10 Foods to Never Reheat to Avoid Bacteria

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You’ve probably been there: Yesterday’s leftovers are still on the table and you don’t want to cook a fresh meal. However, reheating food isn’t always as simple as reaching for the microwave or oven. Reheating certain foods can cause chemical changes that can make them more dangerous than good. Bacteria and toxins can form even in what appears a safe dish. Your health may be at stake, it’s not just a matter of taste or texture.

In this guide to sidestepping stomach troubles, we will tell you of ten common grocery items that turn into ‘hazardous’ after reheating. Think of it as kitchen friendly advice to help keep you or your appetite out of trouble. A little bit of care and some attention will tell you which leftovers you can eat cold and which are best avoided.

Seafood

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It’s a gamble when it comes to reheating seafood — for taste and for health. Some types, such as shrimp or fish, can go bad pretty quickly and smell very fishy when you reheat them. Besides that, bacteria can grow as a result of improper storage. Many seafood related foodborne illness outbreaks were related to improper reheating of seafood. If you have leftover seafood, you often want to eat it cold, in a salad or sandwich.

Spinach

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Although spinach is full of nutrients, reheating can cause the formation of harmful compounds. When reheated, its nitrates can be converted into carcinogenic nitrosamines, or into nitrites, which can lead to a type of cancer called leukemia. The risks are relatively low, but it’s safer to have cooked spinach fresh or cold in pasta salads or wraps. Cold spinach is also charming, in a crunchy green superhero in disguise sort of way.

Potatoes

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Potatoes make good homes for Clostridium botulinum if they are left around at room temperature for too long. The spuds pose a potential health risk because reheating doesn’t destroy the toxins. Only reheat mashed potatoes or baked spuds once, and make sure to get them in the fridge quickly if you have leftovers. Or better yet, take those potato leftovers and turn them into potato pancakes so you don’t have to have that meal again.

Rice

Rice? That’s a surprise. The bacteria, Bacillus cereus, can grow on cooked rice after it’s been cooled down and the toxins that the bacteria makes won’t be killed by reheating. Rice, simply because it is improperly stored, is one of the most common causes of food poisoning worldwide. Leftover rice should be refrigerated and MUST NOT remain at room temperature. A quick tip? If you don’t know how long it’s been exposed, don’t take the risk.

Pizza

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Most of us have nuked a cold slice of pizza and can’t resist it, but it’s not always the best idea. Bacteria can live on meat and cheese, even if stored properly, as toppings. Reheating pizza in the microwave is also often a soggy mess. If you have to reheat it, put it in the oven for a crispy crust, or eat it cold, some say it’s better cold.

Mushrooms

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Mushrooms are fragile and will rot if not stored properly. Heating them up can break down the proteins in them, which can cause digestive discomfort. They’re best eaten immediately after cooking or cold in a salad. While mushrooms don’t tend to reheat well, they’re a great leftover ingredient to use in sauces or spreads.

Pasta

Pasta is a sneaky food to reheat, believe it or not. The risk, however, isn’t from the noodles themselves, but the creamy sauces. If left unrefrigerated for too long, dairy based sauces can develop bacteria such as Listeria. To be safe, store the pasta and sauces separately and then warm through thoroughly as well. Or forget reheating and indulge in cold pasta salad, a classic for a reason!

Eggs

If boiled or scrambled eggs are reheated, they can be dangerous. Reheating breaks down the high protein contents in the eggs in a way that can cause stomach discomfort. Salmonella can also live on improperly stored eggs. Why not eat yesterday’s omelet cold in a sandwich or a salad rather than microwaving it? This is a fun way to repurpose your leftovers without the microwave.

Oils

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Some oils, like olive or canola, can break down to create harmful compounds when reheated. It is especially the case with fried foods. Reheated oils may produce free radicals that can damage your health. The solution to this is to eat fried leftovers cold or to crisp them up in a safe, low heat method.

Chicken

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Reheating chicken might not sound so bad on the surface but in food safety terms it’s a red flag. Although chicken is a great source of protein, reheating it tends to change the internal structure of the meat, making it difficult for some to digest. It gets worse, because if the chicken is stored incorrectly, bacteria, like Salmonella can grow. In many cases, reheating won’t make it safe, especially if the chicken was left out for too long before storage.

Disclaimer: This list is solely the author’s opinion based on research and publicly available information.