tag:theconversation.com,2011:/ca/topics/everyday-science-29660/articlesEveryday science – The Conversation2023-12-20T22:11:26Ztag: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>
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<figcaption><span class="caption">Paul Kelly performs his song How To Make Gravy.</span></figcaption>
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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>
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<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>
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<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>
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<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>
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<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>
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<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>
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<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>
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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 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/1159842019-05-10T10:39:34Z2019-05-10T10:39:34ZWhat happens when a raindrop hits a puddle?<figure><img src="https://images.theconversation.com/files/272916/original/file-20190506-103075-yq4lnf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The math of raindrops.</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/rain-on-asphalt-tarmac-road-creating-318261128?src=P0QMTPgKihYHilqhp1RT_A-1-23">Stefan Holm/shutterstock.com</a></span></figcaption></figure><p>Have you ever taken a walk through the rain on a warm spring day and seen that perfect puddle? You know, the one where the raindrops seem to touch down at just the right pace, causing a dance of vanishing circles? </p>
<p>Even before I entered the field of <a href="https://scholar.google.com/citations?user=twVj7FwAAAAJ&hl=en">fluid flow research</a> nearly 15 years ago, I was fascinated by the waves that appear after a raindrop hits a puddle. </p>
<p>As I became focused on the study of <a href="https://doi.org/10.1017/S0022112010004416">unstable waves in liquid sheets</a> – geared toward <a href="https://doi.org/10.1017/S0022112010004416">mitigating undesirable waves in industrial coating</a> and <a href="https://doi.org/10.1016/j.compfluid.2008.05.005">atomization processes</a> – my fascination with puddle waves turned into an obsession. What is going on? Where does the pattern come from? Why does the impact of rain in a puddle look different than when rain falls elsewhere, like in a lake or the ocean?</p>
<p>It turns out that it all has to do with something called <a href="https://www.cambridge.org/us/academic/subjects/mathematics/fluid-dynamics-and-solid-mechanics/waves-fluids-1?format=PB&isbn=9780521010450">dispersion</a>. </p>
<p>In the context of water waves, dispersion is the ability of waves of different wavelengths to each move at their own individual speeds. Looking down on a puddle, we see a collection of such waves moving together as one ripple in the water.</p>
<p>When a raindrop touches down, imagine it as a “ding” to the water surface. This ding can be idealized as a packet of waves of all different sizes. After the raindrop falls, the packet’s waves are ready to begin their new life in the puddle.</p>
<p>However, whether we see those waves as ripples depends on the body of water that the raindrop lands on. The number and spacing of rings that you see depends on the height of the puddle. This has been verified in some very cool <a href="https://doi.org/10.1119/1.3556140">ripple tank experiments</a>, where a drop of the same velocity falls into a container with water at different depths. </p>
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<figcaption><span class="caption">A model of waves in a dispersive puddle, after a raindrop hits. The initial wave bundle caused by the raindrop splits into waves of different sizes. Large waves in the center move more slowly than small waves at the perimeter.</span></figcaption>
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<p>Shallow puddles enable ripples, because they are much thinner than they are wide. The balance between the surface force – between the water puddle and the air above it – and the gravitational force tips in favor of surface force. This is key, since the surface force depends on the curvature of the water surface, whereas the gravitational force does not. </p>
<p>An initially still shallow puddle becomes curved at the surface after the raindrop hits. The surface force is different for long waves than for short ones, causing waves of different sizes to separate into ripples. For shallow puddles, the long waves move slowly away from the point of impact, while the short waves move fast, and the really short waves move really fast, becoming tightly packed at the perimeter. This creates the enchanting pattern that we see.</p>
<p>Raindrops may react differently in other situations. Imagine that rain is hitting a lake or ocean – or those deep pothole puddles that require galoshes. Here, the raindrop hits the water, but the force due to gravity becomes more important. It moves waves of all sizes at the same speed which may overpower the rippling effect due to the surface force. </p>
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<figcaption><span class="caption">A model of waves in a nondispersive puddle, after a raindrop hits. The initial wave bundle caused by the raindrop stays intact and travels at a single speed.</span></figcaption>
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<p>The combination of teaching undergraduate partial differential equations while simultaneously continuing to research liquid sheets led to what I’ve been calling the <a href="https://people.rit.edu/nsbsma/home/Puddles.html">“puddle equation</a>.” When solved, the equation creates an animated simulation of what happens after a raindrop hits a puddle. It’s a simplified version of an equation in one of our group’s <a href="https://doi.org/10.1103/PhysRevFluids.1.073604">more recent research endeavors</a>, but it’s also consistent with the <a href="https://www.cambridge.org/us/academic/subjects/mathematics/fluid-dynamics-and-solid-mechanics/waves-fluids-1">classical description of ripples</a>.</p>
