Beef steaks used in a steak sandwich often benefit from a short stay in a liquid marinade. One of the most common is flank steak, which because of its location, contains some amount of tough, connective tissue. Marinating in an acidic liquid marinade not only helps soften this connective tissue, but also enhances its flavor. Timing is important, however, as a long soaking time can cause the meat to become mushy, rather than tender.
Add 1 cup of liquid acidic ingredients for each pound of beef to a small mixing bowl. This can include one or more ingredients, such as all soy sauce or a combination of 1/2 cup each of low-sodium soy sauce and balsamic vinegar. These ingredients work to soften the bonds of the connective tissue and tenderize the meat.
Add ingredients that enhance the flavor of the steak. For a slightly sweet taste, stir in brown sugar and seasonings such as fresh thyme and black pepper. For a savory flavor, forget the brown sugar and instead add minced garlic and onions, and substitute Worcestershire sauce for the soy sauce. For a hot or spicy flavor, add seasonings such as Mexican oregano, chili powder or cayenne pepper, cumin and lime juice.
Pour the marinade over steaks arranged in a single layer in a baking dish.
Turn the steaks two to three times with tongs to coat the meat thoroughly with the marinade.
Cover the dish, using a sheet of aluminum foil if the baking dish does not have its own cover.
Marinate the steaks in your refrigerator for 15 minutes to one hour, turning the meat every 15 minutes with tongs to ensure it marinates evenly.