'Soy sauce, also commonly known as shoyu, is the best known flavor enhancer in Asian cooking. Made the old-fashioned way — through a careful fermentation process that can take as long as 18 months — it’s a healthy and nourishing product.
The best quality soy sauce is not only fermented in a traditional manner but also unpasteurized to retain beneficial enzymes and nutritional cofactors.
Tamari is a variant that is made only with soybeans (without any wheat). As far as I know, all the brands of tamari and most brands of shoyu sold in health food stores have been pasteurized. Though not optimal, these are far superior to the commercial soy sauces sold in supermarkets and used by the restaurant industry.'