Katsuo Dashi (かつおだし)

Katsuo Dashi (かつおだし)
Main Umami Ingredient: Inosinic acid
Extraction method: Boiling or boiled water

This aromatic and flavorful seafood based dashi is made from katsuobushi (dried skipjack tuna that is shaved into thin flakes) and is mostly used in the Kanto region of Japan.

The production process for katsuobushi can take several months, with variations based on different regions. First the tuna is cut into fillets which are then simmered for about two hours. This helps to solidify the protein and to prevent the inosinic acid from breaking down when smoked. Once deboned, the fillets are repeatedly smoked then cooled for about a month until they become extremely hard, creating arabushi, the more common type of katsuobushi. 

‘True’ katsuobushi is made by then fermenting the arabushi, although nowadays this is less common given the lengthy and time consuming process. The charred surface of the arabushi is trimmed and shaped into what is called hadakabushi before Aspergillus mold is applied to ferment the filets into honkarebushi. The mold helps to draw out the moisture while breaking down protein and fat, resulting in a cleaner, richer, umami flavor. The fermentation stage can last for six months as the fillets alternate between the humid fermentation room and being dried in the sun, before the solid, hard block of ‘true’ katsuobushi is created.

Katsuobushi is then shaved into flakes, which was traditionally done by hand using a wooden box called a kezuriki with a sharp blade on top and a drawer below to catch the shavings. There are two types of shavings based on thickness. Kezuribushi, also known as hanakatsuo, are most common. Paper thin they are roughly 0.2mm or less in thickness and typically used for dashi, sauces or as a garnish. Atsukezuri are thicker and have a stronger, smokier flavor making them more suitable for sauces.

Try creating your own katsuo dashi using the katsuobushi in our DASHI: “Umami” Care Package and use it our Spinach Ohitashi (Spinach Steeped in Dashi) Recipe or our Tonjiru (Pork Miso Soup) Recipe.

Learn more in our Dashi: The Ultimate Guide.