Physics of food shows secrets of popcorn

To most people, it may be just a fun food to munch while watching a movie. But to a couple of French investigators, popcorn is a biomechanical enigma waiting to be explained.

AFP

Cameras recording at 2,900 frames per second helped show what happened when a kernel of corn strutted its stuff.

When the temperature reached 100 degrees Celsius (180 degrees Fahrenheit), some of the moisture inside the corn started to turn into steam, the researchers found.

As the temperature rose to around 180 C (356 F), pressure built to around 10 bar, or 10 times the atmosphere at sea level. Unable to withstand the stress, the outer shell broke open, causing a dramatic drop in pressure that forced the kernels starchy innards to expand and protrude.

$The first thing to emerge from the fractured shell is a limb-shaped structure -- a leg -- that comes into contact with the surface of the pan and starts to compress under the heat.$
Tensed and then released, the leg causes the corn to leap up -- a height ranging from a few millimetres to centimetres (tenths of an inch to several inches)-- and emit a pop from the sudden release of water vapour. A few milliseconds later, the granules spewing from inside expand to form a spongey flake.

Tensed and then released, the leg causes the corn to leap up -- a height ranging from a few millimetres to centimetres (tenths of an inch to several inches)-- and emit a pop from the sudden release of water vapour. A few milliseconds later, the granules spewing from inside expand to form a spongey flake.

$Evolution from fracture to flake takes less than 90 milliseconds -- 0.09 of a second. The popcorns leap results from an intriguing combination of thermodynamics and fracture mechanics, rather than just the blast of pent-up gases.$
The study appears in a British journal, the Royal Society Interface.