Popcorn

Pre-Columbian Amerindians domesticated maize (Zea mays) by 5000 BCE. The earliest variety of maize was popcorn (Zea everta), which has small, hard kernels. This hard outer covering, or endosperm, makes unpopped kernels difficult to chew or grind. The easiest way to render them edible is to heat the kernel. Heat converts moisture inside the kernel into steam, which puts pressure on the endosperm. When the outer covering can no longer contain the pressure, the kernel pops, or everts, and exposes the tender inner part of the flake.