<p>I use this <a href="https://people.rit.edu/nsbsma/home/Puddles.html">approximate description of puddle waves</a> as one way to get students excited about math by relating it to the world around them.</p>
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<a href="https://images.theconversation.com/files/272852/original/file-20190506-103057-7zoxc0.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/272852/original/file-20190506-103057-7zoxc0.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/272852/original/file-20190506-103057-7zoxc0.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=514&fit=crop&dpr=1 600w, https://images.theconversation.com/files/272852/original/file-20190506-103057-7zoxc0.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=514&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/272852/original/file-20190506-103057-7zoxc0.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=514&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/272852/original/file-20190506-103057-7zoxc0.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=646&fit=crop&dpr=1 754w, https://images.theconversation.com/files/272852/original/file-20190506-103057-7zoxc0.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=646&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/272852/original/file-20190506-103057-7zoxc0.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=646&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">A model of waves in a dispersive puddle, after a raindrop hits. The top three figures show what happens after a drop hits the puddle, with arrows indicating the passage of time. The bottom figure shows the cross-sectional view through the puddle, highlighting that the initial wave bundle caused by the raindrop splits into waves of different sizes. Large waves in the center move more slowly than small waves at the perimeter.</span>
<span class="attribution"><span class="source">Nate Barlow</span></span>
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<p>The study of surface-force-driven waves is important for applications such as coating processes involved in making <a href="https://doi.org/10.1016/j.jpowsour.2018.09.019">batteries</a> and <a href="http://dx.doi.org/10.1021/acsenergylett.8b01556">solar cells</a>. </p>
<p>Such waves also appear as a result of the leg stroke of a <a href="https://doi.org/10.1038/424621a">water strider</a> insect, but <a href="https://doi.org/10.1038/nature01793">research has found</a> that the water strider isn’t specifically looking to make those waves to enable travel. </p>
<p>The beauty of puddle waves is no small thing by itself. By connecting nature with its primal language – mathematics – we gain access to its control panel, allowing us to observe every little detail, uncovering all the secrets.</p><img src="https://counter.theconversation.com/content/115984/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Nate Barlow 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>Why does the impact of rain in a puddle look different from when it falls elsewhere, like in a lake or the ocean? A ‘puddle equation’ dives deep into the secret math of ripples.Nate Barlow, Assistant Professor of Mathematical Sciences, Rochester Institute of TechnologyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/745632017-03-16T11:34:50Z2017-03-16T11:34:50ZHow chemistry can make your ironing easier<figure><img src="https://images.theconversation.com/files/160978/original/image-20170315-5332-1rl83tr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Where'd I leave my bunsen burner?</span> <span class="attribution"><span class="source">Shutterstock</span></span></figcaption></figure><p>I hate ironing, I’ll do more or less anything to avoid it. So faced with a giant pile of laundry I got easily distracted. I started to wonder why those shirts emerged from the machine looking like a tangled bag of rags. How come the cotton clothes get crumpled so easily? And what’s with easy-iron garments, why don’t they need so much pressing? </p>
<p>Since I’m a scientist I know its important to understand the theory behind a methodology. And so it became imperative, before unleashing the iron and its board, that I found the answers to these pressing questions.</p>
<p>It turns out that the wrinkles in my shirts are all down to the chemisty of plant-based fabrics. Cotton, linen, hemp and so on are predominantly made of cellulose. Cellulose is what’s known as a polymer because it consists of thousands of glucose molecules joined together to form linear chains. Each glucose subunit is “sticky” because it can <a href="http://pubs.acs.org/doi/full/10.1021/ja0257319">bind to neighbouring cellulose molecules</a> via something called hydrogen bonds. Individually, these bonds are very weak, but together they form a strong network that gives the fabric its strength.</p>
<p>These hydrogen bonds are particularly dynamic in that they are forever breaking and then rapidly reforming. As a result, clothes start taking on the shape that they are left in. This isn’t a problem if I get around to putting freshly ironed shirts on a hanger. But it is an issue when I chuck them in a heap on <a href="http://dictionary.cambridge.org/dictionary/english/floordrobe">the “floordrobe”</a>. As they sit there in a pile, the bonds break and reform, the clothes take up the new shape of the fabric, and the creases set in place.</p>
<h2>Just add water</h2>
<p>Things get even worse when water enters the equation (like in the washing machine). Water molecules insert themselves between the cellulose molecules, break up the hydrogen bonds and act like a lubricant, allowing the cellulose molecules to <a href="https://books.google.com.sa/books?id=SYzNAgAAQBAJ&pg=PT117&lpg=PT117&dq=cellulose+ironing&source=bl&ots=0YkNkiWYL-&sig=eXsUL7Tn818uBUOiuNwVQrmsRl4&hl=en&sa=X&redir_esc=y#v=onepage&q=cellulose%20ironing&f=false">slide over each other</a>. Then, when the fabric dries, the cotton keeps its now wrinkled shape. And that is the state of the pile of shirts that now stands before me.</p>
