Take a walk down a Japanese grocery store, and you will certainly find shoyu brands like Kikkoman and Yamasa. Those are koikuchi, which is simply referred to as shoyu in Japan (though itfs better known to the Western counterparts as dark soy sauce).
An interesting history lesson here: Even though tamari was the first shoyu produced in Japan back in the 16th century (more about tamari, on p11), a new recipe for shoyu was created during the Edo period around 1700, by increasing the amount of wheat to match the amount of soybeans in its formula. This resulted in the birth of koikuchi, a robust flavoured shoyu with a pronounced aroma that was about to become a game-changer in the realm of soy sauce. With the rapid development of Edo and the industrialisation of manufacturing processes, coupled with the fact that a simple condiment is able to greatly enhance the flavours of non-expensive food items, koikuchi very quickly earned its reputation as an indispensable ingredient in Japanese cooking. Today, koikuchi makes up more than 80 percent of Japanese domestic soy sauce production and consumption.
Given its popularity and richly layered flavours, it comes as no surprise that koikuchi makes a great all-purpose seasoning, be it for dipping, marinading, or cooking.