Is raw hamburger meat bad if it is brown on the outside?

No, not necessarily. Beef starts to turn brown when it is being refrigerated due to a process called oxidation. If it is frozen it can be good for up to a few months. read more

Pink Outside, Brown Inside. Ground beef starts out purple because there is no air inside the animal. As soon as the grinding process starts, however, it comes into contact with oxygen. That turns the outside of the meat bright pink. Retailers wrap the meat in a plastic that lets oxygen continue to pass through, allowing it to retain its vivid color. read more

As meat gets older, or it is held in such a way that prevents oxygen from reaching it, the oxymyoglobin loses its ability to oxidize and it turns brown. This is why you sometimes find ground beef that is red on the outside and brown in the middle. read more

As the U.S. Department of Agriculture points out, it’s common for the inside portion of packaged ground beef to become more brown or gray in color, even while the outside remains red. read more