Preparing meals in bulk and reheating is a great way to save time in the kitchen and can also help to reduce food waste. You might have heard the myth that you can only reheat food once before it becomes unsafe to eat.
The origins of food myths are often obscure but some become embedded in our culture and scientists feel compelled to study them, like the “five second rule” or “double-dipping”.
The good news is that by following some simple steps when preparing and storing foods, it is possible to safely reheat foods more than once.
Why can food make us sick?
There are many ways bacteria and viruses can end up in foods. They may occur naturally in environments where food is harvested orcontaminatefoods during processing or by food handlers.
Viruses won’t grow in foods and will be destroyed by cooking (or proper reheating). On the other hand, bacteriacangrow in food. Not all bacteria make us sick. Some are even beneficial, such as probiotics in yoghurt or starter cultures used to make fermented foods.
However, some bacteria are not desirable in foods. These includebacteriawhich reproduce and cause physical changes making food unpalatable (or spoiled), and pathogens, which cause illness.
Some pathogens grow in our gut and cause symptoms of gastroenteritis, while others produce toxins (poisons) which cause us to become sick. Some bacteria even produce special structures, calledendospores, which survive for a long time – even years – until they encounter favourable conditions which allow them to grow and produce toxins.
While cooking and reheating will generally kill pathogenic bacteria in foods, they may not destroy toxins or endospores. When it comes to reheating foods, toxins pose the greatest risk of illness.
The risk increases in foods which have been poorly handled or cooled too slowly after initial cooking or reheating, since these conditions may allow toxin-producing bacteria to grow and proliferate.
The food ‘danger zone’ is between five and 60 degrees.Photo byElla OlssononUnsplash
Foods that are best able to support the growth of these bacteria are deemed “potentially hazardous” and include foods or dishes containing meat, dairy, seafood, cooked rice or pasta, eggs or other protein-rich ingredients.
A common culprit of food poisoning linked to reheated foods isStaphylococcus aureuswhich many people carry in their nose or throat. It produces a heat-stable toxin which causes vomiting and diarrhoea when ingested.
Food handlers can transfer these bacteria from their hands to foods after cooking or reheating. If the contaminated food is kept within the temperature danger zone for an extended period,Staphylococcus aureuswill grow and produce toxins. Subsequent reheating will destroy the bacteria but not the toxins.
How to keep food safe to eat, even when reheating
To limit the growth of bacteria, potentially hazardous foods should be kept outside of the temperature danger zone as much as possible. This means keeping cold foods cold (less than 5°C) and hot foods hot (above 60°C). It also means after cooking, potentially hazardous foods should be cooled to less than 5°C as quickly as possible. This also applies to reheated foods you want to save for later.
When cooling foods, Food Standards Australia New Zealandrecommendsthe temperature should fall from 60°C to 21°C in less than two hours and be reduced to 5°C or colder in the next four hours.
In practice, this means transferring hot foods to shallow containers to cool to room temperature, and then transferring the covered containers to the fridge to continue cooling. It’s not a good idea to put hot foods straight into the fridge. This can cause the fridge temperature to increase above 5°C which may affect the safety of other foods inside.
If food has been hygienically prepared, cooled quickly after cooking (or reheating) and stored cold, reheating more than once should not increase the risk of illness. However, prolonged storage and repeated reheating will affect thetaste, texture, and sometimes the nutritional quality of foods.
If food has been hygienically prepared, cooled quickly, and stored cold, reheating more than once should not increase the risk of illness.Photo byElloonUnsplash
When it comes to safely reheating (and re-reheating) foods, there are a few things to consider:
- Always practice good hygiene when preparing foods
- After cooking, cool foods on the bench either in small portions or in shallow containers (increased surface area reduces cooling time) and put in the fridge within two hours. Food should be cold (less than 5°C) within the next four hours
- Try to reheat only the portion you intend to immediately consume and make sure it is piping hot throughout (or invest in a thermometer to ensure the internal temperature reaches 75°C)
- If you don’t consume reheated food immediately, avoid handling it and return it to the fridge within two hours
- Err on the side of caution if reheating food for vulnerable people including children, elderly, pregnant or immunocompromised people. If in doubt, throw it out.
With the ever-increasing cost of food, buying in bulk, preparing meals in large quantities and storing unused portions is convenient and practical. Following a few simple common sense rules will keep stored food safe and minimise food waste.
This article was originally published on The Conversation.
FAQs
If food has been hygienically prepared, cooled quickly after cooking (or reheating) and stored cold, reheating more than once should not increase the risk of illness. However, prolonged storage and repeated reheating will affect the taste, texture, and sometimes the nutritional quality of foods.
