Researchers reveal the physics of popcorn’s pop

In an early episode of the CBS comedy the Big Bang Theory, Physicist Sheldon Cooper (Jim Parsons) temporarily loses his job and decides to study the science behind scrambled eggs in his off time.

“I finally have the time to test my hypothesis, about the separation of the water molecules from the egg proteins, and its impact vis-a-vis taste,” he said.

Now, in the real world, a pair of French scientists have presented us with the physics behind popcorn. Published in the journal Royal Society Interface, the research “Popcorn: critical temperature, jump and sound” provides the science behind cooking popcorn in nearly every detail.

The history of popcorn predates its adoption as a movie-time staple by thousands of years. Originally from the Americas, the oldest known popcorn was found in a cave in central New Mexico and is believed to be 4,000 years old.

An early Spanish account of a Aztec religious ceremony reads, in part “they scattered before him parched corn, called momochitl, a kind of corn which bursts when parched and discloses its contents and makes itself look like a very white flower; they said these were hailstones given to the god of water,” according to Popcorn.com’s Encyclopedia Popcornica.

Given its history, it seems unusual that it hasn’t received more attention.

The French team took what is likely the closest ever look at popcorn. They used high-speed imaging technology, originally developed to see how trees break in storms to watch the popcorn blow at 2,900 frames per second.

“We took advantage of this technique to study … the mysterious and fascinating jump of popcorn. As we started to observe popcorn explosions, it turned out that this phenomenon contains interesting physics,” lead author and PhD student at the CNRS in Paris, Emmanuel Virot told the Guardian.

First the team solved the mystery of the popcorn’s “pop”. The researchers determined that the distinctive sound is due to pressurized water vapor rapidly escaping from the kernel’s interior.

Water inside the kernel, roughly 14% of the mass, vaporizes when heated but is contained by the shell until it reaches the right temperature. When the vapor finally, violently escapes the shell acts as an acoustic resonator, amplifying the sound.

According to the researchers that ideal popping temperature which forces the vapor to escape and the starchy interior to expand is 356 degrees Fahrenheit (180 degrees celsius). When cooked at a slightly cooler temperature, 338 degrees Fahrenheit only one-third of the kernels popped, but at the higher temperature that rose to 96 percent.

The team also found that when the kernels popped they were propelled by a “leg” of expanding starch. A freeze frame analysis showed that the explosion shared similar to the dynamics of a human performing a somersault.

“A piece of popcorn has a singular way of jumping, midway between explosive plants such as impatiens, and muscle-based animals such as human beings,” the researchers write in their paper.

Even if you only, ever eat popcorn at the movies the French team have at least given you something to think about if the movie isn’t very good.

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