When meat is ground, much more of it is exposed to harmful bacteria. That's one reason to cook hamburger thoroughly. Don't depend solely on appearance. A hamburger patty can turn brown on the outside before it reaches a safe internal temperature of 160 degrees.
Other tips from the U.S. Department of Agriculture:
* Keep it cold. Buy hamburger just before you leave the store. Refrigerate or freeze when you get home.
* Store ground beef at 40 degrees or below and use within two days.
* Well-wrapped frozen hamburger will keep indefinitely, but is best if used within four months.
* Never put cooked hamburgers on the same plate that held raw patties or reuse the packaging materials.
* Don't partially cook ground beef to use later. This allows harmful bacteria to survive to the point where subsequent cooking may not destroy them.
