Kochi (Tosa) Prefecture — named for the katsuobushi capital of Japan
Tosazu (土佐酢) is a refined Japanese vinegar dressing made by simmering katsuobushi (bonito flakes) in rice vinegar with mirin and soy sauce, then straining. Named after Tosa (Kochi Prefecture), historically famous for its katsuobushi production. Tosazu combines the brightness of rice vinegar with the deep umami of katsuobushi, creating a more complex, rounded acid dressing than plain sanbaizu. Used for sunomono, as a marinade for thin-sliced white fish (Tosa-style), and as a dipping sauce for cold tofu. The tosa technique of applying lightly to white fish then serving after brief marination is called 'Tosa-ae' and is a distinctive Kochi preparation.
Bright rice vinegar acid with round bonito umami depth — more complex than plain sanbaizu
{"Tosazu ratio: 100ml rice vinegar + 2 tbsp mirin + 1 tbsp soy + 5g katsuobushi","Simmer briefly (not boil) — boiling makes katsuobushi bitter","Steep 5 minutes off heat, then strain through cheesecloth","Resulting dressing: more complex and rounded than plain sanbaizu","Kochi connection: Tosa region is Japan's bonito (katsuo) cultural heartland","Applications: sunomono dressing, fish marinade, cold tofu, octopus salad"}
{"Premium tosazu: use katsuobushi + sababushi blend for extra depth","Cold-infuse version: katsuobushi in cold rice vinegar overnight, no heat required","Tosa-ae white fish: score thin flounder sheets, marinate 5 minutes in tosazu — delicate, elegant","Tosazu reduction: reduce by half for concentrated glaze application on fish","Add yuzu or sudachi juice after straining — bright citrus lift to the dressing"}
{"Boiling the katsuobushi — bitterness and harsh compounds extract at high temperature","Not straining thoroughly — floating katsuobushi debris affects texture","Using too much soy — should be bright acid with umami support, not soy-forward","Storing too long — katsuobushi compounds oxidize and dressing becomes stale within 2-3 days"}
Kochi Regional Cuisine Documentation; Japanese Dressings — Tsuji reference