Tough cuts of meat can be tenderized in any number of ways. Butcher shops typically use mechanical "jackard" tenderizers, which perforate the meat and cut the tough muscle strands into short, manageable lengths. Home cooks more often rely on powdered meat tenderizers, which use enzymes to soften the meat. If you don't have ready access to either of those common tools, there are still a number of ways you can make a tough piece of meat tenderer.
The simplest way to tenderize a tough cut is to pound it thinner. The muscle fibers in tough cuts of meat are denser than those in tender cuts and have stronger bonds holding them together. When you pound the cut, you physically sever the bonds between muscle fibers. The effect is strongest if you have an actual meat mallet, with its flesh-tearing diamond-shaped points, but any blunt object will do.
For example, you might wrap a rolling pin in plastic wrap to keep it from direct contact with the raw meat and use its side to pummel the tough cut. Even a regular hammer from the toolbox works, provided you wrap it carefully to keep the hammer and meat from contaminating each other.
Pound the entire surface of a steak or chop with your blunt object, then use the tip of a sharp knife to sever any long seams of fat or connective tissue in several places. For very tough cuts, pound them into cutlets of 1/4 inch thickness or less. This can almost double their size, so you might opt to cut each portion into two pieces.
Cooks are often advised to tenderize tough cuts of meat by marinating them. Traditional-style marinades are usually based on acidic ingredients, including wine, citrus juices and even Coca-Cola. Asian cooks sometimes use tea, which adds flavor as its tannins break down the bonds within the muscles.
These marinades do little to tenderize tough meats, in real-world terms, but other marinades do in fact offer a verifiable tenderizing effect. Mildly acidic dairy products such as buttermilk and yogurt definitely help, for reasons that aren't clearly understood. So do marinades made from crushed or juiced tropical fruits such as pineapple, mango, papaya and kiwi, which contain the very enzymes that are used in powdered meat tenderizers.
Marinades act only on the portion of the meat they contact directly, usually the surface. You can magnify their effect by pounding the meat first, creating tears in the surface that allow the marinade to penetrate.
Use this technique carefully with fruit-based marinades. If you leave them too much time to work, they can give the meat an unpleasantly mushy texture.
Another way to make tough cuts palatable is by slicing them thinly, across the grain. This is exactly the technique that's used with London broil, Korean kalbi and other dishes using tough, fibrous cuts. Slicing the meat to 1/4 inch or less shortens the tough muscle fibers and makes them easier to chew. Even a beef heart, one of the toughest cuts of all, can be quickly seared or stir-fried if it's first sliced wafer-thin.
When all else fails, any tough cut can be tamed by cooking. Long, slow cooking eventually softens the tough muscle fibers in any cut and melts its fat and connective tissues. The end result is mouthwateringly lush, rich and rich and flavorful -- think of pot roast or pulled pork -- and tender enough to cut with a fork. The classic technique, called braising, browns the meat first to develop its flavors and then simmers it slowly in a flavorful liquid.