So what is that red liquid you are seeing in red meat? Red meats, such as beef, are composed of quite a bit of water. This water, mixed with a protein called myoglobin, ends up comprising most of that red liquid.
In fact, red meat is distinguished from white meat primarily based on the levels of myoglobin in the meat. The more myoglobin, the redder the meat. Thus most animals, such as mammals, with a high amount of myoglobin, are considered “red meat”, while animals with low levels of myoglobin, like most poultry, or no myoglobin, like some sea-life, are considered “white meat”.
Myoglobin is a protein, that stores oxygen in muscle cells, very similar to its cousin, hemoglobin, that stores oxygen in red blood cells. This is necessary for muscles which need immediate oxygen for energy during frequent, continual usage. Myoglobin is highly pigmented, specifically red; so the more myoglobin, the redder the meat will look and the darker it will get when you cook it.
This darkening effect of the meat when you cook it is also due to the myoglobin; or more specifically, the charge of the iron atom in myoglobin. When the meat is cooked, the iron atom moves from a +2 oxidation state to a +3 oxidation state, having lost an electron. The technical details aren’t important here, though if you want them, read the “Bonus factoids” section, but the bottom line is that this ends up causing the meat to turn from pinkish-red to brown.
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- It is possible for meat to remain pinkish-red all through the cooking if it has been exposed to nitrites. It is even possible for packagers, through artificial means, to keep the meat looking pink, even after it has spoiled, by binding a molecule of carbon monoxide to produce metmyoglobin. Consumers associate pink meat with “fresh”, so this increases sales, even though the pink color has little to do with the freshness of meat.
- Pigs are often considered “white meat”, even though their muscles contain a lot more myoglobin than most other white meat animals. This however, is a much lower concentrate of myoglobin than other “red meat”, such as cows, due to the fact that pigs are lazy and mostly just lay around all day. So depending on who you talk to, pigs can be considered white meat or red meat; they more or less sit in between the two classifications.
- Chickens and Turkeys are generally considered white meat, however due to the fact that both use their legs extensively, their leg muscles contain a significant amount of myoglobin which causes their meat to turn dark when cooked; so in some sense they contain both red and white meat. Wild poultry, which tend to fly a lot more, tend to only contain “dark” meat, which contains a higher amount of myoglobin due to the muscles needing more oxygen from frequent, continual usage.
- White meat is made up of “fast fibers” that are used for quick bursts of activity. These muscles get energy from glyocogen which, like myoglobin, is stored in the muscles.
- Fish are primarily white meat due to the fact that they don’t ever need their muscles to support themselves and thus need much less myoglobin or sometimes none at all in a few cases; they float, so their muscle usage is much less than say a 1000 pound cow who walks around a lot and must deal with gravity. Typically, the only red meat you’ll find on a fish is around their fins and tail, which are used almost constantly.
- Some fish, such as sharks and tuna, have red meat because they are fast swimmers and are migratory and thus almost always moving; they use their muscles extensively and so they contain a lot more myoglobin than most other sea-life.
- For contrast, the white meat from chickens is made up of about .05% myoglobin with their thighs having about .2% myoglobin; pork and veal contain about .2% myoglobin; non-veal beef contains about 1%-2% of myoglobin, depending on age and muscle use.
- The USDA considers all meats obtained from livestock to be “red” because they contain more myoglobin than chicken or fish.
- Beef meat that is vacuum sealed, thus not exposed to oxygen, tends to be more of a purple shade. Once the meat is exposed to oxygen, it will gradually turn red over a span of 10-20 minutes as the myoglobin absorbs the oxygen.
- Beef stored in the refrigerator for more than 5 days will start to turn brown due to chemical changes in the myoglobin. This doesn’t necessarily mean it has gone bad, though with this length of unfrozen storage, it may have. Best to use your nose to tell for sure, not your eyes.
- Before you cook the red meat, the iron atom’s oxidation level is +2 and is bound to a dioxygen molecule (O2) with a red color; as you cook it, this iron loses an electron and goes to a +3 oxidation level, and now coordinates with a water molecule (H2O). This process ends up turning the meat brown.
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