"There is another reason why there is little point in trying to tenderize meat by marinating it. According to Harold McGee, author of "On Food and Cooking" (Collier Books: $21), protein-digesting enzymes do most of their work during cooking and only begin to really get going at around 120 degrees. Even then, they do most of their work at the surface. "Unless you have days and days," summarized McGee, "the only thing you are going to get from marinating meat is flavor."
But what flavor! "It is right at the surface, where the meat meets the fire during grilling, that you get much of the flavor," said McGee, who is particularly enamored of the effect of red wine marinades on meat. In fact, he suggests doing a comparison test:
"First, grill an unmarinated steak and then grill one that has been marinated in red wine for about two hours," he said. "The wine-y steak will taste like there is much more steak, richer and more mouth-filling than one that hasn't been marinated. A wine marinade greatly increases the complexity of flavor and contributes chemicals that the meat doesn't have. Then when it meets the fire, those chemicals combine in tremendously complex ways and you end up with hundreds of aromatic compounds."
Fruit juices also make good marinades because of their natural sugars. "Browning reactions that give you flavor and color come from sugars reacting with proteins at very high temperatures," explained McGee. "If there is a little extra sugar, then the browning reactions are enhanced."
McGee advises against soaking meat for longer than two hours in an acid marinade. "Any longer than that and the meat will have a kind of mealy stuff on the surface. The structured meat tissue becomes tiny protein particles, fine for a pate but not what you want in a steak."
Of course, once you give up trying to tenderize meat with a high-acid marinade, you can use low-acid marinades, let the meat soak for longer periods of time and avoid the problem, suggests an article in the current issue of Cook's Illustrated. A bath of olive oil, a small amount of balsamic vinegar, garlic and herbs took 24 hours to penetrate to the heart of two-inch beef cubes."