From Scientific American:
Do you like popcorn? It’s not only a tasty snack but also fascinating to watch when it pops in the pot. Why does it do that? What makes the small popcorn kernel jump into the air and change its appearance? Where does the characteristic popping sound come from, and does every corn pop? There are many good questions about this simple snack. In this activity you will perform some popcorn science—and even get to snack on your results!
There are many corn varieties that can differ significantly from popcorn, which are not just dried kernels of the sweet corn we eat. Popcorn is actually a special variety of corn, and it is the only one that pops. The key to popcorn is the unique design of its kernels. Most importantly, its kernel consists of a very hard, mostly nonporous outer shell called pericarp. Inside the kernel there is not only the seed for a new corn plant but also water and soft starch granules that serve as a food source for the seed during germ sprouting. Although popcorn has been around for thousands of years, scientists only recently resolved the mystery behind the popping sound and the detailed mechanisms of how the popcorn bursts.
The reason why popcorn pops is the water trapped inside its kernel. If the kernel is heated to a high enough temperature, this water will transform into steam. Due to the hard and mostly nonporous shell, the steam has nowhere to go, resulting in a buildup of pressure inside the kernel. Once the pressure gets high enough and the temperature reaches about 180 degrees Celsius (355 degrees Fahrenheit), the kernel hull bursts and the popcorn is turned inside out. The characteristic popcorn consistency and white-yellowish foamy appearance results from the starch inside the popcorn kernel. With …