London broil is not a cut of meat, but a type of beef preparation that involves marinating then slowly cooking a thick cut of meat. According to a 2011 article in "The New York Times," London broils can come from the round, flank, shoulder or sirloin of the cow. Regardless of the cut, the London broil is always one to two inches thick and very lean. The thickness of the steak means slow-cooking is in order, as searing over high heat is not possible. Because of the lack of fat, marinate the meat to soften and flavor it. Preparing a London broil on a gas grill requires a time commitment, but the final product is worth the wait.
Prepare a marinade by combining garlic cloves and salt in a mixing bowl. London broil lacks the marbling found in other cuts of meat. This fat melts when heated, keeping the meat moist throughout. Using a marinade will help you prevent the steak from drying out. Two popular marinades for London broil begin with garlic and salt. The first is wine-based and have you whisk together the garlic, salt, red wine, balsamic vinegar, soy sauce and honey. For a Latin-American flavor, combine garlic and salt with citrus juices to create a Cuban-style mojo marinade.
Remove your meat from its packaging and pat it dry with paper towels. Set it in a zipper freezer bag and pour the marinade over the top. Refrigerate for two to four hours.
Preheat your grill to medium. Your grill is ready for use when the internal temperature reaches 400 degrees Fahrenheit.
Indirectly grill your London broil. On a gas grill, turn off half of your burners. Set the meat on the cool side of the grill and cover. Cook seven to nine minutes each side until an instant-read thermometer reaches 135 degrees Fahrenheit to achieve medium-rare. For medium, cook nine to 11 minutes each side, or until the thermometer reads 145 degrees Fahrenheit. According to Raichlen, preparing a London broil to medium-well or well is not recommended, as it will produce a dry and tough steak.
Remove the meat from the grill and let stand for 10 minutes. The steak will continue to cook when removed from the grill and increase 10 degrees to the desired doneness. Letting the meat stand also allows the steak's juices to collect.