be careful using colour to determine doneness in a burger.
game meats like bison and elk take a very long time for the "red" to be cooked out in the center. if you cook it that long, you'll end up with something better suited for a hockey rink than a bun.
as far as contamination goes, i prefer my burger rare and bloody, but i would never serve one that way unless requested.
The way that you wander is the way that you choose. The day that you tarry is the day that you lose.
Sunshine or thunder, a man will always wonder where the fair wind blows.