Tosazu Tosa Province Vinegar Katsuobushi Infused Dressing

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