Video: Why Does Popcorn Pop?

Editor’s note: As the Oscars approach, we’re celebrating America’s favorite movie snack by bringing back this story, first published in 2014.

Popcorn is truly ancient. Archaeologists have uncovered popcorn kernels that are 4,000 years old. They were so well-preserved, they could still pop. In 2012, scientists discovered popcorn cobs that were grown even earlier — more than 6,000 years ago.

Dolores Piperno, a paleobotanist with the Smithsonian’s Tropical Research Insitute, says corn, and specifically popcorn, helped lay the foundations for the Aztec empire.

“When you have a very highly productive crop like corn, that makes the rise of high civilizations possible,” she says.

Piperno grows the wild, great-grandaddy of modern corn — a weird grain called teosinte. It has just a few kernels on each stalk, and they’re too hard to eat or to grind into flour. But teosinte has a special property that almost makes up for these shortcomings: It can pop.

“All early corns were popcorns,” Piperno says. “They were around for millennia before these other forms of corn.”

After a couple of thousand years, the Mesoamericans managed to cultivate varieties of corn that were good for flour, but they still ate popcorn. The Aztec language even has a word for the sound of many kernels popping at once — totopoca.

After the Spanish invaded, popcorn spread around the world, and soon people began to figure out how popcorn actually works.

It turns out that rock-hard kernel — the thing that makes teosinte and popcorn impossible to eat raw — is the key.

“It acts as a pressure cooker,” says David Jackson, a food scientist at the University of Nebraska. He says the durable kernel keeps water and starch sealed inside. When a kernel is heated, the starch liquefies and the pressure builds until the seed coat breaks.

“The pressure cooker essentially fails, and it explodes outward into a popped kernel,” Jackson says.

The liquefied starch froths outward, cooling and solidifying in a fraction of a second. If you look at a popped kernel under the microscope (or watch Skunk Bear’s latest episode), you can actually see the bubbles that were formed by the expanding steam. That’s why popcorn is so light and fluffy — it’s made of bubbles.

Now there’s something to think about next time you’re stuck watching a bad movie.

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