Some cuts of meat are more tender than others. That's just a culinary and biological fact.
If you like tender meat (and who doesn't?), there are a few things you can do. The most straightforward are to buy tender cuts of meat and prepare them properly. In general, this means not overcooking them.
Or you can learn how to tenderize cuts of meat that would otherwise be tough. There are exactly three ways to do this.
Which one to use depends on what type of meat it is, and why it's tough in the first place.
What Makes Tough Meat Tough?
In general, exercise toughens muscles, whether it's your muscles or an animal's. And meat is a muscle. So the more exercise a muscle gets, the tougher the meat will be.
That means that in the case of a steer, the big muscles around the leg and shoulder, which are used for locomotion and supporting the animal's weight, are tougher.
Muscles high up along the back and ribs get less exercise, so they're more tender. This is where the expression "high on the hog" comes from, but it applies equally to beef, lamb, and veal (although lamb and veal are pretty tender all over).
Muscles also toughen with age, so the younger an animal is, the more tender its meat will be.
Finally, overcooking meat can cause it to become tough. That's because heat causes the proteins in the meat to become firmer.
It also basically squeezes the juices out of it, and dry meat is tough meat.
What Makes Meat Chewy?
Chewiness isn't exactly the same as toughness — although tough meat is certainly chewy. Chewiness is related to connective tissue, and the length of the muscle fibers.
Connective tissue can mean thick pieces of gristle in between muscles, or it can mean the sheets of fibrous collagen that surround muscle fibers.
Either way, connective tissue is chewy. You need to deal with it somehow.
Finally, not all muscles have the same structure. Within a muscle, the muscle fibers are grouped together in bundles. Some bundles have more fibers in them than others, which causes the grain of the meat to be more coarse. Long, thick muscle fibers will be tougher to chew.
Cooking Meat Can Make it Tender
There are three ways to tenderize a tough piece of meat. The first way is to cook it.
Meat that's high in connective tissue can be tenderized by cooking it until the collagen melts away, which starts to happen when it's heated to between 160° and 200°F. And when it melts, it turns into gelatin.
This doesn't happen right away. It can take hours. Tenderizing in this manner will require patience.
But your patience will be rewarded. Gelatin is soft and moist, and it coats and surrounds the muscle fibers, giving the meat a moist, succulent texture — even though it's been cooked well-done.
One of the main techniques for accomplishing this is braising, which is a moist-heat cooking technique where the meat is immersed at least partially in some sort of liquid which is then maintained at a gentle simmer for a period of time sufficient to break down the collagen.
Another method is a traditional barbecue, which basically involves heating the air around the meat to about 225°F and letting it cook for a long time, sometimes 8 hours or more. And it doesn't have to be plain air — sometimes it's smoke, which adds flavor.
Either way, melting the collagen in meat is a great way to tenderize it.
Pound It With a Meat Mallet
Another way to deal with the collagen is to break it up by force. There are a number of fancy machines and tools to do this, but the most basic way is with a meat mallet.
Meat mallets usually have two surfaces — a flat side and a side with a lot of pointy bits on it.
Pounding a steak with the pointy side of the mallet will cut up the connective tissues as well as the muscle fibers themselves. This allows a steak with a lot of connective tissue to be cooked over high heat without being too tough to eat.
Steaks tenderized like this are sometimes called cube steaks, because the indentations created by the mallet are shaped like cubes.
Pounding also has the advantage of flattening the meat, which allows it to cook more quickly. The longer a steak spends over the heat, the drier it gets. And since dry meat is tougher, preserving the juices will produce a more tender steak. (This also works with chicken cutlets, like for making chicken piccata.)
Slice It Thinly Against the Grain
Finally, there's slicing — specifically, slicing thinly and against the grain.
We talked about those muscle bundles earlier. Flank steak happens to have very long muscle fibers, and they run the length of the steak.
You could cook a flank steak perfectly medium rare, but if you sliced it along the grain, it would feel like you were chewing a mouthful of rubber bands.
Slicing against the grain shortens those fibers, which means much less work for your jaws and teeth to do.
But Wait. What About Marinating?
You may have noticed that I haven't mentioned marinating. One of the most common misconceptions out there is that you can tenderize a piece of meat by marinating it. However, this simply isn't so. Although it's a great technique for imparting flavor, marinating does not tenderize meat.