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7 Common Foods You Should Never Reheat Without Caution

Foods That Are Unsafe To Reheat

Reheated leftovers can raise disease risk, especially when not cooked or stored right. Refrigerate potatoes right after cooking to prevent botulism and refrigerate chicken and eggs within 2 hours of cooking. Reheat them evenly and thoroughly at 165°F. While leftover oil must always be discarded, you can refrigerate cooked rice and mushrooms soon after cooking and preserve for a day.

Ayurveda advises against reheating food because the energy and the good properties of the food are lessened and the oils are affected. People with mucus congestion, the kapha type, are particularly cautioned not to reheat food.

We all have leftovers lurking in our fridge. And no doubt, they are often lifesavers at the end of a long hard day of work. But what we often don’t realize is that some of these foods cause more harm than good after being reheated. From declining nutritional value to contamination by bacteria like Escherechia coli or Salmonella, these health risks are very real.

Here are 7 foods that could potentially be unsafe to eat when they are reheated – particularly if they weren’t cooked or stored right.

1. Eggs

There’s good reason most people eat their eggs freshly made. Besides tasting heaps better, it is also safer to avoid reheating eggs – unless you know how to do it right. Bacteria can thrive at temperatures between 40 °F and 140 °F and spoil the food or make you ill. Which is why leaving cooked eggs out at room temperature for a length of time and then reheating for use later is never a good idea.

How to stay safe: According to the Food and Drug Administration (FDA), you can store cooked egg dishes in the refrigerator for a few days, but must consume no later than 3 to 4 days after. Also, avoid keeping the eggs out of your fridge for longer than 2 hours. This could be no more than an hour if it is warmer weather and temperatures are higher than 90 °F. When you reheat eggs, ensure they reach an internal temperature of at least 165 °F before you eat/serve them.1

2. Oil

There is no way to reheat oil right. It’s best to discard used oil.

One food you should never ever reheat and reuse is oil that has been used for deep frying. While it can seem like a waste to toss out a big batch, it may be better for your health to do just that. When you heat oil to deep fry something, it destabilizes the structure of the oil and breaks it down. If you have heated it to over 375 °F, it accumulates a toxic substance called HNE or 4-hydroxy-2-trans-nonenal that raises your levels of bad low-density lipoprotein (LDL) cholesterol. This in turn is responsible for raising the risk of heart disease and stroke, among other things.2

How to stay safe: When you reuse any oil that has been heated up for frying, it breaks down further and becomes more viscous and dark. If you notice reheated oil is gluey, dark, foamy, or acrid smelling, that’s a sign it isn’t safe for reusing.3

3. Potatoes

Potatoes come with a caveat on this list. Not all potato-based foods are problematic when reheated. It all depends on how well you store the potatoes after cooking them. Unfortunately, potatoes are the ideal growing environment for botulism-causing bacteria Clostridium botulinum. If you leave them out to cool at room temperature and don’t put them away to chill in the refrigerator quickly, you run the risk of allowing the bacteria to thrive. If you seal up the potato, it locks out oxygen, making it even more conducive for these bacteria to breed. This is also why storing cooked potatoes in foil has been linked to some cases of botulism.4 So when you do end up reheating them, especially if you just zap them quickly in the microwave and don’t let the heat penetrate all the way through, it could spell trouble.

How to stay safe: Put cooked potatoes in the refrigerator almost as soon as you have finished your meal.

4. Rice

Rice, like potatoes, can pose a risk when reheated or reused. This again is because of bacteria that can multiply if the cooked rice isn’t stored right or is stored for too long. Rice has naturally occurring bacterial spores that can sometimes survive the cooking process. Under the right conditions, like being left at room temperature, these spores multiply. Reheating them will unfortunately not be enough to rid the rice of the spores or the potentially poisonous substances produced by them. And that could bring on a bout of food poisoning.5

How to stay safe: Be sure to put the rice away as soon as possible after you cook it. Also, don’t reheat and eat rice that has been refrigerated over a day – it could cause digestive issues including diarrhea or vomiting.

5. Chicken

Chicken is another favored breeding ground for bacteria ranging from Escherichia coli to Salmonella that can cause you to fall sick with diarrhea or food poisoning.6 If the chicken you plan to reheat hasn’t been cooked and stored right, you run the risk of these problems.

Since a microwave oven does not heat food evenly, reheating cooked chicken in the microwave oven does not eliminate all the bacteria. Use a conventional heating method.7

How to stay safe: Chicken, as with any meat, must be prepared properly by cooking to at least 165 °F. Once cooked, it needs to be cooled and put away for storage in the refrigerator within 2 hours of cooking. Have leftovers for up to 2 to 3 days and no later.8 Be sure to reheat your chicken for at least 2 minutes at a temperature of 70 °C (approximately 160 °F) or higher.9 Be especially careful if you reheat in the microwave as the chicken may not get heated all the way through. Use a food thermometer to check if the temperature of the thickest/central portion of the chicken has reached at least 160 °F.

