What Are Bonito Flakes?
Your Ultimate Guide to Katsuobushi
LAST UPDATED: August 14, 2025
READ TIME: 20 minutes
Table of Contents
What Are Bonito Flakes?
Bonito flakes are the shavings of simmered, smoke-dried, and fermented skipjack tuna (Katsuwonus pelamis).
In Japan, where this essential seasoning was invented, it is called katsuobushi (鰹節 or かつおぶし). Katsuo means "skipjack tuna", and bushi means “block” or “chunk.” It certainly is a fish block, as the processing makes it harder than wood (right). It is the world’s hardest food, and when shaved, it’s likely also the thinnest—some styles are even translucent (below). Katsuobushi is shaved with a kezuriki, which is essentially a specialized wood shaver with a compartment to catch the flakes. The shavings are called katsuobushi as well, but they are also referred to as kezuri-katsuo (削り鰹, “shaved skipjack”), or katsuo-kezuribushi.
What Do Bonito Flakes Taste Like?
Bonito flakes have a savory, meaty, slightly fishy flavor that is elevated by their rich, smoky aroma.
Katsuobushi is renowned for its strong umami character. Umami is the fifth taste, alongside sweet, salty, sour, and bitter. It is the source of savoriness, the “essence of deliciousness.” Katsuobushi has a very high concentration of inosinic acid and a good amount of glutamic acid, both of which contribute deep umami flavors. The smoke-drying and fermentation processes also increase the inosinate and glutamate levels found in fresh katsuo, magnifying the umami!
Additionally, inosinate dissolves easily in water, so when making dashi or other types of soup stock, the thinness of the shavings provides more surface area to accelerate the inosinate dissolution even further. Japanese chefs will deftly remove the flakes before the other amino acids and aroma compounds have time to dissolve and thus alter the flavor. Essentially, the chemical composition and form of bonito flakes allow for pure umami to be imparted into any liquid. When used as a topping, the thin, delicate shavings also dissolve easily in the mouth, which enhances the mouthfeel and overall sensory experience of the dish.
Along with umami, katsuobushi is also associated with the concept of kokumi. Kokumi describes foods or chemical compounds that enhance the five tastes by amplifying or prolonging their effects, creating a deeper sense of “heartiness.” So bonito flakes not only impart umami directly—they also elevate the tastes of other ingredients with their kokumi qualities.
Why Do Bonito Flakes Move?
Bonito flakes are thin, light, and dry, so heat and steam make them twist and curl as the air rises and they absorb the moisture.
Rest assured, they are not alive. When you see them squirming around on top of your food, it’s because they’re so thin, light, and dry that heat makes them move as the air rises, and steam makes them move as they absorb the water vapor. This affects each shaving differently as they have different lengths and thicknesses, which makes it look like they're all dancing. It's an exciting sight, but it's short-lived. The movement stops as soon as the shavings have been saturated. That is, unless you're eating outside, as a simple breeze can reanimate them due to their feathery lightness.
When the shavings become saturated from the steam of hot rice, for example, they soften, which makes them melt in your mouth more easily than other chewy dried fish products. As soon as the dancing slows down, it's time to eat!
What Are Bonito Flakes Made Of?
Authentic katsuobushi is made solely from skipjack tuna, or katsuo.
Bonito flakes are so intensely tasty that most people are surprised to learn that they are not seasoned at all. Their flavor comes solely from the tuna and the long smoking and drying process. Authentic katsuobushi is made from skipjack tuna, or "katsuo" (Katsuwonus pelamis). Skipjack is sometimes informally called “bonito” due to their similar appearance and culinary use, but keep in mind that bonito is a different tribe of 8 species (the Sardini tribe) within the same family (Scombridae—the mackerel, tuna, and bonito family). So while they’re related and look similar, bonitos are not tuna (the Thunnini tribe).
It can get confusing because lower-grade bonito flakes are actually made with bonitos (like the Atlantic bonito—Sarda sarda) instead of skipjack. They are a less expensive alternative, typically used for export markets or cheaper products. They lack the deep umami richness of skipjack, so they are a less premium, less authentic product. True katsuobushi must be made with katsuo. Some products are even explicitly called "shaved skipjack" instead of "bonito flakes" to make it clear they don't use actual bonito.
How Are Bonito Flakes Made?
The process of making katsuobushi is complex and meticulous, often leveraging traditional methods that have been passed down through generations. From start to finish, it can take anywhere from 2 months to over 2 years.
There is some variation depending on the region and companies involved, but generally speaking, these are the steps:
- Catching the Fish
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- Katsuo has two primary fishing seasons—one in spring (May to June), called “first catch”, or hatsu-gatsuo, and one in autumn (September to November), called “returning catch,” or modori-gatsuo. However, fishing does happen year-round and production of katsuobushi continues outside of these peak seasons using frozen fish. Traditional fishing techniques, even pole-and-line fishing, are sometimes used in the artisanal katsuobushi process to ensure freshness and quality. The catch is often flash-frozen on the boat and delivered to a processing plant.
