How to Use Katsuobushi: The Essential Umami-Rich Ingredient

A Japanese ingredient that looks uncannily like pencil shavings, katsuobushi is skipjack tuna (a.k.a. bonito fish) that’s been smoked and dried over the course of several months, and shaved into flakes. While the reference to school supplies may not be the most appetizing description, katsuobushi is actually packed with warm, smoky, umami flavor. 

Below, we share how to use katsuobushi in two different applications, including a simple dashi (soup stock) recipe that can be used to make soups, simmered dishes, dipping sauces, and more; as well as an okaka onigiri (rice ball) that harnesses the flavor of the sea. 

But first, a little background on this unique Japanese ingredient.

During the Katsuobushi Factory Tour in Makurazaki, Kagoshima, we had the chance to visit the facilities at Ninben, a company that’s been producing the ingredient for over 300 years. There, a rich, smoky aroma hangs in the air, as workers go about fileting, simmering, deboning, smoking and drying, molding and fermenting, and finally sun-drying the fish until it resembles a smooth piece of wood. 

To use katsuobushi, this rock-hard block must be shaved into bonito flakes, called kezuribushi. From there, the shaved katsuobushi is packed up into convenient pouches that are sold at supermarkets nationwide.

Time equals flavor, and the several-month-long, labor-intensive process of making katsuobushi helps concentrate the umami of bonito, making the flavor accessible to people in their home kitchens with mere minutes of prep. 

There are two types of katsuobushi: honkarebushi and arabushi. Arabushi is just dried and smoked, while honkarebushi also involves a process of shaving the fat off of the filet’s surface and repeatedly adding mold and drying it to enhance the katsuo’s flavor through fermentation. 

Arabushi has a bold smoky flavor that works well in dishes flavored with soy sauce, while honkarebushi is mellower and rich in umami, perfect for delicate dishes. While arabushi can be produced in around a month, honkarebushi takes at least three months, which also factors into its higher price point.  

Katsuobushi’s flavor and texture are also impacted by how thick or finely it is shaved. Thinly-shaved dried bonito flakes are tender, almost melting in the mouth, and make for a pretty garnish, while thick katsuobushi flakes are more commonly used to make flavorful soup stocks. 

Katsuobushi is the main ingredient in dashi, Japanese soup stock, which is an essential component in Japanese cuisine. Dashi is incredibly versatile. Use it as a base for miso soup, adding miso and your choice of ingredients like tofu and scallions; beat it into eggs and make dashimaki tamago, a rolled omelet; or cook chawanmushi, the savory steamed egg custard. 

Besides dashi, katsuobushi is also used as a topping for okonomiyaki and takoyaki, a garnish for dishes like tofu, and seasoning for a variety of foods, including onigiri rice balls. Okaka is one such common seasoning made from bonito flakes. 

Here are a couple of simple katsuobushi recipes—katsuo dashi and okaka onigiri—to show two very different preparations of the ingredient. 

There are a few different types of dashi. Awase dashi is a soup stock that contains both kombu (seaweed) and katsuobushi, shiitake dashi is made from steeped shiitake mushrooms, and niboshi dashi uses dried sardines.

Here, we’ll make a basic katsuo dashi to harness the pure flavor of katsuobushi. This dashi can be used in soups, stews, and more. 

• 2 packed cups of katsuobushi
• 4 cups of water

1. To make katsuobushi dashi, first bring a pot of water to a boil.
2. Add the katsuobushi and bring it up to a boil again, then reduce the heat and allow it to simmer for 30 seconds.
3. Cut the heat and let the katsuobushi steep for 10 minutes.
4. Strain out the katsuobushi, reserving the liquid—this is your dashi.

In a tightly-sealed container, dashi can be kept for 3-5 days in the fridge.  

A common onigiri filling, okaka is made with seasoned katsuobushi flakes. It takes just five minutes to make and is great for a quick topping over a bowl of rice, or tightly packed in a rice ball for a portable snack.

• 450g (2.5 cups) cooked short-grain Japanese rice
• 20g (2 packed cups) katsuobushi
• 1 tbsp white sesame seeds
• 2.5 tbsp mentsuyu
• Nori seaweed sheets

Makes 3-4 onigiri. 

1. In a dry pan on medium-low heat, toast the katsuobushi until fragrant. At this point, if you’re wondering “Why are my bonito flakes moving,” it’s because they’re shaved so thinly that even a little bit of rising steam makes the katsuobushi sway as if they’re dancing in a breeze.
2. Mix in the sesame seeds and pan-fry for a minute or so before adding the mentsuyu. Stir until the katsuobushi is coated evenly and the liquid has been cooked off. Turn off the heat and transfer the okaka to a bowl. 
3. For onigiri, it’s best to use warm, freshly-cooked rice. Prepare a bowl full of cold water. While shaping the rice balls, occasionally dip your hands in the water to prevent the rice grains from sticking to you. 
4. Okaka can be used as a filling for onigiri, or it can be mixed in with the grains of rice. If you decide to use okaka as a filling, it’s also nice to season the outside of the onigiri, so keep a small dish of salt handy to dip your fingers in occasionally as you shape your rice balls. 
5. Just before eating, wrap your onigiri in a fresh, crisp piece of nori seaweed. Optionally, toast the nori briefly over a lit burner, by quickly swiping the sheet back and forth over the flame, until you can smell the aroma of the nori. Then, use it to wrap up your rice ball before serving.

Onigiri are best served at room temperature on the same day.

To learn more about this traditional Japanese ingredient, join the Katsuobushi Factory Tour in Kagoshima, or Discover the "Food of the Gods" in Mie Prefecture.