Why Does a Popcorn Kernel Pop When Heated?

Popcorn is one of the most popular snacks in the United States. According to the National Popcorn Board, over 16 billion quarts of popped popcorn is eaten in the U.S. every year. It is fun to prepare and to eat, but there is a scientific explanation of popping corn's ability to expand when heated.

History

The oldest popcorn discovered by archaeologists is over 4,000 years old. Native Americans believed that the popping was caused by spirits who became angry when heated.

Popcorn As a Grain

Popcorn is a grain and like most grains it has a hull protecting its inner contents. Unlike many other grains, popcorn has a hull that is both very strong and resistant to water. Inside the hull, popcorn contains dense starch and small amounts of oil and water.

Popping

When popcorn is heated, the starch inside becomes soft and the water converts to steam. The steam builds pressure against the strong hull. The hull weakens and eventually pops. The soft starch solidifies into a white foam-like structure when it is exposed to air.

Old Maids

It is thought that old maids, or kernels that don't pop, have leaky hulls, preventing steam from building up and exploding the hulls.

Popping Tips

Popcorn is best popped under medium high heat. Popcorn popped using high heat explodes the hull before the starch softens completely, resulting in small, tough popcorn.

References

• National Popcorn Board