More food physics
A neat article on Nature about physicists helping to make the perfect piece of popped popcorn (which Peter Piper picked. No, wait…)
Popcorn is made by heating corn kernels until the pressure inside them builds up enough that it pops the hard outer shell and forces the starchy interior to explode outwards. “Good” popcorn, aside from being served with lots of salt, has big, light, fluffy pieces. This means we want the explosion of the popcorn to be as powerful as possible - we want the pressure inside to very high when the kernel explodes! But this is hard to do, as you can’t do much to the corn except heat it. So, physicists at Stanford Medical School in California realised that if they could lower the pressure outside the kernel then the pressure difference between the inside and outside would be bigger - and the kernel would explode with even more force and hence be bigger. (It’s interesting to think about the “limiting case” where you pop kernels in a vacuum. When the kernel pops, will it just keep expanding forever? After all, there’s no air to slow it down or stop it, right? The catch is that as it expands, it will cool down, and eventually the steam turns back into water and the starch “sets” into a normal kernel. We don’t have to worry about this for corn in a saucepan however, because everything happens so quickly that heat loss isn’t important - that’s why corn comes out hot. We call this type of process adiabatic, meaning no heat is lost to (or gained from) the environment.)
But this isn’t just theory! To try it out, they simply attached a vacuum pump to their pressure cooker - this reduces the amount of air inside, and hence the pressure. The resulting kernels were about twice the size of normal ones, and for minimal effort. All of this means that next time you go to the movies, they can offer you a SuperMegaGIANT sized popcorn container that has only half as much popcorn as a regular Small size!
If you want some more details, have a read of their paper online at the arXiv. Just follow the PDF link. There is maths, but there’s a lot of text as well to make it quite readable.