What Actually Happens to Metal in the Microwave

If you’re a person who has used the microwave a good number of times, there’s a decent chance that you’ve accidentally put metal in there – even though you know you’re not supposed to.

For me, it’s usually when I was in a sleep-deprived state – I left the spoon in or whatever – though some instances have been more disturbing (like when I was microwaving something and a piece of it burned and sparked like metal but it was just supposed to be food???).

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But why can’t you put metal in there, and what happens inside the magical box if and when you do?

Let’s learn some science, shall we?

Here’s how your microwave works: you press start and it begins producing negatively charged electrons that bounce around the positively charged walls of your unit. The activity produces electromagnetic waves in the microwave frequency that begin bouncing around, too, and the food you stick in there absorbs the resulting microwaves, thanks to the water and fats it contains. These particular molecules are very good at absorbing microwave radiation. The waves makes the water molecules vibrate and heat up, transferring warmth to the other, non-water molecules in the food.

Except microwaves don’t just give energy to the molecules in food – they give energy to anything they touch.

So what if you put metal in there?

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The metal still heats up, but without surrounding non-metal molecules to transfer the energy to, the microwaves either bounce off the metal and into the internal circuitry of your microwave, which can result in overheating and possibly fire, or get absorbed by the metal, which can make it super hot.

The way to definitely start a fire is to put something flammable, like paper, in with a thin metal – aluminum foil, the tines of a fork, a gold foil rim on a tea cup – because as the microwaves knock electrons loose in the metal, they concentrate in the creases, building up and up and up until the charge finds somewhere to jump. That’s what those awesome arcs are, if you’ve ever seen those.

Along with metal, you should never put styrofoam in there.

I know, but what about takeout containers??

Well, they’re made of heat-unstable plastic that can warp or melt in the microwave, not to mention release harmful chemicals into your food.

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Also avoid cold-storage tubs, like the ones that held your sour cream, yogurt, or cream cheese because of similar issues.

For your convenience, the FDA labels containers “microwave safe,” so all you have to do is read some labels.

So, the next time you accidentally start a fire in your microwave, you’ll totally be able to explain why!