Usukuchi shoyu is a variety of soy sauce which has a pale golden color and a mild flavor. In Japan, usukuchi is particularly popular in the Kansai region; it is also used in recipes from other parts of Japan. This more mild soy sauce is useful for delicate sauces, especially those which are designed to be pale in color, and some people enjoy it because the rich layered flavors of darker soy sauces are a bit too intense for them. Many Asian markets stock usukuchi shoyu, and it can also be found in the Asian foods aisle at your local grocer if you live in a reasonably large area.
Like other forms of soy sauce, known in Japan as shoyu, usukuchi shoyu is made by fermenting soy beans with salt. In addition to soy beans, usukuchi also calls for lightly toasted wheat, which helps keep the flavor mild, and mirin, a sweet liquid made from fermented rice. Usukuchi shoyu is typically fermented for a relatively brief period of time, which prevents it from developing an overwhelming flavor.
Although usukuchi is less strongly fermented, it does tend to be more salty than other types of soy sauce. This trait can make usukuchi shoyu a bit challenging for cooks; as a general rule, cooks should add soy sauce to their food, allow the food to rest, and then see how salty it tastes. Salty flavors can develop or mellow after the soy sauce has been mixed with the food for a few minutes, and it is better to be patient than bitterly salty.
You may sometimes see usukuchi labeled as “light” soy sauce. In Western terms, “light” typically conveys the idea of a more healthy product, but in Asia, the “light” is simply a reference to the color, not to the fat content. Good usukucki shoyu varies in tone, but it tends to be pale yellow to amber in color. There may also be a small amount of sediment at the bottom of the bottle, which is not a cause for concern.
Like other soy sauces, usukuchi keeps best when kept out of bright light and temperature extremes. Some people like to refrigerate their shoyu, and while this is not strictly necessary, it can be a good way to keep it shelf stable. When using shoyu in cooking, pour a small amount into a dish and pour it from the dish into the pan; you do not want steam entering the soy sauce bottle as you sprinkle it over cooking food, as this can contaminate it.