White meat and dark meat (sometimes called red meat) are both muscle tissue. The differences between white meat and dark meat lie in their chemical composition. Further, how the animal can use each source muscle for meat determines how light or dark it will be.

To some this question of white meat and dark meat comes down to color alone. Chickens and turkeys, for instance have both white meat and dark meat. The breasts of both of them provide the white meat, as do the wings. The legs and thighs are generally composed of darker meat. You’ll quickly see this distinction doesn’t carry to all birds. Duck for instance, is almost all dark meat.

Much has to do with the way muscles are intended for use. In chickens and turkeys, the breasts and the wings aren’t used much. The legs are, since the animals tend to stand on them, and walk on them. Thus they have both white meat and dark meat.

Ducks, on the other hand, make significant use of their breast tissue for flying and swimming. As a result they tend to offer much darker meat. Chickens and turkeys almost never fly, but may do so if they really must escape.

Muscles that are used for quick escapes, like the breast of a chicken, are called fast-twitch fibers. They have smaller amounts of pigment and rely primarily on the production of the chemical glycogen, which is stored in the muscle tissue. For fast-twitch muscles, gylcogen stores are greater and quickly accessed when a chicken flies to evade capture.

Muscles that receive sustained activity, like the wings and breast of ducks or geese, or the legs of chickens are called slow-twitch fibers. In order to keep activity at appropriate levels, the muscles need a constant supply of oxygen. Myoglobin is a protein that stores oxygen in the muscle cells and has quite a bit of pigment, resulting in a darker colored muscle.

Glycogen is present in slow-twitch fibers, and any animal may need to access it to make a quick escape. Mostly, slow-twitch fibers are used all the time for walking or standing, or in the case of ducks and geese, for flying and swimming. Glycogen is present in lower amounts and is outnumbered by the myoglobin cells.

Other red meat animals stand or walk, with only an occasional “need for speed,” have a mixture of myoglobin and glycogen. Any farmer can attest that pigs are quite capable of sudden speedy action like charging or fleeing. In beef, most cows tend to walk and stand, though they too can speed up for short periods of time. Yet both animals are not sources of white meat and dark meat, since they have more slow-twitch than fast-twitch fibers.

People may ask about farming practices, and how it is possible that caging animals results in any fast-twitch fibers at all. Animals never get to access fast-twitch fibers if they spend their lives in tiny boxes. The answer to this is that limiting caging has not produced an overall genetic affect on these animals. They are still biologically programmed to have fast and slow-twitch muscles. Whether this will remain depends on chemical manipulation of an animal’s genetic code or early treatment of the animals. You’ll note that veal, for instance, through certain types of feeding and containment is almost white meat.