Food, glorious food. Without it we would perish, or at the very least complain a lot. Yet the way we store it might not be keeping us as safe from illness as we think.
Consumer demand for convenient, fresh foods with minimal preservatives has led to increased sales of refrigerated, ready-to-eat food products in recent years that are often just warmed up by consumers. But inadequate refrigeration of these foods is a significant cause of foodborne illnesses, particularly listeriosis. Caused by Listeria monocytogenes, listeriosis symptoms include fever, sickness and diarrhoea among others. In severe cases, if it spreads to the brain, it can lead to meningitis.
There are several proven precautions we can all take to reduce the risk of listeriosis at home, however. These include following the use-by dates on unopened prepackaged food products; and not storing packets of food for too long after they have been opened, ideally eating them within two days.
Unfortunately, one of the most important measures we should all be taking is something that not many of us do: ensuring our fridges at home are below 5℃.
Though stringent measures are in place in the food industry to make sure food is kept at the right temperature, at home we’re left to our own devices. And we’ve found that people just aren’t using their fridges properly, increasing their own risk of foodborne illness.
There are two types of bacteria that can be present in food, which cause either decomposition or food poisoning. When refrigerated below the recommended 5℃, these bacteria are less able to grow. But as the temperature rises, the bacteria can grow faster, increasing the likelihood of spoilage and food poisoning.
In our study of listeriosis risk factors, we found that although 79% of respondents knew the importance of refrigeration, 84% were unaware that fridges should be 5℃ or less. Furthermore, 65% said they “never check” the temperature of their refrigerator. Later research led us to find that 50-85% of domestic refrigerators were actually operating at higher temperatures than the recommended guidelines, when taking single temperature readings.
We have also looked at how temperature fluctuates in fridges using wireless sensors to track changes on a minute by minute basis over six consecutive days. Surprisingly, we found that no refrigerator was under the recommended 5℃ for the full six days. Around 91% of the fridges had mean temperatures that were higher than the recommended 5℃. Overall, average operating temperatures ranged from -1.7℃ up to 17.9℃. To put that into perspective, the mean temperature for summer 2016 in the UK was 14.9℃.
Not cool enough
We also found a significant relationship between how consumers used their fridges and how the temperature changes, too. For example, there was around a 4.5℃ difference between the centre of the fridge and the door storage area.
Many of the people we spoke to were confused about what the actual operating temperature should be and how the fridge dial setting related to it. But this is no easy thing to understand – we established that there is no significant association between mean operating temperature and dial settings.
But those who had refrigerator thermometers, or reported to have checked the temperature during the six days, were no more likely of having refrigeration temperatures within recommended guidelines. Consequently, there is clearly a need for people to properly understand why home refrigerators should be under 5℃, and how to properly find out if their fridge is cold enough.
There’s no need to rush out and buy a new fridge though. Although we found older refrigerators took longer to get back down to the right temperature, there were no significant differences in the operating temperatures according to refrigerator age or type – though we did find that the greater the room temperature, the greater the operating temperature of the fridge.
No one intends to subject food to unsafe storage temperatures, that’s why we all have refrigerators in the first place. But we can’t just expect them to be at the correct temperature all of the time – they do fluctuate. Although the fridges in this study felt cold to the touch, and their owners believed them to be at the correct temperature, the only way to really tell is by using a refrigerator temperature thermometer.