A concentrated dark brown sauce with a slightly sweet, smoky flavor, oyster sauce is made from dried oysters, salt and water, with cornstarch and caramel added for consistency and color. The sauce originated in southern China, where cooks use it as a seasoning, drizzling it over simply cooked vegetables or mixing it into a meat and vegetable stir-fry. Oyster sauce also can be served as a dipping sauce for roasted meats. Avoid the least expensive products, as they lack a rich oyster flavor. Once opened, oyster sauce should be stored in the refrigerator.