What Temperature Should My Fridge Be?

Most people set the fridge dial once when the appliance arrives and never think about it again. Since the dial is usually not a temperature and the fridge has no display, that means most fridges are running at a temperature nobody in the household could state.

The numbers

Fridge: 0 to 5 degrees Celsius, with 4 a good target.

Freezer: minus 18 degrees Celsius.

The fridge range exists because bacterial growth slows dramatically below 5 degrees and stops almost entirely near freezing. Above 5, common food-poisoning bacteria multiply fast enough to matter within hours.

The freezer figure is a standard rather than a biological threshold. At minus 18, microbial activity has stopped entirely and the remaining concern is quality: enzyme activity and ice crystal formation, both of which slow further as temperature drops.

The dial is not a temperature

This is the detail that causes most of the confusion. On the majority of fridges, the control is numbered 1 to 5 or 1 to 7, and those numbers refer to cooling power, not degrees.

Setting it to 5 does not mean 5 degrees. On most models it means maximum cooling, which is the opposite of what someone aiming for 5 degrees would intend. Someone setting a dial to 1 believing they have selected 1 degree has in fact selected the warmest setting available.

The only way to know the actual temperature is to measure it.

How to check

An inexpensive fridge thermometer settles it in a day.

1. Put the thermometer on a middle shelf, not the door and not against the back wall.
2. Leave it overnight, with the door used normally.
3. Read it first thing, before the door has been opened.

If the reading is above 5, turn the dial towards colder by one step and check again after 24 hours. Small adjustments, one at a time, since a fridge takes several hours to stabilise.

It is worth checking in summer as well as winter. Ambient kitchen temperature affects how hard the appliance has to work, and a setting that holds 4 degrees in January can drift upward in August.

Where things should go

Temperature is not uniform inside a fridge, and the layout most people use does not match it.

Coldest, usually the bottom and back: raw meat and fish, always on the lowest shelf in a sealed container so nothing can drip onto food below. This is the single most important placement rule.

Middle shelves: dairy, cooked meats, leftovers.

Top shelves: ready-to-eat foods, drinks.

Salad drawer: vegetables and fruit that need chilling, which is most of them but not all.

The door, the warmest area: condiments, jars, things with a long shelf life and high acidity or sugar.

The door being warmest matters because it is where most fridges have a moulded egg rack and a milk shelf. Both would keep better inside. The door temperature swings every time it opens, and milk in particular sours faster there.

What should not be refrigerated

• Tomatoes, which lose flavour and develop a mealy texture below about 12 degrees.
• Potatoes, where cold converts starch to sugar, affecting taste and browning.
• Onions and garlic, which soften and sprout.
• Bananas and unripe stone fruit, which stop ripening and discolour.
• Bread, which goes stale faster in a fridge than at room temperature, though freezing it works well.
• Olive oil, which solidifies and clouds.

How full to keep it

Around three quarters full is the useful target.

A well-stocked fridge holds temperature better, because the contents act as a thermal mass and limit how much warm air enters when the door opens. An almost-empty fridge warms quickly every time it is opened.

Packed completely full is also a problem, because air must circulate for cooling to be even. Blocking the vents at the back creates warm pockets, and food at the front of a crammed shelf can sit several degrees above the setting.

Energy

A fridge is one of the few appliances running continuously, typically using around 1 kWh a day, so it is a steady rather than dramatic cost.

Straightforward ways to reduce it:

• Let hot food cool before putting it in, though not for so long that it sits in the danger zone. Covered and cooled within an hour or two is the usual advice.
• Keep the door seal clean and check it grips a sheet of paper. A failed seal is a continuous leak.
• Leave a gap behind the appliance so the condenser coils can shed heat, and vacuum them occasionally.
• Do not set it colder than needed. Every extra degree of cooling costs energy for no benefit.
• Defrost the freezer if ice builds up, since a layer of frost insulates the contents from the cooling element.

After a power cut

A closed fridge holds a safe temperature for around four hours, and a full freezer for around 24 to 48 hours depending on how full it is.

The rule is to keep the doors shut. Opening a freezer to check on it is the main reason contents thaw. Food that still contains ice crystals can generally be refrozen; food that has warmed above 5 degrees for more than a couple of hours should be discarded rather than tasted.