Olfactory">reported</a> to be much higher in Asian populations than in those of European descent. </p>
<p>Other genes are involved in determining preference or avoidance of bitter flavours. For example, a compound known as PROP (6-n-propylthiouracil) is commonly found in green vegetables such as broccoli, and contributes to <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4853779/">creating a bitter taste</a>. People who have the gene for a bitter receptor known as TAS2R38 are able to taste the compound, either mildly or very strongly. Those without the gene for this receptor are unable to taste it. This explains why some people like their greens more than others.</p>
<p>The CSIRO is developing a genetic kit with the goal of predicting whether or not individuals will like particular foods. </p>
<p>Working with people in their own homes, we have tested and validated a “PROP kit” for detecting and rating bitterness intensity in food. Our preliminary analysis of DNA collected from test subjects’ saliva and cheek cells showed that those who could taste bitterness had the TAS2R38 bitter receptor, and those that could not taste bitterness did not have this receptor. The test also allowed us to predict which consumers were bitter tasters and which were non-tasters.</p>
<p>This sort of kit gives us an idea of why some people like their greens more than others. The kit will be further tested and validated in a much larger cohort of Australians of both Asian and European descent. </p>
<h2>Saliva can alter the taste of food</h2>
<p><a href="https://www.ncbi.nlm.nih.gov/pubmed/12002816">Saliva is vital</a> in helping us eat food safely, and it lubricates and transports taste molecules from food to our taste buds. </p>
<p>Saliva contains an enzyme called <a href="http://onlinelibrary.wiley.com/doi/10.1002/star.201000150/pdf">amylase</a>, which breaks down starch into sugars. If you’ve ever noticed that some children keep bread in their mouth for a long time, it’s because as the amylase in their saliva acts on the starch, more sugar is produced and the bread tastes sweeter.</p>
<p>There are <a href="http://www.nature.com/icb/journal/v59/n1/abs/icb19811a.html">other enzymes in saliva</a> that act on fat and protein, and control how we perceive food. The composition of saliva in each person is different. It changes throughout the day, and is influenced by what you eat, what exercise you have done, your mood, and even whether it is light or dark outside.</p>
<p>Proteomics (the study of proteins and their function) is an approach that can measure differences in the protein composition of different people’s saliva. The types and level of proteins and enzymes present in saliva <a href="http://www.tandfonline.com/doi/full/10.3109/07388551.2012.687361">vary from person to person</a>, and this changes the way flavour is released from food in our mouth. </p>
<p>The bacteria that live in our mouths, part of our <a href="https://theconversation.com/healthy-guts-are-swarming-with-bugs-so-what-do-they-do-65105">microbiome</a>, also have an influence. For example, <a href="http://pubs.acs.org/doi/abs/10.1021/jf801873h">bacteria change the flavours of food</a> by increasing the production of molecules that create particular taste experiences. The types of bacteria that are present create a <a href="https://www.sciencedaily.com/releases/2008/11/081110181811.htm">unique response</a> in each individual. </p>
<p>Research into individual food preferences – whether they be as a result of our genetics, saliva or the way we chew – may one day guide food manufacturers to produce healthier options of our everyday foods. </p>
<p>Hopefully this may contribute to consumers making better menu selections and decrease the number of food-related diseases currently affecting Australians.</p><img src="https://counter.theconversation.com/content/68168/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Ingrid Appelqvist does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Your genes, your saliva and the bacteria that live in your mouth all shape how food tastes and what you prefer to eat.Ingrid Appelqvist, Research Group Leader and Food R&D policy leader, CSIROLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/646702016-12-08T19:05:15Z2016-12-08T19:05:15ZKitchen Science: the chemistry behind amazing meringue and perfect cappuccino<figure><img src="https://images.theconversation.com/files/147311/original/image-20161124-15368-15bva5q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">It's the chemistry that makes it taste so great.</span> <span class="attribution"><span class="source">Shutterstock</span></span></figcaption></figure><p>Whether it’s frothing milk for a cappuccino or beating egg whites into meringue for a <a href="https://en.wikipedia.org/wiki/Pavlova_(food)">pavlova</a> or <a href="https://en.wikipedia.org/wiki/Macaroon">macaroons</a>, you can thank chemistry for the reactions that make them possible. </p>
<p>Beating egg whites with a whisk or frothing milk with steam disrupts – or partly “<a href="https://en.wikipedia.org/wiki/Denaturation_(biochemistry)">denatures</a>” – the neatly folded and tightly curled chains of amino acids within milk or egg white protein. </p>
<p>Once disrupted, the amino acid chains unfurl and expand to take up more space. It’s a bit like unravelling a ball of wool. The extra space is the volume of froth on your coffee or the fluffiness of the meringue. </p>
<h2>Go froth and multiply the bubbles</h2>
<p>When frothing milk for a cappuccino, the steam and pressure denature both <a href="https://en.wikipedia.org/wiki/Casein">casein</a> and whey proteins. </p>
<p>Understanding froth science helps create a better milky foam. The best froth, used in <a href="https://en.wikipedia.org/wiki/Latte_art">latte art</a>, is called a <a href="https://en.wikipedia.org/wiki/Microfoam">microfoam</a>. </p>
<p>Microfoam is made in two steps. <a href="http://coffeegeek.com/guides/frothingguide/advancedguide">First</a>, you introduce air into milk by placing the tip of the steamer within the milk. Then you slowly bring it close to the top until the milk mixture starts to hiss. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/147310/original/image-20161124-15330-1cekkqz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/147310/original/image-20161124-15330-1cekkqz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/147310/original/image-20161124-15330-1cekkqz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/147310/original/image-20161124-15330-1cekkqz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/147310/original/image-20161124-15330-1cekkqz.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/147310/original/image-20161124-15330-1cekkqz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/147310/original/image-20161124-15330-1cekkqz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/147310/original/image-20161124-15330-1cekkqz.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The secret is small bubbles.</span>
<span class="attribution"><span class="source">duncan c</span>, <a class="license" href="http://creativecommons.org/licenses/by-nc/4.0/">CC BY-NC</a></span>
</figcaption>
</figure>
<p>Then you plunge the steamer tip deeper into the milk to create a whirlpool. This gently mixes the foam evenly throughout the milk so it becomes thick and velvety. </p>
<p>According to <a href="http://coffeegeek.com/guides/frothingguide/advancedguide">Coffeegeek</a>, froth that is totally white on the top means you made too much foam, or it has not been mixed evenly through the milk. </p>
<p>If you overheat the milk, the protein gets totally denatured and can no longer form bonds across protein strands or incorporate enough air bubbles to make a decent froth structure. </p>
<p>Interestingly, skim milk can produce <a href="https://scienceandfooducla.wordpress.com/2015/07/21/the-science-of-steamed-milk-understanding-your-latte-art/">more froth with larger air bubbles</a> because it has a higher protein content.</p>
<p>So what does coffee froth have to do with meringue? </p>
<h2>Boom meringue</h2>
<p>Compared to milk, the amino acid chains in egg white <a href="https://en.wikipedia.org/wiki/Egg_white">albumen</a> are much longer. Like knitting, if you have a bigger ball of wool, you can knit a longer scarf. </p>
<p>So when egg white protein chains unfold, they can incorporate a lot more air between their stretched amino acid strands compared to milk proteins. </p>
<p><a href="http://www.exploratorium.edu/cooking/eggs/pavlova-pop.html">Exploratorium science</a> provides more detail on how beating also exposes some amino acids that repel water – i.e. are “hydrophobic”. </p>
<p>When egg whites get beaten, these water-wary amino acids come into close contact with other water-loving (i.e. hydrophilic) amino acids. Next, water molecules from egg whites, the air and amino acids all jockey to get into the best possible position to be near components they like, and to get as far away as possible from the ones they do not like. </p>
<p>They incorporate air into the structure to help them do this. Some of the amino acid strands also make “bridges” between them to try to stabilise the meringue. This is why meringue does not deflate as much as cappuccino froth. </p>
