Freezer temperature: why -18°C, and what kitchens record

Food hygiene law does not set one. Across England, Wales, Scotland and Northern Ireland, it asks you to keep food at temperatures that do not put health at risk, but gives no number for a freezer.

• Law in all four nations Food labelled as quick-frozen has its own rules, with -18°C or colder as the standard. They allow short rises to -15°C in transport, and shop display freezers can run up to -12°C. Each nation has its own regulations. They apply when food is placed on the market, which the law defines to include holding it for sale, and they name mass caterers, such as restaurants, canteens and schools, among the places quick-frozen food is delivered to. Whether that makes them apply to your own freezer is a point of law for your council or a solicitor, and this guide does not answer it.
• Guidance in England and Wales The FSA pack's "Prove it" sheet sets -18°C or below as the figure for frozen food, and says the freezer's own display, or a dial thermometer, will do for checking it when you open up.
• Guidance in Scotland CookSafe asks you to record fridge and freezer checks on its cold food record.

Our advice Treat -18°C or colder as your working figure and write it into your food safety plan. A freezer kept at -18°C or colder keeps the food at the guidance figure, and at the quick-frozen figure too.

Guidance The FSA likens a freezer to pressing pause. Bacteria stop growing while the food is frozen, but they are still there, and they wake up again as the food defrosts.

So freezing is a way to keep food, never a way to make it safe. Food that went into the freezer contaminated comes out contaminated. What you freeze, and how you defrost it, matters as much as the freezer temperature.

Guidance in England and Wales The FSA pack accepts the number on the freezer's own display, or on a dial thermometer, read at opening. An infra-red gun only reads the surface; if its number looks high, check again with a probe.

No law sets how often to check. Once a day at opening is what the guidance packs expect. Our advice Check again at closing too, so a freezer that fails in the evening is spotted before it has all night to warm up.

• Our advice Every so often, check the display against your probe. Push the probe between two packs and give it a minute to settle. If the two disagree by more than a degree or two, trust the probe and get the freezer looked at.
• Our advice A freezer runs a defrost cycle from time to time, and the air reading jumps while it does. So does a reading taken straight after a delivery has gone in or the door has been open. If a reading is warm, wait ten minutes with the door shut, then check again before you decide anything.
• Our advice Name every freezer. "Freezer 2" means nothing a month later if there are three. Use names the whole team knows, such as "Chest freezer, back corridor".

How to set up a daily cold storage record, and what to write down, is in our fridge temperature log guide.

A single warm reading after the door has been open is common. A freezer that stays warm, or is climbing, is a problem. Start with the food, not the display: the FSA pack's freezing method sorts frozen food by how it feels, because that tells you how far it has defrosted.

No UK source we read sets a temperature for throwing away food from a failed freezer. The "refreeze if it is below 40°F" rule you may read online is American.

Our advice If in doubt, throw it out. Make a list of what you moved, cooked and threw away, with the time and who did it: that is your record for the inspector and for any insurance claim.

• Keep the door shut. A closed freezer holds its cold for a good while. Every opening lets it out.
• Guidance How long it lasts. The FSA and Food Standards Scotland give home cooks a rough guide: a full freezer should keep food frozen for up to about 48 hours, and a half-full one for about 24 hours. Both call these estimates. The FSA adds that a cut of under 4 hours should not make food unsafe, and points businesses with questions to their council.
• In a kitchen, go by the food. Those hours are home advice. When the power comes back, or the engineer leaves, sort the stock with the four checks above.
• Our advice Know before it happens where the stock would go: another freezer on site, a neighbouring business, or your supplier. Keep the engineer's number by the freezer.

• Guidance Put frozen deliveries away as soon as they are checked in.
• Guidance Fresh food goes into the freezer before its use-by date passes, never after, with the day you froze it written on it.
• Guidance Cool cooked food first, and get it into the freezer once it is cold. Smaller portions, in freezer bags or lidded tubs, freeze faster and defrost faster.
• Guidance Label everything that goes into the freezer with what it is and when it went in.
• Guidance in England and Wales Once food is defrosted, the FSA pack says its life depends on how many days it had left on its date when you froze it. Freezing stops the clock; it does not reset it.

How long food can stay frozen is about quality, not safety. GOV.UK's home advice suggests 2 to 3 months for meat and 3 to 4 months for baked goods, fruit and vegetables. Freezer burn, the dry, pale patches on badly wrapped food, spoils the eating but does not make food unsafe. Our advice Pick your own times for each kind of food, write them in your food safety plan, and rotate the freezer like any other store: oldest at the front.

