One of the realities of meat cookery is that only a few parts of most animals, such as the loin and tenderloin, are naturally tender. The others need varying degrees of help, and techniques for making tough cuts into satisfying meals are among the most treasured cooking secrets. For example, acidic liquids such as wine, buttermilk and even coffee can be used to help tenderize pork and other roasts.
There are many ways to tenderize your meats, from pounding cutlets with a mallet to marinades and commercial powdered tenderizers. All have the same goal, which is to relax or cut the tough muscle fibers. Mechanical tenderizers and meat mallets cut the fibers physically. Commercial tenderizers contain enzymes that break down the proteins, while acidic liquids weaken the bonds between the fibers. It's unclear whether coffee is a tenderizer because of its acidity or because of its enzymes, but many cooks swear to its effectiveness.
Large cuts such as roasts are too thick to tenderize mechanically, and both enzyme tenderizers and marinades tend to make the surface unpleasantly soft without doing anything for the middle. You can get around that by using a marinade injector, essentially a giant syringe for pumping coffee or other marinades directly into the middle of the roast. That's not usually necessary with pork roasts. Aside from the loin, most pork roasts are well-marbled and have lots of collagen. If cooked correctly they'll become tender on their own, but coffee can definitely play a role.
Pork shoulder and leg roasts are the toughest portions of the hog, and they'll benefit most from slow cooking. Use the finest grind of coffee as part of a dry rub for slow-roasting, where its dark and earthy flavor will complement the other sweet and spicy flavors. Apply the rub and let it rest overnight, so the flavors can infuse and the coffee's modest tenderizing powers can take effect. Then slow cook the roast at low temperature until it's tender. Alternatively, soak the roast in strong, black coffee overnight and then braise it slowly in coffee in your oven or slow cooker. Either way it will become a rich and tender "pot roast," suitable for slicing or shredding.
You can also use coffee on pork loin and tenderloin roasts, which don't need tenderizing but can still benefit from the flavor. They're best when cooked quickly at higher temperatures, because they're lean and will dry out if cooked too long. Apply the coffee-based dry rub overnight for a loin roast or for three to four hours for the smaller tenderloins. Start a loin roast at 450 degrees Fahrenheit until it's well browned, then reduce the temperature to 325 F and cook it until a meat thermometer in the thickest section reads 135 to 140 F. Let it rest for 20 minutes, until the temperature reaches a food safe temperature of 145 F or higher. Tenderloins can be cooked completely at the higher temperature.