Why Don’t All Popcorn Kernels Pop?

If a kernel stays unpopped, that's because it's missing one key thing.

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Photo: Steve Cukrov (Shutterstock)

Popcorn always seems like nothing short of a miracle to me. With heat properly applied, it transforms from this tiny hard nearly inedible nodule, into a puffy and crisp treat that tastes like concentrated corn. It’s easy to take popcorn for granted since we’re so used to eating it at movie theaters and at home, but I still think it’s pretty awesome.

When we pop some popcorn, whether it’s on the stove, in an air popper, or the microwave, we’re almost always left with a few kernels that never blossomed into their full potential. But why didn’t those little guys pop? The answer all comes down to one thing: water.


What popcorn kernels need to properly pop

As dry as those little kernels look on the outside, their content includes a little bit of water trapped within its hull. When that water is heated to the right temperature, the steam generated bursts the kernel, flipping it inside out. Scientific American has a great explainer on this process. The fluffy delicious part is a result of the starch contained within the kernel. As the raw kernel explodes, the starch gelatinizes and transforms into a fluffed-up kernel of popcorn as it cools off. And Scientific American says that the popping noise isn’t from the kernel bursting, but rather the rapid release of steam that comes out once the hull bursts open. Whip that one out at parties.


This 2005 piece from the New York Times reports that one scientist, Bruce Hamaker, figured out that the mechanism that guarantees a good pop comes down to the raw kernel’s hull. It’s made out of a few sheets of cellulose, which composes the hard element of the kernel’s exterior. When cellulose is heated up, those sheets transform into tightly bonded crystals, so tight that water can’t get past its barrier. If the hull isn’t strong enough, water can find its way out before it turns into steam, and without the steam, you get a dud. Science!

Next time I pour some popcorn into my big movie bowl, I’ll know exactly what happened to those poor little stragglers at the bottom. Then I’ll dig into the rest, kick back on the couch, and enjoy the movie.