<p>This is where the hot, steaming iron comes in. The combination of heat and moisture quickly breaks the hydrogen bonds. As I apply these with a bit of pressure, all the cellulose molecules are forced to lie parallel with each other, so flattening the cloth.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/160966/original/image-20170315-5354-1odnx10.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/160966/original/image-20170315-5354-1odnx10.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/160966/original/image-20170315-5354-1odnx10.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=424&fit=crop&dpr=1 600w, https://images.theconversation.com/files/160966/original/image-20170315-5354-1odnx10.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=424&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/160966/original/image-20170315-5354-1odnx10.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=424&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/160966/original/image-20170315-5354-1odnx10.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=533&fit=crop&dpr=1 754w, https://images.theconversation.com/files/160966/original/image-20170315-5354-1odnx10.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=533&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/160966/original/image-20170315-5354-1odnx10.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=533&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 Chemistry of Ironing.</span>
<span class="attribution"><span class="source">Andy Brunning / Compound Interest</span></span>
</figcaption>
</figure>
<p>But what if I want to avoid doing the ironing? The wrinkled look is always an option and, as an academic, I can just about pull it off. But occasionally I do need a pressed shirt. I could go with the <a href="http://www.oldandinteresting.com/laundry-starch-history.aspx">age-old practice of starching</a> my clothes to keep them crease free. This works because starch is also a polymer made from glucose, so it too can form all those sticky hydrogen bonds.</p>
<p>But, unlike cellulose, starch is a branched polymer. This means that if I apply it to cellulose, it sticks and acts like a scaffolding holding all the cellulose molecules in place. The drawback is that it gives me a rather stiff look and more to the point the starch is soluble so it just comes out in the wash. The net result is that it doesn’t do much to reduce my list of chores – I still need to iron and I’d just have to apply starch too boot.</p>
<p>What I need is a more permanent version of starch. And that’s exactly what I get in easy-iron clothing. Originally, <a href="http://www.slate.com/articles/news_and_politics/explainer/2007/02/why_do_clothes_wrinkle.html">formaldehyde was used to permanently link cellulose molecules together</a>, stopping them sliding about and limiting the amount of wrinkles that formed. More recently, formaldehyde (which isn’t very nice stuff) has been replaced with friendlier (but even less easy to pronounce) <a href="http://www.hoffmancentre.com/wp-content/uploads/2016/12/chemistry_and_nanotech_work_to_make_carefree_clothing.pdf">cross-linkers such as dimethyloldihydroxyethyleneurea</a>. The wrinkle-resistant shirts are good in a pinch but they have a slightly plastic feel that I don’t particularly like and they still release tiny amounts of formaldehyde which can irritate the skin.</p>
<p>The pile of laundry is still waiting for me. But at least I have the theory of ironing all straightened out, and so I suppose I’d best just get on with the practical session. Or maybe I’ll go for that crumpled look and just call myself a theoretical ironist.</p><img src="https://counter.theconversation.com/content/74563/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Mark Lorch 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>If it weren’t for chemistry, that pile of wrinkled shirts would take even longer to sort out.Mark Lorch, Professor of Science Communication and Chemistry, University of HullLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/628542016-07-26T12:24:33Z2016-07-26T12:24:33ZDoes drinking hot tea in summer really cool you down?<figure><img src="https://images.theconversation.com/files/131406/original/image-20160721-32610-1rlsu1f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Refreshing – or a sentence to sweat?</span> <span class="attribution"><a class="source" href="http://www.shutterstock.com/cat.mhtml?lang=en&language=en&ref_site=photo&search_source=search_form&version=llv1&anyorall=all&safesearch=1&use_local_boost=1&autocomplete_id=&searchterm=tea%20summer&show_color_wheel=1&orient=&commercial_ok=&media_type=images&search_cat=&searchtermx=&photographer_name=&people_gender=&people_age=&people_ethnicity=&people_number=&color=&page=1&inline=247474183">Shutterstock</a></span></figcaption></figure><p>I remember as a child, on the rare warm days that we used to get in Britain, my grandmother telling me to “have a cup of black tea … it will help cool you down”. As a seven-year-old, this seemed like a crazy idea, especially when all I wanted was a cold lemonade and another ice cream. But it appears that this old wives’ tale may actually be more Stephen Hawking than Stephen King.</p>
<p>The idea of drinking hot drinks in warm weather goes back hundreds of years. <a href="http://www.bbc.co.uk/news/magazine-27991440">Tea, or “chai” is one of the most popular drinks in India</a>, and many of the <a href="https://en.wikipedia.org/wiki/List_of_countries_by_tea_consumption_per_capita">leading consumers of tea per capita are in tropical or desert regions</a>. Recently, evidence has begun to emerge that drinking hot drinks may really help to <a href="http://www.ncbi.nlm.nih.gov/pubmed/22574769">cool you down</a>, too.</p>
<p>In 2012, <a href="http://sydney.edu.au/health-sciences/about/people/profiles/ollie.jay.php">Ollie Jay</a> published the <a href="http://www.ncbi.nlm.nih.gov/pubmed/22574769">first of a series</a> of papers to see if drinking a warm drink can actually lower the amount of heat stored by the body compared to a cold drink. In this first study, volunteers were asked to cycle at a relatively low intensity for 75 minutes in around 24°C heat, 23% relative humidity, while consuming water at either 1.5˚C, 10˚C, 37˚C or 50˚C. </p>
