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.