How do I defrost food safely?

The three safe defrosting methods, how long each takes, and why the kitchen counter is not one of them.

Difficulty: beginner
Time: 20 min
Read: 2 min
Safety: caution

Short answer

In the fridge is the safest method — allow 24 hours per 2kg. For speed, use a sealed bag under cold running water, or the microwave's defrost setting followed by cooking immediately. Never leave raw meat out on the counter.

Bacteria multiply rapidly between about 5°C and 60°C. A joint left on the counter spends hours with its outer layer in that range while the centre is still frozen, which is precisely the situation safe defrosting is designed to avoid.

Safety

Never defrost meat, fish or poultry at room temperature — the outside reaches bacterial growth temperatures long before the centre thaws. Cook food thoroughly after defrosting, and do not refreeze raw food that has been thawed unless you cook it first.

What you'll need

Fridge space
Sealed bags (optional)
Microwave (optional)

Step by step

Plan ahead and use the fridge where you can.The safest method by a clear margin. Allow roughly 24 hours per 2kg, and put it on the bottom shelf on a plate.
Always put defrosting meat on a plate at the bottom of the fridge.It drips as it thaws. Bottom shelf means nothing beneath it can be contaminated.
For speed, use cold water in a sealed bag.Submerge the sealed food in cold water, changing it every thirty minutes. Roughly an hour per 500g. Cold water, never warm.
Use the microwave defrost setting only if cooking immediately.It warms the edges and starts cooking parts of the food, so it must go straight into the pan or oven.
Check it is fully thawed before cooking.Press the thickest part and check for ice in the centre of a joint or bird. Partly frozen food cooks unevenly and unsafely.
Cook thoroughly and check the temperature.75°C in the centre for most things, 74°C for poultry. This is what deals with any bacteria that multiplied during thawing.
Do not refreeze raw thawed food.You can refreeze it once it has been cooked. Refreezing raw food that has thawed increases both risk and quality loss.
Cook some things straight from frozen.Many vegetables, fish fillets, sausages and mince are designed for it. Check the packet — it saves both time and the whole question.

Tips

Freeze in portions you will actually use. A single large block takes a day to thaw; four flat portions take a few hours.
Freezing flat in a bag dramatically reduces thawing time compared with a lump — more surface area, less thickness.
Label everything with the date and contents. Frozen food is genuinely unrecognisable after a month.

Common mistakes

Defrosting meat on the kitchen counter — The outer layer spends hours in the bacterial growth range while the centre is still frozen.
Using warm water to speed it up — It brings the surface straight into the danger zone. Cold running or changed water is both safe and reasonably fast.
Cooking meat that is still partly frozen — The outside overcooks while the centre may not reach a safe temperature at all.

Questions people ask

How long does it take to defrost a chicken?

In the fridge, roughly 24 hours per 2kg — so a large chicken needs a full day or more. In cold water in a sealed bag, about an hour per 500g with the water changed every thirty minutes.

Can you refreeze food that has been defrosted?

Not raw. You can cook thawed raw food and then freeze the cooked dish. Refreezing raw thawed food increases both the safety risk and the quality loss.