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 shouldn't you reheat food twice? ›
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 can I reheat food? ›
Fact or Fiction: You Shouldn't Reheat Leftovers More Than Once. Technically – fact. But don't panic. This just means you should portion what you're going to eat and heat only that, rather than reheating the whole of your leftovers, re-refrigerating what you don't eat, and repeating.
Do you agree that foods should not be reheated more than once? ›
The Food Standards Agency recommend only reheating food once, but actually you can do it as many times as you like as long as you do it properly. Firstly, store your leftover food well – that means keeping it as cool as possible in between servings. However, beware putting hot food straight into the fridge.
Why reheating food is discouraged? ›
But if experts are to go by, reheating is not good for your health. “It is important to understand that not all foods react well to this process,” said Garima Goyal, a clinical dietitian. That is because reheating certain foods can lead to a loss of flavour, texture, nutritional value, and safety.
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.
Once it has been cooked, how often can you reheat it? Well the Food Standards Agency recommends only reheating food once, but actually several times is fine as long as you do it properly. Though that is not likely to improve the taste.
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.
How many times can you reheat lasagna? ›
Technically, you can reheat lasagna multiple times so long as you bring it up to an internal temperature of 165° each time. This temperature kills most bacteria that might be present in your leftovers. That said, the quality degrades with each reheat, so we suggest reheating lasagna one time only.
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.
Here's the deal on those spuds. When cooked potatoes are left out at room temperature or warmed up for a second time, they can take a toxic turn for the worst. Why? Warm temperatures promote the growth of the rare bacteria, botulism, that is commonly found in potatoes.
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.
What is the rule for serving reheated foods? ›
If you reheat previously cooked and cooled potentially hazardous food, you must reheat it rapidly to 60°C or hotter. Ideally, you should aim to reheat food to 60°C within a maximum of two hours to minimise the amount of time that food is at temperatures that favour the growth of bacteria or formation of toxins.
Why can't you reheat food a second time? ›
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 is it bad to reheat things multiple times? ›
Because the quality decreases each time food is reheated, it is best to reheat only the amount needed. Cooked foods that cannot be used within four days should be frozen for longer, safe storage.
Why is it bad to reheat food in the microwave? ›
Microwave ovens can cook unevenly and leave "cold spots" where harmful bacteria can survive.
What is the maximum amount of time allowed for safely reheating food? ›
The maximum safe time for reheating food is 2 hours. This prevents food from sitting in the 'Danger Zone', where bacteria multiply rapidly, for too long. A thorough reheating should reach an internal food temperature of 165°F.
How long is it safe to keep leftover food after cooking? ›
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.
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.
Can you reheat lasagna twice? ›
Technically, you can reheat lasagna multiple times so long as you bring it up to an internal temperature of 165° each time. This temperature kills most bacteria that might be present in your leftovers. That said, the quality degrades with each reheat, so we suggest reheating lasagna one time only.
