Begin by placing your ground beef in a large bowl.
Mix together Guinness, Worcestershire, minced onion, and garlic powder in a small bowl.
Pour over the top of the beef, and mix into the meat. The liquid will mix in completely.
Marinate for at least 1 hour, up to 8 hours in the fridge.
Heat up your grill to a medium-high heat
Divide the meat into 6 portions, and form hamburger patties. The thicker the burger the longer it will take to cook. It's best not to go over about 1".
Grill each patty for approximately 5 minutes each side (for medium-medium well burgers).