What Makes Popcorn Pop?
While popcorn is growing in the field, it looks like any other kind of corn, but kernels of popcorn are extra-hard. When popcorn is heated, the natural moisture in the kernels turns to steam.
Good popping popcorn must have just the right moisture content so there will be just the right amount of steam in the grains and all of them will pop.
The pressure of the steam bursts the kernel with a popping sound, and the starchy insides expand to many times the size of the original kernel. Other kinds of corn dry out when heated, but do not pop.
The American Indians discovered popcorn. They sometimes popped corn by tossing the kernels into the fire and waiting for them to pop out.