Why does popcorn go "pop"?
Inside each kernel is a tiny pressure cooker.A popcorn kernel holds a little water. When it is heated, that water tries to turn into steam. The hard hull traps the steam, so the pressure inside keeps rising, and at about 180℃ the hull can no longer hold and bursts. At that moment, the starch, softened by the heat, puffs up all at once and sets into that fluffy white shape.
A pressure cooker with a hard shell
Popcorn kernels are wrapped in a hard hull that steam can hardly pass through. Inside are starch and a little water. When the kernel gets hotter than 100℃, the water inside tries to turn into steam, but it is trapped by the hull, so the pressure inside builds up, just like in a pressure cooker.
Bursting together at about 180℃
In an experiment published by French researchers in 2015, they heated kernels in an oven at different temperatures. At 170℃, only 17 out of 50 kernels popped, but at 180℃, 48 out of 50 popped. The researchers also explain that calculating from the strength and thickness of the hull gives a popping temperature of about 180℃.
The numbers are the same as in the article: results from an experiment in a study published in 2015 (Virot & Ponomarenko).
Starch puffs up like foam
When the hull breaks, the trapped steam spreads out all at once and puffs up the starch, which has been softened by the heat. As it cools, it sets in that foam-like shape. This is what the white, light part of popcorn really is.
The "pop" sound and the jump
The same study used a high-speed camera together with sound recordings. The "pop" is thought to come not from the hull cracking, but from the steam inside escaping. The researchers also found that the puffed-up starch pushes against the floor like a leg, which makes the kernel jump into the air.
Want to know more?
- Kernels that are dried out too much do not have enough water, so the steam pressure inside cannot build up enough, and they do not pop well.
- Other kinds of corn can puff up a little, but not nearly as much as popcorn varieties.
- A popped kernel jumps anywhere from a few millimeters to a few centimeters high.
Quick quiz: test yourself
Why does popcorn pop?
Show the answer
- Steam inside bursts the hard hull
- The oil inside burns and explodes
- The hull melts and opens a hole
Steam inside bursts the hard hull The water inside tries to turn into steam, and the hard hull traps it, so pressure rises. At about 180℃ the hull bursts and the starch puffs up.
The water inside tries to turn into steam, and the hard hull traps it, so pressure rises. At about 180℃ the hull bursts and the starch puffs up.
Next quiz ›Sources
- Popcorn: critical temperature, jump and sound (Journal of the Royal Society Interface, 2015)The Royal Society (Virot & Ponomarenko)
- How popcorn got its popScience News Explores (Society for Science)
- To Pop or Not to Pop... That Is the QuestionUniversity of Georgia Cooperative Extension
This article was written after checking the sources above as of 2026-10-03. Explanations may change as research progresses. Photo credits are shown below each photo.
