Buddhist monks from China introduced soy sauce into Japan in the 7th century, where it is known as shōyu (醤油 shōyu).
Shōyu is traditionally divided into five 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 flavour, sometimes enhanced by the addition of small amounts of alcohol as a natural preservative. The widely varying flavours of these soy sauces are not always interchangeable, some recipes only call for one type or the other, much like a white wine cannot replace a red’s flavour or beef stock does not make the same results as fish stock.
Some soy sauces made in the Japanese way or styled after them contain about fifty percent wheat. Varieties such as:
- Koikuchi – Originating in the Kantō 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 made from roughly equal quantities of soybean and wheat. This variety is also called kijōyu (生醤油) or namashōyu (生しょうゆ) when it is not pasteurized.
- Usukuchi – Particularly popular in the Kansai region of Japan, it is both saltier and lighter in colour than koikuchi. The lighter colour arises from the use of amazake, a sweet liquid made from fermented rice, that is used in its production.
- Tamari – Made mainly in the Chūbu region of Japan, tamari is darker in appearance and richer in flavour than koikuchi. It contains little or no wheat. Wheat-free tamari can be used by people with gluten intolerance. 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 (味噌溜り), as this is the liquid that runs off miso as it matures. The Japanese word tamari is derived from the verb tamaru (溜る) that signifies “to accumulate”, referring to the fact that tamari was traditionally a liquid byproduct made during the fermentation of miso (type of seasoning). Japan is the leading producer of tamari.
- Shiro – 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 – This variety substitutes previously made koikuchi for the brine normally used in the process. Consequently, it is much darker and more strongly flavoured. This type is also known as kanro shōyu (甘露醤油) or “sweet shōyu”.
Newer varieties of Japanese soy sauce include:
- Gen’en – This version contains 50% less salt than regular shōyu for consumers concerned about heart disease.
- Usujio – This version contains 20% less salt than regular shōyu.
All of these varieties are sold in the marketplace in three different grades according to how they were made:
- Honjōzō – Contains 100% genuine fermented product
- Kongō-jōzō – Contains genuine fermented shōyu mash mixed with 30–50% of chemical or enzymatic hydrolysate of plant protein
- Kongō – Contains Honjōzō or Kongō-jōzō shōyu mixed with 30–50% of chemical or enzymatic hydrolysate of plant protein
All the varieties and grades may be sold according to three official levels of quality:
- Hyōjun – Standard grade, contains more than 1.2% total nitrogen
- Jōkyū – Upper grade, contains more than 1.35% of total nitrogen
- Tokkyū – Special grade, contains more than 1.5% of total nitrogen
Soy sauce is also commonly known as shoyu, and less commonly shōyu, in Hawaii and Brazil.