Cooling and storing leftovers

Why

Bacteria multiply quickly in food at roughly 5 to 60 °C – exactly the temperatures cooked food passes through as it cools. A large pot of goulash, sauce or stock cools slowly because its centre is far from the walls, and it can sit in the warm range for hours; Clostridium perfringens, a bacterium that forms tough spores, typically causes food poisoning from dishes cooked in large batches and kept warm. That is why cooked food should go into the fridge within 2 hours at the latest, divided into shallow containers where it cools faster. A fridge at 5 °C or below only slows bacteria down, it doesn't stop them, and many causes of food poisoning give nothing away in appearance or smell, so the sniff test tells you nothing about safety. Storage times differ between authorities: the UK FSA advises eating leftovers within 2 days, the US USDA gives 3–4 days.

How to do it

• Don't leave cooked food standing warm for more than 2 hours, or 1 hour at most when it's above 32 °C.
• Divide a large pot into shallow containers, or stand it in a sink of cold water and stir now and then.
• Don't wait for food to cool completely on the counter: put warm food in small containers straight into a fridge set to 5 °C or below.
• Eat leftovers ideally within 2 days, cooked rice within 1 day, otherwise freeze them in time; write the date on the container.
• Reheat only once, until piping hot all the way through, at least 74 °C in the centre; stir while reheating so no cold spots remain.

If it goes wrong

Food that has stood warm for more than 2 hours, say overnight on a switched-off hob, is best thrown away: boiling it again kills most bacteria, but not their tough spores or the toxins some of them have already produced in the food, and you can't smell it. Next time divide a large pot into smaller containers as soon as it's cooked and cool them in cold water.