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? ›
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.
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.
Can I reheat potatoes twice? ›
Where possible, always consume your potatoes and potato dishes fresh. If you do reheat, only do so once and ensure it is piping hot all the way through.
Should food only be reheated once? ›
Remember, reheating means cooking again, not just warming up. Always reheat food until it is steaming hot all the way through (you should only do this once). Do not put food into hot holding without reheating it properly first. Check that reheated food is steaming hot all the way through.
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.
Is it safe to reheat pasta? ›
Pasta can be reheated to no ill effect, but the key is in doing it well to avoid soggy pasta or a bowl of dried-up noodles. You also want to consider what's in the dish as you want to be careful not to overcook the proteins or vegetables, for example.
Which foods should not be reheated? ›
The 9 foods you should never reheat or risk potentially deadly consequences
- Rice. First up on the watch list is any dish involving rice - think curries, stir fries and risottos. ...
- Eggs. Eggs shouldn't be reheated full stop, according to Dr Duvenage. ...
- Mushrooms. ...
- Spinach. ...
- Potatoes. ...
- Seafood. ...
- Chicken. ...
- Oil.
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 shouldn't you reheat potatoes? ›
These are some of the foods that shouldn't be reheated and consumed later. 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.
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.
Why is it unsafe to reheat food? ›
Reheating leftovers in slow cookers, steam tables or chafing dishes is not recommended because foods may stay in the "Danger Zone," between 40 °F and 140 °F too long. Bacteria multiply rapidly at these temperatures.
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.
Can I eat week old Chinese food? ›
The Gist: Chinese food leftovers can last three to four days in the fridge. Food should never be left at room temperature for more than two hours. Store leftover Chinese food in airtight containers, not the original takeout container.
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.
What meat can you not reheat? ›
Reheating chicken is not advisable more generally because it has a higher density of protein than red meat - when reheated, proteins break down differently and can upset the stomach.
Why is bread not a high risk food? ›
Low risk foods are foods that do not provide ideal conditions for bacteria to grow. They are typically foods that are high in acid or sugar, as well as salted foods, dry foods or canned and vacuum-packed foods. Some examples of low risk foods include: Dry goods - Crackers, biscuits, flour, plain breads and rolls.
The quickest method to reheat scrambled eggs is in a microwave-safe dish. Cook on high for 20–30-second intervals, stirring in between to heat evenly. Omelets and quiches. Reheat multi-ingredient egg dishes in the oven for the best results.
Can bacteria grow in a freezer? ›
Keeping food in the freezer
Freezing acts as a 'pause' button prior to any use-by date expiring and most bacteria cannot grow at these low temperatures. Your freezer should be around -18°C.
Why does frozen food 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.
How many times is it safe to reheat leftovers? ›
However, the Food Standards Agency (FSA) recommends that food is only reheated once, so follow this guidance wherever possible. When you reheat food, you must ensure it is piping hot all the way through. This indicates that you have properly reheated it and the bacteria has been destroyed.
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.
