Why Do Peeps Explode in the Microwave?

Every kid's favorite Easter-time party trick just so happens to have an interesting science lesson behind it.

marshmallow Easter peepsLI Cook/Shutterstock

Easter is just full of tradition—church services, Easter egg hunts, brunch with the family, and of course plenty of sweet treats. Among all the chocolate bunnies and Cadbury Eggs, the marshmallow Peeps are one of the most recognizable Easter treats. Love ’em or hate ’em, the sugar-sweet marshmallow chicks can offer one fascinating experience for kids and adults alike; just pop it in the microwave. If you have strong feelings about Peeps, you won’t want to miss these 13 foods everyone either loves or hates.

For those who’ve never nuked a Peep, here’s what happens: They grow bigger and bigger and bigger (watch it happen here) and could eventually explode if you leave them in too long. If you take them out before they get a chance to pop, instead of going back to their normal shape and size, they deflate into what can only be described as a Peep puddle. What’s up with that?

The basic ingredients of Peeps are sugar, corn syrup, and gelatin, which are whipped together to create air bubbles. Normally those air pockets help keep Peeps in shape, giving them their distinctive squishy, spongy texture. But when you put them in the microwave, the heat makes those air bubbles grow—gasses naturally expand more than the solids you find in foods. The growing air bubbles are trapped inside the Peep, pushing against the marshmallow walls and expanding the treat into a monster. When the air bubbles cool, they deflate, and the Peep collapses like a grounded hot air balloon—and its original structure has been destroyed. Ever wondered why they had bunny and chick shapes in the first place? These are the myths and legends behind Easter traditions.

This experiment works in the kitchen, but you get something else—something yummier—when you roast a marshmallow (or Peep) over a fire. Instead of growing, growing, growing, it might expand a bit, but it usually just browns. That’s because an open flame is hotter than a microwave, and it’s focused on the outside of the Peep, roasting it a lot and only expanding it a bit. (It’s a different reaction altogether.) Sugar molecules break down and caramelize, while the gelatin’s bonds break up and turn the inside texture from foamy to ooey-gooey. End result: a perfectly toasted marshmallow. For more fun with Peeps and other goodies, check out these 15 Easter basket ideas the whole family will love.

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Marissa Laliberte
Marissa Laliberte-Simonian is a London-based associate editor with the global promotions team at WebMD’s Medscape.com and was previously a staff writer for Reader's Digest. Her work has also appeared in Business Insider, Parents magazine, CreakyJoints, and the Baltimore Sun. You can find her on Instagram @marissasimonian.Marissa Laliberte-Simonian is a London-based associate editor with the global promotions team at WebMD’s Medscape.com and was previously a staff writer for Reader's Digest. Her work has also appeared in Business Insider, Parents magazine, CreakyJoints, and the Baltimore Sun. You can find her on Instagram @marissasimonian.Marissa Laliberte-Simonian is a London-based associate editor with the global promotions team at WebMD’s Medscape.com and was previously a staff writer for Reader's Digest. Her work has also appeared in Business Insider, Parents magazine, CreakyJoints, and the Baltimore Sun. You can find her on Instagram @marissasimonian.