By Aarthi Katakam '21
It’s 3:21 am, and the whole world is asleep.
A microwave beeps. Hark! It’s a Choate student with their favorite witching hour snack – popcorn. Anyone could tell you about how great popcorn is, but there’s more magic in that little bag than just the taste. There’s a whole lot of interesting science that explains just why popcorn pops.
Anatomy of a corn kernel
There are three main parts of a corn kernel: the pericarp, the germ, and the endosperm. First is the pericarp, which is the hard, protective outer layer of a kernel that puts the “pop” in popcorn. Inside the kernel is the germ, which is the seed embryo. The endosperm is what makes up most of the kernel and is composed of water and starch granules. The water inside each corn kernel is the first key step to popping. What happens to the water inside the microwave? And why does that make popcorn pop?
The magic of microwaves
Microwaves are a type of electromagnetic radiation that has wavelengths from 30 cm to 1 mm, which is fairly large. These waves are what give that magic box its name. As the microwaves are emitted, they cause water molecules in food to vibrate and become excited. This produces friction between the molecules, leading to an increase in temperature.
POP!
When the water inside popcorn kernels is heated enough to turn into steam, the pressure inside builds because of the hard pericarp. When the temperature reaches about 180 degrees Celsius, the pressure inside is about 135 psi. This is enough for the pericarp to rupture, causing the kernel to turn inside out, or pop. While the pericarp is bursting, the starchy part of the kernel that formed the endosperm begins to goop out, forming a foam-like substance which quickly cools into what we know and love as popcorn.
There’s a sweet spot for heating up popcorn. If the temperature is too low, the steam will seep out of the kernel before the pressure can build. If the temperature is too high, the kernels will pop too quickly without giving the starch a chance to seep out and foam, leading to hard pieces that are a pain to eat.
A final question must be answered to fully understand the science of popcorn: what makes the popping noise? Most people used to say that the popping noise was caused by the pericarp cracking, but scientists discovered that this wasn’t true. Instead, it was caused by the release of steam resonating through tiny cavities in the kernels.
Now, equipped with all your newfound knowledge, I hope that you’ll appreciate the science behind your next bag of popcorn and enjoy it just a little bit more.
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