December 3, 2007

Can popcorn pop underwater?

Surprisingly enough, when you google this question, you don't get an answer. Popcorn works by heating up the tiny amount of water in the kernel, which then forces open the watertight shell, causing the little explosion of tasty goodness. It takes a minute or so in an air popper to heat the kernel to the point of popping. So it would seem that you could toss some kernels into a pot of boiling water for a minute and achieve the same effect - the water heats up the kernel, which pops. But what would the result be of a kernel popping underwater?

I got conflicting ideas from some superstars of chemistry. Erik felt that popcorn wouldn't do anything underwater because of density or air pressure or lava or something. I wasn't really paying attention. Patrick thought that the kernels would pop, sending droplets of hot water shooting into the air. He was ok with my experimenting in the microwave but told a long and intricate tale about how he wouldn't take me to the emergency room if superheated water and kernels on the stove caused scalding burns to my face and eyes. I figured that if I call myself a scientist (even if it's just a social scientist), I should test this empirically.

The microwave experiment. I filled a ramekin with about 1/4 cup of water, tossed in about 10 kernels of popcorn, and microwaved it for 3 minutes. At the end of that period of time, I took the ramekin out of the microwave. The little kernels were emitting bubbles from underneath the water, but they hadn't popped as far as I could tell.

The stovetop experiment. I filled the bottom of a sturdy pot with about 1/2 cup of water and heated it on the gas stove until it was boiling. I tossed in one kernel, and nothing happened. Then I tossed in a couple more. Nada. No geyers of sizzling water (fortunate for me, but unfortunate for science). Thinking perhaps they needed more time, I tossed in about a dozen kernels, put on a lid, and waited 3 minutes. The kernels happily bubbled from beneath the glassy surface, like a kid swimming in his above-ground pool. They, like the kid, ended up a bit pruney and out of breath, but no worse for the wear.

So the experiments weren't nearly as exciting as I had hoped. Thus ends my tenure as mad scientist extraordinaire.


Trey said...

No clue if this is right, but the kernels might pop via radiation as opposed to conduction. Since conduction would take longer, you might want to try a pressure cooker with the kernels, or cooking the kernel for longer.

patrick said...

I suspect Erik is right. Water is more viscous and denser than air, so it slows the little puff of air when the kernel first ruptures. With the escaping air slowed, there is no pop. Once the pressure escapes (slowly), no amount of further cooking will make the kernel pop.

I think it's pretty much the same as popping a balloon underwater. Try it. :)

My horror stores were a bit on the conservative side. I just didn't want the hassle of driving to the hospital in a snowstorm.

Adam said...

Besides the additional tension that water places on a popcorn kernel preventing it from popping, is the fact that if the kernel is underwater its internal temperature will not reach more than 212 degrees. The reason being that all the surrounding water is colder than this and hence not boiled off yet. You could in theory put the pot under pressure, but that would likely prevent the gas from expanding as well. Since the water inside a kernel must be well above 212 to pop, the kernel will never pop underwater.

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