1. For the teriyaki marinade, combine the soy sauce, mirin, vinegar, sugar, ginger, garlic and beer in a small saucepan. Cook over high heat until the mixture reduces by half. Let cool.
2. Marinate the London broil in the teriyaki marinade, cover and refrigerate for at least 20 minutes or up to 8 hours.
3. Preheat the grill.
4. Grill the steak on each side until it is cooked through, about 4 to 8 minutes per side, depending on the desired doneness and thickness of the steak.Serving Size: about 1/3 pound