Meat eaters are not a monolith. Some seem to relish in the visceral aspects of eating animals, even going so far as to butcher their own, while others prefer to purchase sterile, shrink-wrapped packages of tenders and/or boneless, skinless breasts.
The latter breed of carnivore usually exercises an abundance of caution when choosing, cooking, and storing steaks, ground meat, or roasts, and that’s a good thing. (Eating bad meat can mess you right up.) Bright red ground chuck rarely sets off any alarm bells — but what about grey meat, brown meat, or meat that is shiny or iridescent in spots? Should red meat always be red, or are these other colours just part of the meaty rainbow?
What is “red” meat anyway?
“Red meat” is not a scientific term, but a culinary one, and is used to refer to meat that is red when raw and dark in colour when cooked. Beef, lamb, goat, horse, venison, elk — these are all examples of red meat.
Sometimes maturity of the animal factors in: A steak from an adult cow is undeniably red, but veal (baby cow meat) is startlingly pale. Meat colour can also vary throughout the animal, depending on how much action a particular piece of muscle saw. Chickens rarely use their breasts, as almost all of their flying is done in short, unsustained bursts, but their little legs carry them around all day. The more use a muscle sees, the more oxygen it needs, and myoglobin — the oxygen-binding protein responsible for carrying said oxygen to those muscles — turns red when exposed to oxygen. This is why chicken legs and dark breasts are both considered “dark” meat; it’s a matter of use.
Why does red meat turn grey?
Picking up a pound of vividly red ground meat, only to find that the inside of your hamburger looks dull and grey once you’ve gotten it home is a common meat-buying experience. And, if you’ve ever bought a packet of steaks, all nestled together and wrapped up tight, you’ve probably noticed a few grey or brown spots once you took them out of the packaging, particularly in areas where the steaks were in close contact with one another.
Neither of these scenarios is cause for alarm and, again, it all comes back to oxygen. According to the USDA, these colour changes are totally natural:
Beef muscle not exposed to oxygen (in vacuum packaging, for example) is burgundy or purplish in colour. After exposure to the air for 15 minutes or so, the myoglobin receives oxygen and the meat turns bright, cherry red. After beef has been refrigerated for about five days, it may turn brown. This darkening is due to oxidation, the chemical changes in myoglobin due to the oxygen content. This is a normal change during refrigerator storage.
Brown or grey colouring on meat doesn’t automatically signify that it has gone bad, but it can signify it has had more time to oxidize. A few grey spots or a less-than-red interior due to a lack of exposure to oxygen pose no threat, but steak with a completely brown exterior is probably best avoided, as it indicates that meat has been oxidizing for at least few days, if not longer.
Luckily, colour is not the only freshness indicator at our disposal. Smell and touch are also available. Toss any meat that has an off, sour, or ammonia-like aroma, and do the same to any with a sticky or slimy feel.
Does red always equal fresh?
Given everything we just covered, you might think that redness is the easiest, most reliable way to to spot a piece of super fresh meat. That would be true, if it were not for capitalism.
Oxygen and oxygen-binding proteins aside, the average meat consumer’s brain associates the colour read with freshness. Supermarkets know this, and know that bright, aggressively red meat is easier to sell than meat with a less vivid hue. Redness, or the lack thereof, hinges on a number of chemical reactions, and those reactions can be interfered with at the meat counter.
According to Harold McGee for the New York Times, treating meat (or fish) with carbon monoxide can keep it looking fresh even if it’s past its prime. Oxygen binds to an iron atom in myoglobin so that it can be carried throughout the body, and carbon monoxide can bind to it in that exact same spot:
Carbon monoxide is an effective colour fixative. It sticks like a leech to myoglobin’s iron atom, turning the molecule a distinctive cherry red and preventing it from reacting with anything else, oxygen included. This is exactly what carbon monoxide in the air we breathe does to hemoglobin in our blood, and why it can asphyxiate us. But at the levels applied to meat and fish, it doesn’t asphyxiate bacteria. So there’s concern that carbon monoxide treatment may mislead consumers into eating fish and meat that’s old enough to have begun spoiling. For this and other reasons, it’s banned in Europe and Japan.
But carbon monoxide only affects the colour. It can’t mask off-odours or make a steak feel less sticky, so use all of your senses when purchasing and preparing meat and you should be fine.
What about that shiny stuff?
Cooked lunchmeat, such as roast beef, can sometimes have a shiny, iridescent surface sheen. According to the USDA, this is due to a wide variety of chemical compounds present on each slice:
Sliced cooked beef or lunchmeat can have an iridescent colour. Meat contains iron, fat, and many other compounds. When light hits a slice of meat, it splits into colours like a rainbow. There are also various pigments in meat compounds which can give it an iridescent or greenish cast when exposed to heat and processing. Iridescent beef isn’t spoiled necessarily. Spoiled cooked beef would probably also be slimy or sticky and have an off-odor.
Iridescence can also be observed in raw meat due to light refracting off of muscles and fat, but its presence is not indicative of spoilage. According to Ohio State University, curing, cooking, and even how the meat is sliced can all have an affect on iridescence, but there’s no reason to worry about it, even if it appears quite green. Trust your nose, and give the meat a little poke. Smelly, sticky meat is never good to eat, no matter what colour it is.