<p>The change in core temperature was slightly greater when 50˚C water was ingested compared to 1.5˚C and 10˚C water. However, when the authors considered the effect of drink temperature on body heat storage, which is a better indicator of total body temperature, the results were very different. Following the ingestion of the warm drink, overall body heat storage was actually lower following exercise than with cooler drinks. </p>
<h2>The sweat factor</h2>
<p>An explanation for these findings appears to be related to how sweating may be influenced by drink temperature. Sweating, and more importantly the evaporation of this sweat, is one of the <a href="https://theconversation.com/from-perspiration-to-world-domination-the-extraordinary-science-of-sweat-62753">key avenues for modulating body temperature and maintaining heat balance</a>. </p>
<p>Due to the increased heat load from drinking a warm drink, there is a compensatory increase in overall sweat output, which outweighs the internal heat gain from the warm drink. Consistently, a 50˚C drink results in a higher whole body sweat loss (around 570ml vs about 465ml for 1.5˚C). In practical terms, this means that more sweat is produced which is evaporated from the skin surface, increasing heat loss from evaporation and reducing body heat storage. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/131969/original/image-20160726-7041-1mx6fjd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/131969/original/image-20160726-7041-1mx6fjd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/131969/original/image-20160726-7041-1mx6fjd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/131969/original/image-20160726-7041-1mx6fjd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/131969/original/image-20160726-7041-1mx6fjd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/131969/original/image-20160726-7041-1mx6fjd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/131969/original/image-20160726-7041-1mx6fjd.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">Cold water: should he drink it?</span>
<span class="attribution"><a class="source" href="http://www.shutterstock.com/cat.mhtml?lang=en&language=en&ref_site=photo&search_source=search_form&version=llv1&anyorall=all&safesearch=1&use_local_boost=1&autocomplete_id=&searchterm=runner%20hot&show_color_wheel=1&orient=&commercial_ok=&media_type=images&search_cat=&searchtermx=&photographer_name=&people_gender=&people_age=&people_ethnicity=&people_number=&color=&page=1&inline=154131425">Shutterstock</a></span>
</figcaption>
</figure>
<p>Importantly, however, this study was conducted under conditions that allowed complete evaporation of sweat – in other words dripping sweat was limited by maintaining a good airflow and keeping humidity low. The results would likely be different in conditions where sweat evaporation is limited, such as in hot and humid conditions. In fact, drinking cold drinks may be more favourable in these circumstances, minimising inefficient sweat losses – dripping sweat – and consequently aiding an individual’s hydration status. </p>
<h2>Mouth or stomach?</h2>
<p><a href="http://www.ncbi.nlm.nih.gov/pubmed/24577060">In a second study</a>, Jay aimed to establish the effect of drink temperature on local sweat rate, and to determine the location of thermoreceptors that may influence sweating. They demonstrated that with differing drink temperatures, colder drinks (1.5˚C) resulted in reductions in local sweat rate compared to when warm drinks were ingested (50˚C), despite identical changes in core and skin temperature.</p>
<p>Interestingly, however, differences in the sweat response were found when fluid was either swilled around the mouth or delivered directly to the stomach via a nasogastric tube. The data showed that only when cold drinks were delivered directly to the stomach did they result in reduced local sweat rate. This data indicates that the sensors responsible for influencing the sweat response, and therefore regulation of body temperature, reside somewhere in the abdominal cavity. </p>
<p>In a <a href="http://www.ncbi.nlm.nih.gov/pubmed/?term=Ice+Slurry+Ingestion+Leads+to+a+Lower+Net+Heat+Loss+during+Exercise">third study conducted in their lab</a>, the team asked people to consume either 37˚C fluid or ice during exercise. In agreement with their previous work, they showed that there was a reduction in heat loss following ice ingestion compared to fluid at 37˚C, as a result of reduced sweat evaporation from the skin surface. </p>
<p>This has implications for endurance performance in the heat. In essence, where changes in body temperature are known to <a href="http://www.ncbi.nlm.nih.gov/pubmed/10066720">influence performance, ice ingestion</a> could result in an increase in body heat, negatively influencing endurance capability. The ingestion of an iced drink prior to exercise and in hot and humid environments, however, should be beneficial. </p>
<p>So, depending on your environmental conditions, maybe reaching for that cup of tea isn’t such a crazy idea after all. Plus the moral of the story: listen to your grandmother’s advice – it’s based on years of experience.</p><img src="https://counter.theconversation.com/content/62854/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>Here’s the science.Steve Faulkner, Research associate, Loughborough UniversityKaty Griggs, Research Assistant and PhD student, Loughborough UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/606592016-06-14T11:49:11Z2016-06-14T11:49:11ZDoes tapping a can of fizzy drink really stop it foaming over?<figure><img src="https://images.theconversation.com/files/125521/original/image-20160607-15045-cx1qsm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Tap, tap, boom!</span> <span class="attribution"><a class="source" href="http://www.shutterstock.com">Shutterstock.com</a></span></figcaption></figure><p>It is one of the distinct sounds of summer: the noise of people tapping the tops of their cans of fizzy drink before opening them. But does this widespread ritual really stop a can of beer or pop from gushing over?</p>
<p>When you open a can of fizzy drink, the refreshing “hiss” is the result of gas bubbles escaping from the liquid as a result of a change in the solubility of the carbon dioxide (CO2) in it. This change occurs due to the pressure inside the can decreasing from <a href="http://hypertextbook.com/facts/2000/SeemaMeraj.shtml">~3 bar (can closed)</a> to 1 bar at atmospheric pressure (can open). The solubility of CO2 in water reduces from ~4.5g in one litre of water at ~3 bar, to ~1.5g at atmospheric pressure, something that is described by <a href="https://www.khanacademy.org/science/health-and-medicine/respiratory-system/gas-exchange-jv/v/henry-s-law">Henry’s Law</a>.</p>
