Q: Is it safe to use raw ground beef that is red on the outside but gray inside?
A: It should be fine. Meat contains a pigment called myoglobin that turns bright red when exposed to oxygen. Grocery stores typically cover ground beef with a plastic wrap that allows some oxygen to penetrate, so that the surface of the meat turns this appealing red color, which consumers have come to associate with freshness. When ground beef is not exposed to oxygen, the myoglobin turns grayish-brown after a few days. It may look less appetizing but is safe.
If the ground meat is gray or brown throughout, however, that usually indicates that it has been in the package for a while and may be spoiling. If you just bought it, you may want to return it. “Spoilage bacteria,” though generally harmless, can make meat smell bad and cause other signs of deterioration. If you still want to eat it, it’s essential to cook it thoroughly.
Of more concern, ground beef is susceptible to contamination from Salmonella, E. coli, and other bacteria that do not affect the color or smell of meat but can make you sick—so it’s essential that you handle and cook all ground beef properly. Use or freeze it within a day or two of purchase and cook it to 160°F (71°C); use a meat thermometer to check. Color is an unreliable indicator of doneness, as the meat can turn brown before it reaches a temperature that kills bacteria; conversely, some ground beef may remain pink after it’s cooked to a safe temperature.
Meat can also turn gray in the freezer. It’s perfectly fine and safe to eat.