6 Foods you should NEVER reheat

You come back home after a long day at work. You dig into the refrigerator, pull out some leftover chicken casserole, and reheat it in the microwave. Doesn’t seem too dangerous, right? But the truth is 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 6 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 a good reason why 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 the weather is warm 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.

2. 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. Find out the different types of olive oil for healthy cooking.

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. 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 better for these bacteria. This is also why storing cooked potatoes in foil has been linked to some cases of botulism. 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.

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. If the chicken you plan to reheat hasn’t been cooked and stored right, you run the risk of these problems.

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.

Be sure to reheat your chicken for at least 2 minutes at a temperature of 70 °C (approximately 160 °F) or higher.

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. 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.

All this can happen if you don’t store and refrigerate spinach properly. If the spinach has been pureed, the conversion is accelerated further. 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. 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: 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.