Popcorn, that delicious, crunchy vehicle for butter, caramel and salt, is seeing its star rise. Americans already consume nearly 50 litres of popped corn a year each, on average. But in the UK, where crisps have traditionally been more popular, popcorn sales have skyrocketed: research firm Mintel found in 2016 that UK popcorn sales had grown 169% in the last five years.
While the internet abounds with tall tales about the origins of the snack food – Native Americans brought it to the First Thanksgiving! American colonists had it for breakfast! – there isn't any evidence to back up those stories. The real tale of popcorn is much more interesting.
It's certainly true that people in the Americas ate popcorn long before Europeans arrived. Popcorn is a specific breed of maize (not the same as the corn you eat on the cob, which is not a popping variety), and archaeologists have unearthed it from numerous caves and dwelling sites across the American Southwest and points farther south. The botanist Thomas Harper Goodspeed, who founded the University of California Botanical Gardens, once received a gift of ancient popcorn kernels from a Chilean archaeologist.
“One evening, at home in Berkeley, it occurred to me to try an experiment with my kernels of pre-Inca popcorn,” he writes in his 1941 book, Plant Hunters in the Andes. “I placed a few on a pie tin and heated them on the electric stove. Much to my surprise, that corn which had been gathered nearly a thousand years ago popped as readily as did last year's crop that had come in a box from the shelves of the neighborhood cash-and-carry store.” The sturdy little kernels had stayed snug in their thick outer skin, which is four times stronger than other corn varieties, for all those years.
Popcorn's pop is the result of that skin's strength, as well as its ability to efficiently transfer heat to the starchy innards of the kernel, so the skin can reach high heat without burning. As the temperature goes up, moisture in the interior turns to steam and starts to press outwards against the skin. The pressure builds as the temperature rises, and when it's nine-times-greater than atmospheric pressure, at just over 200C (400F), the skin finally splits, and the starch and steam expand explosively as the pressure equalises.
It is certainly possible to pop popcorn without any machinery
Scientists have found that you can double the size of the final popped kernel by using a vacuum pump to lower the pressure of the air in the pot where the kernels are heated, so when they spring out, they expand even farther than usual.
It is certainly possible to pop popcorn without any machinery – holding an ear of corn over a fire will do the trick – but the machinery, some might argue, is half the fun. In China, there are still a few street vendors who pop corn on the roadside using a cast-iron drum with the kernels sealed inside. The drum is turned as if on a spit over a flame, and when a pressure gauge indicates the time is right, the vendor puts a long canvas bag over its mouth and cracks the seal. The kernels split suddenly as the pressure outside them drops, exploding like tiny cannonballs into the sack. (See a video here.)
One of the first commercial machines for popping corn the way most of us are familiar with appeared in 1885, the invention of an Illinois confectioner named Charles Cretors who was experimenting with peanut roasters. Cretors' poppers were baroque contraptions powered by small steam engines, where popcorn kernels were heated in a mixture of lard and butter and a small mechanical clown, “Mr Roasty Toasty”, turned a crank and put on a show.
In food history writer Andrew Smith's book Popped Culture, he relates the story of Cretors taking his popping wagon on the road to the 1893 World's Fair. “He and his assistant, as the C Cretors Company later claimed, shouted out: ‘Try the new taste sensation! Free! Popcorn popped in butter – a revolutionary new method just patented! Try a bag for free!’” Smith writes. “Customers descended upon his wagon immediately. The clown perched atop the popcorn popper cranked furiously. As the enticing smell of hot, buttered popcorn drifted down the Midway, the crowds grew larger, attracted as much by the novelty of the show put on by the steam engine and the little clown as by the popcorn.” The Cretors Company is still a leading manufacturer of popcorn machines.
As it happens, home cooks are learning that popcorn is not the only seed capable of such explosive feats
Today, popcorn is having a bit of a moment as a health food. While you might think of it as a salty, buttery snack for special occasions like a movie or a carnival, the fact that it is a whole grain and – before being dressed up with seasonings – low in fat and salt has made it fertile ground for marketers.
In fact, it seems that this healthy image – never mind that most packaged popcorns do have substantial toppings – is behind some of popcorn's sudden expansion in the UK, according to the Mintel report. (Making it yourself at home – with an air popper, or just on the stove, is a better way to make sure your expectations line up with reality.)
As it happens, home cooks are learning that popcorn is not the only seed capable of such explosive feats. It turns out you can pop many seeds with hard shells, including rice, wheat, barley, and amaranth. Still, they don't expand nearly as much as popcorn. Going to the movies and ordering a small popped amaranth? Unlikely. For now, popcorn is safely ensconced in our hearts, and bellies.
Join 800,000+ Future fans by liking us on Facebook, or follow us on Twitter, Google+, LinkedIn and Instagram
If you liked this story, sign up for the weekly bbc.com features newsletter, called “If You Only Read 6 Things This Week”. A handpicked selection of stories from BBC Future, Earth, Culture, Capital, and Travel delivered to your inbox every Friday.