Why popcorn pops and jumps

Settled in 2015 by Emmanuel Virot, Alexandre Ponomarenko (ESPCI Paris / École Polytechnique).

Everyone who has watched popcorn pop has seen kernels jump, but the physical origin of the critical popping temperature, the jump, and the characteristic 'pop' sound had not been rigorously studied together. In 2015 Virot and Ponomarenko used high-speed video synchronized with acoustic recordings and thermodynamic modeling of the kernel as a pressure vessel to show that popping reliably occurs near 180 degrees Celsius, consistent with the moisture inside reaching a critical vapor pressure that ruptures the hull. They found the jump comes from a starchy 'leg' that forms at the rupture point and buckles against the surface like a tiny spring-loaded foot, and that the pop sound is produced by the release of water vapor rather than the hull cracking itself, tying all three everyday observations to one consistent physical picture.

A kernel of corn turns itself into a tiny self-launching pressure-vessel-and-catapult, and it does so at a strikingly precise, reproducible temperature.

Explanations that circulated

• Popcorn jumps because it is literally propelled by an explosive release of steam like a tiny rocket — high-speed imaging instead showed the kernel jumps by pushing off the ground with a small starchy 'leg' that forms and buckles at the moment of popping, an elastic/mechanical launch rather than a jet-propulsion one.

References

• Popcorn: critical temperature, jump and sound, E. Virot, A. Ponomarenko, Journal of the Royal Society Interface, 2015