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Name: Colleen F.
Status: educator
Age: 50s
Location: N/A
Country: N/A
Date: 7/21/2004

Why do marshmallows puff up when heated in a microwave instead of melting like other candy?


Marshmallows expand because they are made of foamed sugar. Microwaves heat the water in the foam and the trapped air causes the marshmallow to swell up. As soon as the microwaves are turned off, the foam collapses into a gooey puddle when the expanded air no longer feels the heating effect of the water.

ProfHoff 889

It's a race against "time". Marshmallows are a foam of air entrapped in sugar and other ingredients. When you put the marshmallow in the microwave two things happen as it heats up. The trapped air expands with increasing temperature and at the same time the marshmallow matrix begins to soften. Since you observe expansion, heating the entrapped air is winning. Should you keep heating however the marshmallow will probably eventually collapse.

Vince Calder

Because marshmallows are mostly air, which is composed of gases. Gases expand when heated. If you left the marshmallows in the microwave long enough they probably would melt.


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