Kochi Prefecture (historic Tosa Province), Shikoku; katsuobushi production tradition linked to fishing culture
Tosazu is a complex Japanese dressing made by infusing katsuobushi (dried bonito flakes) directly into a warm rice vinegar, soy sauce, and mirin mixture, then straining to produce a clear, amber-colored liquid with a unique layered flavor profile—the sharpness of rice vinegar softened by mirin's sweetness, deepened by kombu or soy umami, and given a distinctive smoky-oceanic note from the bonito infusion. The name 'Tosa' refers to the traditional katsuobushi-producing province of Kochi on Shikoku island. Tosazu is the foundation for both sunomono (vinegared salads) and dressed seafood preparations—it is milder and more complex than plain rice vinegar seasoning, functioning as a finishing sauce rather than a marinating acid. The technique: heat equal parts rice vinegar, soy sauce, and dashi to just below simmering, add a generous handful of katsuobushi, remove from heat, steep 5 minutes, then strain through muslin. The resulting tosazu can be stored refrigerated for weeks and diluted or used at full strength depending on application. Tosazu dresses tako (octopus) sunomono, wakame seaweed salads, and cold seafood appetizers. It can also be reduced slightly to create a syrupy glaze for grilled fish.
Mellow acid from rice vinegar; oceanic smoky depth from katsuobushi infusion; sweet-savory balance from mirin-soy
{"Katsuobushi infusion into vinegar mixture creates the characteristic Tosa-style depth","Equal parts rice vinegar, soy sauce, and dashi as the base before bonito infusion","Heat to just below boiling, add katsuobushi, steep and strain—never boil the bonito","Stores well refrigerated—can be made in advance and used across multiple preparations","Functions as a finishing sauce or dressing rather than a cooking acid—added after preparation is complete"}
{"A few seconds of kombu in the warming vinegar before bonito adds additional umami depth","Tosazu reduction: reduce by half for a glossy glaze for grilled salmon, yellowtail, or sea bream","Standard sunomono ratio: 3 parts tosazu to 1 part additional rice vinegar for milder dressing","Tako sunomono: lightly tenderized octopus with cucumber and tosazu is the canonical application"}
{"Boiling the katsuobushi infusion which creates harsh, bitter flavor compounds","Using low-quality packaged katsuobushi—the infused flavor reflects the bonito quality directly","Over-reducing which concentrates the salt and acid beyond usable dressing consistency","Adding too much salt before tasting—soy sauce already provides significant salinity"}
Shizuo Tsuji — Japanese Cooking: A Simple Art