Makurazaki (Kagoshima) and Yaizu (Shizuoka) cities, Japan — primary katsuobushi production centres with centuries of tradition
Katsuobushi (dried, fermented, smoked bonito) production is one of the most complex food transformations in any culinary tradition — a six-month to two-year process that converts fresh skipjack tuna into a product so different from its origin that the connection seems impossible. The production process involves: filleting fresh katsuo into four lobes (honbushi) or in smaller sizes (kobushi), simmering the fillets briefly to firm the proteins, then smoking over hardwood (oak, cherry) in alternating smoke-and-rest cycles over several weeks to dry and infuse. The smoked product (arabushi) is already useable at this stage, providing the most robustly flavoured katsuobushi common in everyday dashi. The finest grade (karebushi or honkarebushi) undergoes additional inoculation with the mold Aspergillus glaucus (and related species), a deliberate fermentation step where the mold grows across the surface, is scraped off, and the process is repeated multiple times over months or years. The mold growth and repeated scraping draws residual fat and moisture from the fish, simultaneously contributing complex amino acids and breaking down proteins further — producing a final product with fat content reduced to almost zero, extraordinary depth of umami, and a woody hardness that requires specialist shaving tools. The resulting shavings dissolve almost completely in hot water, their flavour compounds transferring instantly into dashi. Quality grades from lowest to highest: hanakatsuo (soft-grade shavings for decoration), arabushi flakes, honkarebushi (aged mold-fermented).
Honkarebushi dashi has an extraordinary clean, deep savouriness — the flavour is simultaneously robust and delicate, with a specific smoky-marine quality and an umami resonance that persists long after swallowing. The complexity of the two-year production is directly perceptible in the dashi's flavour depth.
The mold fermentation cycle (for honkarebushi) must be carefully managed — excessive humidity causes unwanted bacterial growth, insufficient humidity slows the beneficial mold process. Each mold scraping session removes fat-laden outer layer, progressively purifying the fish's flavour. Wood choice for smoking affects the arabushi flavour profile — different regions use different hardwoods reflecting local tradition. Shaving angle on the katsuobushi plane (kezuriki) determines thickness and surface area of the shavings, which affects dashi extraction speed and character.
Buy whole honkarebushi and invest in a quality kezuriki (katsuobushi shaving box) — freshly shaved katsuobushi makes demonstrably superior dashi. The shavings should be almost transparent and curl naturally; proper thickness is approximately 0.1–0.2mm. For ichiban dashi (first dashi): add cold shavings to cold water, heat to 60°C (not boiling), hold for 3 minutes, then strain — this produces the clearest, most delicate dashi with the cleanest flavour. Arabushi shavings used in the same way but heated to near-boil and steeped 4–5 minutes produce a more assertive, smoky dashi suitable for heartier preparations.
Using pre-shaved katsuobushi beyond its use-by date — katsuobushi oxidises rapidly once shaved, and stale shavings produce flat, cardboard-flavoured dashi. For arabushi dashi: steeping too long (more than 3–4 minutes) extracts bitter compounds from the protein. For honkarebushi dashi: shaving too thin produces very rapid extraction, which can make the dashi overly intense.
The Japanese Culinary Academy's Complete Japanese Cuisine Series