Why can't you reheat food more than once? ›
If you do reheat food, make sure the whole dish is steaming hot throughout. While almost all foods can be reheated countless times, it is best practice to avoid reheating the same meal again and again. Each time your food is made less hot, stored and reheated, the probability of harmful bacteria increases.
How many times is it safe to reheat food? ›
There are no limits to how many times you can safely reheat leftover home-cooked meals. However, best practice is to limit the number of times you do so. More often than not, you wouldn't need to reheat one type of dish more than once.
Why should food not be heated again and again? ›
Bacterial Growth: Every time food is heated, cooled, and reheated, it provides an opportunity for bacteria to multiply. Bacteria can survive the initial cooking process and, when food is reheated, they may continue to grow and multiply rapidly, increasing the risk of foodborne illnesses.
Can I eat 5 day old leftovers? ›
Leftovers can be kept for 3 to 4 days in the refrigerator. After that, the risk of food poisoning goes up. If you don't think you'll be able to eat leftovers within four days, freeze them right away. Frozen leftovers will stay safe for a long time.
How bad is it to reheat food that says do not reheat once cooked? ›
Food handlers can transfer these bacteria from their hands to foods after cooking or reheating. If the contaminated food is kept within the temperature danger zone for an extended period, Staphylococcus aureus will grow and produce toxins. Subsequent reheating will destroy the bacteria but not the toxins.
What foods are not safe to reheat? ›
- Oct 17, 2023, 07:14 PM IST. 7 Foods Items That Can Turn Toxic When Reheated. ...
- Vegetables With High Amounts of Nitrate. Vegetables with high amounts of nitrate, like carrots, turnips, celery, or spinach, can turn toxic when reheated. ...
- Rice. ...
- Potatoes. ...
- Mushrooms. ...
- Cold Pressed Oil. ...
- Eggs. ...
- Chicken.
The FDA advises that food should be reheated only once before consumption. Frequent reheating can lead to bacterial growth, potentially causing foodborne illnesses. When food is reheated multiple times, it may not reach the required temperature to kill harmful bacteria.
Is there a limit to reheating food? ›
Food should only be reheated once. If ovens or grills are used for reheating make sure they are preheated. If you are reheating food in a microwave, stir it regularly to make sure the centre of the food is thoroughly heated. It is very important to keep food hot until serving to prevent harmful bacteria from growing.
Why does it say "do not reheat"? ›
the danger of bacteria breeding in food when food is neither steaming hot throughout nor cold. This includes, for example, food that is only partially reheated or 'warmed' rather than thoroughly reheated. that reheating foods can carry risk of foodborne disease even if the food is not raw or being cooked from scratch.
Even though a popular food item, it isn't too safe to reheat potatoes. A bacteria called Clostridium botulinum that releases a toxic chemical would be grown if cooked potatoes are kept at room temperature for longer. So, leftover potatoes should be stored in the fridge.
Why is reheated food never as good? ›
One particularly notorious oxidation reaction is known as the “warmed-over flavor,” an unpleasant taste that some people encounter when eating reheated meats like pork or chicken, Luck said. This phenomenon tends to occur with fattier cuts, she added, because it's tied to the oxidation of fat.
Will I get sick if I eat food left out overnight? ›
Cooked food can only stay in the temperature danger zone for so long before it becomes unsafe to eat. Havern explains: "The maximum amount of time perishable foods can [spend] in the danger zone is two hours. At two hours, the food must be consumed, stored correctly, or thrown away.
Is it safe to eat 2 year old frozen meat? ›
Food that is stored in a freezer at zero degrees will be safe to eat indefinitely. However, if meat is frozen too long it may lose quality and taste. If you are unsure if meat is still fresh, you can determine this once it has been thawed.
Why should you cover food in the fridge? ›
Store ready-to-eat foods such as cooked meats, pies and dairy products such as cheese, butter, cream and yoghurt in the top part of the fridge. Covering and wrapping food stops harmful bacteria from being passed from raw foods to ready-to-eat foods. It also stops food from drying out and becoming stale.
Can I eat soup that has been in the fridge for a week? ›
For best safety and quality, plan to eat refrigerated soup within 3 to 4 days or freeze it. And avoid letting soup set at room temperature for more than TWO hours.
Can you reheat baby food twice? ›
If you're using a microwave, give the food a good stir to get rid of any hot air pockets, and always check the temperature before feeding your baby. Any already-cooked food you're feeding your child should only be reheated once.
Can you microwave two ready meals at once? ›
Increase the cooking time for two items if you are cooking them together in the microwave. This is because the additional food will absorb some of the heat and moisture from the microwave, which can slow down the cooking process.
What is time temperature abuse? ›
Time temperature abuse is the act of allowing foods to stay in the temperature danger zone of 41 to 135 degrees Fahrenheit. Along with cross-contamination, time temperature abuse is a common source of foodborne illness, making it a major health code violation.
