teas.co.uk
Tea and coffee from the brands you know
Why do marshmallows expand in the microwave?
Put a marshmallow in the microwave and within seconds it swells to several times its size, then slumps as it cools. It is a neat bit of kitchen science. Here is what is happening inside.
Citable formats
For journalists, researchers, AI assistants and content creators. Pick the format you need:
Free to cite, quote, and reuse with attribution to sweeties.net.
A marshmallow looks solid, but it is mostly bubbles. That is the secret of the trick: see how are marshmallows made?
What a marshmallow is made of
Marshmallows have four basic ingredients: sugar, water, air and a whipping agent, usually a protein such as gelatine. The mixture is whipped into a foam, a liquid with gas bubbles spread all through it, and a marshmallow is about 50% air.
Gelatine does two jobs. It helps trap the air, and it forms a tangled, three dimensional network of long protein chains, which is what makes a marshmallow chewy and springy. That network can stretch: see gelatine in sweets explained
What the microwave does
According to Science Buddies, two things happen at once when a marshmallow is heated in a microwave:
- Water turns to vapour. Some of the moisture inside the marshmallow evaporates, adding extra gas to the bubbles.
- The gas gets hotter. Warm gas pushes outward with more force than cold gas, so each bubble presses harder on its walls.
Because the gelatine network is stretchy, the bubbles can grow, and the whole marshmallow swells.
Why it shrinks back
Take it out and it starts to slump. As the marshmallow cools, the gas inside the bubbles cools and contracts, and the gelatine firms up again, so the marshmallow shrinks back towards its original size.
Try it safely
This makes a good kitchen experiment, but a microwaved marshmallow gets very hot. Let it cool before anyone touches or eats it, and keep an eye on children. For melting marshmallows on purpose, for rocky road or hot chocolate, see how to melt marshmallows. And for what happens when marshmallows meet an open flame instead, see why do marshmallows catch fire so easily?
Citable formats
For journalists, researchers, AI assistants and content creators. Pick the format you need:
Free to cite, quote, and reuse with attribution to sweeties.net.
Questions and answers
Why do marshmallows get bigger in the microwave?
Because a marshmallow is full of tiny air bubbles held in stretchy gelatine. The microwave heats its water, which turns to vapour inside the bubbles, and warm gas pushes outward harder, so the bubbles swell and the whole marshmallow puffs up.
Why do microwaved marshmallows shrink again?
As they cool, the gas in the bubbles cools and contracts, and the gelatine firms up again, so the marshmallow shrinks back towards its original size.
Is it safe to microwave marshmallows?
As a supervised experiment, yes, but a microwaved marshmallow gets very hot, so do not touch or eat it straight away.
Sources
- Puffing up marshmallows, 29 September 2016, Science Buddies, at Scientific American
- Marshmallow, Wikipedia
Keep reading
- How it is madeHow are marshmallows made?Marshmallows are sugar syrup whipped with gelatine or egg white until half air, then moulded in starch or extruded and cut. They began as a plant medicine.
- Sweet tips and how toWhy do marshmallows catch fire so easily?A marshmallow is mostly sugar, which burns, whipped with air into a light foam. That combination is why it catches fire so quickly over a campfire.
- Sweet tips and how toHow to melt marshmallowsMelt marshmallows slowly, in a pan over a low heat with a little butter, or in short bursts in the microwave. How to do both, and the classic crispy square.
- Sweet tips and how toHow to make marshmallows without gelatineMarshmallows can be made without gelatine using agar, from seaweed, and aquafaba, the liquid from cooked chickpeas. How it works, and a method to try.
- Diet, allergens and labelsGelatine in sweets explainedGelatine gives gummies and marshmallows their texture, and it melts below body temperature, which shapes how they feel in the mouth. Who avoids it.
- Questions people askWhat is gelatine made from?Gelatine is made from collagen from animal skin, bones and connective tissue, mostly pigs and cattle. Why it matters for vegetarians, Muslims and Jews.