Unless you're an enterprising toddler with a passion for button-pushing, you know better than to put metal in your microwave. But that's just the start of what shouldn't go in your kitchen's magic box.
Microwaves use electromagnetic radiation to heat your food. (Incidentally, it's about the same amount of radiation as you get from your smartphone.) The waves emitted cause the water, fat, and sugar molecules to frantically flip back and forth—about a million times a second. That friction then spreads out and "heats" your food.
While some foods bask under such attention—microwave popcorn, we're looking at you—not everything is meant to be nuked. Before you press "start," check out this short list of things you should never put in the microwave.
1. Recycled products
Weirdly, some eco-friendly products, from paper towels to waxed paper, contain flecks of metal. Tiny though they may be, they can still cause sparks and (worst-case scenario) even flames. To err on the side of caution, use only recycled products that indicate on the packaging that they are microwaveable.
2. Plastic containers
You've probably heard this one before, but the reason goes deeper than the potential for melting. Many plastic containers contain bisphenol-A, or BPA, an industrial chemical that’s been linked to cancer, brain problems, heart disease, obesity, and diabetes, among other health-related issues.
Heating BPA-containing plastic in the microwave can release toxic fumes and leach this potentially noxious chemical into your food. (This is even more likely to happen with a container of rich, fatty foods.)
“Double-check to make sure your plastic storage containers are labeled ‘microwave-safe,’” says Doug Rogers, president of Mr. Appliance, an appliance repair franchise. Better yet, heat up foods only in glass or porcelain containers.
Styrofoam to-go containers aren’t just a nightmare for the planet (they take a minimum of 500 years to decompose). As a form of plastic, they, too, can potentially release harmful chemicals into your food when heated, and can melt.
“Plate your doggie-bag items if you’d like to reheat them,” cautions Frank Proto, chef-instructor at the Institute of Culinary Education in New York City.
An egg's hard shell makes it a bad match for your microwave.
“Pressure can build up [inside the shell] and explode,” Proto says.
Don't even think about reheating an already hard-boiled egg, either. Not only could it explode—potentially after you remove it from the oven and decide to peel it—but the explosion can make a sound of 86 to 133 decibels. That’s similar to a chain saw or thunder on the high end. We're not saying it's enough to damage your hearing (although scientists have looked into it), but we'd prefer not to take any chances.
5. Chinese takeout
We have nothing against moo shu pork. It's really the paper pail you brought it home in that's a microwave no-no. Many Chinese takeout containers have metal handles, which can spark a fire.
6. Thick liquids
Dense food items like tomato sauce and oatmeal will form large bubbles as they boil. While that’s not the end of the world, the cleanup that will need to be done afterward could feel like it.
"They’ll cause large bits to break and splatter,” Proto says.
It’s unclear why anyone would want to nuke grapes or raisins, but either way—don’t.
“They emit plasma when microwaved, which can cause them to smoke and even explode,” Rogers explains. (See a demonstration here.)
Plasma, an ionized gas, is made when electromagnetic waves rip molecules apart into electrically charged ions. This doesn’t happen if you have enough food inside your oven to absorb the waves’ energy. But grapes and raisins simply aren’t big enough to do that.
8. Travel mugs
Many travel mugs are made from stainless steel, "which blocks the heat from warming the liquid and can damage your microwave,” Rogers says. If your to-go cup is plastic, be sure to check the bottom and ensure it’s marked “microwave safe" before you nuke it.
9. Apples and pears
Whole apples and pears are two more fruits to put on your “no nukes” list.
“Like an egg’s tight skin structure, a lot of moisture is held under the skin of these fruits,” Proto says.
Heat them whole in your microwave, and you'll have a fruity explosion on your hands.
Although they don’t have a shell and their skin is soft enough to peel, potatoes will still explode if you try to pop them as is into your microwave. No one’s saying you can’t bake one (don't all microwaves come with a “potato” setting?) but to avoid russet chunks splattered on the walls of your oven, “make sure the skin is pierced,” Proto says.
Some veggies such as carrots gobble up an impressive amount of minerals from the soil they’re grown in. This makes them nutritious, but the minerals are also excellent conductors of electricity—and prone to catch on fire.
Green peppers, kale, and green beans are also at risk of this phenomenon, known as "arcing." If you speed-cook these specific veggies, watch them closely. If they start firin’ up, remove them right away so you don’t damage your oven.
12. Tightly closed dishes
Even if you’re heating something in a glass or BPA-free-plastic container, you’re in for a mess if you leave it tightly sealed.
“Pressure and steam can build up and cause an explosion. It can also crack the lid,” Proto says. Feel free to vent.
We’ve all turned on the microwave's cook function when we meant to turn on the timer. But this simple mistake has big consequences.
“Beware of turning on the microwave with nothing in it,” Rogers says. “If there’s nothing to absorb the microwaves, they're absorbed by the actual appliance, which could cause it to combust if left running for an extended time.”
And let's be real here. Despite all the foods you now know you shouldn't put in the microwave, what would you do without yours?