In the warmer months, it's a good idea to turn the temperature on your fridge down a bit to compensate for warmer air coming in, and vice versa in winter. However, there's a lot more to getting the temperature just right in your fridge and freezer.
If you don't want to make your friends sick at your next dinner party, you'll want to make sure the fresh meat you've stored in your fridge's chiller compartment doesn't spoil before you get around to cooking and serving it. But you also don't want to turn the temperature on your fridge down so low that your fresh vegetables in the crisper freeze and are unusable.
The fridge temperatures below are a good guide to keeping food safe.
Fresh food: between 0°C to 4°C.
Freezer: close to -18°C.
Chiller compartment: close to 0°C.
The Australian Standard for fridges uses a fresh food compartment average temperature of 3°C. It's a good target to aim for because it means not freezing foods yet still keeping them below 4°C.
Exceptions to the rule
Some fruit and vegetables keep much better at temperatures higher than 5°C. Farmers, chefs and retailers might need to know the precise details for storage and transport, but for the average consumer, it can help to know where best to store things within your fridge. There are some refrigeration rules that are easy to learn – for example, some tropical fruits can deteriorate in the fresh food compartment of a normal fridge and are better stored in slightly warmer environments. See our table with some other common examples.
Most fridges have at least one warmer area – the most obvious of these is the dairy compartment. Usually located at the top of the fridge door, some maintain temperatures around 8°C. This keeps butter and foods like soft cheeses ready to serve. But these foods can also be kept at colder temperatures, so it is possible to move them out in favour of foods such as green beans, which also like a warmer temperature.
Should I change the fridge temperature...
...when I've put in fresh groceries?
Once you've got your fridge temperatures right, you shouldn't need to fiddle with the settings. If a fridge does its job properly, turning the temperature control to colder when you put in a large load of groceries won't speed up the cooling process – it'll just mean your food ends up colder.
You should notice that your fridge reacts when you stack it with a 'warm' load of food by starting the compressor to cool it down. If it doesn't do this, you can try setting it colder for a while, but don't let the food get too cold before turning it back up. Alternatively, have it checked by a service person or, if it's old, consider buying a new fridge.
...from summer to winter and vice versa?
You may find your freezer gets warmer – not colder as you might expect – during the winter months. It's a good idea to keep an eye on temperatures using a fridge/freezer thermometer or two, particularly in the height of winter and summer.
Why does food go off?
Foods spoil if they undergo a chemical or physical change. Chemical changes include ripening, maturing or oxidising, also known as going rancid. Physical changes include:
Mechanical stress – poor packaging and handling.
Cooling – freezing or changes in phase.
Heating – cooking and migration of moisture.
Microbial micro-organisms – bacteria and fungi causing mould – spoil food by eating the cell structure and then increasing in number. Think of how sliced ham gets slimy when it's been in the fridge too long. Some micro-organisms are bad not only because they spoil the smell, texture and nutritional value of food, but also because they're poisonous! While most pathogenic micro-organisms can be easily killed by thorough cooking, some produce toxins that aren't destroyed that simply.
Raw foods can be especially risky. Some bacteria can be fatal to certain people, particularly infants, those with a serious illness, and the elderly. For the rest of us they mean (at the very least) a few days close to a toilet.
Blanching can have a positive effect on preserving vegetables. A sudden increase in temperature and cooling deactivates the enzymes that cause some foods to ripen and go off.
The low temperature in your fridge slows down the growth of most bacteria and mould. They aren't destroyed; they just slow down till it warms up again. If you put in some already rotten food, it isn't going to magically be okay when it's cooled down. And not all bacteria stop growing below 4°C, such as Listeria monocytogenes. Some foods are considered risky and/or highly perishable. These foods are best stored just above freezing temperature in your fridge's chiller.
Some foods deteriorate suddenly when they get below certain temperatures. This often occurs when the food freezes. Other foods undergo subtler changes when they get too cold, such as some tropical fruits and vegetables. Foods like lettuce are mostly water, so they freeze easily when in temperatures below 0°C and when they thaw you can see the cell structure has been destroyed – they turn into a jelly-like mess.
Other foods don't freeze until much colder. Ice-cream has some components that freeze at around -15°C. Others freeze at much colder temperatures. For longer-term storage you'll want to freeze some foods, but even if a food remains frozen, fluctuations in temperature can be very detrimental. For example, if ice-cream is warmed above -15°C on a regular basis then you'll see physical changes. The ingredients separate and crystals form, spoiling the texture and taste.
Another example is frozen peas which can lose moisture. You'll see this as loose ice crystals that form within the packet.
Freezer burn occurs when water moves out of the surface of a frozen food. When air reaches the frozen food, it causes dehydration and oxidation. It's generally caused by non-airtight packaging, and it happens more when temperature fluctuations are high. When the food thaws you'll see the texture has spoiled.
Oxidisation and other chemical changes are also slowed right down at -18°C. Fatty foods tend to have a shorter storage life in the freezer as the fats become rancid faster than some of the other ageing effects.