The Popcorn Mystery: Case Closed

Scientists in France have finally worked out how exactly it is that popcorn gets its distinctive pop, in a study published recently in the Journal of the Royal Society Interface.

The authors’colleagues were using high-speed cameras (2900 pictures per second) to investigate drops of water on leaves, in regard to trees breaking during storms. “We took advantage of this technique to study … the mysterious and fascinating jump of popcorn,” said Emmanuel Virot, a PhD student at the CNRS in Paris and the paper’s lead author. “As we started to observe popcorn explosions, it turned out that this phenomenon contains interesting physics.”

They discovered that at an optimum temperature of 180°C, water inside the kernel becomes steam, and the increased pressure is enough to burst the shell open, leading to the starch interior expanding to become light and fluffy. The popcorn jumps into the air via a starch ‘leg’ which emerges from the broken shell, propelling it up like a gymnast doing a somersault. All of this happens in just one-fifteenth of a second.

And as for the noise, a microphone synchronised to the camera showed that this was heard 94 milliseconds after the kernel initially splitting, leading them to conclude that it must be due to the release of pressurised water vapour, similar to the popping of a champagne cork. The cavity inside the kernel acts as an ‘acoustic resonator’, producing the popping noise.

For once, this is a movie featuring popcorn, not accompanied by it, although the researchers said that they and their fellow scientists did frequently enjoy snacking on the popcorn after experiments!