On Shōdoshima (literally the “island of small beans”), famous for its soy sauce and olive trees, nearly twenty producers still use traditional kioke, wooden barrels, for soy sauce fermentation. These barrels are handmade with cedar and bamboo: Boards are nailed together and tied up with several circles of interwoven bamboo. Kioke have a diameter of roughly 2.6 meters and are 2.3 m tall.
Soy sauce is a crucial ingredient in Japanese cuisine, used to season vegetables, meats and fish. Its importance comes from the flavor that it imparts to dishes and from its nutritional value. The traditional soy sauce making process is long and complex despite the fact that the ingredients are common and simple (soy, wheat, salt, and water). Locally-grown soybeans are soaked in water for several hours and then steamed. After being stewed, they are placed on a bamboo plate and left to rest outside for 3 days, during which time the first fermentation begins. As soon as they start to become moldy, the soybeans are rinsed in salt water, dried, and mixed with roasted, cracked wheat. The ingredients are then mixed and pressed to obtain a sort of paste that is placed in wooden barrels to ferment. After fermenting for around one year, during which the product is carefully monitored, the paste is spread on fabric and then covered and pressed to squeeze out the soy sauce. Some say that the main ingredient for this soy sauce is the kioke, since the wood it is made of contains a number of yeasts and microorganisms that contribute to fermentation and add complexity to the final flavor.
After the Second World War, Japanese fermented food producers were pushed to stop using wooden tools and to opt for stainless steel tanks instead. The presence of kioke soy sauce on the market is very low, and it gets lower every year due to the small number of remaining producers and carpenters that can make new barrels and maintain them. As a matter of fact, this traditional job is now being promoted, in an attempt not to lose all the knowledge regarding fermented food, which is something very important in Japan.