Marinating beef is one effective way to enhance its natural flavor with the tastes and aromas of herbs, spices and other seasonings. Acidic marinades also offer a small degree of tenderization, which is useful when you're cooking a relatively tough cut of beef. Freezing marinated beef can accentuate both its flavor and tenderness, though it requires care if the beef was previously frozen.
There are two problems with refreezing beef that's already been frozen and thawed. First, any thawed piece of meat suffers some loss of moisture and texture. That's because ice crystals form inside the muscle fibers as they freeze, rupturing the cell walls. That's not always bad, because it helps tenderize tough cuts and your marinade can replace some of the lost moisture. The second issue, food safety, is more serious. Most cooks are wary of thawing and refreezing meats, because it creates opportunities for bacterial growth and food-borne illness. That's a well-justified concern, but it can be minimized with proper food handling technique.
You can safely thaw meats in the microwave or under cold running water if you're going to cook them immediately, but if you plan to refreeze the beef you should do it in the refrigerator. Steaks and flat roasts can thaw overnight, while thicker roasts might need a day and a half. Be sure to place your beef in a watertight container, so any juices that leak while it's thawing will be contained and not contaminate other foods in your refrigerator. If you'll be slicing the beef into small strips, it's easiest to cut while it's still slightly frozen.
Perishable foods such as beef should never be at room temperature for longer than two hours in total before they're cooked, and that has to include both cutting the beef and mixing it into the marinade. If you're slicing a large quantity of thawed beef, divide it into sections and only have one at a time on your cutting board. Mix your marinade ahead of time and chill it before combining it with your beef. Refrigerate the beef immediately and marinate it as directed in your favorite recipe. If you'll be freezing the beef in its marinade, it might not need any initial marinating time at all.
If the beef has been kept at refrigerator temperatures throughout the process, this will provide little opportunity for bacterial growth. The acidity of most marinades provides an extra degree of protection, because it discourages potential pathogens. The final step in safe handling of your beef is to refreeze it appropriately. Use clean, sterile utensils and freshly washed hands, and package the beef into small, flat bags or containers. Those freeze more quickly than larger packages. You can freeze the beef with or without its marinade. Beef frozen in the marinade will have a much stronger flavor.
When you want to use the frozen beef, thaw it overnight in your refrigerator. Drain the beef well before cooking it, because the wet marinade will prevent it from browning. If you'll be grilling or pan-searing the beef, pat it dry first with paper towels. If you usually use your marinade to make a sauce, you have two choices. The safest is to package up some marinade separately, without beef in it, and freeze it for later use. The marinade from your beef can also be used, but it's essential to bring it to a full boil to kill any potential pathogens.