<p>Before the can is opened, microscopic gas bubbles attach to the inside of it (nucleation). When the can is opened, these bubbles increase in size, due to the decrease in the solubility of CO2. When these bubbles reach a certain size they detach from the inside of the can and rise up to the top of the can due to buoyancy and displace liquid in their path (as shown in Figure 1).</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/126503/original/image-20160614-22383-tgmpwj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/126503/original/image-20160614-22383-tgmpwj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=330&fit=crop&dpr=1 600w, https://images.theconversation.com/files/126503/original/image-20160614-22383-tgmpwj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=330&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/126503/original/image-20160614-22383-tgmpwj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=330&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/126503/original/image-20160614-22383-tgmpwj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=415&fit=crop&dpr=1 754w, https://images.theconversation.com/files/126503/original/image-20160614-22383-tgmpwj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=415&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/126503/original/image-20160614-22383-tgmpwj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=415&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Figure 1: the bubble formation upon opening a bottle of sparkling water.</span>
<span class="attribution"><span class="source">Images captured specifically for this article</span></span>
</figcaption>
</figure>
<p>So what part could tapping the top of the can play in this process? Whether or not this technique actually works is the subject of some debate but there is a theory explaining why it may work. As described earlier, the bubbles in an unopened can nucleate at the walls (Figure 2a) so tapping the can before opening could dislodge some of the bubbles, enabling them to float to the top of the liquid. </p>
<p>When a can is opened, the bubbles expand (Figure 2b) with those deeper within the liquid travelling further than those near the surface, displacing more of the drink and possibly resulting in greater amounts of ejected liquid. A “tapped” can will have fewer of these “deep” bubbles and so less liquid will be dislodged – and possibly sprayed out – than an “untapped” can (Figure 2c).</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/126504/original/image-20160614-22380-9q1ycb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/126504/original/image-20160614-22380-9q1ycb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=485&fit=crop&dpr=1 600w, https://images.theconversation.com/files/126504/original/image-20160614-22380-9q1ycb.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=485&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/126504/original/image-20160614-22380-9q1ycb.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=485&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/126504/original/image-20160614-22380-9q1ycb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=609&fit=crop&dpr=1 754w, https://images.theconversation.com/files/126504/original/image-20160614-22380-9q1ycb.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=609&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/126504/original/image-20160614-22380-9q1ycb.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=609&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Figure 2: a possible mechanism for why tapping a can before opening may reduce gushing.</span>
<span class="attribution"><span class="source">Diagram drawn specifically for this article</span></span>
</figcaption>
</figure>
<p>Bubbles also can be dislodged from the side of the can with violent shaking, of course – but this method introduces more turbulence which increases the energy of the system, resulting in more bubbles in the drink and more spraying when opened. Sharply tapping the top of an open beer bottle with another has a similar effect, commonly resulting in a <a href="http://www.npr.org/sections/thesalt/2013/11/20/246390302/beer-tapping-physics-why-a-hit-to-a-bottle-makes-a-foam-volcano">colossal gush of beer foam</a>. This is because pressure waves caused by the impact create tiny “<a href="http://arxiv.org/abs/1310.3747v1">mushroom clouds</a>” inside the bottle that eject huge quantities of liquid as they escape. </p>
<h2>Glass and gushing</h2>
<p>The debate of tapping aside, the actual material that the container is made from may also reduce gushing. It has been shown that the amount of foam formed when pouring beer into glasses of different “wettabilities” – the extent to which water wets a material – can affect not only the amount of beer head formed but also <a href="http://www.ntu.ac.uk/apps/news/184319-15/A_coated_pint_glass_can_control_foaming_of_beer_and_other_liquids_study_sh.aspx">the size of the bubbles</a> on the inside of the glass. This information is relevant when such bubbles are thought to be the cause of gushing. </p>
<p>Another important factor when it comes to the level of gushing is the stabilisation of the bubbles caused by the presence of large molecules in the drink. This is why some beers have long-lived foam heads compared to the short-lived bubbles at the surface of, say, sparkling water. But such foam stabilising agents are a conversation for another day.</p>
