Popcorn

Why popcorn pops

Popcorn — Zea mays everta — is a specific subspecies of maize whose kernels have an unusually hard, water-tight outer hull (the pericarp). Each kernel contains about 14% moisture trapped inside.

When heated above 180 °C, the moisture turns to steam. Pressure builds inside the hull until — at around 9 atmospheres — the hull bursts and the starchy interior puffs explosively, expanding 30–50 times its original volume in milliseconds. Other corn varieties have softer hulls that can’t build up the necessary pressure; they don’t pop.

Older than you think

Archaeological evidence puts popcorn at the cradle of human agriculture. Cobs found in New Mexico’s Bat Cave date to around 5,600 years ago; even older popped kernels have been found in Peru at 6,700 years old. Pre-Columbian peoples roasted, ground, and ate popcorn long before it was a movie snack.

Two pop shapes

Popped kernels come in two distinct shapes:

• Butterfly (snowflake) — irregular, with multiple wings. The texture most people picture; what movie theaters use because it looks bigger.
• Mushroom — round and compact, denser. Used by candy companies for caramel corn and chocolate-coating because it has fewer fragile points to break.

Different cultivars are bred for one shape or the other.

The movie-theater connection

Popcorn became cinema-standard in the Great Depression. Movie theaters initially banned outside food, but with ticket sales falling, they started selling popcorn themselves — high margins (one of the cheapest foods to mark up dramatically), strong aroma to attract customers, and a salty thirst trigger that boosts soda sales. The combination became central to theater economics.