Soy sauce, the pivotal seasoning of Chinese cooking, can be broken down into two broad categories, light and dark. This does not refer to the color of the liquid, but to its thickness. Dark soy sauce contains molasses, making it more viscous than light soy sauce. To see if a soy sauce is light or dark, shake the bottle and watch the sauce drain down the neck of the bottle. A light soy sauce will leave the glass clean almost immediately; a dark sauce will cling longer.
Pearl River Bridge-brand soy sauce, made in China, is widely available at Asian supermarkets. Pearl’s Superior Soy Sauce is a light version; Pearl’s Mushroom Soy Sauce is the dark version. A 21- to 22-ounce bottle of either costs less than $2. Kikkoman soy sauce, the most widely available supermarket brand of soy sauce, is brewed in the Japanese style, which is lighter in texture and sweeter than Chinese soy sauce and is not appropriate for Chinese stir-frying.