6. Mushrooms

Mushrooms are best consumed the same day, in fact soon after, they are prepared. The protein content in mushrooms is known to deteriorate rapidly if they are not stored right. Mushrooms are also likely to be infected by microorganisms.

How to stay safe: Store mushrooms in the coldest part of the fridge within 2 hours of cooking. Discard them if they’ve been left outside for more than 2 hours. Use them up within 24 hours. Heat it once at 160 °F and avoid storing or reheating it further.

7. Spinach, Beets, And Celery

Spinach is a healthy food choice that can give you loads of vitamins and minerals. However, it is also a high nitrate vegetable. And while that’s fine in itself, these nitrates are converted to nitrites due to bacterial action – and this is not good if you’re already consuming a lot of nitrites and nitrates in your diet.

Very high nitrite intake through diet has been linked to raised cancer risk. In babies, excess nitrite in the body combines with oxygen-carrying oxyhemoglobin to form methemoglobin that is not capable of carrying oxygen. This in turn can cause “blue baby syndrome,” where the infant has respiratory and digestive issues as tissues are deprived of oxygen supply.

While spinach does contain nitrates which may turn into harmful nitrosamines in the body, you can counter this by storing the spinach right and having other foods rich in antioxidants, such as fruits and fresh veggies.

All this can happen if you don’t store and refrigerate spinach properly. If the spinach has been pureed, the conversion is accelerated further.10 Beets and celery are other high nitrate vegetables that can have similar effects as spinach when reheated.

But do be aware that this connection is still tenuous. The European Food Information Council, which had first suggested this link, has now backed off following questions on how adequate the evidence was.11 Further research and wider studies are needed to clearly establish just what happens and the extent of the risk. But it’s still worth playing safe and storing these veggies with care.

How to stay safe: Blanching spinach and celery can remove some of the nitrates in them. You could also cook these  immediately after chopping them.12 Always cool down your cooked spinach fast and put it away in the refrigerator as soon as possible after cooking. Store it at 4 °C for up to 12 hours. For anything longer, it is safer to freeze it instead. While reheating ensure it stays on the boil for a minimum of 1 minute after it comes up to a boil.13

3 Tips To Store Food Right

Remember, storing the food right is just as important as heating it right. As long as you follow these food-storing tips and reheat the food to 165 °F, there’s no cause for worry.

  • Cool food rapidly: To prevent bacterial growth, cool food rapidly so it reaches the safe refrigerator-storage temperature of 40° F fast. Divide large amounts of food into shallow containers. Rapidly chill hot food in an ice or cold water bath.
  • Wrap leftovers well: Cover leftovers, wrap them in airtight packaging, or seal them in storage containers (except potatoes) for storage in the refrigerator. Immediately refrigerate or freeze the wrapped leftovers for rapid cooling.
  • Store leftovers safely: Leftovers can be kept in the refrigerator for 3 to 4 days or frozen (0 °F or below) for 3 to 4 months. Although safe indefinitely, frozen leftovers can lose moisture and flavor when stored for longer times in the freezer.14

References   [ + ]

1. Egg Safety: What You Need to Know. Food and Drug Administration.
2. Is reusing cooking oil safe?. Columbia University in the City of New York.
3. Is it safe to re-use oil used for frying?. Penn State College of Agricultural Sciences.
4. Botulism from baked potato sparks Health Canada warning. CBC News Canada.
5. Cooking. Food Standards Agency.
6. Chicken from Farm to Table. United States Department of Agriculture Food Safety and Inspection Service.
7. Gessner, Bradford D., and Michael Beller. “Protective effect of conventional cooking versus use of microwave ovens in an outbreak of salmonellosis.” American journal of epidemiology 139, no. 9 (1994): 903-909.
8. Important Food Safety Tips for Poultry. National Chicken Council.
9. Storage of cooked chicken. Australian Chicken Meat Federation Inc.
10, 13. Message to Healthcare Colleagues on Nitrate/Nitrite in Vegetables and Methaemoglobinaemia in Infants. Department of Health and Centre for Food Safety, Food and Environmental Hygiene Department.
11. Independent reader successfully overturns expert advice against reheating spinach. European Food Information Council.
12. Nitrate and Nitrite in Vegetables and Infant Feeding. Center For Food Safety.
14. Storage Times For The Refrigerator And Freezer.

Disclaimer: The content is purely informative and educational in nature and should not be construed as medical advice. Please use the content only in consultation with an appropriate certified medical or healthcare professional.