Kitchen Science
Marshmallows are mostly sugar and water wrapped around air bubbles. When you cook marshmallows in a microwave oven, several things happen at once. The microwave makes the water molecules vibrate very quickly—which makes the water heat up. The hot water warms the sugar, which softens a little. The hot water also warms the air bubbles.
As the air in the bubbles warms up, the air molecules bounce around faster and faster and push harder against the bubble walls. Since the sugar walls are warm and soft, the bubbles expand, and the marshmallow puffs up.
When our marshmallows cooled down, the bubbles shrunk and the sugar went hard again so it became dry and crunchy, a bit like meringue. That’s because some of the water in the marshmallow evaporates when the marshmallow is hot.
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| Getting our marshmallows ready to go in the microwave |
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| BIG marshmallows! |
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| The marshmallows puffed up with heat. |
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| As the marshmallow cooled it got harder and more sticky |
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| When the marshmallow cooled, the air bubbles shrunk and it went hard and crunchy. |
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