Many recipes for long-cooking grilled meats, like ribs and the smoked chicken halves recipe from Fine Cooking #117, call for a mop as well as a barbecue sauce. Here is the difference between the two.
Mop A thin liquid that is generously and repeatedly brushed (or “mopped”) onto meat as it grills to keep it moist. Using a mop tool like the one shown above is ideal because it holds a lot of liquid, but you can also use a basting brush. The liquid is often beer, or juice, and vinegar based—the vinegar’s acid penetrates the meat, adding flavor. Since the mop is used while the meat is still raw or undercooked, it shouldn’t be applied toward the end of cooking, and leftovers should be thrown away.
Barbecue Sauce A thick glazing liquid that’s brushed onto grilled food when it’s almost done. Barbecue sauce is a flavorful mixture of salty, sweet, sour, and spicy ingredients cooked down until nicely balanced and thick enough to coat the meat. Sugar (or another sweet element) is what gives the sauce its shiny glaze, but sugar burns easily; a light char will caramelize the flavors, but left too long on the heat, the sauce will burn, so it’s added only in the last minutes of grilling. (Check out the Apple-Bacon Barbecued Ribs recipe shown)