Buddhist monks introduced soy sauce into Japan in the 7th century, where it is known as "shoyu". The Japanese word "tamari" is derived from the verb "tamaru" that signifies "to accumulate", referring to the fact that tamari was traditionally from the liquid byproduct produced during the fermentation of miso. Japan is the leading producer of tamari. Japanese soy sauce or sho-yu (????, or ??), is traditionally divided into 5 main categories depending on differences in their ingredients and method of production. Most but not all Japanese soy sauces include wheat as a primary ingredient, which tends to give them a slightly sweeter taste than their Chinese counterparts. They also tend towards an alcoholic sherry-like flavor, due to the addition of alcohol in the product. Not all soy sauces are interchangeable. Koikuchi (???, "strong flavor") Originating in the Kanto region, its usage eventually spread all over Japan. Over 80% of the Japanese domestic soy sauce production is of koikuchi, and can be considered the typical Japanese soy sauce. It is produced from roughly equal quantities of soybean and wheat. This variety is also called kijoyu (???) or namashoyu (?????) when it is not pasteurized. Usukuchi (???, "light flavor") Particularly popular in the Kansai region of Japan, it is both saltier and lighter in color than koikuchi. The lighter color arises from the usage of amazake, a sweet liquid made from fermented rice, that is used in its production. Tamari (????) Produced mainly in the Chubu region of Japan, tamari is darker in appearance and richer in flavour than koikuchi. It contains little or no wheat; wheat-free tamari is popular among people eating a wheat free diet. It is the "original" Japanese soy sauce, as its recipe is closest to the soy sauce originally introduced to Japan from China. Technically, this variety is known as miso-damari (????), as this is the liquid that runs off miso as it matures. Shiro (??, "white") A very light colored soy sauce. In contrast to "tamari" soy sauce, "shiro" soy sauce uses mostly wheat and very little soybean, lending it a light appearance and sweet taste. It is more commonly used in the Kansai region to highlight the appearances of food, for example sashimi. Saishikomi (????, "twice-brewed") This variety substitutes previously-made koikuchi for the brine normally used in the process. Consequently, it is much darker and more strongly flavored. This type is also known as kanro shoyu (????) or "sweet shoyu". Shoyu (koikuchi) and light colored shoyu (usukuchi) as sold in Japan by Kikkoman, 1 litre bottles.Newer varieties of Japanese soy sauce include: Gen'en (???, "reduced salt") Low-salt soy sauces also exist, but are not considered to be a separate variety of soy sauce, since the reduction in salt content is a process performed outside of the standard manufacture of soy sauce. Amakuchi (???, "sweet flavor") Called "Hawaiian soy sauce" in those few parts of the US familiar with it, this is a variant of "koikuchi" soy sauce. All of these varieties are sold in the marketplace in three different grades according to how they were produced: Honjozo hoshiki (??? ???) Contains 100% naturally fermented product. Shinshiki hoshiki (?? ???) Contains 30-50% naturally fermented product. Tennen jozo (?? ???) Means no added ingredients except alcohol. All the varieties and grades may be sold according to three official levels of quality: Hyojun (???) Standard pasteurized. Tokkyu (???) Special quality, not pasteurized. Tokusen (???) Premium quality, usually implies limited quantity. Other terms unrelated to the three official levels of quality: Hatsuakane (???) Refers to industrial grade used for flavoring, powder. Chotokusen (????) Used by marketers to imply the best.