<p>When the whipped-up egg white is cooked, <a href="https://en.wikipedia.org/wiki/Ovalbumin">ovalbumin</a> – the main protein in egg white – becomes completely denatured, meaning it cannot return to its former shape. This is what makes meringue solid.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/147309/original/image-20161124-15330-1q7e9yu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/147309/original/image-20161124-15330-1q7e9yu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/147309/original/image-20161124-15330-1q7e9yu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/147309/original/image-20161124-15330-1q7e9yu.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/147309/original/image-20161124-15330-1q7e9yu.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/147309/original/image-20161124-15330-1q7e9yu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/147309/original/image-20161124-15330-1q7e9yu.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/147309/original/image-20161124-15330-1q7e9yu.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The perfect pair: cappuccino and meringue use the same underlying chemistry.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<p>Exploratorium’s <a href="http://www.exploratorium.edu/cooking/eggs/eggscience.html">science of cooking eggs</a> includes hints on using chemistry to make better meringue. Try these:</p>
<ol>
<li><p>Use a metal bowl. Clean plastic bowls still hold tiny molecules of fat. These get in the way when amino acid chains try to network and block air being incorporated into the foam. (This is another reason why skim milk froths better than full-cream milk.) </p></li>
<li><p>Add a drop of vinegar or lemon juice. These acidic liquids donate positively charged hydrogen ions to negatively charged protein strands, neutralising them. This slows down the rate at which new bonds between the amino acid chains are made and gives more time for them to unfurl and incorporate air while being beaten. </p></li>
<li><p>Use eggs at room temperature. Warmer egg whites will foam up better than cold ones from the fridge. This is because the proteins strands can move more at the higher temperature and are already starting to unfurl. It’s a bit like being given a head start in a race to unravel a ball of wool. </p></li>
</ol>
<h2>Cappuccino versus meringue</h2>
<p>When it comes to a battle of strength, meringue foam beats cappuccino froth. Milk froth is less stable than egg white foam. This is why your frothy coffee will flatten if you leave it to sit, while a cooled pavlova holds its structure for quite a while. </p>
<p>Egg white has more sulphur-containing amino acids than milk protein, which means it can make very strong disulphide bridges between amino acids across protein strands when beaten. These hold the fully denatured proteins in their new shape.</p>
<p>The changes foods undergo during cooking are really food chemistry reactions. So next time you’re enjoying a coffee and a macaroon, you can thank chemistry for the froth and the crunch.</p><img src="https://counter.theconversation.com/content/64670/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Clare Collins is affiliated with the Priority Research Centre for Physical Activity and Nutrition, the University of Newcastle, NSW. She is an NHMRC Senior Research fellow. She has received funding from a range of research grants including NHMRC, ARC, Hunter Medical Research Institute, Meat and Livestock Australia. She has consulted to SHINE Australia and Novo Nordisk. Clare Collins is a spokesperson for the Dietitians Association of Australia on some specific nutrition issues, including Australia's Healthy Weight Week.</span></em></p>The same chemical reaction is behind the frothing of milk in your cappuccino and the whipping of egg whites in sweet meringue.Clare Collins, Professor in Nutrition and Dietetics, University of NewcastleLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/607962016-06-23T20:02:31Z2016-06-23T20:02:31ZKitchen Science: beyond the sweetness of sugar<figure><img src="https://images.theconversation.com/files/127696/original/image-20160622-19745-nfomj1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Sugar is a surprisingly versatile substance.</span> <span class="attribution"><span class="source">Shutterstock</span></span></figcaption></figure><p>We all know the nutritional “evils” of sugar as a potential cause of <a href="https://theconversation.com/sugar-isnt-just-empty-fattening-calories-its-making-us-sick-49788">obesity</a>, chronic disease and <a href="https://theconversation.com/australian-sugary-drinks-tax-could-prevent-thousands-of-heart-attacks-and-strokes-and-save-1-600-lives-56439">death</a>, through to being a potentially <a href="https://theconversation.com/sugar-may-be-as-damaging-to-the-brain-as-extreme-stress-or-abuse-53813">brain damaging substance</a>. </p>
<p>However, sugar has been part of the human diet for millennia, and it has some fascinating and highly practical uses. </p>
<h2>Preserving and drying</h2>
<p>We all know that jam contains sugar, but it’s not just there to make it sweeter. </p>
<p>Food has a short shelf life if it is not properly stored or preserved. So preserving including curing was vital to ensure food continues to be available year round in the days before the refrigeration and canning.</p>
<p>Most foods that can spoil relatively quickly have a lot of water in them, along with nutrients that make them a great place for bacteria to grow. These bacteria can both cause spoilage and even be toxic or infectious to us.</p>
<p>One of the simplest ways to make the food less hospitable to bacteria is to remove water. This is known as reducing the <a href="http://drinc.ucdavis.edu/dairychem4_new.htm">water activity</a>. Something that is completely dry has a water activity of 0 (relatively small amount of foods), while water has an activity of 1, with table sugar sitting at around 0.2. Reducing the water activity in food below 0.70 can seriously limit bacteria growth. </p>
<p>This is exactly what making jam does. Firstly, the fruit is heated with sugar and pectin (a type of fibre). This helps to breakdown tough cell walls and sterilises the mixture. </p>
<p>The lowering of the water activity then stops bacteria growing, thus prolonging the life of the jam. Although once opened, moulds and yeasts can still grow – as many of us will have discovered when popping open a jar of jam that has sat untouched for too long. </p>
<p>This is also why preserves that are lower in sugar, as well as other lower or reduced sugar products, may not last as long as traditional jams. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/p93p312iu3I?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">How to make jam.</span></figcaption>
</figure>
<p><a href="http://www.scienceofcooking.com/curing_foods.htm">Sugar (and honey) curing</a> have also been used for centuries. </p>
<p>Sugar can be dissolved in water to make a solution. If there is enough sugar in the solution – such as a sugar syrup – it will draw water molecules out of the food cells, effectively lowering the food’s water activity.</p>
<p>This happens via a process of osmosis. When there are more particles – such as sugar molecules – in a solution outside of a cell than there are inside the cell, this is called a hypertonic solution. In this case, water tends to flow out of the cell into the surrounding solution.</p>
<p>This technique has been used with products such as meat and fish to prevent spoilage. Swedish gravlax is one example of such a food, which uses sugar and salt in its cure. </p>
<p>Sugar may potentially be preferable to salt, as unlike salt, sugar (typically sucrose) penetrates the cells of the food less than salt and therefore can be removed more easily.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/127683/original/image-20160622-19783-z1nnsc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/127683/original/image-20160622-19783-z1nnsc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/127683/original/image-20160622-19783-z1nnsc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=398&fit=crop&dpr=1 600w, https://images.theconversation.com/files/127683/original/image-20160622-19783-z1nnsc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=398&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/127683/original/image-20160622-19783-z1nnsc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=398&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/127683/original/image-20160622-19783-z1nnsc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=500&fit=crop&dpr=1 754w, https://images.theconversation.com/files/127683/original/image-20160622-19783-z1nnsc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=500&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/127683/original/image-20160622-19783-z1nnsc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=500&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Gravlax is a traditional cured salmon that uses sugar to remove water from the fish flesh as part of its preparation.</span>
