How does popcorn pop?

Asked by: Tasha McArthur, York

Explosions occur when there is a sudden expansion of gas: that’s what happens when popcorn pops. A popcorn kernel has a moist, starchy inside confined in a tough outer coat. This coat stops gases escaping, so when cooked, the water inside doesn’t evaporate, but becomes superheated above its normal boiling point. When the coat eventually splits under the pressure, the water vaporises. The starchy mix expands, because it’s suddenly full of tiny holes of steam. We call this cooked, starchy foam ‘popcorn’. To experiment at home, try puncturing the coat of some popcorn kernels – it should stop the pop.

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