In Mexico, particularly in the towns and cities, corn tortillas are often made nowadays by machine and are very thin and uniform, but in many places in the country, they are still made by hand, even when the "nixtamal" is ground into masa by machine. 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.