<span class="attribution"><span class="source">Schefferbird/Wikimedia</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<h2>Sugar glass and toffee</h2>
<p>A major, but not terribly nutritious, use of sugar is in confectionery and the making a wide variety of boiled sweets and toffees. In fact, you make see-through sugar glass, white boiled lollies and dark bonfire toffee from essentially the same ingredients. But how?</p>
<p>The key is temperature, and you will need a jam thermometer (and a lot of care) to do this properly. </p>
<p>Essentially, heating up dry sugar with a sugar syrup and a little water to 150°C, then cooling on a greased baking sheet will produce <a href="https://gosciencegirls.com/sugar-glass-edible-science-kids/">clear sugar “glass”</a> from opaque sugar. </p>
<p>To turn it white, like table sugar, you need to stretch it, which simply varies the crystal size so it becomes opaque and white.</p>
<iframe src="https://datawrapper.dwcdn.net/RtoJM/1/" frameborder="0" allowtransparency="true" allowfullscreen="allowfullscreen" webkitallowfullscreen="webkitallowfullscreen" mozallowfullscreen="mozallowfullscreen" oallowfullscreen="oallowfullscreen" msallowfullscreen="msallowfullscreen" width="100%" height="360"></iframe>
<p>It seems the key temperature for colour changes for sucrose, or table sugar, is about 160°C, with fructose caramelising at a lower temperature of 110°C, and maltose at a slightly higher temperature of 180°C. </p>
<p>The different temperature thresholds for various sugars partly explains why caramelisation occurs at different temperatures in different foods. It also helps explain why cooking with honey or foods containing fructose brown at lower temperatures. </p>
<p>When sucrose caramelises, it initially needs to break down to fructose and glucose. These then react to form new aromatic compounds, which have complex flavours and the familiar brown colours, including caramelan, caramelen and caremelin. </p>
<p>This process also produces a number of smaller compounds, such as 2,3-butanedione, which has an intense butter-like flavour, and esters and lactones, which are compounds that give rum its distinct sweetness. </p>
<p>Other compounds produced in this process include the nutty tasting furans and the maltol. However, if this heating continues, all the sweetness of the sugar will be lost and burnt bitter flavours take over.</p>
<p>It is important to note caramelisation is different to the <a href="https://theconversation.com/kitchen-science-from-sizzling-brisket-to-fresh-baked-bread-the-chemical-reaction-that-makes-our-favourite-foods-taste-so-good-58577">Maillard reaction</a>, which is the typical browning that occurs when baking bread, and is not associated with the distinct caramel flavours. </p>
<p>Although we should be careful to control our intake of sugar, it is fascinating both chemically and physically, and is an ingredient that can be used sensibly to enhance flavour and preserve food for longer. </p>
<p><em>This article is part of the <a href="https://theconversation.com/au/topics/kitchen-science">Kitchen Science</a> series, exploring the amazing physics and chemistry going on in our kitchens every day. If you’re an academic with an idea for a Kitchen Science article, <a href="mailto:tim.dean@theconversation.edu.au">get in touch!</a></em></p><img src="https://counter.theconversation.com/content/60796/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>The authors do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Sugar is maligned for its effects on our health, but it’s an amazing substance and can be used for more than just making things taste sweet.Duane Mellor, Associate Professor in Nutrition and Dietetics, University of CanberraNenad Naumovski, Asistant Professor in Food Science and Human Nutrition, University of CanberraLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/585772016-06-02T20:23:21Z2016-06-02T20:23:21ZKitchen Science: from sizzling brisket to fresh baked bread, the chemical reaction that makes our favourite foods taste so good<figure><img src="https://images.theconversation.com/files/124757/original/image-20160601-1943-ztswi7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The Maillard reaction is what gives brisket it's brown colour and delicious flavours.</span> <span class="attribution"><span class="source">Shutterstock</span></span></figcaption></figure><p>Have you ever wondered how freshly baked bread gets its a golden brown crust and why it smells so good? Or how nondescript green berries turn into beautiful brown coffee beans with a rich alluring aroma? </p>
<p>The answers to these questions lie in a series of complex of chemical reactions, known as Maillard reactions, which give many foods their familiar flavours and colours. These sensory properties even guide us in how we choose foods and help create our initial perceptions of their quality.</p>
<p>As the name suggests, Maillard reactions were first described by a French physician and biochemist, Louis-Camille Maillard, in 1912. These reactions produce hundreds of chemical compounds that give colour and aroma to some of our favourite foods such as roast meat, potato chips, bread and other bakery products, coffee, chocolate and confectionery. </p>
<p>Maillard reactions occur between <a href="http://www.britannica.com/science/amine">amine groups</a> of amino acids or proteins and “reducing” sugars, such as glucose and fructose. These sugars are so named because they act as chemical <a href="https://simple.wikipedia.org/wiki/Reduction_(chemistry)">reducing agents</a>.</p>
<p>These reactions occur most rapidly under conditions of low moisture and at temperatures above about 130°C. Hence, they tend to kick in when we fry, bake, grill or roast. </p>
<p>Maillard reactions are also referred to as browning reactions because of the colour they impart to foods cooked in this way. When meat is grilled or roasted, only the surface is usually hot enough to cause browning. The interior can retain a pinkish colour because the cooking temperature stays below that required for Maillard reactions to occur rapidly. </p>
<p>Foods cooked by boiling or steaming do not turn brown or acquire the complexity of flavours because the temperature only reaches about 100°C. Likewise with cooking in a microwave oven.</p>
<p>The colour of chocolates, fudges and toffees are produced by the reaction of sugars with milk proteins. </p>
<p>The initial products of Maillard reactions are small volatile molecules, which are responsible for the aromas we get from freshly baked bread and coffee. More complex reactions then take place to form larger molecules responsible for the golden to brown colours. This is why the aroma of baking bread is sensed before the crust browns. </p>
<p>The later Maillard reactions are not well understood. We do know that some of the molecules they form have unpleasant flavours and may even be toxic, or the source of carcinogens that occur in charred meat. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/124892/original/image-20160602-1955-1rjl5e6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/124892/original/image-20160602-1955-1rjl5e6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/124892/original/image-20160602-1955-1rjl5e6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/124892/original/image-20160602-1955-1rjl5e6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/124892/original/image-20160602-1955-1rjl5e6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/124892/original/image-20160602-1955-1rjl5e6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/124892/original/image-20160602-1955-1rjl5e6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/124892/original/image-20160602-1955-1rjl5e6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The Maillard reaction not only turns it golden brown, but also releases mouth watering aromas.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<h2>The colour of flavour</h2>
<p>A common misconception is that Maillard reactions are the same as caramelisation. Although both are favoured by conditions of low moisture, caramelisation occurs when sugars are heated to high temperatures in the absence of proteins. The common food flavour and caramel colour is produced by heating a mixture of glucose and sucrose to 160°C.</p>
<p>Maillard reactions don’t only take place in a hot oven though. They can also occur slowly at ambient temperature, resulting in gradual changes to aroma, flavour, colour, appearance, texture, shelf-life and nutritional value of stored foods. </p>
<p>In this way, Maillard reactions are responsible for the colour of honey, as well as deterioration during storage of dry goods such as flour and powdered milk. Maillard reactions are also implicated in the gradual loss of viability of seeds.</p>
<p>Maillard reactions can also have detrimental consequences. Unsightly blemishes may appear on chips after frying if their reducing sugar content exceeds 0.03% of dry matter. Potatoes destined for commercial chip production are carefully monitored to ensure reducing sugars are below this level.</p>
