A tiny kernel sits in a pan or microwave.

It looks harmless.

Then suddenly—

POP.

The kernel turns inside out, expanding into a fluffy piece of popcorn.

But why does it explode?

And why does the explosion happen from inside the kernel?

In Why Popcorn Explodes From the Inside Out, we explore the surprising combination of heat, water, pressure, and starch that transforms a hard corn kernel into one of the world's favorite snacks.

We begin with the kernel itself.

Popcorn is a special variety of corn with an unusually hard outer shell called the pericarp.

Inside that shell is starch and a small amount of water.

That tiny amount of water is the key to everything.

As the kernel heats up, the water inside begins turning into steam. ...