How do we know?
↻ One of the pages with a moving picture
Scientists dated very old corncobs from Peru.
- Inside each kernel is a tiny drop of water tucked into soft starch. Popcorn needs about 13.5–14% water to pop.
- As the kernel heats, the water turns to steam. The pressure inside climbs to about 135 pounds per square inch!
- Popcorn’s hard hull holds the steam in until it bursts. Of the four main kinds of corn, only popcorn pops.
- The soft starch puffs out and cools into a fluffy flake. The first bit forms a “leg” that flips the kernel into the air.
Scientists dated old corncobs, husks and stalks dug up near Peru’s northern coast. The oldest cobs turned out to be popcorn, about 2,000 years older than people thought!
People at Paredones and Huaca Prieta in Peru were cooking corn up to 6,700 years ago.
Super-fast cameras have even shown the starch “leg” that flips a popping kernel into the air.
Wow number
40–50× One kernel can swell to 40 to 50 times its original size!
Myth or fact?
All kinds of corn can pop. Myth. Only popcorn has a hull just right to hold the steam until it bursts.
Popcorn jumps when it pops. Fact. A “leg” of starch flips it, like a gymnast.
Think about it
Scientists think the “pop” sound comes from escaping steam. What could you test to find out?
Where in the world?
Paredones and Huaca Prieta, Peru where people were cooking corn up to 6,700 years ago, and the oldest cobs are popcorn — 7.9167° S, 79.4333° W.
Where these facts come from
Every number on page 82, and who measured it
This page tells us about the drop of water inside each kernel and how big a kernel can puff up.
What Makes Popcorn Pop — The Popcorn Board, a group of U.S. popcorn farmers and makers
popcorn.org/All-About-Popcorn/What-Makes-Popcorn-Pop
We checked it on 31 October 2026
This page tells us how steam builds up pressure inside a popcorn kernel.
How does popcorn pop? · Popcorn: Ingrained in America's Agricultural History — The U.S. National Agricultural Library
nal.usda.gov/exhibits/speccoll/exhibits/show/popcorn/how-does-popcorn-pop-
We checked it on 31 October 2026
This page tells us about very old popcorn found in Peru.
Ancient Popcorn Found—Made 2,000 Years Earlier Than Thought in Peru — National Geographic, a science and exploring magazine
nationalgeographic.com/adventure/article/120119-national-popcorn-day-corn-peru-archaeology-food-science
We checked it on 31 October 2026
This page is the science paper about the old corncobs from the coast of Peru.
Preceramic maize from Paredones and Huaca Prieta, Peru — The science paper about ancient corn and popcorn from Peru, shared by the U.S. National Library of Medicine
pmc.ncbi.nlm.nih.gov/articles/PMC3277113
We checked it on 31 October 2026
This page tells us how super-fast cameras showed the starch "leg" that makes popcorn jump.
Popcorn: critical temperature, jump and sound — A science paper that filmed popcorn popping, shared by the U.S. National Library of Medicine
pmc.ncbi.nlm.nih.gov/articles/PMC4345489
We checked it on 31 October 2026
Has this changed?
How popcorn pops is not going to change.
What does change is the history: scientists keep digging up old corncobs, and the oldest popcorn keeps getting older.
Words from this page
- kernel
- A single seed of corn.
- hull
- The hard outer skin of a kernel.
Try it!
Be a kernel detective.
1. Ask a grown-up for a few unpopped kernels and a few popped pieces. 2. Look at both with a magnifying glass. Find the hard, shiny hull on a kernel. 3. On a popped piece, find the torn hull and the fluffy starch. (Looking only, no eating!)
What happens: you can see where the hull split open and the starch puffed out.
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