<p>An undesirable product of Maillard chemistry is <a href="https://en.wikipedia.org/wiki/Acrylamide">acrylamide</a>. This is a chemical that can be detected in tiny amounts in a range of fried or roasted foods, including potato chips, coffee, cocoa, chocolate and cereal-based bakery products, sweet biscuits and toasted bread (but not in steamed buns). </p>
<p>Acrylamide has been mentioned as a <a href="http://www.cancer.org/cancer/cancercauses/othercarcinogens/athome/acrylamide">possible carcinogen</a>, although according to Food Standards of Australia and New Zealand, the body that oversees the safety of our food, there is <a href="http://www.foodstandards.gov.au/consumer/chemicals/acrylamide/Pages/default.aspx">no direct evidence</a> it causes cancer in humans. Acrylamide does not occur in raw foods or foods cooked by boiling or steaming.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/124758/original/image-20160601-1923-d6pt7n.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/124758/original/image-20160601-1923-d6pt7n.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/124758/original/image-20160601-1923-d6pt7n.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/124758/original/image-20160601-1923-d6pt7n.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/124758/original/image-20160601-1923-d6pt7n.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/124758/original/image-20160601-1923-d6pt7n.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/124758/original/image-20160601-1923-d6pt7n.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/124758/original/image-20160601-1923-d6pt7n.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">You can almost smell it from here.</span>
<span class="attribution"><span class="source">THINK Global School</span>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span>
</figcaption>
</figure>
<h2>Beyond the kitchen</h2>
<p>Some aspects of the Maillard reaction have long been implicated in human ageing and health conditions. </p>
<p>Examples include loss of elasticity of connective tissue and the appearance dark spots on skin due to effects on collagen, cataract formation due to reactions with the lens protein crystallin, changes in neural proteins contributing to neuropathology and dementia, and glycation of haemoglobin due to elevated blood glucose levels in diabetes. </p>
<p>The importance of Maillard reactions in the kitchen and beyond is well established, even though these reactions are still not well understood more than a century after they were first described. </p>
<p>Nevertheless, we can take advantage of their benefits while continuing to learn about this fascinating area of chemistry.</p>
<p><em>This article is part of the <a href="https://theconversation.com/au/topics/kitchen-science">Kitchen Science</a> series, exploring the amazing physics and chemistry going on in our kitchens every day. If you’re an academic with an idea for a Kitchen Science article, <a href="mailto:tim.dean@theconversation.edu.au">get in touch!</a></em></p><img src="https://counter.theconversation.com/content/58577/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Les Copeland does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Have you ever wondered how freshly baked bread gets its a golden brown crust, or why coffee beans smell so good? You can thank the miracle of the Maillard reaction.Les Copeland, Professor of Agriculture, University of SydneyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/593102016-05-19T19:37:23Z2016-05-19T19:37:23ZKitchen Science: the many wonders of humble flour<figure><img src="https://images.theconversation.com/files/123129/original/image-20160519-22307-ja6ydp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">You need the right one for the job.</span> <span class="attribution"><span class="source">Shutterstock</span></span></figcaption></figure><p>Have you ever wondered why you have so many different types of flour in your pantry? You might have cornflour and arrowroot, self-raising, and plain flour. And if you like to bake bread, possibly strong bakers’ flour. </p>
<p>The reason for such diversity is that each of these flours has different chemical and physical properties that help them do their job in recipes. </p>
<h2>No lumps</h2>
<p>Cornflour has an interesting property that makes it perfect for making smooth custard and sauces. This is because it does not “whet” very readily and typically forms clumps. Cornflour starch is a large chain-like molecule that is tightly wrapped up in starch granules, so it doesn’t dissolve in water, as do salt or sugar. </p>
<p>These large molecules tend to clump together as they are “hydrophobic”, which means they have a tendency to avoid water. This is likely caused by tiny mutually repelling charges on the water and starch molecules. </p>
<p>The action of mixing a small amount of water with starch to make a paste helps to prevent the clumping, and helps to disperse the starch (the colloid) to form an emulsion, which is a solid dispersed within a liquid, but not fully dissolved. </p>
<p>Although, as soon as you stop mixing the paste, the starch starts separating from the water. So make sure you mix the paste just before you are about to put it in the sauce.</p>
<p>Pastes of cornflour in water are often described as a non-Newtonian fluid. These are remarkable substances that bend our conception of how a fluid normally works.</p>
<p>A non-Newtownian fluid can be poured, but if you strike it quickly, it will go stiff and hard. This is because the colloid changes the surface tension of the fluid to make it behave as if it were solid when struck. This tends to work only when the starches are uncooked.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/Mxd_LJr0BWg?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
</figure>
<h2>So what happens when starches are cooked?</h2>
<p>If you add starch to a heated sauce, the sauce thickens. This is how we thicken gravies and sauces, and can set a blancmange. </p>
<p>This effectively is forming a <em>plastic</em>, although not quite in the way we normally think of plastics. </p>
<p>The effect of heating starches in water helps to breakdown the bonds in the starch molecules. This starts to form hydrogen bonds with water in what is called <a href="http://www.thenakedscientists.com/HTML/experiments/exp/cornflour-and-gravy/">gelatinisation</a>. In this process, water is acting as a plasticiser. </p>
<p>The result is a semi-permanent solution as the starches dissolve. This is why cooked starches go transparent, unless you add other things to the sauce, of course. </p>
<p>To make the gel more permanent, starches can be modified to help stabilise the hydrogen bonds that form with water. If you don’t do this, the starch can start to retrograde and collapse, releasing water. You can see this if a blancmange or custard has been left for a few days. </p>
<p>These retrograde starches are found in pasta, unripe bananas and rice that has been cooled. These are hard for us to digest, but can be good source of food for the bacteria in our large intestine. This may be good for us but can result in a little flatulence.</p>
<h2>Strong for light bread</h2>
<p>Cornflour and arrowroot are very rich in starch and low in protein, so they are great for thickening sauces. </p>
<p>However, if you want to bake bread, you are often told you need strong bakers’ flour. Why? What is wrong with normal flour? </p>
<p>The answer is simple: not enough gluten. While it is trendy in some quarters to avoid gluten, unless you have an intolerance to it or coeliac disease, consumption of gluten is perfectly fine. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/123131/original/image-20160519-22310-74w5ou.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/123131/original/image-20160519-22310-74w5ou.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/123131/original/image-20160519-22310-74w5ou.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=398&fit=crop&dpr=1 600w, https://images.theconversation.com/files/123131/original/image-20160519-22310-74w5ou.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=398&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/123131/original/image-20160519-22310-74w5ou.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=398&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/123131/original/image-20160519-22310-74w5ou.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=500&fit=crop&dpr=1 754w, https://images.theconversation.com/files/123131/original/image-20160519-22310-74w5ou.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=500&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/123131/original/image-20160519-22310-74w5ou.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=500&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">If you mix flour with water, and then rinse until the water runs clear, this removes all the starch, leaving behind the gluten.</span>
<span class="attribution"><span class="source">ilovebutter/Flickr</span>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>In fact, developing the bonds between the two proteins that make up gluten (gliadin and glutenin) gives a dough the stretch and potential to capture bubbles of gas that can give bread its <a href="http://www.rsc.org/chemistryworld/Issues/2009/October/Ontherise.asp">structure</a>.
