Yesterday I brought you the secret of how many licks it takes to get to the center of a Tootsie Pop. And today I bring you another delicious treat – the secret to why popcorn actually pops, or more importantly, the critical temperature at which popcorn bursts.
Who doesn’t love popcorn?
The study was conducted by French physicists Emmanuel Virot and Alexandre Ponomarenko and is published in the journal Royal Society Interface.
As described in the study:
“Popcorn bursts open, jumps and emits a ‘pop’ sound in some hundredths of a second. The physical origin of these three observations remains unclear in the literature. We show that the critical temperature 180°C at which almost all of popcorn pops is consistent with an elementary pressure vessel scenario. We observe that popcorn jumps with a ‘leg’ of starch which is compressed on the ground. As a result, popcorn is midway between two categories of moving systems: explosive plants using fracture mechanisms and jumping animals using muscles. By synchronizing video recordings with acoustic recordings, we propose that the familiar ‘pop’ sound of the popcorn is caused by the release of water vapor.”
To come to their conclusion, Virot and Ponomarenko used high-speed cameras that record at 2,900 frames per second while heating the popcorn in an oven, cranking up the heat a few degrees at a time.
As the temperature rises, the popcorn begins to steam. When the temp finally reaches 180C (356F), the pressure inside climbs to around 10 times the atmospheric pressure at sea level, according to BBC News. Once critical temperature and pressure are reached, pressurized water vapor within the kernel rapidly escapes from the interior. As vapor is expelled, the cavity inside the kernel acts as an “acoustic resonator” resulting in an audible pop. “Such a scenario has been applied to … the ‘pop’ of a champagne bottle cork,” the authors write.
“We found that the critical temperature is about 180 C (356 F), regardless of the size or shape of the grain,” Virot, from the École Polytechnique near Paris, told the AFP news agency, adding that “The evolution from fracture to flake takes less than 90 milliseconds — 0.09 of a second.”
Image Courtesy of Wikimedia Commons (CC BY-SA 3.0)