Just in time for the US season of summer blockbusters, we finally have an explanation of the method behind the madness. No, not the celebrity rumour mill, and not how to win at the box office. New research has answered a far more important question – how does popcorn pop?
The official research was published in Interface, the Journal of the Royal Society by Emmanuel Virot, a doctoral candidate at the École Polytechnique in Paris, and Alexandre Ponomarenko, a researcher at the National Center for Scientific Research in Grenoble, France.
But if you’re wondering if you can build your doctorate on your favourite snack, don’t get too excited.
The scientists were actually studying tree limbs breaking in varying wind speeds when the proverbial kernels started popping.
Just for fun, they focused the high-speed camera they were using on their actual course of research on popcorn.
Once Virot and Ponomarenko had captured footage of popcorn exploding, it became clear there was something interesting going on that hadn’t yet been discovered. By playing back the video in slow motion, they were able to determine what it is that makes hard corn kernels pop into something edible.
The team increased heat to the unpopped kernels in deliberate increments since temperature is clearly the main factor here. First, they noticed that 34 per cent of heated kernels popped once the temperature reached 170 degrees Celsius, but it took another 10 degrees Celsius before 96 percent of the kernels had popped.
Because science, Virot and Ponomarenko also recorded a bunch of measurements to popcorn kernels, both popped and unpopped. They found that the key to popping all the kernels is to bring them to a high enough temperature all at the same time – nobody likes those dud kernels at the bottom of the bowl. Practically speaking, pan popping may be the way to go.
So what is the temperature change triggering? It turns out popcorn exploding relies on the tiny amount of water hidden away in a mass of starch within each unpopped kernel. The water trapped inside the kernel turns into vapour and expands as it is heated, steaming up the starch until it bursts through the hull of the kernel at a high enough temperature.
That exploded mess of starch is what cools into the fluffy popcorn shapes you know and love. Manufacturers already know about this process, since they’ve studied the perfect amount of kernel moisture to ensure that pops occur uniformly, even in your microwavable bag – 13 to 14.5 per cent moisture is ideal.
Here’s where the pop comes from: as the gooey starch insides grow with the expansion of the kernel’s trapped moisture, a starch “leg” is formed that pushes against the bottom of the pan until the outer shell splits. That leg launches the kernel into the air when the starch finally breaks open the hull, creating the namesake popping effect.
And contrary to popular belief, the actual sound of the pop doesn’t come from the splitting hull at all. Virot and Ponomarenko liken the auditory effect to the sound of a volcano erupting or a champagne cork popping – once the water vapour is released, the empty chamber inside the kernel where it was stored resonates sound once the pressure is released.
Check it out in slow motion: