 Corn tortillas are customarily served and eaten warm; when cool, they often become rubbery or grainy as the cooked starches stale.The largest tortilla producer in the world is the Mexican company Gruma, headquartered in Monterrey.Traditionally throughout Mesoamerica from pre-Columbian times into the mid-20th century, the "masa" was prepared by women using a "mano" (a cylinder-shaped stone like a rolling pin) and "metate" (a stone base with a slightly concave top for holding the corn).