Although central South Carolina tends to enjoy a mustard-based sauce, the east Carolina style is all about vinegar. Now, mop sauce is a little bit different from barbecue sauce. People usually apply regular barbecue sauce shortly before serving. Mop sauce, however, is brushed onto the meat while it cooks -- like a baste -- sometimes with an actual mop head. Because this mop sauce is thin and acidic, it soaks into the meat while it cooks, adding a new level of flavor.
East Carolina mop sauce is basically just vinegar and hot sauce. It's best used on ribs or pulled pork. Because ribs are very fatty and sweet, the vinegar cuts the fat and enhances the taste of the rest of the meat. Some may also use it as a finishing sauce. People describe this sauce as tangy, spicy and peppery.