Popcorn

Popcorn or popping corn is a type of corn, which explodes from the kernel and puffs up when heated. Corn popping was originally discovered by Native Americans, but became popular as a snack food during the United States Great Depression. Corn is able to pop because, unlike other grains, its kernels have a hard moisture-sealed hull and a dense starchy filling. This allows pressure to build inside the kernel until an explosive "pop" results. Some strains of corn are now cultivated specifically as popping corns.

A similar popcorn-making device can still be seen on the streets of some Chinese cities today. The corn is poured into a large cast-iron canister that is then sealed with a heavy lid and slowly turned over a curbside fire in rotisserie fashion. When a pressure gauge on the canister reaches a certain level, it is removed from the fire, a large canvas sack is put over the lid, and the seal is released. With a huge boom, all of the popcorn explodes at once and is poured into the sack. Individual consumers can also buy and use specialized popping appliances that typically generate no more than a gallon of popped corn per batch. Some of these appliances also accept a small volume of oil or melted butter to assist thermal transfer from a stationary heating element, but others (such as the one pictured here) are "air poppers" which rapidly circulate heated air up through the interior, keeping the unpopped kernels in motion to avoid burning and blowing the popped kernels out through the chute.

Producers and sellers of popcorn consider two major factors in evaluating the quality of popcorn: what percentage of the kernels will pop, and how much each popped kernel expands. Expansion is an important factor to both the consumer and vendor. For the consumer, larger pieces of popcorn tend to be more tender and are associated with higher quality. For the grower, distributor, and vendor, expansion is closely correlated with profit: vendors such as theaters buy popcorn by weight and sell it by volume. For both these reasons, higher-expansion popcorn fetches a higher profit per unit weight. Popcorn will pop when freshly harvested, but not well: its high moisture content leads to poor expansion and chewy pieces of popcorn. Kernels with a high moisture content are also susceptible to mold when stored. For these reasons, popcorn growers and distributors dry the kernels until they reach the moisture level at which they expand the most. This differs by variety and conditions, but is generally in the range of 14–15% moisture by weight. If the kernels are over-dried, the expansion rate will suffer and the percentage of kernels that pop at all will decline.

Popcorn is usually served salted or sweetened. In North America, it is traditionally served salted, although a sweetened version, generally called caramel corn, is also commonly available. In the United Kingdom, ready-made popcorn is available either salted or simply sweetened with sugar, both varieties being equally popular. Toffee popcorn is also available, but tends to be more expensive. Popcorn is a popular snack at sporting events and in cinemas, where it has been served since 1912. The Boy Scouts of America sell popcorn door-to-door as a primary fundraiser, similar to Girl Scout cookies.