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Dried bonito flakes are integral to Japanese cuisine. These flakes of fermented fish can instantly impart a burst of umami flavor into any savory dish.

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What Are Bonito Flakes?

Bonito flakes, or katsuobushi, are flakes of smoked, fermented, and dried bonito fish or skipjack tuna. After producers clean and fillet the fish, they simmer and smoke it a few days at a time for a month before sun-drying. Aspergillus glaucus, a bacterial mold culture, is applied to encourage a protective mold, which further ferments the fish, and absorbs any remaining moisture. The mold is periodically scraped off and allowed to reform as the fish dries. When the drying process is complete, the finished fish will resemble pieces of hard, petrified wood. Producers then shave the fish using a sharp plane set into a wooden box, called a katsuobushi kezuriki.

Commercially sold katsuobushi comes pre-shaved in a sealed bag; once exposed to oxygen, the shavings lose their airy shape and color, so they are best used immediately. Alternatively, you can store katsuobushi in the freezer between uses.

4 Types of Bonito Flakes

Katsuobushi is available in a few different grades, with slightly different usages:

  1. Karebushi: To be classified as katsuobushi, fish fillets must undergo a three-step process: They must be simmered, smoked for a minimum of one month, dried, and fermented with a bacteria culture for at least two weeks. Katsuobushi that repeats the drying and fermentation process twice is known as karebushi, “dried fillet,” which has a depth of flavor ideal for a dashi base.
  2. Honkarebushi: If the drying and molding process is completed at least three times, the katsuobushi can be classified as honkarebushi, or “true dried fillet.” Some high-end honkarebushi repeat this process for years, resulting in a staggeringly complex depth of flavor.
  3. Hanakatsuo: Katsuobushi shaved into thin, pale pink flakes are known as hanakatsuo, which are most commonly used as a delicate, flavor-packed garnish.
  4. Kezurikatsuo: These shavings are thicker than hanakatsuo, with a higher concentration of chiai (shavings from dark meat), making them ideal for infusing a sauce or braising liquid with rich umami flavor.
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How to Use Bonito Flakes

You can use dried bonito flakes in various Japanese dishes, either as a seasoning or garnish. Here are some of its primary uses:

  • As a topping: Along with other ingredients, like aonori (dried seaweed powder) and Japanese mayonnaise, bonito flakes are among the main condiments for dishes like okonomiyaki, a savory cabbage and egg pancake, or takoyaki, grilled octopus balls.
  • As a filling: