Lamb, live sheep before the age of one year, and the flesh of such animals. Mutton refers to the flesh of the mature ram or ewe at least one year old; the meat of sheep between 12 and 20 months old may be called yearling Mutton. The meat of sheep 6 to 10 weeks old is usually sold as baby lamb, and spring lamb is from sheep of five to six months.
The mild flavour of lamb is preferred in most Western countries; the stronger flavour of mutton is considered desirable in many Middle and Far Eastern countries. Milk-fed lamb is especially delicate in flavour. The colour of the lean deepens, as the animal grows older. In the lamb it ranges from light to dark pink; in yearling mutton it is medium pink to light red; in mutton it is light to dark red in colour. The fat, soft and creamy white to pale pink in the lamb, hardens and whitens in older sheep. Bones also harden and whiten, becoming porous in the yearling and extremely hard in the mature animal.
In the United States the carcass may be separated into sides and then divided into wholesale cuts; it may be cut straight across into saddles; or it may be cut into leg, loin, shoulder, breast, and shank. The outer fat covering, or fell, may be removed from the cuts. U.S. quality grades for lamb include prime, choice, good, utility, and cull; mature mutton grades are choice, good, utility, and cull.
The primary lamb- and mutton-consuming countries (on a per capita basis) are New Zealand, Australia, Greece, Uruguay, and Ireland. The leg, Saddle (upper back portion of the carcass from last rib to legs), and shoulder, although they contain higher proportions of bone to meat, are considered the finest cuts by some cooks. In the United States popular cuts include individual chops from the ribs or loin, the leg, and the so-called crown roast, made by forming the rib section, or rack, into a circle.