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What can and can't go in a microwave? An expert reveals the answers

Microwave ovens are practically everywhere — homes, work places, schools, hospitals, you name it. Yet despite their popularity, most of us aren’t absolutely sure what can and can’t go into these cooking wizards.

That’s why we turned to Bob Schiffmann, president of International Microwave Power Institute. With 55 years of experience working with microwave ovens, he’s recognized as THE expert on the subject. You’ll be surprised at what he has to say.

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Here's everything you can and shouldn't put in a microwave

1. What about plastics?

“Almost all plastics are safe in the microwave,” says Schiffmann, “but if an item is marked ‘not microwave safe’— obviously don’t use it in the microwave!” Rule of thumb: always check labels and warnings on all items before placing in a microwave.

Caveats:

  • Don’t heat dry foods in plastic because the plastic may melt.
  • Don’t use single-use containers like those containing yogurt, cottage cheese and margarine.
  • Don’t use pitted or warped/melted plastic containers.

When covering food with plastic wrap, make sure the wrap doesn’t touch the food. Also, cover the food lightly so steam can escape; otherwise, you can be steam-burned and that can be serious!

2. Styrofoam is actually safe, but there are some exceptions

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Styrofoam can safely be used in the microwave when heating pure liquids, such coffee or water for tea.

Caveats:

  • Do not continue heating once it boils.
  • Do not heat items containing fats or solids, like soups or Ramen noodles.

3. Paper is OK as long as it's the right kind of paper

Paper towels, wax paper, parchment paper, paper plates and bowls are fine in the microwave.

Newspaper is not sanitary and it leaches ink into whatever you’re cooking, so don’t use it.

Brown paper bags are never safe in the microwave because they can’t withstand a lot of heat and can catch fire. They also may emit toxic fumes and may contain germs that can be passed on to food.

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4. Are glazed ceramics safe?

When made with properly formulated glazes, glazed ceramics — everything from stoneware to china — can be used in the microwave. Corning Ware and glass cookware like Pyrex and Anchor Hocking are safe. HOWEVER, beware of glazed ceramics that are made in China — regardless of price and name. Because China does not adequately regulate the industry, some manufacturers are using glazes that contain high amounts of lead and arsenic — dangerous elements that can leach into foods when microwaved.

Another issue with using glazed ceramics in the microwave concerns the amount of heat the dish or cup retains. To make sure your coffee cup or mug won’t overheat in the microwave, put a half cup of water in the cup and microwave it for 30 seconds. If the cup is hotter than the water it contains, don’t microwave it.

5. What about ceramics that are handmade by you or a friend?

According to Sarah Millfelt, president of the Northern Clay Center in Minnesota, handmade ceramic dishes and cups are okay for use in the microwave as long as the glaze is not cracked and there is no metallic trim. To make sure the cup won’t overheat, Schiffmann recommends doing the water test as noted above.

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6. Dishes/cups with metallic trim. Yay or nay?

If there’s metallic trim on an item, it’s never safe to use in the microwave. Never. Not only will the metal overheat, it could arc and damage the oven or the dish.

7. Is aluminum foil ok?

Schiffmann did the initial tests on using aluminum foil in microwave ovens and the results still hold true today. Aluminum foil can be used to wrap the ends of chicken or turkey or duck legs so they don’t get overcooked. But, aluminum foil that is crumpled, bent or in small pieces cannot be used as it can arc and spark, especially if it’s too close to the sides of the microwave.

8. Twist ties — a definite no no!

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Because they arc and spark, twist ties should never be used in microwaves. Period.

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9. Beware of metal handles on Chinese take-out containers

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Remove the metal handles on these containers before heating food as the handles overheat and can cause the container to burn.

10. Metal pans — here's what you need to know

Microwaving food in a metal pan is not unsafe but it is inefficient. That’s because the microwaves cannot penetrate metal, so they only reach the top of the food, Schiffmann explains. (Now you know why you can’t re-heat coffee in a stainless steel go-cup.) In non-metal containers, microwaves can penetrate all sides to cook more quickly.

That means you can leave all-metal spoons in your coffee cup or bowl of cereal in the microwave and they won’t get overheated. Just make sure they’re all metal. Utensils with wood or plastic handles may become hot because of the rivets or screws holding them.

11. What about staples on tea bags?

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No need to remove the staple when microwaving a tea bag in water. It was Schiffmann who conducted studies for Lipton Tea Company that proved the staple on the tea bag tag is safe in the microwave.

One last piece of expert advice: Never run the microwave with nothing in it. The heat has nowhere to go and can end up damaging the magnetron and ruining the microwave.

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