katsuobushi

Katsuobushi is skipjack tuna that has been filleted, smoked, dried, and colonized by mold until it rings like wood when struck. The first element, katsuo (鰹), appears in the Man'yoshu, the eighth-century poetry anthology, as a prized coastal fish. The second element, bushi (節), means joint or node, describing the woody block the fish becomes after months of curing. The full compound katsuobushi entered written records in the Edo period, in cookbooks and merchant inventories from roughly the seventeenth century.

The technique of drying katsuo existed earlier in cruder forms. Dried fish called nikatsuwo (煮堅魚) appear in Nara-period tax records from 718 CE, listing preserved skipjack as tribute from coastal provinces. The smoking and mold-inoculation method that defines modern katsuobushi was developed in Tosa province, now Kochi prefecture, in the early Edo period. A merchant named Jintaro Matsumoto is credited in Kochi regional histories with refining the mold-ripening technique around 1680.

The mold is Aspergillus glaucus, also classified as Eurotium herbariorum in some taxonomies. It is inoculated deliberately, allowed to colonize the fish for two to three weeks, then scraped off and re-applied in multiple cycles over four to six months. Each cycle pulls more moisture out of the flesh and concentrates the glutamate and inosinate that give dashi its depth. The finished katsuobushi block can last for years without refrigeration.

Shaved into thin curls with a specialized plane called a katsuobushi-kezuriki, the dried fish dissolves in hot water within minutes to produce ichiban dashi, the primary stock of Japanese cuisine. Nineteenth-century trade records show katsuobushi moving from Tosa and the Izu Peninsula to Edo by sea freight in enormous quantities. Today Japan produces about twenty thousand tons annually, with industrial shaving replacing handwork in most commercial kitchens. Traditional makers in Makurazaki and Yaizu still maintain the centuries-old mold-inoculation process.