Tortilla is the most important corn food in Mexico, Central America, Venezuela, and Colombia. In Mexico, nearly 52% of the corn is used for human food, mainly in the form of nixtamalized (lime-cooked) products. In particular, the lower socioeconomics groups depend on tortillas as the main source of calories and protein. The technology for tortilla production has been transmitted from generation to generation in Mesoamerica. In Central America and Mexico, many tortillas are still made by the ancient Aztec technology. In the traditional tortilla preparation, corn is lime-cooked in pots over a fire and steeped, to form the nixtamal. The nixtamal is washed by hand or with mechanical washers to remove the skin, or pericarp, and then ground on a stone grinder (called "metate") to form the masa. Small portion of masa are formed by hand into a flat cake, which is baked on a flat stone used as a griddle, called comal. The resulting tortillas are round flat products, of about 20 cm in diameter. Recent tortilla production technologies include modern machinery, for less labour and continuous processing, but the same principles are still followed.