Why does popcorn pop?
The explosive science that turns tough kernels into a tasty cinema treat
1. Critical temperature
Temperature is key; only 30 per cent of kernels pop when heated to 170°C, compared to over 90 per cent at the optimum 180°C.
2. Water content
Popcorn kernels are about 10-20 per cent water. When heated, the pressure in the kernel increases as the water vaporises.
3. Breaking point
Once the pressure inside the kernel reaches a certain level, the tough outer shell bursts open.
High-pressure steam escaping through the kernel fracture causes the characteristic popping sound.
As the kernels cook, starch molecules expand and soften to form spongy ‘flakes’.
Scientists discovered that a ‘leg’ of starch expanding against the pan’s surface propels the popping corn into the air.
The kernel appears to turn inside out as it rotates, with the soft, starchy innards expanding outwards.
This article was originally published in How It Works issue 086
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