Stronger bakers’ flours simply tend to have more of these proteins (around 11 to 13g of protein per 100g, compared to nine to ten grams in normal flour). So, when choosing a flour to make bread, if you want a light airy bread, a strong flour is needed. </p>
<h2>What’s in a bad pie?</h2>
<p>However, if you want to make a light crumbly pastry, gluten can be your enemy. Most of us have eaten a pie where the pastry was a little leathery, so what went wrong? </p>
<p>In terms of protein, this time less is more. This is also why fat is used, which helps the gluten to form. The more the pastry is worked, the more gluten is developed, and the tougher the <a href="https://www.theguardian.com/science/2014/feb/20/recipe-fat-flour-water-science-pastry">pastry</a>.</p>
<p>Flours have many fascinating properties. This is why you need a range of different flours in your pantry if you want to cook a range of different things. So, when choosing the flour to cook with, it is important to make the correct choice and work it properly. </p>
<p><em>This article is part of the <a href="https://theconversation.com/au/topics/kitchen-science">Kitchen Science</a> series, exploring the amazing physics and chemistry going on in our kitchens every day. If you’re an academic with an idea for a Kitchen Science article, <a href="mailto:tim.dean@theconversation.edu.au">get in touch!</a></em></p><img src="https://counter.theconversation.com/content/59310/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>The authors do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>From non-Newtownian fluids, to hydrophobic starch, to plasticisation - various flours can do amazing things. But you must choose the right one for the job!Duane Mellor, Associate Professor in Nutrition and Dietetics, University of CanberraNenad Naumovski, Asistant Professor in Food Science and Human Nutrition, University of CanberraLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/586332016-05-05T19:46:34Z2016-05-05T19:46:34ZKitchen Science: A salt on the senses<figure><img src="https://images.theconversation.com/files/121301/original/image-20160505-17469-g0b76o.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Salt seems common enough, but it has some astounding properties.</span> <span class="attribution"><span class="source">Shutterstock</span></span></figcaption></figure><p>When we say “salt”, we usually mean the stuff we sprinkle on our chips, which is sodium chloride (NaCl). But, technically speaking, this is just one example of a salt. </p>
<p>In chemistry, a <a href="https://en.wikipedia.org/wiki/Salt_(chemistry)">salt</a> is an ionic compound that comes from the neutralisation reaction of an acid and a base. Let me explain that for you.</p>
<p>Molecules that have an electrical charge are called ions. Those with a positive charge are cations, and those with a negative charge are anions. They’re like the opposite ends of a magnet, so anions attract cations.</p>
<p><a href="https://www.khanacademy.org/science/chemistry/acids-and-bases-topic">Acids</a> are substances release positively charged hydrogen ions (H+) when in water, while bases release negatively charged hydroxide ions (OH-) in water. When mixed together, they neutralise each other and produce a salt.</p>
<p>So salts are just made up of positively charged cations bound with negatively charged anions. Sodium chloride is a positive sodium ion (Na+) bound with a negative chloride ion (Cl-). The properties of salts differ, depending on which ions are combined. </p>
<h2>Salty</h2>
<p>Not all salts are safe to eat, and not all of them taste salty. The cation determines if a salt has a salty flavour, and the anion determines the intensity of that flavour.</p>
<p>To interact with our taste receptors, salts first have to split back – or <a href="https://en.wikipedia.org/wiki/Dissociation_(chemistry)">dissociate</a> – into their ions. This requires a solution, such as saliva or water. So if you stick your tongue out until it dries and put salt on it, you won’t taste the saltiness.</p>
<p>While adding salts to water is a pretty safe chemical reaction, in their elemental state, each component can be highly reactive. Sodium and chlorine both react violently with water, but are stable when their ions are together in a salt. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/mzEOL-N2cbw?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Sodium has a famously energetic response to water.</span></figcaption>
</figure>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/BXCfBl4rmh0?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Chlorine is also rather nasty stuff.</span></figcaption>
</figure>
<p>Humans have been adding salt to food for thousands of years for two simple reasons: it’s a cheap and natural preservative; and it makes food taste better. </p>
<p>Adding salt makes food last longer by reducing the “<a href="https://en.wikipedia.org/wiki/Water_activity">water activity</a>” of foods. Salt essentially soaks up the water, creating a “dry” environment where it is difficult for the bacteria that spoil food to grow. Salt also draws water from the moist insides of bacteria to the drier environment, killing them. </p>
<p>At the right levels, salt tastes good. It is likely that salty evolved as a pleasant taste to encourage us to consume the required amount. Salts are important in many biological processes, like nerve signalling, so we need some salt in our diets.</p>
<p><a href="http://www.ncbi.nlm.nih.gov/books/NBK50958/">Salt is also a flavour enhancer</a>. Add a little salt and almost everything tastes better. For example, adding salt to chicken soup doesn’t just make it saltier, it makes it taste thicker, more balanced and more “chickeny”. Salt does this in a number of ways. </p>
<p>Salt suppresses the bad flavours in food, allowing the more pleasant ones to dominate. When <a href="http://www.ncbi.nlm.nih.gov/pubmed/8788095">researchers</a> mixed bitter and sweet solutions together in a taste test, adding salt made the mixture taste sweeter. But in the sweet solution on its own, adding salt didn’t improve the flavour as much. </p>
<p>Many <a href="http://ajcn.nutrition.org/content/72/6/1424.full">vitamins and antioxidants taste bitter</a>. Adding salt to foods that naturally contain, or are fortified, with these bitter compounds make them taste better. That’s why we often add salt to our green veggies. </p>
<p>Salt also reduces the amount of unbound water, known as the “water activity”. This leads to a relative increase in the concentration of the other flavour components, improving the aroma, flavour and “thickness” of foods. </p>
<p>This can improve flavour in low fat or sugar-reduced versions of foods. So check your nutritional panels; you might be trading excess kilojoules for excess salt, which is not necessarily healthier. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/121300/original/image-20160505-17469-1500wrs.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/121300/original/image-20160505-17469-1500wrs.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/121300/original/image-20160505-17469-1500wrs.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=397&fit=crop&dpr=1 600w, https://images.theconversation.com/files/121300/original/image-20160505-17469-1500wrs.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=397&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/121300/original/image-20160505-17469-1500wrs.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=397&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/121300/original/image-20160505-17469-1500wrs.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=499&fit=crop&dpr=1 754w, https://images.theconversation.com/files/121300/original/image-20160505-17469-1500wrs.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=499&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/121300/original/image-20160505-17469-1500wrs.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=499&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Salt forms into crystals when it forms.</span>
<span class="attribution"><span class="source">Tim Simpson/Flickr</span>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<h2>Defensive eating</h2>
<p>Habitually eating too much salt is linked to conditions such as cardiovascular and kidney disease. Excess salt in a single dose is not good either. Without enough water to match, excess salt disrupts the processes that depend on a particular salt concentration. </p>
<p>Excess salt also stimulates the <a href="http://www.ncbi.nlm.nih.gov/pubmed/15153450">bitter and sour taste receptors</a>, as part of “defensive eating”. This is why adding some salt to food improves taste, but adding too much spoils the meal.</p>
<p>The level of salt that tastes pleasant or unpleasant varies among individuals. This is partly due to our genes, but acclimatisation also occurs depending on our normal dietary habits. </p>
<p>People with a diet normally high in salt adapt to prefer more salt. Those with low salt diets in early life eat less salt and <a href="http://hyper.ahajournals.org/cgi/pmidlookup?view=long&pmid=9095076">have lower blood pressure</a> in later life. However, we can use this acclimatisation in reverse as a strategy for reducing salt intake. </p>
