Kōji-muro (Edo underground kōji chamber)

A production room beneath Edo

Kōji-muro were dedicated rooms for growing kōji, the mold culture used in sake, miso and other Japanese ferments. Excavations in Edo/Tokyo distinguish these production chambers from anagura, underground stores for goods or valuables. The Yotsuya I-chome excavation covered three town-house properties and found about 100 chambers grouped in 26 clusters. Its chronology begins in the Kan’ei era (1624–1645), peaks in the middle to later seventeenth century and ends there around the late seventeenth to early eighteenth century. These figures describe that excavation, not a citywide total.

The underground form was not universal across Japan. The Edo examples differed from above-ground earthen kōji rooms described in Itami. The chamber made a sheltered workspace, while limited ventilation could complicate the conditions needed for kōji cultivation.

Shaft, passage and chamber

Archaeologist Hiroshi Koizumi describes a common arrangement: a vertical shaft descended several metres into the Kantō loam, then a short horizontal passage opened into a larger room. Shaft profiles varied; some had step-like footholds. Passages were exceptionally low and narrow, and the main rooms were also low enough that an adult would work bent over. The chamber plan could be square or trapezoidal, and its ceiling could curve into a barrel-like cross-section. Some walls carried small holes thought to have held crosspieces.

These are generalized observations across excavated examples, not a complete specification. Not every chamber had the same shaft, chamber shape or connections. The cutaway shows only the recurring relationship between ground level, shaft, passage and low room; it is not a measured reconstruction of one Yotsuya chamber.

A later room at Kanda

Amanoya near Kanda Myōjin offers a separate later example with a different documented history. A 2018 Ministry profile records its process. Japan’s Ministry of Agriculture, Forestry and Fisheries reports that the business began in 1846 and that rice kōji is made in a room about six metres underground. The same article describes equal amounts of rice and rice kōji held at about 60°C for around ten hours to make its amazake. Those details belong to Amanoya’s reported process; they should not be projected onto the older Yotsuya archaeological chambers.

Kōji cultivation itself is a mold-growth stage. In kōji amazake, enzymes from kōji act on rice starch during a warm holding step. Linking the chamber to rice kōji and the rice-koji amazake preparation shows two documented uses while keeping the building distinct from the food made with it.

Sources and limits

The archaeological center’s Yotsuya booklet anchors the chamber count and chronology; Koizumi’s archaeological account describes the common shaft-and-room form and warns that ordinary storage holes are different. The MAFF profile documents Amanoya as a separate later example. The linked excavation photograph records exposed chamber remains during fieldwork; the generated cutaway is a source-guided explanation, not an excavation image or a measured reconstruction.