Our advice A blast chiller makes cooling before freezing much quicker, but no UK law or guidance requires one. How to cool food fast without one is in our cooling food guide, and how long cooked food keeps is in our food shelf life guide.

Law in all four nations Food has to be defrosted in a way that keeps the chance of harmful bacteria growing, or toxins forming, as low as possible. The law does not say how.

Guidance in England and Wales The FSA pack's order of preference:

1. In the fridge, which is best.
2. Under cold running water, in a container. For raw meat and poultry, the container must be sealed.
3. In the microwave, on its defrost setting.
4. At room temperature only if you have to, following the maker's instructions, for as short a time as possible.

Our advice In the fridge, defrost on the bottom shelf in a tray, below ready-to-eat food. Food defrosted in the microwave should be cooked straight away.

Before cooking, check there is no ice left in the middle: feel it, or push a skewer through. A whole bird's legs should move freely. Cook from frozen only where the maker says you can, or you have a method you have proved works. More on defrosting and the fridge in our danger zone guide. Each method in detail, how long defrosted food keeps and when it can be refrozen are in our defrosting food guide.

• Guidance in England and Wales The FSA pack asks you to get freezers serviced regularly, to sort them out so there is room for air to move, and to keep the door shut as much as you can.
• Our advice Do not pack it to the lid. A chest freezer piled above its load line, or an upright with packs against the fan, cannot hold its temperature.
• Our advice Ice building up on the walls, frost on the door edge or a seal that has split all mean warm air is getting in. Defrost and clean the freezer when the ice gets thick, moving the stock to another freezer first, and get a damaged seal replaced.
• Our advice Keep the condenser at the back or underneath free of dust and boxes, so the freezer can get rid of its heat.

Home freezers carry stars instead of a temperature: three or four stars means -18°C. Those are appliance ratings, not food safety rules, and a commercial freezer is set by its controller, so read the temperature, not the stars.

Law in all four nations Fish that will be eaten raw or barely cooked, such as sushi or ceviche, has to be frozen to kill parasites, and so does cold-smoked, cured or marinated fish unless the process itself kills them: every part of the fish at -20°C or colder for at least 24 hours, or -35°C or colder for at least 15 hours. Farmed Atlantic salmon is usually exempt. Wild fish is not.

A normal kitchen freezer running at -18°C does not meet this. Ask your supplier whether the fish has already been treated, and check with your council before you do it yourself.

• What temperature do you run your freezers at, and how do you know?
• Where are your daily freezer readings, and what did you do the last time one was warm?
• Is everything in the freezer labelled with what it is and when it was frozen?
• How do you defrost food, and where?
• What would you do if a freezer broke down tonight?

Have your readings and your answers written down. What else to have ready is in our EHO inspection guide.

Paper works: a line for each freezer on your daily checks, and a note in the diary when something goes wrong. ChefsRecords is an iPhone app for the daily records:

• Daily readings: the ready-made Opening Checks and Closing Checks each have a freezer reading, with the note "Aim for -18°C or colder." Add a line for every freezer you have. Each reading is saved with who took it and when.
• A warm reading: anything warmer than -18°C shows in orange, and the app asks "What was done about it?" with one-tap answers: "Food moved to another freezer", "Thawed food thrown away", "Door/defrost fixed, will re-check" and "Reported for repair", or your own words. It does not force an answer, because food hygiene law sets no freezer figure, but give one: your inspector will want to see it. A warm reading with no answer is listed for the manager or supervisor who signs off the day.
• Stock: the optional Stock Check - Fridges and Freezers has "Oldest stock at the front and used first, in fridges and freezers" and "Freezer food wrapped, labelled with what it is and date frozen".
• A breakdown: a manager or supervisor can log a Repairs incident, type Refrigeration ("Fridge or freezer failure, temperature drift"), with photos, what was done, and who checked the fix worked.

What it does not do today: the app has no record of food defrosted, no date-frozen field on stock, no sensor that reads the freezer for you, and no ready-made list for sorting stock after a failure. Write what you moved, cooked and threw away in the incident.

A freezer reading over the target. The reading is saved as it was taken, and the app asks what was done about it.

Which plan. Checklists come with Standard and Pro, and are open in the 14-day free trial. Incidents can be logged on every plan; the trial and the free plan keep up to 20.

Get ChefsRecords on the App Store (iPhone) ›
14 days free. No card required.

Related guides

The fridge temperature log guide, the danger zone guide, the food shelf life guide, the cooling food guide, the delivery checks guide, the stock rotation guide and the probe check guide.