At least six localities (all in the United States of America) claim to be the "Popcorn Capital of the World": Valparaiso, Indiana; Van Buren, Indiana; Marion, Ohio; Ridgway, Illinois; Schaller, Iowa; and North Loup, Nebraska. According to the USDA, most of the maize 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.
Each kernel of popcorn contains a certain amount of moisture and oil. Unlike most other grains, the outer hull of the popcorn kernel is both strong and impervious to moisture, and the starch inside consists almost entirely of a hard, dense type.
As the oil and the water are heated past the boiling point, they turn the moisture in the kernel into a superheated pressurized steam, contained within the moisture-proof hull. Under these conditions, the starch inside the kernel gelatinizes, softening and becoming pliable. The pressure continues to increase until the breaking point of the hull is reached: a pressure of about 135 psi (930 kPa) and a temperature of 180°C. The hull ruptures rapidly, causing a sudden drop in pressure inside the kernel and a corresponding rapid expansion of the steam, which expands the starch and proteins of the endosperm into airy foam. As the foam rapidly cools, the starch and protein polymers set into the familiar crispy puff.
Popping results are sensitive to the rate at which the kernels are heated. If heated too quickly, the steam in the outer layers of the kernel can reach high pressures and rupture the hull before the starch in the center of the kernel can fully gelatinize, leading to partially popped kernels with hard centers. Heating too slowly leads to entirely unpopped kernels: the tip of the kernel, where it attached to the cob, is not entirely moisture-proof, and when heated slowly, the steam can leak out of the tip fast enough to keep the pressure from rising sufficiently to break the hull and cause the pop.
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.
Two explanations exist for kernels which do not pop at proper temperatures, known in the popcorn industry as "old maids". The first is that unpopped kernels do not have enough moisture to create enough steam for an explosion. The second explanation, according to research led by Dr. Bruce Hamaker of Purdue University, is that the unpopped kernel may have a leaky hull.
Popcorn varieties are broadly categorized by the shape of the kernels, the color of the kernels, or the shape of the popped corn. While the kernels may come in a variety of colors, the popped corn is always white as it is only the hull (or pericarp) that is colored. "Rice" type popcorns have a long kernel pointed at both ends; "pearl" type kernels are rounded at the top. Commercial popcorn production has moved mostly to pearl types. Historically, pearl popcorns were usually yellow and rice popcorns usually white. Today both shapes are available in both colors, as well as others including black, red, and variegated. Commercial production is dominated by white and yellow.
In popcorn jargon, a popped kernel of corn is known as a "flake". Two shapes of flakes are commercially important. "Butterfly" flakes are irregular in shape and have a number of protruding "wings". "Mushroom" flakes are largely ball-shaped, with few wings. Butterfly flakes are regarded as having better mouthfeel, with greater tenderness and less noticeable hulls. Mushroom flakes are less fragile than butterfly flakes and are therefore often used for packaged popcorn or confectionery, such as caramel corn. The kernels from a single cob of popcorn may form both butterfly and mushroom flakes; hybrids that produce 100% butterfly flakes or 100% mushroom flakes exist, the latter developed only as recently as 1998. Growing conditions and popping environment can also affect the butterfly-to-mushroom ratio.
Cretors' invention introduced the first patented steam-driven popcorn machine that popped corn in oil. Previously, vendors popped corn by holding a wire basket over an open flame. At best, the result was a hot, dry, unevenly cooked confection. The Cretors' machine popped corn in a mixture of one-third clarified butter, two-thirds lard and salt. This mixture could withstand the 450°F temperature needed to pop corn and it did without producing much smoke. A fire under a boiler created steam that drove a small engine; that engine drove the gears, shaft, and agitator that stirred the corn and also powered the attention-attracting clown – the Toasty Roasty Man. A wire connected to the top of the cooking pan allowed the operator to disengage the drive mechanism, lift the cover and dump popped corn into the storage bin beneath. Exhaust from the steam engine was piped to a hollow pan below the corn storage bin and kept freshly popped corn uniformly warm for the first time ever.
An equally ingenious 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 which is then sealed with a heavy lid and slowly turned over a curb-side 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 popcorn explodes at once and is poured into the sack.
Individual consumers can also buy and use specialized popping appliances which 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 shown above) 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. However, the great majority of popcorn sold for home consumption is now packaged with various flavoring agents for use in a microwave oven. One of these common artificial-butter flavorants, diacetyl, has been implicated in causing respiratory ailments.
Some shipping companies have experimented with using popcorn as a biodegradable replacement for expanded polystyrene packing material. However, popcorn has numerous undesirable properties as a packing material, including attractiveness to pests, flammability, higher cost and greater density than expanded polystyrene. A more processed form of expanded corn foam has been developed to overcome some of these limitations.
The world's largest popcorn ball was unveiled in October 2006 in Lake Forest, Illinois. It weighed 3,415 pounds (1550 kilograms), measured 8 feet (2.4 m) in diameter and had a circumference of 24.6 feet (8 m).
Air-popped popcorn is naturally high in fiber, low in calories and fat, contains no sodium, and is sugar free. This can make it an attractive snack to people with dietary restrictions on the intake of calories, fat and/or sodium. For the sake of flavor, however, large amounts of fat, sugar, and sodium are often added to prepared popcorn, which can quickly convert it to a very poor choice for those on restricted diets.
One particularly notorious example of this first came to public attention in the mid-1990s, when the Center for Science in the Public Interest produced a report about "Movie Popcorn", which became the subject of a widespread publicity campaign. The movie theaters surveyed used coconut oil to pop the corn, and then topped it with butter or margarine. "A medium-size buttered popcorn," the report said, "contains more fat than a breakfast of bacon and eggs, a Big Mac and fries, and a steak dinner combined. The practice continues today. For example, according to DietFacts.com, a small popcorn from Regal Cinema Group (the largest theater chain in the United States) still contains 29g of saturated fat, as much as three Big Macs and well over an entire day's daily reference value.
Popcorn is included on the list of foods that the American Academy of Pediatrics recommends not serving to children under four, because of the risk of choking. It is one of the top causes for children choking to death (along with hotdogs and balloons). Special "hulless" popcorn has been developed that offers an alternative for small children and for people with braces or other dental problems who may otherwise need to avoid popcorn.