To analyze the grinding results the dispositions of the source and ground material must be computed. To quantify this characteristic the grinding degree is calculated, which is a ratio of sizes relative to the grain disposition. The grinding degree relative to grain size d80 is shown:  formula_6  where the value signifies 80% mass is of size smaller than the grain. There are three methods used for corn dry-milling:  Tempering degerming is the most common process used for grain dry-milling in the industry. Corn dry milling consists of several steps. The following paragraphs describe all the steps of dry milling as well as the equipment used during these steps in detail. A chamber is used at this section in order to mix the corn and water and let them temper for 10 to 30 minutes. For more efficient separation, differential moisture content between germ and endosperm is desired. Tempering of kernel leads to moisture uptake. Because of the differential swelling of germ and endosperm, the germ becomes more flexible and resilient during tempering while there is no movement of material out of kernel. The objective of degermination in corn dry milling is to break down kernel to pericarp, endosperm and germ. Beall operation is used for fulfilling this goal which separates the kernels received form tempering section into tails and throughs. Beall degerminator is known for its high yield of flaking grits; however, other manufactures have lower power requirement. Pilot plant Beall has an inner cone rotating at 800 rpm. One of the advantages of Beall degermination is weight adjustment at tailgate for increment the residence time by holding back the material. Aspiration is a unit operation used for separating the pericarp from the mixture of endosperm and germ, using terminal velocity which is affected by particle size, shape and density. Gravity separation is a method used for separating the components of a mixture with different specific weight. Gravity separation in dry milling is utilized in order to separate endosperm from germ. Roller mills use cylindrical rollers for grinding different materials, especially grains, which can even be an appropriate substitution for hammer mill and ball mills. Sifting is used in order to adjust the distribution of endosperm particle  There are two methods for oil recovery used in industry: 1) Corn expelling which is not commercially used in the US for corn germ oil recovery due to its low oil yield and presence of residuals oil in solid products; however, it is simple and cheap.