Leftovers can cause food poisoning. Learn how to store cooked food in the fridge and the best way to reheat them.
Even a tiny amount of harmful bacteria can be dangerous when we eat leftover food. While that packet of nasi lemak bought earlier in the morning might still seemingly smell and taste fine later in the day, it might have already harboured enough toxic pathogens to leave you feeling nauseated and ill.
“The immune system in healthy adults can deal with small amounts of bacteria and viruses. But larger numbers of such bugs can make us quite sick,” explains Ms Charmaine Toh, a dietitian with National Healthcare Group Polyclinics (NHGP).
Indeed, vulnerable people such as pregnant women, people with weakened immune systems or the elderly can die from food poisoning.
Common symptoms of food-borne illness — usually known as food poisoning — can be mild or severe. These can include nausea, vomiting, diarrhoea, stomach cramps, headaches and fever.
While most episodes last only a day or two, some infections can be nasty. Hepatitis A or typhoid can cause severe illnesses lasting many weeks. Some food-borne illnesses can even result in long-term health issues involving the immune system, gut or kidneys.
Ms Toh says one of the most common causes of food-borne illness is the improper storage of cooked foods. While cooking destroys most pathogens, bacteria can be reintroduced to food later on, and leftovers can become a breeding ground for toxic strains such as Staphylococcus aureus, Salmonella enteritidis, Escherichia coli and Campylobacter.
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Eating reheated food is safe as long as we observe food safety. Here are the best ways to reduce the risk of food poisoning when taking care of leftovers:
Once food has been cooked, it should be stored in the fridge or freezer within two hours, says Ms Toh. Leftovers must be put in shallow containers or distributed into smaller portions for quick cooling and refrigerated at or below 4°C within two hours.
In general, refrigerated leftovers can be stored for three to four days in a covered container. Food destined for the freezer should be labelled with the freeze date and stored in freezer-quality resealable bags or sturdy glass/plastic containers.
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When food is left to thaw at room temperature, bacteria present can multiply to unsafe levels. While freezing does inactivate bacteria, some may remain alive and can begin to multiply when the food returns to room temperature.
Thaw frozen food in the refrigerator in a container to catch the drips (thereby preventing cross-contamination), or use a microwave oven. Thaw small items quickly under running water and place them in a leakproof bag. Cook all thawed food immediately and do not refreeze.
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Take-out food containers are often made of foam, plastic or paper and may not be microwave-safe. Store and reheat take-out items in food-safe containers. Certain plastics are safe, while ceramics and glass are the best.
“Never reheat or store food in plastic containers that were not intended for food. Containers meant for one-time use, such as margarine tubs, tend to warp or melt in the microwave, and this may allow harmful substances in certain plastics to leach into the food,” says Ms Toh. Avoid plastics and containers that are visibly damaged, stained or have a bad smell.
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Reheating food kills bacteria. It is important to use the right method of reheating to ensure all bacteria are destroyed. Whether oven-baking, sautéing or microwaving, Ms Toh recommends that leftovers be brought to a minimum temperature of 74°C — use a food thermometer to check — and soups, sauces and gravies should be brought to a rolling boil.
When using a microwave oven, give your leftovers a good stir in the middle of heating and allow the hot food to stand for a few minutes afterwards, as the heat will continue to radiate through the food. Do not forget to use a microwave-safe covered container — leftovers heat more evenly and retain their moisture better when covered.
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Avoid cross-contaminating your food by storing cooked and ready-to-eat items separately from raw food, especially raw meats, advises Ms Toh. Use a separate, properly-covered container for each food item, and adopt a “first-in, first-out” principle when consuming leftovers.
Adds Ms Toh, “Do not store perishable food in the refrigerator door, especially milk. The temperature of food stored in the door can increase when the refrigerator is opened, so store foods that can go bad quickly on the main shelves of the refrigerator.”
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This article was last reviewed on
22 Nov 2023
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