Japan’s soy sauce is officially divided into five main types.
The Japanese Agricultural Standard groups shōyu according to differences in ingredients and production method. The five recognized types are koikuchi, usukuchi, tamari, saishikomi, and shiro. They are not simply five levels of darkness; each has a distinct balance of soybeans, wheat, salt, fermentation, color, and flavor.
Koikuchi is the standard style and accounts for most domestic production. Usukuchi is lighter in color but often saltier, making it useful when cooks want to season food without darkening it. Tamari is richer and contains little or no wheat. Shiro is pale, sweet, and made mostly from wheat. Saishikomi is brewed using previously made soy sauce in place of ordinary brine, producing a darker, fuller flavor.
“Five” refers to the official Japanese classification, not every soy-sauce product sold in Japan. Regional styles, sweetened sauces, reduced-salt versions, and different quality grades also exist. This is why lists that count commercial varieties may be longer, while the standard classification still has five principal categories.