A popcorn kernel's strong hull contains the seed's hard, starchy endosperm with 14-15% moisture, the latter of which turns to steam as the kernel is heated. The pressure continues building until it exceeds the hull's ability to contain it. The kernel ruptures and explodes, allowing the contents to expand, cool, and finally set in a popcorn puff 20 to 50 times the size of the original kernel.
Some strains of corn (taxonomized as Zea mays) are cultivated specifically as popping corns. The Zea mays variety everta, a special kind of flint corn, is the most common of these.
Corn was first domesticated 9,000 years ago in what is now Mexico. Archaeologists have discovered that people have known about popcorn for thousands of years. In Mexico, for example, remnants of popcorn have been found that date to around 3600 BC.
A Mexican folk myth popular in the city of Teotihuacn talks about a wealthy farmer called Gonzalo Qudre. He owned over 100,000 acres of corn that was the main source of food to the citizens of Teotihuacn. Qudre had surplus corn that he decided to dry up some to feed the chickens on his farm. On a summer day, while he was feeding the chickens, he heard a popping sound. As frightened as he was about the sudden noise, he looked down to see a white piece of fluff. After examining it, he found out that it was a kernel. He tasted it and decided to keep the secret for decades as the people believed he had supernatural power to turn stone into food. So he was worshiped until his death. As he was dying, he asked his counselor to spread the secret in the city's temple. He was later buried in the pyramids.
Popping of the kernels was achieved by hand on the stovetop through the 19th century. Kernels were sold on the East Coast of the United States under names such as Pearls or Nonpareil. The term popped corn first appeared in John Russell Bartletts 1848 Dictionary of Americanisms. Popcorn is an ingredient in Cracker Jack, and in the early years of the product, it was popped by hand.
Popcorn's accessibility increased rapidly in the 1890s with Charles Cretors' invention of the popcorn maker. Cretors, a Chicago candy store owner, created a number of steam powered machines for roasting nuts, and applied the technology to the corn kernels. By the turn of the century, Cretors had created and deployed street carts equipped with steam powered popcorn makers.
During the Great Depression, popcorn was fairly inexpensive at 510 cents a bag and became popular. Thus, while other businesses failed, the popcorn business thrived and became a source of income for many struggling farmers, including the Redenbacher family, namesake of the famous popcorn brand. During World War II, sugar rations diminished candy production, and Americans compensated by eating three times as much popcorn as they had before. The snack was popular at theaters, much to the initial displeasure of many of the theater owners, who thought it distracted from the films. Their minds eventually changed, however, and in 1938 a Midwestern theater owner named Glen W. Dickson installed popcorn machines in the lobbies of his theaters. The venture was a financial success, and the trend soon spread.
In 1970, Orville Redenbacher's namesake brand of popcorn was launched. In 1981, General Mills received the first patent for a microwave popcorn bag, with popcorn consumption seeing a sharp increase by tens of thousands of pounds in the years following.
At least six localities (all in the Midwestern United States) claim to be the "Popcorn Capital of the World;": Ridgway, Illinois; Valparaiso, Indiana; Van Buren, Indiana; Schaller, Iowa; Marion, Ohio; and North Loup, Nebraska. According to the USDA, corn used for popcorn production is specifically planted for this purpose; most is grown in Nebraska and Indiana, with increasing area in Texas. As the result of an elementary school project, popcorn became the official state snack food of Illinois.