Muscles contain varying proportions of pigments. Muscles which are used for physical activity contain large quantities and are darker in colour. As red meat is cooked the myoglobin changes from a purple red to a greyish brown in colour. The legs and wings, which do the most work, tend to be darker and tougher due to the myoglobin present. Other parts of the bird, eg breast, have less myoglobin and therefore become white during cooking.
Game is generally tougher than poultry, beef, pork and lamb.
This is due to game animals being wild and having an active life. There are very many different types of offal, such as kidney, brain and tongue, and other parts of the body such as tail and feet. Products such as gelatine and stock cubes are also by-products of the meat processing industry. For example, gelatine is obtained by boiling bones and the connective tissue from skins and hoofs. Lean meat is a nutritious food, which in moderate amounts can make a valuable contribution to intakes of protein, long chain fatty acids, B vitamins, vitamin D, iron and zinc.