The microwave has simplified daily life, allowing us to heat food quickly and efficiently. However, not all foods are safe to reheat in this appliance. Some can lose nutrients, others change flavor, and in certain cases, they can become harmful to your health by developing dangerous bacteria or toxins. Below, we explain more foods that should not be reheated, along with some additional foods that can also be problematic.
1. Rice (Oryza sativa)
Rice is one of the most consumed foods in the world, but improperly reheating it can lead to serious health problems. Bacillus cereus , a bacterium that can survive initial cooking, multiplies if rice is left at room temperature and reheating doesn’t eliminate its toxins. This bacterium can cause food poisoning, with symptoms such as vomiting and diarrhea.
Tip: Store the rice in the refrigerator as soon as possible and make sure to heat it to over 75°C to avoid risks.
2. Vegetables rich in nitrates
Vegetables such as spinach ( Spinacia oleracea ), chard ( Beta vulgaris ), celery ( Apium graveolens ), beets ( Beta vulgaris ), and turnips ( Brassica rapa ) contain nitrates, which are harmless when eaten fresh. However, when these vegetables are reheated, the nitrates can be converted into nitrosamines, compounds that are potentially carcinogenic under certain circumstances.
Tip: It’s best to eat these vegetables fresh or avoid reheating them multiple times.
3. Chicken (Gallus gallus domesticus)
Chicken contains proteins that change structure when reheated, which can make it more difficult to digest. Additionally, chicken is prone to bacterial contamination, especially from Salmonella and Campylobacter . If it is not heated evenly, these bacteria can survive.
Tip: Stir the chicken in the microwave to ensure it heats evenly and always check that the internal temperature exceeds 75°C.
4. Potatoes (Solanum tuberosum)
Cooked potatoes left to cool at room temperature can be dangerous, as Clostridium botulinum can grow and produce toxins that cause botulism, a serious illness that affects the nervous system. Reheating potatoes does not always eliminate this toxin.
Tip: Store cooked potatoes in the refrigerator and heat them in a pan or oven to ensure they heat evenly.
5. Fish (various species)
Reheating fish not only affects its texture and flavor, making it dry, but it can also increase the risk of food poisoning if it’s not stored properly. Bacteria like Listeria monocytogenes can grow in improperly refrigerated fish.
Tip: Avoid reheating fish in the microwave. Use the oven or a frying pan for more even heating.
6. Eggs (Gallus gallus domesticus)
Cooked eggs can be dangerous when reheated, as their proteins can become toxic and cause digestive problems. Additionally, microwave cooking can create a buildup of steam inside the egg, which could cause it to explode if not handled properly.
Tip: Reheat the eggs in a pan over low heat to avoid accidents and health problems.
7. Mushrooms (Agaricus bisporus and other species)
Cooked mushrooms are another food that can be dangerous when reheated. The proteins in mushrooms can break down rapidly if left at room temperature, which not only affects their flavor but can also cause digestive problems, such as stomach pain or bloating. Furthermore, if they are not refrigerated properly, they can develop bacteria.
Tip: Refrigerate cooked mushrooms as soon as possible, and if you decide to reheat them, do so at a low and constant temperature to avoid problems.
8. Sauces and stews with cream or milk
Sauces or stews containing dairy products, such as cream or milk, can separate when reheated. This not only affects their texture but can also create an environment conducive to bacterial growth if not properly refrigerated. Creams often curdle, and sauces can lose their creamy consistency when reheated.
Tip: When reheating these dishes, do so over low heat and stirring constantly to prevent the milk or cream from separating.
9. Overheated oils
Reheating oils like olive, corn, or sunflower oil can be problematic, as oils repeatedly subjected to high temperatures can release toxic compounds such as acrylamide, which has been linked to cancer risks. These oils can lose their healthy properties and produce harmful substances if reheated multiple times.
Tip: Avoid reusing or reheating oils that have already been used for frying or cooking. It’s best to use small amounts of fresh oil each time.
Additional dangers of reheating food
Improper or repeated reheating of food can cause it to lose nutritional value and, in some cases, can be a health hazard. Bacteria such as Escherichia coli , Salmonella , or Listeria can grow in improperly refrigerated or heated food. Reheated food can also lose its original texture and flavor, becoming less appealing and less nutritious.
Microwaves can be very useful, but it’s important to be careful with the foods you reheat. Avoid foods that become dangerous when reheated and always make sure to store your food properly. If you have any doubts about the safety of reheated food, it’s best not to take any chances.
