Question: How does popcorn pop?
About the article "Popcorn", section "Abstract".

Candidate passages:
  "How does a frog jump?"
"How does a letter get through the mail?"
"How do they get toothpaste in the tube?"
"How do they make a baseball glove?"
"How do they make a hot dog roll?"
"How do they make a surfboard?"
"How do they make baseballs?"
"How do they make bowling balls?"
"How do they make bubblegum?"
"How do they make cartoons?"
"How do they make chocolate?"
"How do they make playing cards?"
"How do they make pennies?"
"How do they make plywood"  "How do they make spaghetti?"
"How do they make tennis shoes?"
"How do they make toothbrushes?"
"How do they make T-shirts?"
"How money is made"  "Is that really lead in a lead pencil?"
"What makes popcorn pop?"
"What's a compass?"
"Where does honey come from?"
"Where does Lumber come from?"
"Where do felt tip pens come from?"
"Who invented the hot dog?"
Popcorn, also known as popping corn, is a type of corn (maize, "Zea mays var.
everta") that expands from the kernel and puffs up when heated.
Popcorn is able to pop because, like amaranth grain, sorghum, quinoa, and millet, its kernels have a hard moisture-sealed hull and a dense starchy interior.
Pressure builds inside the kernel, and a small explosion (or "pop") is the end result.
Some strains of corn are now cultivated specifically as popping corns.
There are various techniques for popping corn.
Along with prepackaged popcorn, which is generally intended to be prepared in a microwave oven, there are small home appliances for popping corn.
These methods require the use of minimally processed popping corn.
A larger-scale, commercial popcorn machine was invented by Charles Cretors in the late 19th century.
Unpopped popcorn is considered nonperishable and will last indefinitely if stored in ideal conditions.
Depending on how it is prepared and cooked, some consider popcorn to be a health food, while others caution against it for a variety of reasons.
Popcorn can also have non-food applications, ranging from holiday decorations to packaging materials.
  "Popcorn" (1991 film), a horror film  "Popcorn" (2007 film), a teen comedy  "Pop Carn" (2003 film), a Tamil film  Popcorn.net, a movie download service  
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.
When the popcorn has finished popping, sometimes unpopped kernels remain.
Known in the popcorn industry as "old maids", the kernels don't pop because they do not have enough moisture to create enough steam for an explosion.
Rehydrating prior to popping usually results in eliminating the unpopped kernels.
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 off-yellow or 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. 
A popcorn maker (also called a popcorn popper) is a machine used to pop popcorn.
Since ancient times popcorn has been a popular snack food, produced through the explosive expansion of kernels of heated corn (maize).
Commercial large-scale popcorn machines were invented by Charles Cretors in the late 19th century.
Many types of small-scale home methods for popping corn also exist.
Commercial popcorn machines are commonly found in movie theaters and carnivals, producing popcorn in a pan of hot oil, which has approximately 45% of its calories derived from fat.
Hot air popcorn poppers appeared for home use in the late 1970s, which produce popcorn with only 5% of its calories derived from fat.
The majority of popcorn sold for home consumption is now packaged in a microwave popcorn bag for use in a microwave oven.