Storing and reheating leftovers safely

Why leftovers become risky

The bacteria that spoil food generally multiply fastest at lukewarm temperatures. In the cold of a fridge they barely grow, and at properly hot temperatures they die or stop, but food that lingers in between lets their numbers swell unseen. The trouble is that food often looks and smells fine even when bacteria have multiplied. Some bacteria also produce heat-resistant toxins, and once formed those toxins are not destroyed by boiling again. That is why storing leftovers matters even more than reheating them.

Cool fast, refrigerate fast

Because people are told not to put hot food in the fridge, many leave it out for hours, and that is the most common mistake. Cooked food should go into the fridge as soon as practical after the meal and within two hours at most, sooner on a hot day. A big pot put in whole stays lukewarm in the middle for a long time, so dividing food into shallow, wide containers cools it much faster.

• Split large pots of soup or stew into several shallow containers
• Once most of the steam has gone, cover and refrigerate straight away
• Do not overpack the fridge, so cold air can circulate
• Do not keep food that has sat on the table for a long time

How long leftovers keep

A commonly recommended guideline is to eat refrigerated leftovers within three to four days. Bacteria still grow very slowly in the fridge, so the longer food sits, the smaller the safety margin. If you will not finish it in that time, freeze it in single portions from the start. Writing the date on the container saves guessing how old it is. Food that spoils easily, such as seafood, egg dishes and anything with cream, is safer eaten sooner.

Take special care with rice and noodles

Leftover rice looks harmless but is one of the classic foods that need care. Rice can carry heat-resistant bacterial spores, so some survive cooking and can multiply and produce toxins while the rice cools slowly at room temperature. Those toxins are not removed by reheating. Avoid keeping rice on warm in the cooker for more than a day or eating rice that sat out all afternoon. Divide any rice you will not eat into portions while freshly cooked, cool it quickly and refrigerate or freeze it. Treat cooked noodles and pasta the same way.

Reheating properly

The most dangerous result is food that is hot at the edges and lukewarm in the middle. Bring soups and stews to a rolling boil, stirring down to the bottom, and in the microwave cover the dish loosely, stop halfway to stir and then continue. Letting it stand for a minute or two afterwards spreads the heat evenly. Thick or chunky food heats through faster if you break it into smaller pieces.

• Check it is steaming hot evenly all the way through
• Stir or turn food halfway through in the microwave
• Reheat only the amount you will eat
• Do not cool reheated food and reheat it again

Thawing frozen leftovers

The safest way to thaw frozen leftovers is to move them to the fridge the day before and let them thaw slowly. In a hurry, use the microwave's defrost setting and heat the food straight afterwards. Leaving it on the counter for hours lets the outside warm up first, where bacteria can grow, so it is best avoided. Refreezing thawed food spoils its taste and texture and cuts the safety margin, so freezing in portions from the start lets you take out only what you need.

Common mistakes and how to judge

Sniffing food and eating it if it seems fine is not a reliable test. The bacteria that cause food poisoning often do not change the smell or taste. Mouldy food, on the other hand, may be affected well beyond the visible patch, so throwing the whole thing away is safer than scraping it off. Wasting food hurts, but if you do not know how many days old it is or how long it sat out, discarding it is the safe choice. Be stricter for food served to pregnant women, babies and young children, older people or anyone with weakened immunity.

If you suspect food poisoning

If you vomit or have diarrhoea after eating, the priority is to prevent dehydration by sipping fluids little and often. If vomiting continues so you cannot keep water down, or you have a high fever, blood in your stool or are barely passing urine, seek medical care without delay. Babies, older people, pregnant women and those with chronic illnesses can deteriorate quickly even after mild early symptoms, so they should see a doctor early. This article is general information; check storage times and methods against the food packaging and official guidance as well.