Milling is an industrial process by which material is ground down into a fine powder. For example, milling dry wheat plant results in whole wheat flour, which can further be separated into flour and wheat germ. The milling process is crucial to the wheat and grain industry, and many more industries rely on milling on a regular basis. Material is usually milled to create a finer product that is more suitable than un-milled product. Many chemical processes rely on fine materials in order to achieve high reaction efficiency. By grinding material into smaller pieces, more total surface area is made available per given unit of mass. Since many chemical interactions occur first along the surface area of a reactant, it stands to reason that the more surface area, the better a chemical reaction occurs. The same is true with the chemical reactions responsible for giving rise to bread. Fine flour reacts better with water and yeast, creating dough that is more likely to ferment and produce carbon dioxide. This gas evolution puffs up the bread and gives it its characteristic fluffiness and height.
When designing parts for the milling process, one must consider the nature of the product they are to be milling. Some products are extremely sensitive to heat. When a material is milled, a great deal of friction is generated. Material can usually disperse heat across its mass, but when milled, the mass of each given particle of material gets smaller and smaller. This doesn’t allow the particle to disperse much heat. The heat from milling can spoil certain products, or adversely affect their freshness. For example, wheat may lose some of its nutrient value and flavor if allowed to get too hot in the milling process. To alleviate this problem, cold mills can be used in place of regular mills. Cold mills used cool mill stones and don’t turn as fast as normal mills. This keeps the temperature within a tight range, allowing sensitive material to be ground up without losing any flavor or freshness. This can allow a mill to produce above average quality flour.