Through the collaborative efforts of the microorganisms inhabiting the wooden barrels and the skilled brewers, tamari soy sauce undergoes natural fermentation and maturation of soybeans.  This traditional method, once commonplace, now accounts for only 1% of the total domestic soy sauce production. We may be a minority, but we value the flavor that can only be achieved through wooden barrel fermentation, and we steadfastly adhere to traditional production methods.

This river has contributed to the local culture through fishing, sake brewing, as well as the production of traditional items like Japanese washi paper and lanterns. It has also been cherished dearly by people in the community. Our tamari soy sauce is one of the cultural treasures nurtured by the community and blessed by the river's bounty.

At Yamakawa Brewery, we ferment and age our tamari soy sauce for over two years in our own brewery. During this period, we perform the 'kumikake' process, wherein we repeatedly pour accumulated brine on the top of the mash. The mash is compressed using heavy stones. This process ensures even circulation so it is fermented evenly. This process is an important element for our tamari to obtain its luster and flavor that define its character. We believe the dedicated time and effort play a key role for its distinctive delicious taste. 

We have always welcomed OEM production of clients' soy sauce-based processed condiments such as dashi and ponzu. Since the time of our predecessors, we have been working together with local restaurants to make their original products. We are proud to offer small-scale production, starting from a minimum of 30 liters, which is uncommon in the industry.

For our brewery, wooden barrels are indispensable elements in crafting our tamari soy sauce. In the mid-1990s, we experimented once by fermenting tamari soy sauce and miso in a plastic tank. Despite using the same ingredients and traditional methods, the resulting product lacked the depth in flavor and aroma that we were expecting. 

In 2019, we purchased a new wooden barrel through the Kioke Revival Project in order to commit ourselves to passing down the tradition of brewing barrel-aged tamari from the past generations to my daughter. With this commitment in mind, we continue to make barrel-aged tamari soy sauce and soybean miso.