<p>So this summer why not try different ways of opening your fizzy drink – and see how much of it you end up wearing.</p><img src="https://counter.theconversation.com/content/60659/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Chris Hamlett 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>Science has some answers.Chris Hamlett, Lecturer in Chemistry and Physics, Nottingham Trent UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/595472016-05-25T13:48:17Z2016-05-25T13:48:17ZWhy alcohol makes you feel warm – and other strange effects it has on the brain<figure><img src="https://images.theconversation.com/files/123625/original/image-20160523-10986-1nb57rz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">It's not that warm, John.</span> <span class="attribution"><a class="source" href="http://www.shutterstock.com/pic-401014273/stock-photo-finger-art-of-couple-woman-is-upset-because-man-drunk.html?src=HajuJjFl-cQyHOo1Ut3w-w-1-83">Shutterstock</a></span></figcaption></figure><p>Alcohol: why do we drink it? People have been consuming alcohol for at least 10,000 years. And when drinking water was rather risky, alcohol seemed <a href="https://www.wdl.org/en/item/3956/">a much safer bet</a>. Amaldus of Villanova, a 14th-century monk, <a href="http://bit.ly/1Rkq1kA">even wrote</a> that alcohol “prolongs life, clears away ill humors, revives the heart and maintains youth”. </p>
<p>Today people will give you many reasons for their decision to drink and most of these reflect the effects it has on mind and brain. But before you get too sozzled, one thing is for sure: it is certainly not a safer, healthier bet than water.</p>
<h2>1. It tastes nice</h2>
<p>It depends on what you are drinking (some drinks like alcopops contain more sugar) and people obviously have different taste preferences. The fact that ethanol is created from sugars is also likely to increase our propensity to drink. For example, <a href="http://www.ncbi.nlm.nih.gov/pubmed/24962796">research suggests</a> that some individuals have a predisposition to prefer sugar and this can make them more prone to developing alcohol addiction. Alcohol also seems to act on some of the same brain areas <a href="http://link.springer.com/article/10.1007/s12078-015-9177-8">activated by sweet tastes</a>.</p>
<p>Yet ethanol is not always perceived as pleasant; it <a href="http://news.psu.edu/story/327406/2014/09/23/research/research-shows-alcohol-sensations-influenced-genes">can be quite bitter</a>. If ethanol is given over time rats show increasing “tasty” responses in their mouth and facial expressions. However, if it’s given after <a href="http://www.webmd.com/drugs/2/drug-7399/naltrexone-oral/details">naltrexone</a>, a substance that reduces <a href="http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2756052/">opioid activity</a> – which signals “liking” something among other things – in the brain, “aversive” reactions increase, <a href="http://www.sciencedirect.com/science/article/pii/S0741832906000437">and less alcohol is consumed</a>. This suggests that the opioid receptors mediate how much we like alcohol. And substances like naltrexone are used to treat people with alcohol use disorder. </p>
<h2>2. I really want a drink</h2>
<p><a href="https://en.wikipedia.org/wiki/Dopamine">Dopamine</a>, a neurotransmitter involved in controlling reward and pleasure in the brain, plays a key role in motivated behaviour and is also associated with many forms of addiction. Ethanol, like all other known addictive substances, <a href="http://onlinelibrary.wiley.com/doi/10.1111/j.1530-0277.2007.00405.x/full">increases the release of dopamine</a>. This can cause you to drink more – why you might want a second, or a third drink, after the first one. </p>
<p>However, after repeated experience with addictive substances like alcohol, dopamine connections <a href="http://onlinelibrary.wiley.com/doi/10.1111/j.1530-0277.1996.tb05936.x/abstract">can remodel themselves</a>, sometimes decreasing the numbers of receptors that bind dopamine. The size of this reduction is associated with a higher <a href="http://ajp.psychiatryonline.org/doi/pdf/10.1176/ajp.161.10.1783">risk of relapse</a> in alcohol addiction. </p>
<h2>3. It makes me feel better</h2>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/123623/original/image-20160523-11028-fcnonv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/123623/original/image-20160523-11028-fcnonv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=398&fit=crop&dpr=1 600w, https://images.theconversation.com/files/123623/original/image-20160523-11028-fcnonv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=398&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/123623/original/image-20160523-11028-fcnonv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=398&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/123623/original/image-20160523-11028-fcnonv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=501&fit=crop&dpr=1 754w, https://images.theconversation.com/files/123623/original/image-20160523-11028-fcnonv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=501&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/123623/original/image-20160523-11028-fcnonv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=501&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">Taking the edge off?</span>
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<p>Drinking alcohol can be a form of “self-medication” used to unwind from workplace stress or <a href="http://shura.shu.ac.uk/5761/1/Macaskill_Motivation_to_drink_alcohol_.pdf">ease study pressures</a>, making it less “aqua vitae” (water of life) and more and “Aqua ad vitae” (water to counteract life). And more than 2,600 years ago the Greek poet Alceus <a href="http://pubs.niaaa.nih.gov/publications/arh23-4/250-255.pdf">suggested</a> that “we must not let our spirits give way to grief … Best of all defences is to mix plenty of wine and drink it”. </p>
<p>Stress is biologically mediated by the hypothalamic pituitary adrenal axis – a feedback system between the brain and the pituitary and adrenal glands. But acute alcohol consumption can stimulate this, increasing the production of several stress hormones including <a href="https://en.wikipedia.org/wiki/Corticosterone">corticosterone</a> and <a href="https://en.wikipedia.org/wiki/Adrenocorticotropic_hormone">corticotropin</a>. But the “stress” response also interacts with the reward effects from the dopamine system, so it may very well feel good.</p>
