Are bonito flakes gluten free?

Are bonito flakes gluten free?

Bonito flakes are shavings of katsuobushi (かつおぶし, 鰹節), which is skipjack tuna that’s been filleted, simmered, smoked, fermented, and dried. This creates a preserved fish with a very hard texture, so it can easily be shaved onto foods. The flakes are technically called kezuribushi, but are more often sold under the name katsuobushi. Besides the fermentation culture that’s applied to the fish and the smoke it naturally absorbs, no other ingredients are added. This means that bonito flakes are naturally gluten free and dairy free.

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Bonito flakes from

Katsuobushi has a strong umami taste, thanks to its high inosinic acid content. It adds a savory, smokey, and lightly fishy flavor. It’s a key ingredient in miso and dashi broth, as well as other Japanese stocks and sauces. Bonito flakes are often used as a topping for cold tofu, salt ramen, okonomiyaki and takoyaki. When grated onto a hot food, the flakes appear to dance from the steam.

Besides adding umami, katsuobushi is very healthy. It’s high in protein, iron, niacin, B12, selenium, potassium, phosphorus, Omega-3 (DHA & EPA), and many essential amino acids. It’s also low in fat and calories. The only downside to consuming bonito flakes is that they may contain the carcinogen benzopyrene, due to the smoking process. The amount of bezopyrene is considered by most to be within safe limits.

Katsuobushi History

There’s evidence that katsuobushi has been made in Japan since the 1600s, starting sometime during the middle of the Edo period (1603-1868). However, the dish has roots even further back, because boiling and hard-drying fish has been mentioned in Japanese texts as early as 718 ADE.

According to one origin story, in 1674 a fisherman named Jintaro was shipwrecked in a storm and washed up on shore in Kochi prefecture. He tried smoking some skipjack tuna, which dramatically improved its flavor. The additional fermentation step for modern katsuobushi wasn’t added until around a century later, when various people discovered that smoked skipjack tuna that had molded was somehow even tastier.

Bonito Flake Types

There are a couple different grades for bonito flakes, and each has a slightly different use in traditional recipes. All katsuobushi must be simmered, then smoked repetitively for a minimum of one month, sun dried, and fermented with a bacteria culture for at least two weeks.

  • Karebushi: Katsuobushi that repeats the drying and fermentation portion of the process twice is called karebushi. It has a good depth of flavor that’s ideal for dashi.

  • Hadakabushi: Made by shaving off the surface fat of arabushi and adjusting their shape.

  • Honkarebushi (aka shiagebushi): If the drying and molding process is completed at least three times, it can be classified as honkarebushi, which means “true dried fillet.” Certain high-end honkarebushi repeat this process for years, resulting in an amazingly complex depth of flavor.

  • Hanakatsuo: A style of katsuobushi shaving that results in thin, pale pink flakes. These are most commonly used as a delicate but flavorful garnish.

  • Kezurikatsuo: These shavings are thicker than hanakatsuo, with a higher proportion of the shavings coming from dark meat. This type is ideal for infusing a sauce or braising liquid with deep umami flavor.

Buy Bonito Flakes

Katsuobushi is most often sold in flake form these days, although you can still purchase a whole block and shave it yourself. Flakes will lose their flavor much more quickly. When the katsuobushi blocks are properly stored in a vacuum sealed bag in the fridge, they can last up to 4 years.


Bonito shaver box with flakes from Roverista

Recipes That Use Katsuobushi


Dashi broth in the making from Umami Info

* Title image courtesy of Masterclass.

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