A little pressure cooker
Popcorn pops because heating builds pressure from water inside a kernel. When its tough outer hull splits, the starch expands into a fluffy, foamy shape.
The familiar snack has packed a surprisingly busy transformation into one tiny seed. There is more going on than a shell simply cracking.
The shell holds things together
The hull keeps the pressure contained until it can no longer hold. As it breaks, the sudden pressure drop lets the heated starch expand.
In Virot and Ponomarenko’s 2015 experiments, most kernels in their oven tests popped at around 180°C. That is an experimental finding, not a universal cooking instruction: the temperature of a pan is not automatically the temperature inside every kernel.
The pop and the jump are different tricks
The researchers’ recordings supported escaping water vapour as the source of the sound, rather than the landing or the hull crack alone.
The jump had another explanation. A small protrusion of starch pressed against the hot surface and bounced the popcorn upwards, like a tiny springy leg. It was not a steam rocket.
A cinema snack in slow motion
The Royal Society’s account describes roughly 400 pieces used to record the jump films. Heating, filming and analysing them took rather longer than eating a bowl.
Next time popcorn catches your eye, remember the three separate questions: why it opens, why it jumps and where the sound comes from. Ordinary things become more interesting when you slow the question down.
For another small kitchen transformation, discover how egg white becomes a cloud of meringue.