What is the fast freeze button and when should I use it?

It runs the compressor flat out to pre-chill the cabinet before warm food goes in, so the new food freezes fast and the food already in there does not thaw at the edges.

Difficulty: beginner
Time: 10 min
Read: 3 min
Safety: caution

Short answer

Switch it on six to twenty-four hours before adding a large batch of fresh food, load the food, and switch it off after 24 hours unless the appliance does that itself. Its purpose is protecting what is already frozen and getting the new food through the freezing range quickly — not making the freezer permanently colder.

Adding several kilos of room-temperature food to a freezer raises the temperature of everything already in it, sometimes for many hours. Fast freeze — also called super freeze or power freeze — solves that by dropping the cabinet several degrees below its normal setting first, giving the new food a reserve of cold to absorb. The secondary benefit is faster freezing, which forms smaller ice crystals and gives noticeably better texture on thawing.

Safety

Fast freeze overrides the thermostat on many appliances and runs the compressor continuously. Left on indefinitely it wastes energy, can freeze items in the fridge compartment on a shared system, and works the compressor harder than intended. Switch it off after 24 hours if the appliance does not do so itself.

Step by step

Switch it on ahead of the load, not at the same time.Six hours is a reasonable minimum and 24 hours is what most manuals suggest for a full freezing capacity load. Switching it on as you put the food in gives you almost none of the benefit.
Check your appliance's freezing capacity before a big batch.On the rating plate, in kilograms per 24 hours — often somewhere between 2kg and 20kg depending on size. Exceeding it means everything freezes slowly, including the food already in there.
Spread the new items out rather than stacking them.Against the walls or the coldest shelf where possible, with space around each item, and not piled against food that is already frozen. Once everything is solid you can pack it together.
Freeze flat and in portions.A thin flat bag freezes in a fraction of the time a block does. Faster freezing means smaller ice crystals, less cell damage and better texture, which is the whole quality argument for fast freeze.
Cool food to room temperature first.Hot food raises the cabinet temperature and dumps moisture into it, which becomes frost. Cool it quickly at room temperature — within about ninety minutes for safety — then chill it in the fridge before freezing if you can.
Switch it off after 24 hours.Most modern appliances cancel it automatically after a set period. If yours has a manual switch with no timer, set a reminder. Left on, it runs the compressor continuously and on a shared system can start freezing things in the fridge compartment.
Use it before a power cut you know about.If planned works or a storm warning give you notice, running fast freeze for a day beforehand buys real extra holding time, because the whole contents start several degrees colder.
Do not use it as a permanent setting.It is not a colder mode to leave on. -18°C is the correct storage temperature, and running colder than that continuously costs energy without extending safe storage.

Tips

Fast freeze on the fridge side — sometimes called super cool — does the same job for a big chilled shop, and the same rule applies about switching it off afterwards.
If your freezer has no fast freeze function, turning the thermostat to its coldest setting a day before a batch cook achieves much the same thing. Remember to turn it back.
Labelling and dating before the food goes in matters more than any button. You cannot write on a frozen bag.

Common mistakes

Switching fast freeze on at the same moment the food goes in — The cabinet has no reserve of cold, so the food already in there warms while the compressor catches up. The point of the function is the pre-chill.
Leaving it on permanently because colder sounds safer — It overrides the thermostat, runs the compressor far more than necessary, and on a shared system can freeze salad and milk in the fridge compartment.

Questions people ask

How much food can I safely add at once?

The freezing capacity on the rating plate, in kg per 24 hours, is the honest limit. Adding much more than that means slow freezing for everything, worse texture, and a spell where the contents sit warmer than -18°C.

Does fast freeze make food last longer?

Not in terms of safe storage time, which is set by holding -18°C. It does improve quality, because fast freezing forms smaller ice crystals that do less damage to cell structure — the difference is most obvious in meat, fish and soft fruit.