Federal grading of beef carcasses is a voluntary program, administered by U.S. Department of Agriculture, in which packers may participate at a fee that pays for the service. The official grade consists of a quality and/or yield grade. It is not mandatory that a carcass be yield graded if it is quality graded. These grades are used to divide beef carcasses into uniform groups so the product can be easily described and understand by both buyers and sellers.

Quality grades in young cattle are intended to identify differences in palatability or eating satisfaction of the product. Quality grades are primarily determined by age (estimated maturity of the carcass) and intramuscular fat (marbling). Cattle are classified into maturity groups A through E, with "A" maturity cattle defined as those less than 30 months of age and "B" maturity defined as those from 30-42 months of age. It is only these two maturity groups that are eligible to be graded prime, choice, select, or standard and the relationship between maturity, marbling, and grade.

Source: www.caf.wvu.edu