Ground beef gets its red color from oxymyoglobin, a compound that forms when myoglobin in meat reacts with oxygen. This interaction is what gives fresh meat its attractive red surface. However, it is normal for ground beef to appear gray inside the package, where oxygen has not penetrated. This lack of exposure to oxygen results in a color that may seem worrisome at first, but is generally harmless.
When to worry
While internal graying is usually not a problem, the external color of ground beef deserves special attention. If the surface or a significant portion of the meat has a gray or brown tint, it is prudent to err on the side of caution and discard the meat. Additionally, any unpleasant odor is a strong indicator that the beef is spoiled and should not be consumed.
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