In ground sirloin, the muscle and fat comes only from a sirloin cut of beef that is found on a steer or heifer's hip, but "ground beef" is a more general term. It indicates that the meat came from one of the seven primal cuts and trimmings, such as "chuck" or "round," but doesn't specify.
The type of ground meat chosen depends upon its intended use. If ground beef is labeled with a specific cut, such as ground round or chuck, the lean and fat come only from that source. The meat can be either fresh or frozen. No water, phosphates, binders or other meat sources are added to ground beef, in accordance with USDA regulations.
If ground beef is identified as "hamburger," the lean meat comes from a primal cut. However, the fat trimmings are permitted to come from other sources.
Ground beef may have no more than 30 percent fat, though some products have less. Most packages of ground beef are between 75 and 85 percent lean, but 95 percent lean is sometimes available. These variations are reflected in the amount of calories and protein in the meat. In general, the leaner the beef, the lower the calorie count and the higher the protein.