9 Things You Should Never Put in a Microwave

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Woman frustrated with microwave
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Home cooks probably know what can be heated in a microwave oven. But do you know what can’t?

Well, for one thing, don’t put anything metal in the microwave, warns Wendy Treinen of GE Appliances. That’s her No. 1 no-no.

I learned this the hard way. In the 1980s, my Catholic girls high school didn’t have a kitchen, just a row of vending machines and a microwave that did more smoking than some of the seniors. Every week or so, someone turned on the microwave with a foil-wrapped burrito or piece of metal cutlery inside.

The result: a damaged microwave oven and some very unhappy nuns.

Following are several more things to keep out of your microwave oven.

1. Plastic

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Microwaving plastic containers may be “the fastest route to ingesting massive quantities of minuscule plastic particles,” according to research from the University of Nebraska-Lincoln.

A study conducted at the university found widely available baby food containers were made of questionable plastic. They contain types of particles — microplastics and nanoplastics — that quickly kill most embryonic kidney cells used in the study.

While that’s not enough research to draw any broad conclusions, it’s generally an unnecessary risk. You can take the amount of food you intend to eat out of Tupperware or other plastic containers and put it on a plate or in a bowl before microwaving.

2. Chinese food containers

Couple eating takeout leftovers
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Microwaves are great for heating up leftover fried rice or kung pao chicken. But take a close look at that takeout container. If it has a metal handle, break it off before you put the container in the microwave.

Alternatively, transfer the food to a microwave-safe dish, suggests Jill Notini, of the Association of Home Appliance Manufacturers.

3. Twist ties and staples

Man putting a mug in a microwave
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Look for any twist ties or staples and remove them from food packaging before you heat an item in a microwave.

Even the little piece of metal inside a twist tie can cause sparks inside a microwave. Hunt down any metal, even something as small as a staple on a tea bag, and remove it.

4. Nuts, seeds and eggs in their shells

colored eggs
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Never cook eggs in their shells in a microwave, Notini tells Money Talks News. Here’s why: When steam builds up inside the shell, the egg may explode.

Unshelled nuts and seeds may explode, too.

Notini’s rule of thumb: “If it’s inside its shell, don’t put it in the microwave.”

5. Non-microwave popcorn

A man in glasses eats popcorn on his couch while watching TV
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Microwave popcorn comes in special packages made for use in a microwave. But microwaving popcorn after just putting it inside a plain brown bag isn’t safe.

“It can catch on fire,” Notini says.

6. Grapes

bulk grapes
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It’s fun to watch YouTube videos that show off the fiery result when grapes are cooked in a microwave. But stick to watching the videos. Don’t try it yourself.

Grapes are sealed in a tight skin. Microwaving them creates a mess, at a minimum, and can ignite a fire in the worst-case scenario.

7. Bread

Woman eating bread
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Toast bread with a conventional oven if you don’t have a toaster. Don’t use a microwave. Microwaving bread products makes them damp and soft … before burning them.

Avoid microwaving any food that’s meant to be crispy, including fried chicken and french fries, GE Appliances’ Treinen tells Money Talks News.

Let me add pizza to the list, too. Folks do that every day, but pizza reheated in a microwave is soggy and sad. Instead, try this:

  • Warm leftover pizza briefly in a nonstick skillet on the stovetop.
  • After the bottom of the crust is crisp, add a few drops of water to the pan and cover with a lid for about a minute.

Mmmmm … Melty cheese, hot toppings and a crispy crust.

8. Milk or formula for babies

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Microwaves are lifesavers for new parents who are too exhausted to make dinner for themselves. But don’t use your microwave to heat breast milk or formula.

“Studies have shown that microwaves heat baby’s milk and formula unevenly,” the U.S. Food and Drug Association warns. “This results in ‘hot spots’ that can scald a baby’s mouth and throat.”

The FDA advises that you always stir baby food after heating, let it stand 30 seconds and taste-test it yourself before feeding.

9. Nothing

Reheating food in the microwave
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Turn the microwave off if there’s nothing inside it.

“You’re dealing with energy here, and that energy needs to go somewhere,” Notini says. “It could be (going) into the walls or into even the little pieces of plastic under the turntable. Those could melt or catch fire.”

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