Izumi Family Residential Dried Bonito Flakes Manufacturing

The Izumi Family Katsuobushi Building: Four Rooms for Making Dried Bonito in Tosa

Behind a tiled house in the fishing town of Usa, in Kochi Prefecture, stands a long, low wooden shed of about 99 square meters. It does not look like much from the lane. Inside, though, the floor plan tells a precise story: four rooms set in sequence, each built for a single step in turning a fresh bonito into a block of katsuobushi hard enough to knock against the table.

This is the Izumi Family Residence Katsuobushi Production Building (Izumi-ke Jutaku Katsuobushi Seizojo). It dates from around 1947, and it is one of several structures of the Izumi family compound listed together as Registered Tangible Cultural Properties. The building sits on the south side of the plot, close to the harbor, its ridge running east to west.

Katsuobushi, dried and smoked skipjack tuna shaved into the flakes that flavor so much Japanese cooking, is rarely thought of as architecture. Here it is. The walls, rooms, and roof were shaped by the work, and the work is the reason the building survives.

A Floor Plan Built Around the Process

The structure measures roughly six and a half ken along its front and two and a half ken in depth, a single-story timber frame under a gabled roof of pantiles. The eastern end drops to a lower roofline, and along the north face a deep earthen-floored eave, about one and a half ken wide, is pulled out to serve as an open work area. Step inside and the four rooms appear in the order the fish moves through them.

The first is the boiling room, where the cleaned and filleted bonito is simmered until the flesh firms. Next comes the smoking room, where the fish is dried over a low wood fire, a stage repeated many times so the moisture leaves slowly and the surface darkens and hardens. Then the mold room, where a cultured mold is brushed onto the dried fillets to draw out the last of the moisture and deepen the flavor. The fourth room is for storage, where the finished blocks rest.

For the most fully cured grade, this cycle of mold and sun-drying is repeated over several months. The result keeps almost indefinitely, which is how a coastal town could send its catch far inland long before refrigeration. A building like this one held the whole sequence under a single roof, at the scale of a family enterprise rather than a factory.

Why It Was Registered, and Why Usa

The building was entered on the national register on November 8, 2004, with the gazette notice following on November 29 that year. Its registration number is 39-0165. The criterion under which it was listed is straightforward: it contributes to the historic landscape of the country. Registered Tangible Cultural Properties form a category created in 1996, distinct from the older designations of National Treasure and Important Cultural Property. Registration is a lighter form of protection, aimed especially at buildings from the modern era that give a place its character, and it leaves owners more freedom in daily use while encouraging preservation.

Usa earns that landscape value. The town is regarded as the birthplace of improved Tosa-bushi, the local style of katsuobushi, with refinements credited by tradition to a maker named Harimaya Kamezo roughly two centuries ago. Methods worked out here spread along the coast. By the 1950s, as catches fell, many producers closed or moved to Shizuoka and Kagoshima, and the number of makers in Usa thinned. Buildings purpose-made for the craft became scarce, which is part of what makes the Izumi compound worth keeping. In 2021 the production technique of Tosa-bushi itself was placed on the national register of intangible cultural properties, recognizing skills such as the local "Tosa cut" of the fish and the mold-application step.

Seeing It, and the Town Around It

The building is part of a private residence and is not open to visitors, so the way to appreciate it is from the public lane, as one element of the Usa streetscape it was registered to protect. The same compound includes the main house, rebuilt after the 1946 Nankai earthquake with rows of projecting "water-cutting" tiles on its gable walls, a detail typical of Tosa houses, and a small preparation room and drying yard tucked behind it. Read together, they show how a single household organized the work of drying fish.

Usa rewards a slower visit. Cross the Usa Ohashi bridge, opened in 1973 where a ferry once carried pilgrims, and the Yokonami Peninsula opens up, with the Yokonami Kuroshio Line tracing a ridge between the open Pacific to the south and the calm Uranouchi Bay to the north. Near the tip stands Shoryuji, the thirty-sixth temple of the Shikoku pilgrimage, founded by tradition by Kukai; its main hall, reached by 170 stone steps, holds a Kamakura-period seated Aizen Myoo carved in wood that is an Important Cultural Property. Back in town, working shops still sell Tosa-bushi, including the smoky, slice-able namabushi that is a Usa specialty, and a taste of it is the most direct way to understand what the Izumi building was made for.