Fostering curiosity in kids (and their parents) since 2011

“What happens in a microwave that makes jawbreakers explode?”

Excerpt from Candy Experiments which says: Never heat a jawbreaker.

The warning from Loralee Leavitt’s book on Candy Experiments that got all our wondering started.

If you’re just joining us, last week I learned that jawbreakers can explode when heated in a microwave. This week, I’m going to find out why.

What happens in a microwave that makes jawbreakers explode?

The 30-second answer (That’s “tl;dr” for all you youngsters out there) 

Jawbreakers explode in the microwave for the same reason raw eggs and popcorn do. All three foods combine a hard outer shell with a relatively wet interior.

The 3-minute explanation for “Jawbreakers explode because they have a hard outer shell and a relatively wet interior”

Your microwave oven is so familiar, I bet you’ve forgotten how cool it really is.

I’m going to simplify things a lot here, but in general microwaves cook food by beaming microwave radiation directly at the water, fat, and sugar molecules inside it. The microwaves agitate these molecules, causing them to rub against one another, creating friction. The friction generates heat, and that heat cooks the food.

Some types of molecules absorb microwaves better than others. Water absorbs microwaves much better than fat or sugar, which is why when you cook a Pepperoni Hot Pocket in the microwave, the water-rich tomato sauce inside can burn your tongue even if the relatively dry pastry outside doesn’t feel super-hot.

In the case of jawbreakers, the microwaves can turn the water in the jawbreakers’ inner layers into steam. But the hard outer shell doesn’t let that steam out. As the cooking continues, the steam expands. At some point, the pressure from the steam becomes intense enough that the outer shell is blown into fragments.

Want to simulate this effect for yourself? Safely, I mean?

Exploding jawbreakers are quite dangerous — you can get some serious burns from them. So …


Cover for Loralee Leavitt's Candy Experiments

Heating jawbreakers is not one of the experiments in this book. Making brittle Peeps is, however, and I highly recommend you try it.

However, if you’d like to test this theory and are willing to clean up a huge mess, you can try microwaving a raw egg in its shell.

If like me, you are not terribly enthused by large messes, you can test it by making some popcorn.

Popcorn pops in your microwave for the same reason that jawbreakers do — the moisture inside the popcorn kernel turns to steam, eventually forcing the hard outer shell to crack apart. (That’s where all the steam you have to avoid when you open the popcorn bag comes from.)

In fact, making some microwave popcorn sounds really good right now. I think I’ll go make some. If the Eleven-Year-Old asks, I’ll tell her I’m not just making a snack, I’m doing science.

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