Usukuchi shoyu

What usukuchi is

Usukuchi shoyu is one of the five soy sauce categories that the Japanese Ministry of Agriculture, Forestry and Fisheries (MAFF) recognises: koikuchi, usukuchi, tamari, saishikomi and shiro. Its name means light mouth, and the word describes colour. A usukuchi soy sauce is paler than a koikuchi sauce, and in the Kansai region it is the standard light sauce used where a clear, pale liquid is wanted in the pan or on the plate.

The category is easy to misread. Usukuchi is not a low-salt version of koikuchi. Its paleness comes from how it is made. Nothing in the MAFF overview describes it as less salty. A cook who reaches for usukuchi to lower sodium is working from a false premise.

Why the colour is pale

MAFF attributes the lighter colour of usukuchi to production choices. The main one it names is a higher salt concentration in the brewing mash. Salt slows the fermentation and the ageing, so a more heavily salted mash darkens more slowly. The mash is the brewing stage in which the soybean and wheat are inoculated with koji and held in salt water while the flavour and colour develop. Because the brewing is slowed, less of the browning that gives koikuchi its depth forms before the sauce is pressed and finished.

MAFF also reports that amazake, a sweet fermented rice drink, may be added in making usukuchi, which gives a milder flavour. No quantity or stage of addition is given.

Where it sits among the soy sauces

The five categories differ by ingredients, salt content, length of ageing and other conditions, and MAFF notes that these together fix the colour and flavour. Koikuchi, the dark-coloured standard, is the common sauce across Japan. Tamari is a thick sauce with little or no wheat. Saishikomi is brewed in another fresh soy sauce rather than in brine, and shiro is the palest. Usukuchi sits between the common dark sauce and the white one in colour, but it is a regional style with its own identity rather than a point on a scale.

For a reader working through the Japanese sauces on this site, usukuchi is a separate subject from koikuchi. It is not a cabinet or process variant of the common sauce, and a page that treats it as one will mislead about why it is pale.

Method

Usukuchi follows the same basic route as other Japanese soy sauce: a koji stage made from soybeans and roasted wheat, then a salt-water mash that ferments and matures in a tank, then pressing and filtering. Makers change three things to keep the colour light: a higher salt concentration, a shorter fermentation, and in some versions the addition of amazake, which lightens the colour and adds sweetness.

Reported salt figures are approximate. One brewer gives 13.8 percent for a light sauce, and traditional versions are described at about 19 percent. A patent for light-coloured seasoning liquor describes fermentation in a salt solution of about 23 percent at 15 to 30 degrees Celsius. The figures differ by product, so no single salt level is given here as the usukuchi standard.

Open points

The sources read do not give a home method, batch masses, moromi temperature or a mould-stage endpoint, so the steps describe production in outline only. Producers' salt and ageing figures should be checked against a brewer's technical documentation before any figure is used for a product.