When Chris and I were first started visiting Japan together as The Japanese Pantry our minds were full of questions for the producers. As time went on we realized some were not relevant and others were, but also that there were things we did not know to ask. One question we learned to ask is: “How old are the barrels that you ferment and age in?” The Japanese cedar barrels are important not in imparting flavor but because of the beneficial bacteria that lives within them. Since it is porous wood, cedar has the ability to store some of that wonderful bacteria that helps flavor the moromi (soy sauce mash).
It’s not really the barrels that are important, it’s the beneficial bacteria that live in those barrels.
The role of the bacteria is so important to the character of the soy sauce that when a brewery buys a new barrel, the brewer will put moromi that has been aging in an old barrel into the new barrel. This inoculates the new barrel. Furthermore, the inside of an aging room at a traditional soy sauce brewery is similarly “alive” with beneficial bacteria. The local bacteria that make their home there are what gives that specific soy sauce its special character and is indeed part of the terroir of that brewery’s soy sauce. Keeping these bacteria intact and happy is so vital that when it comes time to rebuild a brewing room, soy sauce companies will carefully remove and then reuse not only the old cedar barrels but also the wood that lined inside of the old brewing room.
As we have learned over and over again, the underlying theme of Japanese food is really fermentation, which is powered by beneficial bacteria.