Is my food still safe after a power cut in hot weather?

This is stressful in the moment and it is mostly decided by one thing you do at the start: whether you open the doors. Insulation is doing all the work, and every opening spends some of it. The rest is a straightforward assessment afterwards, made much easier if you have set up the freezer trick described at the end before it ever happens.

Safety

Step by step

1. Keep the doors shut. That is the main thing.An unopened fridge holds a safe temperature for several hours, and a well-filled freezer holds food frozen for the best part of a day or more — some sources put a full freezer at around a day and a half, a half-empty one at appreciably less. Opening the door repeatedly to check destroys that. Decide what you need, or better, do not open it at all.
2. Fill the space in the freezer.A full freezer holds its temperature far longer than a half-empty one, because the frozen mass is the reservoir. If a power cut is forecast — a storm warning, planned works — fill gaps with bottles or containers of water and freeze them in advance. They also become useful cold packs afterwards.
3. Move fridge items into the freezer if you have warning.Milk, cooked meats and other high-risk chilled items moved into the freezer before the power goes stay safe much longer, because the freezer has far more thermal reserve than the fridge.
4. Use a cool box for what you actually need.Rather than opening the fridge repeatedly, take out what you will need for the next few hours at the start and put it in a cool box with ice packs. Then leave the appliances alone entirely.
5. Judge the freezer by ice crystals.When the power returns, look at the food rather than the appliance. Food that is still solid or still contains ice crystals and is still properly cold is safe and can be refrozen, though quality may suffer. Food that is fully thawed and warm must not be refrozen — cook it thoroughly immediately and eat or freeze the cooked result, or discard it.
6. Judge the fridge by time and temperature.Put a thermometer in and check. If high-risk chilled food — cooked meats, dairy, prepared salads, sandwiches, raw meat and fish, anything labelled keep refrigerated — has been above 8°C for more than a couple of hours, discard it. Hard cheeses, butter, unopened preserves, whole fruit and vegetables, and anything ambient are generally fine.
7. Discard rather than assess when the timing is unknown.The most common real situation is coming home to a fridge that has clearly been off for an unknown length of time. There is no way to reconstruct it, and no sensory test that works. Throw out the high-risk items.
8. Set up the frozen coin trick before you ever need it.Freeze a cup of water solid, then put a coin on top of the ice and leave it in the freezer. If you return to find the coin still on the surface, the freezer stayed frozen. If it has sunk to the middle or the bottom, the contents thawed and refroze while you were away — which no other check can tell you. It costs nothing and it answers the hardest version of this question.
9. Check whether it is your fault or the network's.Before assuming an outage, check the consumer unit for a tripped breaker or RCD, since a single faulty appliance can knock out a circuit and leave the freezer off while the lights work. If the whole street is out, the distribution network operator is the one to contact — in Great Britain, calling 105 connects you to them.

Tips

• The frozen coin trick is the only reliable way to know what happened to a freezer while you were away, and it takes two minutes to set up.
• A freezer thermometer with a maximum-temperature memory does the same job with more precision and is inexpensive.
• Blankets or towels thrown over a freezer add useful insulation during a long outage, provided they do not block the ventilation once the power returns.
• If a long outage is forecast, a bag of ice from a shop in the fridge compartment buys hours for the chilled food.
• Keep a written list of what is in the freezer. If you do have to discard a load, it makes an insurance claim far easier, and some home insurance policies cover freezer contents.

Common mistakes

• Opening the fridge and freezer to check on things — Every opening exchanges cold air for warm and spends the insulation budget. The single most effective action in a power cut is to leave the doors shut.
• Refreezing thawed food to save it — Freezing stops bacterial growth but does not reverse it. Refrozen thawed food carries whatever multiplied while it was warm, and it will do so again on the next thaw.
• Smelling or tasting food to decide — Harmful bacteria typically do not change smell, appearance or taste, and tasting is never a safe test. Time and temperature are the only usable criteria.
• Assuming the freezer is fine because it is cold inside now — It may have thawed and refrozen while you were out. Only a coin on ice, or a thermometer that records the maximum, can tell you.

If it doesn't work

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