Sour cream is light cream deliberately soured by lactic-acid bacteria into a thick, glossy, spoonable cream with a clean tang. The culturing does double duty: it thickens the cream to a soft, scoopable body and turns the milk sugar into the lactic acid that gives the fresh, gentle sourness. It is the cooling counterweight of the table — dolloped on tacos, baked potatoes and borscht, swirled into dips and stroganoff, and folded into batters and doughs for a tender, moist crumb.