<h2>4. It helps me overcome my inhibitions</h2>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/123621/original/image-20160523-11000-j1jhb3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/123621/original/image-20160523-11000-j1jhb3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/123621/original/image-20160523-11000-j1jhb3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/123621/original/image-20160523-11000-j1jhb3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/123621/original/image-20160523-11000-j1jhb3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/123621/original/image-20160523-11000-j1jhb3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/123621/original/image-20160523-11000-j1jhb3.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">
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<span class="caption">Cin cin.</span>
<span class="attribution"><a class="source" href="http://www.shutterstock.com/pic-390643270/stock-photo-people-leisure-celebration-friendship-and-bachelor-party-concept-happy-male-friends-drinking.html?src=3pjimUXjVzeol4z2hidbcQ-1-43">Mates by Shutterstock</a></span>
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<p>Alcohol is known <a href="http://onlinelibrary.wiley.com/doi/10.1111/j.1530-0277.2010.01218.x/full">to reduce inhibitory control</a> in the prefrontal cortex – the part of the brain associated with decision-making and social behaviour – coming more under the control of mid-brain dopamine neurons. This leads to the loss of self-restraint that people report when drinking. </p>
<p>One noticeable effect – after just a few drinks – is <a href="https://theconversation.com/how-alcohol-makes-you-friendlier-but-only-to-certain-people-41730">an increase in sociability</a>. But the loss of inhibition probably also underlies risk taking behaviour while under the influence and goes some way towards explaining <a href="http://onlinelibrary.wiley.com/doi/10.1111/j.1530-0277.1993.tb00837.x/abstract">the association</a> between drinking and accidents and injuries.</p>
<h2>5. It helps me sleep</h2>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/123629/original/image-20160523-11004-oobbv2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/123629/original/image-20160523-11004-oobbv2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/123629/original/image-20160523-11004-oobbv2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/123629/original/image-20160523-11004-oobbv2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/123629/original/image-20160523-11004-oobbv2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/123629/original/image-20160523-11004-oobbv2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/123629/original/image-20160523-11004-oobbv2.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">
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<span class="caption">Passing out: not quite the same as getting some kip.</span>
<span class="attribution"><a class="source" href="http://www.shutterstock.com/pic-318334130/stock-photo-drunk-young-handsome-man-resting-on-couch-in-the-living-room-with-head-on-the-floor.html?src=z7ylkD0egxbtYKS8-j706Q-1-2">Shutterstock</a></span>
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<p>Despite the fact that we may opt to partake in a night cap, <a href="http://onlinelibrary.wiley.com/doi/10.1111/acer.12006/full">research shows</a> that certain doses of alcohol may reduce the amount of slow wave and REM sleep we have. So it may help us to drop off faster, but alcohol doesn’t result in a better quality of sleep. REM sleep is important for cognitive processes <a href="http://www.nature.com/neuro/journal/vaop/ncurrent/full/nn.4304.html">such as memory consolidation</a> so reducing the time in which this process occurs has a detrimental effect on memory. Consolidation of emotional memories may be particularly affected. </p>
<p><a href="http://www.sciencedirect.com/science/article/pii/S0028390815001999">It is also known</a> that alcohol acts on the process of long-term potentiation – the way in which neurons remodel the connections between them after learning. So alterations in both REM and slow wave sleep after drinking may potentially disrupt the brain’s memory processes.</p>
<h2>6. It eases my pain</h2>
<p>This known effect has been used to support alcohol’s consumption throughout history: consume it and you can successfully dull your perception of pain. Pain-causing signals are detected by sensory neurons (or nociceptors) <a href="http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2964977/">that pass this information</a> through chemicals such as glutamate, via synapses in the spinal cord, up into the brain. But this <a href="https://en.wikipedia.org/wiki/Spinothalamic_tract">ascending signal</a> can be “dampened down” by alcohol, which is how it achieves some of its pain-dulling effects. </p>
<p>Unfortunately, research suggests that this pain dampening effect <a href="http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4412487/">is highly variable</a>. And while some people do consume alcohol to help relieve chronic pain, it is possible for tolerance to occur such that <a href="http://pubs.niaaa.nih.gov/publications/PainFactsheet/Pain_Alcohol.pdf">pain relief lessens over time</a>. Enhanced pain sensitivity may even happen <a href="http://link.springer.com/article/10.1007%2FBF02246289">in chronic drinkers</a>.</p>
<h2>7. A drink will warm me up</h2>
<p>Not quite. While alcohol can make you feel warm temporarily this is a perception generated by heat sensitive neurons (thermoreceptors) <a href="https://en.wikipedia.org/wiki/Thermoreceptor">located in your skin</a> that detect a rise in your skin temperature from an increase in blood flow in the vessels close to the skin’s surface. In fact, alcohol actually lowers your core body temperature because the rush of blood to the skin’s surface is a means of body cooling. </p>
<p>So while you may feel warm on the outside, you are getting cold on the inside. Alcohol consumption <a href="http://www.ncbi.nlm.nih.gov/pubmed/18420115">has also been shown</a> to reduce the perception of cold air temperatures but it is thought that this effect may not come from changes in the dilation of blood vessels but may originate in the brain itself.</p>
