First a little background, Popcorn or “zea mays everta” is a special kind of Flint corn, also known as “Indian corn” and sometimes “Calico corn”. Flint corn is readily recognizable as the kernels have a hard outer shell, likened to flint, hence the name. This hard outer shell is essential in making popcorn kernels pop. In fact, popcorn is the only type of corn that will pop for reasons we’ll see in a moment.
So why does popcorn pop? There are three main elements of popcorn that have to come together to produce popcorn kernels that are good for popping. Those three elements are: the percentage of water content; hard, undamaged, water impermeable shell; and a starchy center.
When the kernels are heated up, the water inside begins to steam. Assuming the water impermeable shell doesn’t have any cracks in it to let the steam escape, this creates a simple little steam/pressure cooker. The starch inside the kernel then turns into a kind of gel-like substance as a result of this. Eventually, the pressure of the steam gets so great that the hard shell bursts, typically around 135 psi. When this happens, the steam rapidly expands, which results in the gel expanding out and hardening into airy foam. What’s going on here is that as the gelatinized starch expands, it forms thin airy bubbled jelly. These jelly bubbles will fuse together and then solidify very quickly as they are exposed to air and cool off. The cooling sets the starch and protein polymers into the white puffy flakes.