<p>This can be slowly adding less to your own food, as well as food manufacturers reducing the levels in their products slowly over time, allowing consumers to adapt.</p>
<p>Potassium chloride is another salt sometimes used to replace sodium chloride. However, as it also tastes bitter, <a href="http://www.ncbi.nlm.nih.gov/books/NBK50965/">so it can only act as a partial replacement</a>. By using even more complex mixtures of salts, we may be able to enhance the salt flavour and so use less. </p>
<p>Another approach is to make the <a href="http://www.ncbi.nlm.nih.gov/pubmed/22062728">salt dissolve more efficiently</a> so the taste hits you faster. By adding salt to the surface of foods, rather than mixing it in, the salt meets the saliva more quickly. Reducing the salt particle size, which increases the surface area, also lets the salt dissolve more quickly in saliva, increasing the “saltiness”.</p>
<p>Another interesting solution has recently emerged from a team of Japanese researchers: a fork that gives your tongue <a href="http://gizmodo.com/this-electric-fork-simulates-a-salty-flavor-by-shocking-1767695828">small electric shocks as you eat</a>. The electrical impulse simulates a salt flavour and reduces the need to add salt to your food.</p>
<p>Much of the salt we eat is hidden in food that many people wouldn’t even call “salty”. And Australians are eating more than the recommendations. So now that you know the science, you can use it to make informed choices on salty foods.</p>
<p><em>This article is part of the <a href="https://theconversation.com/au/topics/kitchen-science">Kitchen Science</a> series, exploring the amazing physics and chemistry going on in our kitchens every day. If you’re an academic with an idea for a Kitchen Science article, <a href="mailto:tim.dean@theconversation.edu.au">get in touch!</a></em></p><img src="https://counter.theconversation.com/content/58633/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Emma Beckett does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>That salt on your table can do amazing things chemically, and to the flavour of your favourite food. But don’t eat too much!Emma Beckett, Postdoctoral Fellow (Human Molecular Nutrition), School of Medicine and Public Health, University of NewcastleLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/581472016-04-28T20:13:04Z2016-04-28T20:13:04ZKitchen Science: gastrophysics brings the universe into your kitchen<figure><img src="https://images.theconversation.com/files/120659/original/image-20160429-28029-1y1mkuk.png?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">You can learn a lot about the cosmos in the kitchen.</span> <span class="attribution"><span class="source">Shutterstock/Wikimedia</span></span></figcaption></figure><p>This title will probably come as a surprise to you. <a href="https://theconversation.com/au/topics/astrophysics">Astrophysics</a> concerns enormous scales of space, time and energy; kitchens are relatively small, homely places. </p>
<p>So how can there be a connection between astrophysics and the kitchen?</p>
<p>Have you ever dropped a just-opened plastic bottle of milk or fruit juice on the kitchen bench and had the contents jumped up and hit you in the face? I have. And when it happened, I suddenly realised there was a connection with the physics of a type II <a href="https://theconversation.com/au/topics/supernova">supernova</a> explosions.</p>
<p>When a massive star – roughly ten times or more the mass of our sun – comes to the end of its life, it is blown apart in a catastrophic explosion known as a type II supernova. </p>
<p>The explosion is triggered by the sudden collapse of the iron core at the centre of the star. The rest of the star follows and slams into the rebounding core, which creates a shockwave that propagates through the star back to the surface. When the shockwave reaches the surface there is no more star to push on, and so the outer layers of the star are ejected violently into space.</p>
<p>On the kitchen bench, dropping a plastic bottle causes the base to flex and push on the liquid above, creating a shock wave. When the shockwave reaches the top of the bottle there is no more liquid to push on, and so the liquid is ejected up into the air.</p>
<h2>Baking the universe</h2>
<p>You can also see the evolution of the universe while baking. </p>
<p>Astrophysicists often use the “raisin loaf” analogy to explain the expansion of the universe. The dough represents space and the raisins galaxies. </p>
<p>Imagine sitting on a raisin in the middle of the dough as it bakes in the oven. As the loaf expands we would see every other raisin move away from us. When we look out into the universe (almost) every galaxy is moving away from our home galaxy, the Milky Way. </p>
<p>At home I often make what I call Hubble Damper in honour of <a href="http://hubblesite.org/the_telescope/hubble_essentials/edwin_hubble.php">Edwin Hubble</a>, who first ascertained that galaxies are moving away from the Earth. He also determined that the farther the galaxy, the faster the recession. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/120444/original/image-20160428-30976-1kxit49.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/120444/original/image-20160428-30976-1kxit49.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/120444/original/image-20160428-30976-1kxit49.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/120444/original/image-20160428-30976-1kxit49.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/120444/original/image-20160428-30976-1kxit49.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/120444/original/image-20160428-30976-1kxit49.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/120444/original/image-20160428-30976-1kxit49.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/120444/original/image-20160428-30976-1kxit49.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Delicious and educational!</span>
<span class="attribution"><span class="source">Stephen Hughes</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>For added realism I add craisins (dried cranberries) rather than raisins. Craisins are red. Galaxies are <a href="http://coolcosmos.ipac.caltech.edu/cosmic_classroom/cosmic_reference/redshift.html">redshifted</a>.</p>
<p>If you are interested in making your own Hubble Damper, here is the recipe. Mix together:</p>
<ul>
<li>450g self–raising flour</li>
<li>a pinch of salt</li>
<li>80g diced chilled butter</li>
<li>185ml water</li>
<li>170g craisins. </li>
</ul>
<p>Bake for 30 minutes at 200°C. Tap the base of the bread; if it sounds hollow, it’s done.</p>
<h2>Sunset in a glass</h2>
<p>One of the first “science” questions children often ask is: “Why is the sky blue?” And it’s a question dreaded by many parents. </p>
<p>If you have one of those children, here is something you can do in your kitchen to explain why the sky is blue. Get hold of a glass of water – a glass with straight sides is best. Put a drop of milk into the water and stir. </p>
<p>Get hold of a LED torch and shine it through the water. When you look at the beam of light end-on, you will see that it is has a yellow tint. If you can’t see the LED light, dilute the milky water. </p>
<p>The fact that the torch beam has a yellow tint means that blue light has been extracted from the beam, which is what we call scattering. </p>
<p>If you perform the experiment at night, switch off the lights in the kitchen and look at the glass of water from the side. You will notice a blue glow. This is the light scattered by the milk. Congratulations, you’ve just made your own blue sky and sunset in your kitchen.</p>
<p>In the atmosphere, molecules in the air scatter blue light from the sun more than the red wavelengths. The blue light comes into our eyes from all directions, which is why the sky is blue. When the sun is close to the horizon, the sunlight has to pass through a greater thickness of atmosphere and more blue light is scattered making the sun appear red.</p>
<p>After my light bulb moment of dropping the milk bottle I decided to explore other connections between astrophysics and the physics of cooking and kitchen appliances. Over the course of about three years I wrote an eBook book called <a href="http://www.stephenhughes.com.au/portfolio/24/">Gastrophysics</a>, which explores the connections, and I learnt a bit of cooking at the same time.</p>
<p><em>This article is part of the <a href="https://theconversation.com/au/topics/kitchen-science">Kitchen Science</a> series, exploring the amazing physics and chemistry going on in our kitchens every day. If you’re an academic with an idea for a Kitchen Science article, <a href="mailto:tim.dean@theconversation.edu.au">get in touch!</a></em></p><img src="https://counter.theconversation.com/content/58147/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Stephen Hughes is the author of the eBook Gastrophysics, upon which this article is based.</span></em></p>From supernovae explosions to the expansion of the universe and why the sky is blue: you can learn a lot about the universe in the kitchen.Stephen Hughes, Senior Lecturer in Physics, Queensland University of TechnologyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/572792016-04-21T20:08:39Z2016-04-21T20:08:39ZKitchen Science: bacteria and fungi are your foody friends<figure><img src="https://images.theconversation.com/files/119403/original/image-20160420-25615-16yhpss.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">You couldn't enjoy cheese like this without the intervention of micro-organisms.</span> <span class="attribution"><span class="source">Shutterstock</span></span></figcaption></figure><p>As you sip a cup of coffee, enjoy a rich chocolate treat or savour the aroma of a piece of Roquefort cheese, have you ever considered the extraordinary contribution made by the microscopic creatures that have worked so hard for your pleasure?</p>
