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. Inside the package, however, the meat eventually turns brown because it no longer has contact with the air. According to the United States Department of Agriculture, the brown or gray meat inside a package of ground beef is perfectly safe to eat and tastes just like the cherry-red exterior.

Over time, your ground beef might lose its bright red surface color. This happens faster if you place it in an air-tight container, blocking the oxygen. Even through the darker color might not be very appetizing, there's nothing wrong with the meat itself. Just make sure you eat or freeze it within one to two days of purchase for the best quality.

While you can't use color to find a fresh package of beef, you can identify the best packages by reading the labels carefully. Many stores list the date on which they ground the beef. Others rely on a “use by” or “freeze by” date. Use these as guides to determine whether your beef is safe to eat.

Even if your meat stays bright red, you need to handle and store it carefully to ensure a safe meal. Make sure that you refrigerate beef immediately after purchase. If you don't use it within 48 hours, package it for the freezer and store at 0 degrees Fahrenheit. The USDA recommends using the beef within four months, but notes that it will stay safe to eat indefinitely if you store it at this temperature. After you cook the beef, you should refrigerate leftovers within one to two hours. Keep them for no longer than three to four days, or freeze for storage of up to four months.