Marinading a pork shoulder overnight adds flavor, although most marinades don't tenderize meat much. Combine oil with a slightly acid ingredient, such as soy sauce, fruit juice or wine, and cover the meat with it. A few marinades, such as pineapple or papaya juice, contain enzymes that break down the meat. Don't use these types of marinades for more than an hour or two or you'll end up with mushy meat.

Refrigerate the marinating pork shoulder at 40 degrees Fahrenheit or cooler. Leaving marinating meat at room temperature allows bacteria to grow quickly and can cause food-borne illness. Throw away any leftover marinade or boil it before using it again. Cook the pork shoulder to at least 145 F, according to the U.S. Department of Agriculture, although most pork shoulders need to cook to 195 F to become fully tender.