<p>As the French chemist <a href="http://www.biography.com/people/louis-pasteur-9434402">Louis Pasteur</a> said: “The role of the infinitely small in nature is infinitely large.” Without microbes, life on this planet would not exist or would be very different to what we see today. </p>
<p>Recent discoveries have revealed the critical roles played by <a href="https://theconversation.com/au/topics/microbiology">microorganisms</a> in driving ecosystems, changing our environment and influencing the health and well-being of people, plants and animals.</p>
<p>One of the most intriguing aspects of microbiology is the almost endless variety of biological and chemical processes attributed to microbes. There are species that can break down pollutants, happily grow on arsenic and the recently-described <a href="http://www.abc.net.au/news/2016-03-11/plastic-eating-bacterium-can-break-down-pet/7238614">bacteria that break down PET plastics</a>.</p>
<h2>The wonders of fermentation</h2>
<p>Nowhere is this biological activity more apparent – and close to home – than through the process of fermentation. This metabolic process is used by many microbes – mostly bacteria and many yeasts – and exploited by humans in numerous industrial and agricultural applications. </p>
<p>Many of us are aware of <a href="http://www.bbc.co.uk/schools/gcsebitesize/science/add_edexcel/organism_energy/respirationrev1.shtml">respiration</a>. The process is used by living cells to convert chemicals, such as sugar, to energy by breaking them down into smaller constituents and liberating the energy within. </p>
<p>In the most familiar version, known as aerobic respiration, oxygen is the final recipient in a chain of chemical reactions that generates water and carbon dioxide and produces energy. </p>
<p>However, many bacteria are able to perform an alternative form of respiration in the absence of oxygen, called anaerobic respiration, which enables survival despite a lack of oxygen. This is a good trick that allows microbes to thrive in anaerobic conditions, such as our gut. Some bacteria live in constantly anaerobic conditions and, for them, exposure to oxygen is lethal!</p>
<p>But many microbes have another strategy: fermentation. Here, molecules such as sugars are only partly broken down; the energy produced is not as great as in respiration, but the cell still survives. </p>
<p>Luckily for us, many of the end-products of this process are very valuable, including compounds such as ethanol and lactic acid.</p>
<h2>Cultured food</h2>
<p>Although most people know that bacteria can turn milk into yoghurt and yeasts convert sugars in grape juice into ethanol or make bread dough rise, there are countless examples from around the world where fermentation is used to produce exotic and unique products of cultural importance. </p>
<p>But many people don’t realise the extent to which fermentation enhances our enjoyment of foods and beverages. In some cases, it may provide benefits beyond the senses. </p>
<p>In Colombia, Central America and Hawaii, Arabica coffee is processed by the “wet method”, which involves a fermentation step of 24 to 48 hours. This is primarily used to remove a thin layer of mucilage surrounding the coffee bean. </p>
<p>This process also imparts desirable flavour and aroma attributes. Of course, roasting and brewing are critical steps in the full development of coffee flavours.</p>
<p>Chocolate production begins when the cocoa bean undergoes a similar fermentation step, which involves a complex succession of bacteria and yeasts producing flavour precursors, including ethanol, lactic acid and acetic acid.</p>
<p>The dairy industry relies heavily on fermentation. One example is the simple “starter cultures”, consisting of one or a few bacteria that turn milk into yoghurt via lactic acid fermentation. </p>
<p>There’s also the complex mix of bacteria and fungi that convert the curd into delicious products such as soft cheeses, blue cheeses and various mature cheeses. </p>
<p>And it’s not only cow’s milk; goat, sheep, buffalo and camel milk are also used by cultures across the world to produce their own varieties of speciality fermented milk products.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/119404/original/image-20160420-25621-99tqzb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/119404/original/image-20160420-25621-99tqzb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/119404/original/image-20160420-25621-99tqzb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=372&fit=crop&dpr=1 600w, https://images.theconversation.com/files/119404/original/image-20160420-25621-99tqzb.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=372&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/119404/original/image-20160420-25621-99tqzb.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=372&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/119404/original/image-20160420-25621-99tqzb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=467&fit=crop&dpr=1 754w, https://images.theconversation.com/files/119404/original/image-20160420-25621-99tqzb.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=467&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/119404/original/image-20160420-25621-99tqzb.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=467&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Many of our favourite food or beverages look like this at some point.</span>
<span class="attribution"><span class="source">Gaël Chardon/Flickr</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<h2>Preservation</h2>
<p>Apart from sensory advantages, fermentation is a form of food preservation that allows perishable foods to be stored for longer. This was an important aspect of food safety before the introduction of refrigeration in the 19th century. </p>
<p>Along with adding salt (curing meat) or sugar (jams and cordials), the acid produced during fermentation rapidly drops the pH of the starting product. In the case of milk, this rise in acidity causes curdling but is also inhibitory to undesirable (and sometimes deadly) bacteria found in the raw milk.</p>
<p>Similarly, fermentation of meat products – traditionally made from pork, but also beef, chicken and turkey – involves a complex microbiological community of species. These generate lactic acid, acetic acid, diacetyl and produce enzymes that break down protein and fats. </p>
<p>Some of the bacteria produce hydrogen peroxide, which will react with myoglobin in the meat and lead to discolouration. To counter this, other bacteria are present that produce the enzyme <a href="http://www.britannica.com/science/catalase">catalase</a>, breaking down the hydrogen peroxide and preserving the pink colour of the meat. </p>
<p>Some of the bacteria can also convert nitrates (added as preservatives) to nitrites, further enhancing the colour of the product.</p>
<p>Fermented foods extend to vegetarian products, including the classic sauerkraut (fermented cabbage), various fermented varieties of tofu (bean curd) and Spanish-style olives. </p>
<p>Farm animals also benefit from fermentation. In regions of the world where fresh pasture is not available year round, chopped plant material (corn, sorghum and cereals) is allowed to naturally ferment to produce silage, which is used as fodder.</p>
<p>It’s not only about flavour, aroma and nutrition though. Many of the microbes used in fermentation are considered as “<a href="https://theconversation.com/au/topics/probiotics">probiotics</a>”. While the jury is still out on the <a href="https://theconversation.com/we-know-too-little-about-probiotics-to-proclaim-their-virtues-33840">beneficial effects of probiotics</a>, many studies have shown that their consumption is linked to health benefits, including boosting the immune system.</p>
<p>So, next time you enjoy a glass of wine and a fine piece of cheese on a crusty slice of sourdough bread, raise a toast to all the hard-working microscopic good guys!</p>
