Pressure from the steam continues to build until the hull ruptures, allowing the kernel to forcefully expand, to 20 to 50 times its original size, and then cool.

Fossil evidence from Peru suggests that corn was present there as early as 4,700 BCE, and popped there over 1,000 years ago.

[4][5][6] Between 2007 and 2011, evidence as early as 4,700 BCE for popping corn were discovered as macrofossil cobs at the Paredones and Huaca Prieta archaeological sites on the northern coast of Peru.

[7] In 1948 and 1950, evidence as early as 3600 BCE for popping corn as ears of popcorn were discovered by Harvard anthropology graduate student Herbert W. Dick[8] and Harvard botany graduate student Claude Earle Smith, Junior (1922–1987),[9][10] in a complex of rock shelters, dubbed the "Bat Cave", in Catron County,[11] west-central New Mexico, and attributed to the Ancestral Puebloan peoples, who maintained trade networks with peoples in tropical Mexico.

Cretors, a Chicago candy store owner, had 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 World War II, sugar rations diminished candy production, and Americans compensated by eating three times as much popcorn as they had before.

Unlike most other grains, the outer hull of the popcorn kernel is strong and impervious to moisture, and the starch inside consists almost entirely of a hard type.

The hull ruptures, 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.

Though the kernels of some other types will pop, the cultivated strain for popcorn is Zea mays everta, which is a variety of flint corn.

Although small quantities can be popped in a stove-top kettle or pot in a home kitchen, commercial sale employs specially designed popcorn machines, which were invented in Chicago, Illinois, by Charles Cretors in 1885.

Cretors's machine popped corn in a mixture of one-third clarified butter, two-thirds lard, and salt.

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.

[29] A different method of popcorn-making involves the "popcorn hammer", a large cast-iron canister that is sealed with a heavy lid and slowly turned over a fire in rotisserie fashion.

Known in the popcorn industry as "old maids",[31] these kernels fail to pop because they do not have enough moisture to create enough steam for an explosion.

Cracker Jack is a popular, commercially produced candy that consists of peanuts mixed in with caramel-covered popcorn.

Once reserved for specialty shops and county fairs, kettle corn has recently become popular, especially in the microwave popcorn market.

Air-popped popcorn (no salt or other additives) is 4% water, 78% carbohydrates (including 15% dietary fiber), 12% protein, and 4% fat (table).

Movie theaters commonly use coconut oil to pop the corn, and then top it with butter or margarine.

[40] Movie theater popcorn contains large amounts of saturated fats and sodium due to its method of preparation.

[42] 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.

Major manufacturers in the United States have stopped using this chemical, including Orville Redenbacher's, Act II, Pop Secret and Jolly Time.

[citation needed][44][45] Popcorn, threaded onto a string, is used as a wall or Christmas tree decoration in some parts of North America,[46][47] as well as on the Balkan peninsula.

However, popcorn has numerous undesirable properties as a packing material, including attractiveness to pests, flammability, and a higher cost and greater density than expanded polystyrene.