Mizuhosu (Onishi Family Residence) Former Koji Room and Earthen Wall

What the Mizuhosu (Onishi Family Residence) Former Koji Room and Earthen Wall Are

The Mizuhosu (Onishi Family Residence) Former Koji Room and Earthen Wall (瑞穂酢（大西家住宅）旧麹室及び築地塀, kyū kōjimuro oyobi tsuijibei) are an early Taisho-era (1912 to 1918) koji room and roofed earthen wall in Nakamachi, Kashihara City, Nara Prefecture, entered on the register of Registered Tangible Cultural Property on 27 February 2023. The koji room stands on the west side of the Onishi vinegar works, south of the South Storehouse, on a base of hexagonal cut stone, with its ridge running east to west. It covers 28 square metres. The wall, 17 metres long in total, encloses an empty plot lying in the kimon, the direction traditionally regarded as unlucky.

Koji is steamed rice inoculated with the mould that turns starch into sugar, the first ingredient of sake and therefore of rice vinegar. Mizuho Co., Ltd. puts koji making at the very start of its process, saying good sake begins with good koji. This building is where that starting point was once managed. It was repaired in the mid-Showa era.

Why It Was Listed

The Former Koji Room and Earthen Wall were registered for their contribution to the historic landscape. The Agency for Cultural Affairs places them among the vinegar production buildings on the west side of the estate.

Outside, the koji room is a single-storey Dozo-zukuri store with a gabled pantile roof, Kirizuma-zukuri with Sangawara-buki, and lean-tos, Geya, on the north and west. The real interest is inside: a wooden koji chamber is built within the earthen shell like a box within a box. The thick walls buffer the outside air, and the timber room inside holds warmth and moisture, a double enclosure for growing the mould.

The earthen wall surrounds a plot left open because it lies in the kimon direction. It shows the idea of keeping buildings out of the kimon direction carried into the layout of a working brewery.

What to Look For

The most unusual feature of the Mizuhosu (Onishi Family Residence) Former Koji Room and Earthen Wall is that nested construction. From outside it looks like any small earthen store, yet inside sits a board-lined chamber designed to keep in the heat that koji gives off as it grows.

Look at the plinth too. The stones are cut to near-hexagonal shapes and fitted together, a pattern known as kikkō, or tortoiseshell, masonry. The rice storehouse to the south stands on a different stone wall along an old property line, so two kinds of stonework survive on one estate.

The wall runs 17 metres in total. Built to enclose an empty plot, it is registered together with the koji room as a single listing.

Visiting

The Mizuhosu (Onishi Family Residence) Former Koji Room and Earthen Wall lie deep within the brewery grounds, and the interior is closed (checked 17 September 2026). No opportunity to see the wooden koji chamber has been announced.

Being south of the South Storehouse at the back of the site, the building is screened by the stores in front of it and cannot be seen from the north street. The walled plot is also inside the enclosure. If you hope to visit, check with the owning company.