Today, 19 January, is Popcorn Day, a day to celebrate one of nature’s fun foods – those crazy little corn kernels that, when exposed to heat, explode violently and morph into cushiony white snacks many times their original size.

We’ve all enjoyed popcorn, but have you ever wondered what makes ’em pop?

Exploding starch frozen in action. (© All Rights Reserved)
Each piece of popped popcorn is a totally unique example of exploding starch frozen in action.
(© All Rights Reserved)

The secret to popcorn’s popping ability lies in the composition of the kernel. The popcorn kernel consists of a hard, watertight outer shell, containing starch and a small amount of water and oil.

When the kernel is heated, the water inside tries to expand to steam, but the hard shell prevents this. The heat also gelatinizes the starch inside the shell. Once sufficient pressure has built up (to an incredible 930 kPa), the kernel bursts open in a violent explosion, freeing the steam and starch.

As the hot starch bursts out of the shell, it expands rapidly to as much as 50 times its original size. At the same time it experiences rapid cooling as it comes into contact with the air outside the shell.   It is this rapid cooling that sets the gelatinized starch into the familiar foamy popcorn puff.

So a popped popcorn is basically a starch explosion frozen in action!


  1. I love popcorn, but reading this just reminded me of how awesome it is! I used to have my art students sketch a piece of popcorn to start to understand composition and line. It was a great exercise because each piece is so original. Thanks for sharing!

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