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Freshly Baked Science

Day 1 .jpg

Marshmallows are Swell

1st December 2018

You may have noticed when making the Melted Snowman Cupcakes , that marshmallows expand like crazy in the microwave! So, what makes them grow when they are heated up?

Marshmallows are mostly made up of water, sugar and gelatin. The gelatin in it acts as an aerating agent, adding lots of air bubbles. This creates the fluffy texture that we know and love! When a marshmallow is given energy, in the form of heat, it increases the volume of air inside the marshmallow.


Luckily, the increased volume of air inside the marshmallow doesn’t cause it to explode, due to their elasticity, given by the gelatin. This means that the marshmallow will just expand to accommodate the increased volume of air, making it puff up to 4 times its original size!


A similar thing happens when you toast marshmallows on a fire! Keep your eyes peeled for another post on how to make ‘Toasted Marshmallow Chocolate Cups’… yes, they are as good as they sound! 

Share your before and after photos, or videos, of marshmallows expanding with the hashtag #STEMintoChristmas for your chance to be featured!

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