Myoglobin is the protein found in muscle that gives beef its cherry red color when exposed to oxygen. Once myoglobin is fully oxidized, it becomes “metmyoglobin” which will turn your steak brown or grey. It can happen when freezing steak as well.
The presence of oxygen, however, eventually turns beef grayish-brown. Myoglobin's chemical compound contains iron, which, after a few days of oxygen exposure, will oxidize. This creates metmyoglobin, which is responsible for the meat turning grayer than your grandpa.
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.
When the meat has no oxygen exposure, it changes to a gray-brown hue. But that does not mean it is spoiled.
Steak can turn gray in the refrigerator because of a process called oxidation. This occurs when the iron in the meat reacts with oxygen in the air, causing the meat to change color. This process does not make the meat unsafe to eat, but it can affect the taste and texture.
Raw steak going bad can be identified by a distinctive smell, dryness, a slimy texture, discoloration, or passing the expiration date. A bad steak may have an intense ammonia-like aroma, be dry and juiceless, have a slimy film on the surface, or change color to dull brown, yellow, or green.
Check for a sour, off-putting odor.
If you don't smell any strong odors, your meat is still fresh and safe to cook. If you notice a sour or rancid smell coming from the meat, throw it in the trash. If your steak is slightly discolored but doesn't have an odor, then it's still safe to cook.
If only the interior is gray, you can bet that oxygen hasn't touched it to turn it red. This means ground beef with a gray interior is safe to eat. On the other hand, meat that looks gray or brown all over (on the inside as well as the top layer) has likely begun to spoil and is not safe to eat.
All that ground beef underneath the top layer has no access to oxygen, so it turns an unappealing color of gray. This will also happen to any beef you store in the freezer.
The meat turns brown in the freezer due to a process known as oxidation. This occurs when the meat is exposed to oxygen, which causes the iron molecules in the meat's hemoglobin to react and change color. This process does not make the meat unsafe to eat, but it can affect the taste and texture of the meat.
The Bottom Line
If the ground beef is gray on the exterior or has another indicator of spoilage, it's best to discard it.
After a time, however, continued exposure to oxygen leads to the formation of metmyoglobin a pigment that turns beef brownish-red. The color change does not mean the meat is spoiled; it does suggest that the meat may not be as fresh.
Information. Frozen beef will be safe indefinitely. However, for best quality, use uncooked steaks, roasts, or chops within four to 12 months, uncooked ground beef within four months, and cooked beef within two to three months.
Once you've thawed something, check the texture: If it's sticky or slimy, it's probably no good anymore. Sorry.
Most "freezer damage" is dehydration, which makes the meat less pleasant to eat but not unsafe. Oxygen does not keep it red…it oxidises the meat and causes it to go brown. This is why refrigerated and old meat goes brown.
I had some meat in the freezer and it got grayish brown spots on it. Does that mean it's bad? Those spots sound like freezer burn, which will not make you sick, but will make the texture of the meat unpleasantly dry. It happens when the surface of the meat comes in contact with air.
Information. Color changes can occur in frozen foods but the foods remain safe to eat. The bright red color of meat as purchased usually turns dark or pale brown depending on its variety. This may be due to lack of oxygen, freezer burn or abnormally long storage.
Is it still safe to eat or should you throw it out? The good news is, even if there's a color change, the meat or poultry is still perfectly fine to eat if stored properly in the refrigerator or freezer and consumed within a safe period of time (up to two days for ground meat and five days for other cuts).
Change in color alone does not mean the product is spoiled. Color changes are normal for fresh product. With spoilage there can be a change in color -- often a fading or darkening. In addition to the color change, the meat or poultry will have an off odor, be sticky or tacky to the touch, or it may be slimy.
Beef that has gone bad will develop a slimy or sticky texture and smell bad or "off." If beef develops a grayish color, that doesn't necessarily mean it has gone bad. Don't taste meat to determine if it's safe to eat or not. Call the USDA's hotline.
That colour actually indicates a lack of exposure to oxygen, which is normal. Grocery stores will often discount meat, such as ground beef, that has turned brown, though it's well within its shelf life. If the meat turns brown or grey on the outside, though, it's likely not yet unsafe, but it is beginning to rot.
Consumers expect fresh ground beef to be bright-red, but at times it may appear brown, mottled red and brown, or even purplish. Color variations can be confusing and may lead to the rejection of acceptable ground beef.
While thawing with cold water or your microwave means you'll need to cook your meat ASAP, you'll have more of a grace period when you thaw inside your fridge. Once raw meat comes up to 35 to 40 degrees Fahrenheit, it'll stay safe and usable for one to two more days.
Does Frozen Meat “Go Bad?” According to the USDA, frozen meat kept at 0°F or lower will always technically be safe to eat. This low temperature prevents the growth of microorganisms and microbes like bacteria and mold. But that doesn't mean it will taste good forever.
While foods are in the process of thawing in the refrigerator (40 °F or less), they remain safe. After thawing, use ground meats, poultry, and fish within one or two additional days, and use beef, pork, lamb or veal (roasts, steaks, or chops) within three to five days.