Pop. Pop. Pop pop. Pop pop pop pop pop. That's the beautiful sound of a bag of kernels transforming into the buttery goodness we call popcorn.
But have you ever stopped to wonder just how popcorn makes those pops? A pair of French physicists have, and now they think they've finally cracked the mystery.
The researchers placed popcorn kernels on a hot plate, and used a high-speed camera and microphone to record what happened (see video above). They hypothesized three potential sources that could be behind the popping noise: the kernel's hull cracking open, the release of highly pressurized water vapor from the kernel, or the popcorn's bounce on the ground.
What did the researchers find? When they synchronized the recordings, they found no sound was emitted when the first crack appeared on the kernel. Instead, the sound emerged shortly after the second crack appeared, which led the researchers to believe the "pop" was caused by the release of vapor.
"More precisely, the pressure drop excites cavities inside the popcorn as if it were an acoustic resonator," the researchers wrote in an article describing their findings, published online on Feb. 11 in the Journal of the Royal Society Interface. "Such a scenario has been applied to... the ‘pop’ of champagne bottle cork."
The researchers also discovered that regardless of the size or shape of the kernel, almost all the popcorn "popped" at a temperature of 180° C (356° F). And they found that after a kernel cracks, a tiny "leg" of starch emerges, compresses under heat, and then acts like a tiny spring -- which makes the popcorn jump.
Now you know. Hungry?