Ground beef should have a bright red color and be free of gray or brown patches. Beef normally has a purple-red color but takes on a cherry-red hue, known as the “bloom,” when exposed to oxygen. While the exterior is bright red, the interior of the meat retains the darker color. Vacuum-packed beef also shows this purplish color. With lengthy exposure to oxygen, ground beef will turn brown. This is a sign that the beef is no longer fresh and needs to be used immediately. Check the label for fat content and the “sell-by” date. The label may also tell you which part of the animal the hamburger comes from, for instance, the round or chuck. For the leanest possible beef, buy a lean cut of meat and ask your butcher to trim the fat and grind it for you.