Shaved katsuobushi and dried kelp—kombu—are the main ingredients of dashi, a broth that forms the basis of many soups (such as miso) and sauces (such as soba no tsukejiru) in Japanese cuisine.

[2] At this stage the fillets are called arabushi (荒節) and most commonly found in stores shaved and packaged for sale under the name katsuo-kezuri-bushi (鰹削り節) or hanakatsuo.

The mold is continually scraped off, with further sun-drying increasing hardness and dryness until the fillet resembles a piece of wood, with less than 20% of its original weight.

When tapped together lightly, they sound almost metallic, and unlike their dull beige outer appearance, when broken open they are a translucent deep ruby color inside.

After the fillets are boiled and their rib bones removed the fish are put in steaming baskets stacked atop one another for one to two hours a few meters above a burning wood fire.

Today katsuobushi is typically sold in bags of small pink-brown shavings, which vary by thickness: smaller, thinner shavings, called hanakatsuo (花鰹), are used as a flavoring and topping for many Japanese dishes, such as okonomiyaki, while the larger thicker, called kezurikatsuo (削り鰹), are favored for making the widely used dashi stock.

[5] Due to the smoking process which involves tar and charcoal, amounts of benzopyrene exceeding EU standards, as much as 37μg per kilogram, have been detected in commercially sold katsuobushi.