This extremely important ingredient in Asian cooking is a dark, salty sauce made by fermenting boiled soybeans and roasted wheat or barley. Although there is essentially one main type of soy sauce widely made in the United States, China and Japan produce a number of varieties ranging in color from light to dark and in texture from thin to very thick. In general, light soy sauce is thinner and saltier than its dark counterpart. Its flavor and color is also lighter, and it may be used in dishes without darkening them. Dark soy sauce is slightly thicker than light soy sauce but generally not as salty. It has a richer flavor and color (which is usually darkened with caramel). Chinese black soy is extremely dark and thick, a result obtained from the addition of molasses. The Japanese tamari is very similiarthick, rich and extremely dark. Unless otherwise indicated on the label, soy sauce may be kept for many months in a cool, dark place. There are also many low-sodium or "lite" soy sauces available on the market. Soy sauce is used to flavor soups, sauces, marinades, meat, fish and vegetables, as well as for a table condiment.
From The Food Lover's Companion, Fourth edition by Sharon Tyler Herbst and Ron Herbst. Copyright © 2007, 2001, 1995, 1990 by Barron's Educational Series, Inc.