Popcorn Is A Pop, Pop, Ever Toppin’, Never Boppin’, Show Stoppin’ Zany Kind Of…. Science
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What happens when you give engineers an ultra-high speed camera to study how trees break in the wind? They make videos of popping corn, obviously.
Ben tried to claim this popcorn on expenses as “research”
French scientists Emmanuel Virot and Alexandre Ponomarenko decided to turn their 2,900 frames per second camera to popping corn out of extra-curricular interest. However it turned into much more than that, as they discovered through the footage that there were some interesting and unknown properties and mechanics involved in the pop.
Corn pops due to moisture inside the kernel of corn being heated up and bursting the corn, literally popping the kernel. As the moisture inside the kernel heats up above 100 degrees Celsius it turns to steam and starts to create pressure inside the corn kernel. This heat and pressure turns the starch inside the kernel into a hot sludgy mess. Once the pressure inside the kernel has built to a high enough pressure, the husk of the kernel cracks, releasing the pressure and forcing the insides of the kernel outwards.
Now from the high speed footage we’re finding out more details about this mechanism.
It turns out the optimum temperature to pop corn is at 180 degrees Celsius, which maximises the pressure inside the kernel. At 170 degrees only 34% of the corn had popped, but increase it to 180 degrees at around 96% of the corn had popped. That last 4 per cent is the bane of popcorn eaters the world over – those annoying unpopped kernels. Turns out that there is no way to get those unpopped kernels to pop – chances are their husk has been damaged or the kernel has been burnt, both of which means the pressure inside the kernel has leaked out and won’t build high enough to burst the kernel.
That bursting point is highly dependent on temperature, the shape of the kernel itself doesn’t make much difference, the research found.
That whole process takes 90 milliseconds, less than the blink of an eye (100 milliseconds, incidentally).
About now Ben is wondering if this was such a great plan
Cool, so what makes the popcorn jump then?
Watching the video of the popping kernel, Virot and Ponomarenko noticed a strange structure forming. As the starch came bursting out a structure dubbed a “leg” started forming. This leg releases the pent up energy by pushing off the hot surface and launching the corn into the air and into an aerial flip. This effect is quite like a gymnast pushing themselves off the ground and upwards into a flip.
The starch leg flipping the kernel into the air
Finally they turned their attention to the pop sound itself. There were a few thoughts, maybe it was the escaping pressurised steam, or the sound of the husk breaking, or maybe the sound of the jump itself. However the sound happens before the jump, and after the opening of the corn kernel. What they found is the rapidly escaping pressure leaves a resonance chamber inside the kernel, and this sudden change in pressure in this chamber creates the popping sound. This is the same effect as when a champagne cork pops.
No. More. Popcorn
So there we go, thanks to two scientists playing around with their new piece of equipment we found out more than we ever thought we would about the mechanics of popping corn.
By Ben Lewis (@BenSciGuy)
Feature image sourced from Wikimedia Commons.
Body image 1 taken by Ben Lewis.
Body image 2 taken by Ben Lewis.
Body image 3 sourced from Royal Society Interface.
Body image 4 taken by Ben Lewis.