The South Carolina barbecue sandwich is the one place in the whole barbecue belt where the sauce is yellow, and that color is the entire identity. The pork shoulder is smoked and pulled the way it is everywhere, but it is dressed in a mustard-based sauce, the bright gold dressing usually called Carolina Gold, built on prepared yellow mustard, vinegar, and sugar rather than on tomato or a thin clear vinegar dip. This is not a tomato sauce with a mustard accent and it is not the near-clear pepper-vinegar of the eastern coast. It is mustard first, and the sandwich is constructed so a sharp, tangy mustard dressing can be the dominant flavor instead of a footnote to the smoke.
The craft is in matching the meat to a sauce that behaves unlike the red ones. Shoulder is used because its fat and collagen survive a long, low wood smoke and finish as the texture of the meat rather than rendering to string. The pull is left uneven, dark bark through soft smoke-saturated interior, so each bite carries both chew and give. The mustard sauce is then tossed through the warm meat rather than poured over it: it is thinner and more acidic than a Kansas City glaze, so it seasons from inside the pile and its vinegar-and-mustard tang cuts the pork's fat the way tomato sweetness never does. The bun is plain, soft, and faintly sweet, chosen to vanish and to soak the loose gold dressing without going to paste, and a scoop of cool slaw on top supplies the crunch and the further acid that a pile of soft, rich, mustard-slicked pork has none of on its own.
The variations stay inside the mustard lineage. A hotter build works pepper into the gold sauce; a sweeter one leans on the sugar until it edges toward a glaze; a hash-and-rice plate runs the same mustard-sauced pork off the bun entirely as the state's other signature service. The wider barbecue map runs other arguments, the eastern whole hog and thin vinegar, the Lexington shoulder and red dip, the Texas brisket and the Kansas City glaze, and each of those regional readings deserves its own article rather than being crowded in here.