Ishigami Sake Brewery Koji Room

A Stone Chamber for Growing Koji, Hidden Inside a Shed

The Ishigami Sake Brewery Koji Room (石上酒造麹室, Ishigami Shuzō Kōjimuro) is a Kojimuro, a room for cultivating koji mold, built around 1896 on the grounds of Ishigami Sake Brewery in Tanaka-cho, Choshi City, Chiba Prefecture, and registered as a Registered Tangible Cultural Property on 27 March 2018 under number 12-249. Of the brewery's five registered buildings, it carries the earliest date in the Agency for Cultural Affairs database.

Koji is the mold, Aspergillus oryzae, that turns the starch in steamed rice into sugars the yeast can ferment; no sake gets made without it. The Ishigami Sake Brewery Koji Room stands toward the south of the plot, west of the rice storehouse. The Agency lists it as a single-storey stone building with a metal roof and 42 square meters of floor area. Choshi City dates it to around 1896 by comparing it with the other Ōya-stone buildings on the site and from oral accounts.

Stone, Cedar and Rice Husks: How the Ishigami Sake Brewery Koji Room Holds Its Heat

The walls are Ōya stone masonry, blocks 30 centimeters thick laid lengthwise. According to Choshi City, this stone chamber is itself enclosed by a single-storey timber shed with a gabled, corrugated-iron roof, so what you see from outside is the shed, and the koji room proper sits within it.

Inside the stone, the Ishigami Sake Brewery Koji Room is lined throughout with cedar boards, and the gap between boards and stone is packed with rice husks for insulation. Straw is laid over the ceiling boards as well. Koji needs warmth and steady humidity for the two days or so it takes to grow, and every layer here, from shed to stone to husk to cedar, serves that purpose.

Choshi Jikan, a local heritage guide, notes that stone-walled koji rooms like this one are rarely seen in breweries today.

The Only One of the Five Registered as a Model of Form

Of the five Ishigami Sake Brewery buildings, only the Ishigami Sake Brewery Koji Room was registered under the criterion of being a model of form; the other four were registered for their contribution to the historic landscape. The Agency calls it a good example of the koji room that no brewery can do without. The Agency's description spells out the build layer by layer, from the way the stone is laid to the cedar lining, the husks and the straw over the ceiling, which suggests the value lies in a Meiji method surviving intact down to its insulation.

Seeing the Ishigami Sake Brewery Koji Room

The Ishigami Sake Brewery Koji Room is one of the most hygiene-sensitive spaces in any brewery, and its interior is not open to the public. Visits to Ishigami Sake Brewery are by reservation, so ask the brewery when you book how much of the site the tour covers and whether photography is allowed. From outside, what you can see is the timber shed; the stone walls are inside it.