A new study by French scientists has resolved a long-standing mystery of why popcorn makes the popping sound by using different techniques including high-speed camera observations, sound recordings and the theory of thermodynamics.
The study, published in the Journal of the Royal Society Interface, concludes that rather than being due to the brittle kernels cracking open or ricocheting around the pan, the distinctive “pop” was due to pressurized water vapor rapidly escaping from the interior. As the vapor is expelled, the cavity inside the kernel acts as an “acoustic resonator” resulting in an audible pop.
According to researchers, popcorn kernels contain around 14 per cent water, which vaporizes at 100C, but is contained by the shell, which acts as a mini-pressure cooker until it reaches breaking point.
Researchers have also identified the critical temperature at which splitting of popcorn kernels is at its peak – 180C. When the kernel cracks, the escaping steam causes the starchy interior to expand into puffy white flakes.
Using a high-speed camera, which took 2,900 frames per second, the researchers also showed that the kernel was propelled into the air by a “leg” of expanding starch. This negates the previous speculation that escaping steam was the reason why the kernel was propelled upwards in a “rocket” effect. Researcher’s use of freeze-frame analysis shows the dynamics of a jumping piece of popcorn are similar to an acrobat performing a somersault. [Shown in video above]
“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 quoted by The Guardian. “As we started to observe popcorn explosions, it turned out that this phenomenon contains interesting physics.”