Why Does Popcorn Pop?

The Chemistry of Popping Popcorn

What happens if you bake a potato and forget to poke holes in it? Yes, it explodes! The same is true for popcorn, but what happens in popcorn is special! Instead of the starch flying out and making a mess, it all hangs together in a delicious bite sized puff called a “flake”. Large flakes have less taste and small flakes have more taste.

Why does popcorn pop? How does popcorn pop? One word, STEAM. That’s right, the same power that drove steam locomotives and steam ships is the “umph” behind a popping kernel of corn. When we make popcorn, either in a stovetop popper or in the microwave, we are simply turning the kernel’s 14% water content into steam. Explosive Steam!

How does popcorn pop exactly? Well, when we heat the kernel, the water at the center wants to boil off. This heating causes the water to expand. Because it can’t escape through the hard shell of the kernel, the water mixes with the dry outer layer of starch. This softens the starch as it continues to heat.

As more heat is applied, the starch continues to soften and then to almost liquefy. The starch’s polymer chain is completely saturated with water, but the chain doesn’t break! The chain simply has no wiggle room inside the kernel.

Finally, as more and more heat is applied, the pressure inside the kernel becomes so high that the kernel cracks and bursts! The liquefied/gel-like starch instantly escapes, just like an exploding potato in the oven, but there’s much less water in a kernel of popcorn than in a potato. This is why the popcorn flake hangs together after exploding.

As the liquefied starch breaks through the popcorn hull, water inside the starch instantly vaporizes into steam as there is no longer any pressure to hold the water in. This outgoing steam pushes on the starch and creates millions of gas pockets between the starch chains.

The water then escapes the popcorn flake as steam rising from the popcorn kettle. This steam is responsible for the light and airy texture of popcorn.