Last updated on 8 June 2012
How chilled is your fridge?
Kaarin Goodburn at the Chilled Food Association gives her views on fridge temperatures.
Why should fridge temperatures be below 5ºC?
Generally, the colder the temperature the slower germs will grow, but cold temperatures don’t stop germs growing altogether.
Some foods need to be kept in the fridge to help slow down germs' growth and keep food fresh and safe for longer. These are foods with a 'use by' date on food that says 'keep refrigerated' on the label, such as milk, meat and ready meals.
Generally, the colder the temperature the slower germs will grow, but cold temperatures don’t stop germs growing altogether. We can use predictive microbiology and growth curves, for example www.combase.cc, to estimate how quickly germs will grow under different conditions.
In warm conditions, one thousand germs can become one million in just under two hours and this can cause food poisoning!
One of the main reasons fridge temperatures are recommend to be set at 5ºC is because of listeria.
Listeria is a food poisoning bacterium that is psychrotrophic – in other words it likes cold temperatures. From the growth models, we know that listeria grows nearly twice as fast at 8°C as it does at 5°C, hence the recommended 5ºC, which helps keep us safe from listeria.
You can use a fridge thermometer to check your fridge temperature. The numbers on the dial in the fridge are not usually an indication of the temperature. It's best to check the fridge's handbook to see how yours works.
So if refrigeration keeps food safe, why do some foods say not to refrigerate?
For some fruits that need to ripen, keeping them in the fridge can affect the taste. The most important food not to keep in the fridge are potatoes, when these are stored in the fridge the starch in the potato is converted to sugar. When baked or fried these sugars combine with the amino acid asparagine and produce the chemical acrylamide, which is thought to be harmful.