In the United States, there are 2 grades of milk, Grade A and Grade B. Since fluid milk is susceptible to bacterial contamination, more stringent health and sanitation standards apply to Grade A milk which is consumed as a liquid than Grade B milk, which used for butter, cheese, and other manufactured products. Currently, more than 90 percent of commercial milk production is classified as Grade A, and more than one-half of the Grade A milk supply ends up being used in manufactured dairy products.
Is milk made according to the strictest sanitary regulations prescribed, inspected, and approved by public health authorities. In most consumer markets, this is the grade of milk used in any products intended for consumption in a fluid form. Grade A is sometimes also called fluid grade milk or market milk
Never seen on store shelves, Grade B is milk that is produced and processed according to sanitary regulations but is approved by public health authorities be used only for manufactured food products. It is also called manufacturing grade milk.