<p>All in all, alcohol has multiple effects on your mind and brain. If you do decide to have a drink, for whatever reason, do so knowledgeably.</p><img src="https://counter.theconversation.com/content/59547/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Claire Rostron 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>Drinking booze can have some quite different effects on brain and body.Claire Rostron, Senior Lecturer, The Open UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/559752016-03-14T08:21:27Z2016-03-14T08:21:27ZWhy do wombats do cube-shaped poo?<figure><img src="https://images.theconversation.com/files/114299/original/image-20160308-22123-14alc8i.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Wombat: something of an enigma.</span> <span class="attribution"><span class="source">Shutterstock</span></span></figcaption></figure><p>Poo comes in many different sizes, from the microscopic poo of the smallest invertebrates, to the largest poo of the African elephants who can each produce over 50kg per day. It also comes in many shapes, such as tubes (dogs), pellets (rabbits) or splats (cows), but the wombat is unique in the animal kingdom in that it produces cubic poo, and lots of it – around 80 to 100 cubes per night.</p>
<p>The <a href="http://animals.nationalgeographic.com/animals/mammals/wombat/">wombat</a> is a large relative of the koala, native to Australia. It is solitary and nocturnal, living in underground burrows during the day but coming out at night to forage on grasses and other vegetation. It also sleeps a lot; an average of 16 hours per day. As it is nocturnal, the wombat has very poor eyesight, so it relies on its sense of smell to navigate and find food. </p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/m52Rdp_b5dQ?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Recorded: wombat cubes.</span></figcaption>
</figure>
<h2>So, what is poo for?</h2>
<p>Poo is produced by all organisms – and species have adapted to utilise it in many different ways, such as a mechanism for seed dispersal, or a food source for animals including dung beetles. Poo can also provide information about the individual who produced it and their diet. The different textures, size, shape and smell can all help to identify the species that produced the poo – this information can be used to survey elusive animals such as the otter (which produces a distinctly fishy-smelling “<a href="http://www.arkive.org/common-otter/lutra-lutra/image-A22038.html">spraint”</a>“, and can also give an estimation of how long ago the poo was produced. Even dinosaurs have left fossilised poo behind, called <a href="http://news.nationalgeographic.com/news/2014/07/140729-dinosaur-coprolite-paleontology-dung-fossil-auction/">coprolites</a>. </p>
<figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/114298/original/image-20160308-22129-jub9nq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/114298/original/image-20160308-22129-jub9nq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=783&fit=crop&dpr=1 600w, https://images.theconversation.com/files/114298/original/image-20160308-22129-jub9nq.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=783&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/114298/original/image-20160308-22129-jub9nq.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=783&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/114298/original/image-20160308-22129-jub9nq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=984&fit=crop&dpr=1 754w, https://images.theconversation.com/files/114298/original/image-20160308-22129-jub9nq.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=984&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/114298/original/image-20160308-22129-jub9nq.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=984&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">Mind your step.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
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<p>However, poo is also very smelly, so it can be used by individuals to communicate their presence to others. Why is this needed? Although contests are frequent in the animal kingdom, they can be fatal – so are avoided if possible. One way of avoiding conflict is to mark your territory with a scent such as poo – this provides information on who you are and where you live.</p>
<p>The wombat is highly territorial so uses its cube-shaped poo to mark its territory, preventing conflict. Wombats have been found to differentiate between various poos and show avoidance behaviour when presented with poo produced by predators and other male wombats. The hormonal content of poo can also be examined, for example so that males can tell when females are most fertile. </p>
<p>Wombats deposit poo outside their burrows and on the tops of rocks and logs, where they are more easily found by other wombats. The distinctive shape is an advantage as the flat sides of the cubes ensure they do not roll off their precarious locations.</p>
<h2>But how is cubic poo produced?</h2>
<p>Wombat poo is cubic, not because the wombat has a square-shaped anus, but because it has a very long and slow digestive process, typically 14 to 18 days, which allows the digestive matter to become extremely dry and compacted. The wombat also has a very long digestive tract, allowing it to absorb the most nutrients and water from its food. The first part of their large intestine contains horizontal ridges that probably mould the poo into cubes, whereas the last part of the large intestine is relatively smooth, allowing the cubic shape to be maintained. The highly compacted nature of the poo means that the rectum is unable to contour the poo into the more <a href="http://io9.gizmodo.com/5872472/the-wombats-cubic-poop-is-one-of-natures-weirdest-superpowers">usual tubular shape</a>.</p>
<p>So, the wombat, with is nocturnal way of life, poor eyesight but excellent sense of smell, uses poo as its main way of telling who lives where and if there are any strangers in the area (thus avoiding conflict), and as a way of increasing its reproductive success. It produces cubic poo as a result of its diet and long digestion. And, the cubic poo is the perfect shape for sitting on top of rocks and logs as it doesn’t roll away. Poo can be clever, too.</p><img src="https://counter.theconversation.com/content/55975/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Louise Gentle works for Nottingham Trent University</span></em></p>Revealed: the secrets of one of nature’s great digestive mysteries.Louise Gentle, Senior Lecturer in Behavioural Ecology, Nottingham Trent UniversityLicensed as Creative Commons – attribution, no derivatives.