This snack food may be a delicate crop, but its popularity has endured for thousands of years.
In 1948, scientists found 6,000-year-old unpopped popcorn kernels in a New Mexico cave.
They placed 10 of the kernels on a wet paper towel for two days. Then they dropped them into hot oil. The kernels popped into a snack you might buy at a modern-day movie theater.
The story shows some of popcorn's most significant characteristics: It's tough, it's resilient, and its popping power doesn't fade.
Popcorn kernels are either round and smooth, like a pearl, or slender and pointy, like a grain of rice. Both kinds are protected by a very hard shell, called the hull. The hull is tough enough to preserve kernels for thousands of years.
The secret to popcorn's "pop" is water. A drop of water sits in the middle of each kernel. When heated, the water turns to steam. The steam pressure pushes against the hard hull until it gives way with a tiny "pop!"
The explosion inflates the starch inside the popcorn, turning the kernel inside out. Popped kernels are 30, 40, even 50 times as big as unpopped ones.
The other varieties of corn - sweet, flint, dent, flour, pod, and waxy - can also pop, but not as well. Even some types of rice will pop. But popcorn's combination of hard shell and soft interior means it pops better than the rest. It tastes better, too. That explains why humans have been eating popped popcorn for the last 8,000 years. (See story below.)
Farmer Frank Morrison of Clearwater, Neb., has grown popcorn all his life. He harvests a whopping 5 million gallons of kernels every year. That's 35 million pounds' worth. They will turn into about 200 million gallons of popped kernels. But that's only a fraction of the 4.3 billion gallons of popped popcorn Americans eat each year.
Farming popcorn is hard. It's a domesticated crop, meaning that it doesn't grow in the wild. It requires the constant care of human beings to sprout and grow.
Mr. Morrison planted this year's crop at the end of April. By the end of June, most of the plants' leaves had sprouted and the ears had begun to form.
About 12 stems, called tassels, emerged from the top of each plant in early summer. Each tassel held tiny pink sacks of pollen, which fertilize every kernel to make it grow.
The pollen, a yellowish dust that feels like flour, naturally drops from the tassels onto a bed of silk at the top of each growing ear of corn. Some pollen blows through the breeze from one plant to others hundreds of feet away.
Morrison hopes that each ear (there are only two on each popcorn plant) will be swollen with plump kernels by October.
Popcorn is a delicate crop. This year, Morrison's corn was beset by hungry crickets and damaged by a small hail storm. Some of the plants' stalks have bent under the weight of the ears.
At harvest time, the ears will be picked, husked, and shucked by machine. Then the kernels are cleaned, bounced, poked, and even polished.
First, a machine removes the "bees' wings," little pieces of cob that may cling to the kernels. A "destoner" removes any foreign material.
Cleaned kernels are sent through a gravity machine. The large tray of kernels is vibrated as air is blown up from the bottom. Lighter, "dud" kernels rise to the top and are shunted off to one side. Next, a color machine removes seeds that aren't golden brown. (A few even have purple and red streaks.)
What's left look like perfect kernels. Now, they must be prepared for popping.
Each kernel is dried for 45 days in an enclosed box, under a lamp. This reduces their water content to the proper popping percentage: about 14 percent.
Once they're dry, Morrison puts a sample in a test popper. Every popcorn farmer tests the same way: One cup of kernels is heated to exactly 480 degrees F. As the kernels pop, they fall into a long tube. They must fill the tube to a height of 40 inches to meet Morrison's requirements.
That means each kernel expands about 40 times. Some expand nearly 50 times.
It's these kernels, with the top pop potential, that Morrison sells to his customers. To ship them overseas, Morrison loads the seeds into a machine and drops them into microwave bags as they roll across a conveyor belt. A suction cup opens the bag and squirts in oil. Heat and pressure seal the bag and wrap it. The whole process takes about 30 seconds.
Six people work in Morrison's factory, packaging microwave popcorn. He sells to more than 50 countries - from Mexico to Malaysia.
Popcorn consumers vary. In Japan, Morrison says, people pay extra for popcorn that is extra white. Extra-white popcorn also tends to be smaller and more tender. Other countries prefer "mushroom" popcorn, used as a base for carmel corn. (It puffs into a spherical shape, so it doesn't break into pieces as easily.) The most common variety (called "butterfly" or just "yellow") pops out in all directions. It's the kind you get at the movies.
All corn is a kind of grass. Many archaeologists (ahr-kee-OHL-uh-jists), people who search for evidence of past cultures, think popcorn developed from a strain of grass growing 8,000 years ago in Central America.
The grass must have produced something that looked like tiny corncobs. Native Americans likely discovered that popcorn popped by accident. Perhaps a dried cob fell into the fire and popped - much to everyone's surprise.
Natives would have saved seeds from the strange but delicious crop, to grow it again. The same incident probably happened around many other campfires across the region. Popcorn had more than one discoverer. Dozens of varieties of popcorn developed across Central and South America.
The popcorn we eat today is a distant relative of these crops. Americans now grow popcorn that is almost entirely yellow or white. Ancient popcorn came in many colors, with bands of purple, red, and brown.
For hundreds of years, farmers have saved seeds from plants that produce the best popcorn. Those seeds are planted for next year's crop. That's why today's popcorn is so fluffy and tasty - it's grown from the best of the best.
Popcorn first came to North America about 2,500 years ago, archaeologists say. The first European explorers of the New World described native Americans making popcorn for food and to use as decorations in their hair. They also used to scatter it during religious ceremonies.
In 1621, the brother of the local chief brought a deerskin bag of popped popcorn to share with English colonists in Plymouth, Mass. The Pilgrims ate popcorn at the first Thanksgiving feast in the New World. That wasn't the first time any European had tasted popcorn, though. Columbus had brought popcorn back from his voyages to the Americas. It quickly caught on in Europe.