Due to the limitation of ancient technology, people use stone mills to grind various foods, such as "small tofu". Use a stone mill to "process" various grains, such as corn flour, corn residue, sorghum rice and so on. With the development of science and technology, all kinds of machinery and equipment are used to process all kinds of food. Using electricity as power has greatly improved the level of productivity and liberated people from heavy labor. Stone mills and stone mills were gradually eliminated.