It's close to that time of year when you get asked the age-old question at the dinner table: White meat or dark meat?
As you know, when someone serves you turkey or chicken at a dinner party, they will politely ask you whether you prefer dark meat or white meat. Which you choose is largely a matter of personal taste. They both taste pretty good if they are smothered with gravy.
So, besides taste, what is the difference between white and dark meat? All of it is muscle tissue, after all. The answer lies in what the bird uses the muscles for and how often it uses them.
Unlike chickens and turkeys, most birds can’t afford the luxury of white meat.
What we call “meat” is, in fact, muscle tissue. To be precise, skeletal muscle tissue. Composed of cells that contract when they receive an electrical impulse, these are “voluntary” muscles and are the prime movers of birds and mammals. Attached to bones, they literally move the animal world by contracting and relaxing.
Two types of voluntary muscle tissue do all this work, “slow-twitch” and “fast-twitch.” Dark meat, actually red meat, is slow-twitch muscle tissue, full of red blood cells and mitochondria which ensure a rich supply of blood and oxygen. These are the muscles that contract more slowly and less often, but are responsible for all sustained muscular effort, such as flying.
Birds that fly a lot haven’t got room for much fast-twitch (white) muscle tissue. Hummingbirds, for instance, have no white meat at all. Only ground-dwelling birds, mostly ratites (birds with a flat breast bone instead of a prominent keel bone), and birds like chickens, turkeys, and grouse, which fly rarely and for only short distances, have the luxury of a lot of white meat because fast-twitch muscle tissue has many fewer red blood cells and cannot provide the oxygen necessary for sustained effort.
That is why ducks and geese have little white meat...even their breast meat (the pectoralis muscle) is dark. Ducks and geese have to fly long distances and need slow-twitch, endurance muscles.
One thing that fast-twitch (white) muscles are good at is sudden movement. Gallinaceous birds (turkeys, grouse) are capable of sudden bursts of flight. (What birder hasn’t been startled by a grouse exploding into flight in front of her?) Birds that don’t do sustained flying don’t need as much of the heavier, redder muscle tissue which is why the pectoralis muscle tissue (breast meat) of chickens and turkeys is white.
In wild turkeys, about one-fifth of the muscle tissue is white. And we humans fool with the genes of domesticated birds just to increase the amount of white meat. But even domesticated chickens and turkeys use their legs and thighs for sustained muscular effort and that is the reason their legs and thighs contain dark muscle tissue.
So, if you want to avoid political discussions at your Thanksgiving dinner table, you can ask your guests if they want "fast twitch" or "slow twitch" meat and see what happens!