When ground beef starts turning brown or gray in the refrigerator, it is an indication that it is beginning to oxidize and lose its freshness. The color change is due to the exposure of the meat to oxygen, which can cause it to go through a process called "metmyoglobin formation." While it may not necessarily mean that the beef is spoiled or unsafe to eat, it is a sign that its quality is degrading.
If the ground beef has only recently started turning brown or gray and has been properly stored in the refrigerator, it may still be safe to consume within a day or two of the color change. However, if it has been in this condition for an extended period or if there are any other signs of spoilage, such as an off smell, sliminess, or an unusual texture, it's best to discard it.
To maximize the shelf life of ground beef, always follow proper food safety guidelines. Store it in the refrigerator at or below 40°F (4°C), use it within a few days of purchase or before the expiration date, and cook it to the appropriate internal temperature (160°F or 71°C) to kill any potential bacteria. When in doubt, it's better to err on the side of caution and avoid consuming ground beef that appears spoiled or has been stored for too long.