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Physicists reveal the secrets of perfect popcorn

French engineers used high-speed imaging techniques and thermodynamic analysis to understand the mechanics behind kernel poppage. (Video: Alexandre Ponomarenko and Emmanuel Virot)

Popcorn lovers of the world, your un-popped kernel nightmare is over.

New research published in the Journal of the Royal Society Interface Wednesday explores the physics of popcorn popping in greater detail than ever before, offering insight into the perfect preparation of this quintessential movie-night snack. French engineers Emmanuel Virot and Alexandre Ponomarenko used thermodynamic analysis and high-speed imaging techniques to understand the ideal temperature for maximum kernel poppage, the mechanics of the popcorn “jump” and the origin of its distinctive popping sound.

The two scientists had already been using their cameras to analyze other kinds of plant dynamics, such as how trees break in the wind, when they decided to train their lenses on popcorn’s puzzling acrobatics.

“We took advantage of this technique to study … the mysterious and fascinating jump of popcorn,” Virot told the Guardian. “As we started to observe popcorn explosions, it turned out that this phenomenon contains interesting physics.”

Salivating already? Here are three lessons on popcorn preparation from Virot and Ponomarenko’s study. Heed them well, and your movie nights will be forever freed from the curse of un-popped kernels.

1. Temperature is key.

It has long been understood that popcorn “pops” due to interior pressure. As the kernel’s contents are heated, moisture in its interior is transformed into water vapor, which expands and pushes against the hull, or pericarp. This fractures the pericarp, causing the hull to burst open and unleash its starchy, billowing contents, known as a “flake.”

Most snackers rely on their microwaves’ automated settings to cook their popcorn, but Virot and Ponomarenko — visionaries that they are — sought a more exact method of achieving maximum poppage with minimum burning. The pair applied their knowledge of engineering and thermodynamics to the task, calculating average hull strength, standard water boiling conditions and critical kernel pressure, and found that 180 degrees Celsius (356 degrees Fahrenheit) is the ideal temperature at which popcorn should be cooked. This finding is consistent with the results of several test batches the researchers prepared: When cooked in an oven set to 170 degrees Celsius (338 degrees Fahrenheit), 66 percent of kernels were left un-popped. At 180 degrees, the un-popped portion dwindled to only 4 percent.

2. Snack acrobatics

The French study also captures the mysterious mechanics of popcorn’s “jump” as it is heated. Scientists previously theorized the motion is caused by the expulsion of vapor when the hull is fractured, which would propel the flake upward like a rocket.

Incredible though rocketing popcorn flakes might be, Virot and Ponomarenko found the jump more closely resembles the somersault of a running gymnast. Using a high-speed camera, the pair analyzed the fracture and expansion of a single piece of popcorn on a hot plate. As the hull breaks open and the starch flake expands, it forms a single “leg.” Pent-up energy from the gradual heating of the kernel is released into the leg, which pushes against the hot plate and launches the entire flake into the air, where it spins an average of 490 degrees before settling back down (not quite the level of an Olympic gymnast, but still respectable).

3. “Pop” music

Vapor release may not be what propels the popped flake into its high-flying aerial acrobatics, but is the source of popcorn’s most distinctive feature: its pop. Virot and Ponomarenko added microphones to their hot-plate experiments to identify the exact source of the popping noise and saw the sound didn’t correspond with the cracking of the hull or the flake’s rebound against the plate. Instead, it’s triggered by the pressure drop inside the kernel, which turns the flake into an “acoustic resonator” — similar to how a champagne bottle “pops” when it’s opened.

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