What is Katsuobushi (Bonito Flake)?

Katsuobushi, or dried bonito flake, is one of the most essential ingredients in Japanese cuisine. Loaded with umami flavor, katsuobushi is used in making stock and as a topping, garnish, and seasoning on everything from noodles to rice to eggs. 

What Is Katsuobushi?

Katsuobushi is made from skipjack tuna, also known as bonito. It's rich in inosinate, a compound that produces the umami flavor. When inosinate is combined with glutamate, an amino acid that is also rich in umami, the two compounds produce a synergistic effect that dramatically increases the umami flavor. For this reason, traditional Japanese soup stock, called dashi, is made from a base of dried bonito flake and a glutamate-rich dried kelp called kombu.

To produce katsuobushi, the bonito are filleted and simmered before undergoing multiple rounds of smoking. Next, it undergoes a process of fermentation and sun-drying which can take several months. The resulting slabs are as hard as wood, with over 80 percent of their moisture removed, and are regarded as one of the hardest foodstuffs in the world.

To cook with katsuobushi, these slabs must be shaved into paper-thin flakes. Shaving the bonito this way exposes surface area, which allows the umami flavors to be quickly released in boiling water. Because the dried bonito also contains amino acids, which dissolve more slowly, Japanese chefs remove the flakes quickly, so that only the inosinate is released, which in turn ensures a more pure umami flavor and aroma and a clearer stock.

Since a relatively small amount of bonito flakes are needed for most recipes, they are not especially expensive, especially per serving.

Katsuobushi Uses

The two most common uses for katsuobushi are for making traditional kombu dashi, or soup stock, and as a topping, garnish, and seasoning for any number of other foods, such as noodles, eggs, rice, vegetables, and tofu. It is also be used as a filling for rice balls and an ingredient in okonomiyaki, or Japanese pancakes. Bonito flakes are used to add umami flavors to soups, stir-frys, and casseroles. It's even used to make treats for cats.

One traditional dish called neko manma, or cat rice, is made by sprinkling dried bonito flakes on a bowl of hot rice. The steam from the rice can make the bonito flakes curl and sway. This movement is caused by the thin flakes reabsorbing moisture via the steam, which happens at different rates due to varying thicknesses. Once the flakes are fully saturated, the movement ceases.

A popular seasoning mix called furikake often includes tiny fragments of dried bonito flakes along with salt and other ingredients such as sesame seeds, dried seaweed, and dried egg. This mixture is sprinkled on anything and everything, much the way salt and pepper are used in western cooking.

How to Cook With Katsuobushi

Many Japanese chefs procure whole katsuobushi slabs and shave it themselves using specially designed graters consisting of a wooden box with a drawer in it for catching the flakes. In Japan, chunks of dried bonito are available, but most home cooks purchase pre-shaved bonito flakes in bags. These flakes are then added to broth or used as a topping, filling, or whatever the recipe requires. 

What Does It Taste Like?

The flavor of katsuobushi can be described as mildly salty, smoky, slightly fishy, and deeply umami—a meaty, savory flavor. Because of the smokiness, it is almost like a cross between dried fish and dried bacon, or perhaps smoked fish jerky; but since it's sliced micro-thin, it's almost feathery, as opposed to chewy. In fact, it's not uncommon to eat the flakes straight out of the bag as a snack.

Katsuobushi Recipes

Use bonito flakes to add deep flavor to broth as well as other Japanese-inspired salads, rice dishes, and more.

• Okaka Onagiri Rice Balls
• Chilled Japanese Okra Salad

Where to Buy Katsuobushi

If you live near a decent-sized Asian or Japanese grocery store, you should have no trouble finding bags of dried bonito flakes sold in various size bags or occasionally in bulk. They're also available online from a wide range of retailers. You can purchase whole katsuobushi blocks online, although remember that you'll also need a box grater to shave it. 

Storage

Because the drying and smoking process is a form of food preservation, dried bonito flakes are extremely resistant to bacterial spoilage. As long as they're kept cool and dry and sealed in either the resealable bag they came in or some other airtight bag or container, dried bonito flakes will last for six months to a year. Their shelf life may be shorter in humid climates.