Microwaves can be a convenient option for reheating foods in a pinch, simultaneously killing bacteria and making your food safe. However, microwaves are also notorious for cooking food unevenly, allowing harmful bacteria to survive and thrive–and leaving you at an increased risk for food poisoning.
According to FoodSafety.gov , 1 in 6 Americans get sick from foodborne illness (aka food poisoning) each year. The biggest culprits are bacteria, including salmonella, listeria and E. coli.
“When reheating in a microwave, the food needs to be stirred at least once to distribute the heat and then put back in the microwave to get to the appropriate temperature ( at least 165°F ),” says Mitzi Baum , CEO of Stop Foodborne Illness . “Follow the safe cooking instructions on packages carefully. They have been developed and tested by food safety scientists to help keep you and your family safe.”
To ensure your food is properly heated throughout, use a food thermometer to check your food has reached the proper temperature.
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“As a food safety expert, my foundational message to consumers is to make a minimal investment and purchase a tip-sensitive, rapid-read digital thermometer from your favorite consumer goods store and use it when cooking most foods regardless of what type of oven you are utilizing,” says Dr. Randall Phebus, Ph.D., professor of food safety at Kansas State University. “This is really the only true assurance that you are protecting your family’s health and is a key component of serving up high-quality food dishes.”
However, there are some foods that you should never reheat in the microwave due to additional risks and nutritional losses. Here's what they are.
5 Foods You Should Never Reheat In the Microwave
1. Infant formula or breast milk
Although the microwave can quickly reheat formula and breast milk, this should never be how you warm it up. “Microwaving formula or breast milk can cause uneven heating, creating hot spots in the bottle,” says Joan Salge Blake, EdD, RDN, LDN, FAND , a nutrition professor and registered dietitian nutritionist (RDN) at Boston University (BU) and author of Nutrition & You. “These very hot parts of the fluid can scald a baby’s mouth.”
The Food & Drug Administration also advises against microwaving breast milk because it destroys nutrients in the heating process.
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2. Stuffed poultry
Stuffed poultry should never be cooked in the microwave, says Dr. Barbara Kowalcyk, Ph.D., Associate Professor and Director of the Institute for Food Safety and Nutrition Security at The George Washington University.
“Stuffed poultry may be labeled ‘ready to cook’, but you should not solely cook it in the microwave,” she says. “Foods labeled ‘ready to eat’ are more safe.”
The USDA adds that while the chicken may cook quickly, the stuffing inside might not reach the appropriate temperature needed to destroy harmful bacteria–leaving the risk of foodborne illness high.
3. Marinades for raw meat or poultry
While marinades provide some wonderful flavors to raw, protein-rich foods before cooking them, you shouldn’t use the uncooked marinade as a finishing sauce for cooked meat or poultry.
“The uncooked marinade can contain pathogens that can cause foodborne illness. The marinades must be boiled first to kill pathogens that can make you sick,” says Dr. Blake. “Since microwaving causes uneven heating, pathogens can still remain after heating. I would never reuse the marinade even if it was brought to a boil in a pot on the stove. It’s better to be safe than sorry.”
4. Leftovers that you've had for more than a week
If you’ve had leftovers in your fridge for seven days or more, toss them–they cannot be saved by reheating in the microwave, per the FDA’s Food Code .
“Very old foods can have spoilage growth (mold, yeasts) and bacteria. If they are in food and not killed during the reheating process, they can cause severe illness,” says Baum. Leftovers are typically safe for three to four days, according to the USDA .
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5. Food left unrefrigerated for 2+ hours
If food has been left out at room temperature for two hours or more, Baum notes that you can’t just “heat the heck out of it” and make it safe to eat. “Some bacteria can survive cooking temperatures and multiply when left out for too long,” she says. (The USDA notes that bacteria grow between 40 °F and 140 °F, and can double in as little as 20 minutes.)
For example, she says that when perishable foods are not stored at safe temperatures, Staphylococcus aureus bacteria grow rapidly and produce toxins that cannot be destroyed by reheating, even at high temperatures.
Related: The Top 3 Packaged Foods Most Likely to Be Contaminated, According to Food Safety Experts
Another example is the bacteria Clostridium botulinum, which causes botulism. “A single spore of it can multiply into 1,000 bacteria in a few hours, and reheating food that’s been contaminated with C. botulinum doesn’t kill the bacteria nor remove the harmful toxins the bacteria has released into the food,” says Baum.
While the microwave can be great for a lot of things (an excellent modern invention!) there are some cases when it's just not a great go-to heating method.
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