<p><em>This article is part of the <a href="https://theconversation.com/au/topics/kitchen-science">Kitchen Science</a> series, exploring the amazing physics and chemistry going on in our kitchens every day. If you’re an academic with an idea for a Kitchen Science article, <a href="mailto:tim.dean@theconversation.edu.au">get in touch!</a></em></p><img src="https://counter.theconversation.com/content/57279/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Enzo Palombo has received funding from Dairy Food Safety Victoria and the Australian Meat Processor Corporation. </span></em></p>Many of us shirk at the thought of bacteria or fungus in our food, but without them, we wouldn’t have many of our favourite foods.Enzo Palombo, Professor of Microbiology, Swinburne University of TechnologyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/565832016-04-07T20:05:57Z2016-04-07T20:05:57ZKitchen Science: everything you eat is made of chemicals<figure><img src="https://images.theconversation.com/files/117592/original/image-20160406-28935-1ml0tol.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Chemicals or a spice rack? Or both?</span> <span class="attribution"><span class="source">Hans Splinter/Flickr</span>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span></figcaption></figure><p><em>This is the first in our ongoing Kitchen Science series exploring the physics, chemistry and biology that takes place in your home.</em></p>
<hr>
<p><a href="http://www.chemfreecom.com/">Earnest websites</a>, <a href="https://www.theguardian.com/science/blog/2008/aug/06/dodgyscienceintvadverts">advertisements</a> and well-meaning <a href="http://www.mamamia.com.au/chemicals-affecting-childs-brain/">popular articles</a> routinely warn us about nasty “chemicals” lurking in our homes and kitchens. Many tout the benefits of switching to a “<a href="http://chemical-free-living.com/">chemical-free lifestyle</a>”. </p>
<p>The problem is: the word “chemical” is entirely misused in these contexts. <em>Everything</em> is a chemical – common table salt (sodium chloride), for instance, and even water (<a href="http://www.dhmo.org/truth/Dihydrogen-Monoxide.html">dihydrogen oxide</a>).</p>
<p>The chemicals in our diet are often put into four broad categories: carbohydrates, proteins, fats and lipids, and everything else. This final group has no defining characteristics but includes vitamins, minerals, pharmaceuticals and the hundreds of trace chemicals each of us consumes every day. </p>
<p>Of course, there are toxic and harmful chemicals, but just as many are completely fine for human consumption. So here’s a handy guide to the chemicals in your kitchen and what they mean for your health.</p>
<h2>The macronutrient chemicals</h2>
<p>Proteins, lipids (such as fats) and carbohydrates are known as the macronutrients. These provide most of our daily energy needs. </p>
<p>Despite <a href="https://theconversation.com/the-race-to-find-even-more-new-elements-to-add-to-the-periodic-table-52747">118 known elements</a> in the <a href="http://www.iupac.org/fileadmin/user_upload/news/IUPAC_Periodic_Table-8Jan16.pdf">periodic table</a>, these three categories predominantly contain just four elements – carbon, hydrogen, oxygen and nitrogen – with trace amounts of the remaining elements.</p>
<p>Chemicals called amino acids link together to create proteins. The richest sources include meat and eggs, but significant amounts are also found in beans, legumes and wheat flour.</p>
<p>Carbohydrates contain just carbon, hydrogen and oxygen atoms, all connected in very particular ways. “Carbs” include sugars, starch and cellulose, all of which are digested differently.</p>
<p>While sugars are one type of carbohydrate, artificial sweeteners, such as <a href="https://theconversation.com/sweet-news-no-evidence-that-artificial-sweetener-aspartames-bad-for-you-12608">aspartame</a> and saccharin, are not actually carbohydrates. </p>
<p>Despite concerns about the <a href="http://www.globalhealingcenter.com/natural-health/two-of-the-most-dangerous-artificial-sweeteners/">health effects of artificial sweeteners</a>, the health spotlight has recently been on the natural sweeteners: the <em>sugars</em>. White sugar (sucrose) and high-fructose corn syrup (a mixture of fructose and glucose) have been linked to a <a href="https://theconversation.com/sugar-isnt-just-empty-fattening-calories-its-making-us-sick-49788">range of widespread health conditions</a>.</p>
<p>Just like carbs, fats only contain carbon, hydrogen and oxygen, but gram for gram release more than twice the dietary energy of either protein or the carbs. Perhaps it’s for this reason fats have copped a lot of bad press for longer than the sugars. Nevertheless, some fat is essential for a healthy diet.</p>
<h2>Acids and bases</h2>
<p>Acid sounds bad. But there are many acids sitting benignly in our pantries and fridges.</p>
<p>Consider varieties of food and drink that are acidic. A classic example we often hear is that Coca-Cola has a pH value of about 3.2 (lower means more acidic, with 7 being neutral). That’s strong enough to remove rust from metal. And it’s true, thanks to the phosphoric acid in Coke. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/d5vZdhB9HcY?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Watch as Coke eats away at surface rust.</span></figcaption>
</figure>
<p>As it happens, the human stomach also contains phosphoric acid (as well as hydrochloric acid), and this has an even stronger acidic pH value. Actually, apples and oranges have a similar pH value to Coke, and lemon juice is ten times more acidic.</p>
<p>The acidic characteristics of food and drink combine with other chemicals to provide flavour. Without some acidic character, many foods would be bland.</p>
<p>Chemically speaking, the opposite of acidic is known as basic, or alkali. While acidic substances have a pH of less than 7, basic foods have a pH greater than 7. Examples of basic foods from the kitchen are fewer, but include eggs, some baked products like cakes and biscuits, and bicarb soda.</p>
<h2>Toxic chemicals in the kitchen</h2>
<p>Obviously, there are also toxic chemicals lurking in our kitchen cupboards. But these are usually kept under the sink and often have pH values at the extreme ends of the spectrum. </p>
<p>Cleaning products such as ammonia and lye (i.e. Drano) are very basic. Soaps and detergents are also at the basic end of the scale.</p>
<p>Acidic cleaning solutions are also common, such as concentrated sulfuric acid, which can also be used to unblock drains.</p>
<h2>Cooking is chemistry</h2>
<p>Cooking itself is really just chemistry. Heating, freezing, mixing and blending are all processes used in the laboratory and the kitchen. </p>
<p>When we cook food, a myriad of different physical and chemical processes simultaneously take place to transform the ingredients (i.e. chemicals) involved. </p>
<p>Carbohydrates are an interesting case study. Simple sugars combine with proteins in the <a href="http://www.scienceofcooking.com/maillard_reaction.htm">Maillard reaction</a>, which is responsible for browning food when it’s cooked. Add a little more heat and caramelisation takes over, while too much heat for too long leads to burnt flavours. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/117594/original/image-20160406-28945-1kr3phz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/117594/original/image-20160406-28945-1kr3phz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/117594/original/image-20160406-28945-1kr3phz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=397&fit=crop&dpr=1 600w, https://images.theconversation.com/files/117594/original/image-20160406-28945-1kr3phz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=397&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/117594/original/image-20160406-28945-1kr3phz.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=397&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/117594/original/image-20160406-28945-1kr3phz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=499&fit=crop&dpr=1 754w, https://images.theconversation.com/files/117594/original/image-20160406-28945-1kr3phz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=499&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/117594/original/image-20160406-28945-1kr3phz.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=499&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">It takes some deft chemistry to make a seasoned smoked brisket.</span>
<span class="attribution"><span class="source">jeffreyw/Flickr</span>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>Starch is another carbohydrate well known for its ability to create gels, such as in a panna cotta. Upon heating, powdered starch combines with water and a completely different texture is created.</p>
<p>So next time you hear someone say “I don’t like to put chemicals into my body”, feel free to chuckle. <em>Everything</em> is made of chemicals. We’d be in a bit of strife without chemicals, not least in the kitchen.</p>
<p><em>This article is part of the <a href="https://theconversation.com/au/topics/kitchen-science">Kitchen Science</a> series, exploring the amazing physics and chemistry going on in our kitchens every day. If you’re an academic with an idea for a Kitchen Science article, <a href="mailto:tim.dean@theconversation.edu.au">get in touch!</a></em></p><img src="https://counter.theconversation.com/content/56583/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Chris Thompson is affiliated with Monash University and the Chemistry Education Association. </span></em></p>Chemicals have a bad rap these days. But the fact is that everything is made of chemicals. Here are some of the chemicals at work in your kitchen.Chris Thompson, Lecturer in Chemistry, Monash UniversityLicensed as Creative Commons – attribution, no derivatives.