- Selecting the Fish
- Back at the plant, the fish are selected for their marbling and size as they thaw.
- Filleting (Namagiri 生切り)
- The selected katsuo are beheaded, de-finned, bled, gutted, and thoroughly rinsed. The fatty belly is then carefully trimmed away because fat is harder to preserve and can create uneven smoking. Each one is then filleted into four uniform pieces—two from the dorsal and two from the ventral side. The goal is for all of them to have a relatively consistent shape, thickness, and texture so that they can be smoke-dried evenly. The dorsal (back) fillets are called obushi (雄節) and are considered the highest quality due to their leanness. The ventral (belly) fillets are called mebushi (雌節) and contain more fat, so they have more flavor but are more challenging to prepare. The back and belly fillets are complimentary—the back provides clean, lean flavor, and the belly offers a richer taste. Obushi means "male cut" and mebushi means "female cut," so they are meant to represent a harmonious marriage. The analogy is quite fitting because obushi and mebushi fillets physically fit perfectly together, just like a loving couple. And when they lock together, they look like a tortoise shell, which has long represented longevity. For these reasons, katsuobushi blocks are often given as wedding gifts to wish the newlyweds a long, happy marriage.
- Selecting the Fillets
- The best quality katsuobushi is made with leaner, muscular fillets, so those that are too fatty are discarded to ensure the finished products are firm, full-flavored, and properly cured. Traditional Japanese methods ensure minimal waste. The unchosen fish, as well as the remaining parts of the chosen ones, are often used culinarily or as fertilizers.
- Basket Placement (Kagodate 籠立て)
- The fillets are precisely arranged by hand in a basket to ensure consistent heat.
- Simmering (Shajuku 煮熟)
- The fillets are simmered just below boiling for about 1-2 hours. Not bringing it to a full boil preserves their texture. The temperature and duration of the simmering are tailored exactly to the qualities and freshness of that batch of fillets. This step distributes the water within the muscles throughout the fillets, facilitating the dehydration processes to come. They are then cooled in a well-ventilated area, which is critical as it toughens the fillets for the smoking stage.
- Deboning (Honenuki 骨抜き)
- The skin of the simmered fillets is then removed and the small rib bones are extracted with tweezers by hand. This meticulous, time-intensive step is crucial as any error can damage the fillets, and any missed bones will cause a fracture as they harden in the following steps. This is why deboning must be done carefully by hand. No machine could replicate the dexterity required.
- Repair (Shuzen 修繕)
- Next, the cracks created in the fillets via deboning are filled with a paste made from tuna scrape (called nakaochi—the fatty meat in between the bones and skin) and the head. They must have a smooth surface to be smoked. This process also helps shape the fillets and prevent mold.
- Smoke-Drying (Baikan 焙乾)
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- The fillets are smoked for up to a month over oak, castanopsis, or pasania wood chips. The wood is carefully selected for its aromatics. Cherry blossom (sakura) wood is often used as kindling. They are smoked for 5-6 hours, then left for a day so that the moisture can rise to the surface, then smoked again the following day. After each smoking round, any cracks are again repaired with the paste. This smoking and drying cycle is repeated 10-15 times, with each session drawing out more water and killing any bacteria that may form. At this stage, the fillets are called arabushi (right). Arabushi has had about 80% of its moisture removed. Most lower-end bonito flake products are made with arabushi, which is about 80% of commercial bonito flake products. To be considered true katsuobushi, the arabushi must go through the final stage of mold application and sun-drying.
- Scraping / Grinding
- The arabushi fillet’s rough surface of built-up tar, smoke residue, and fat is scraped off using a wheel grinder. They must be smooth so that the mold can attach to it. After this step, the arabushi is called hadakabushi.
- Mold Application (Kabitsuke 黴付け) and Sun-Drying
- The hadakabushi fillets are then coated with Aspergillus glaucus, a beneficial mold (not a malignant mold) that stimulates fermentation. They are cured with this mold for several weeks in a controlled environment, then they are sun-dried. When this mold-coating and sun-drying process is done once, it can be called true katsuobushi. When done at least twice, it is called karebushi (below). Karebushi has had 85%+ of its moisture removed. The additional coatings of mold bring out even more umami flavor from the katsuo. And when it is done three or more times, it is called honkarebushi, the highest-grade katsuobushi. It is also the hardest, almost rock-like. The most exquisite honkarebushi, with an immense complexity of flavors, is made by repeating this process for over 2 years.
- Shaving (Kezuri 削り)
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- The finished katsuobushi blocks are either sold whole or shaved into flakes using a kezuriki, and quickly packaged in airtight containers and stored in a cool, dry environment prior to shipment. When shaving a whole block yourself, start shaving from the smallest part first (the tail), holding the fillet at a ~45° angle and pushing outwards. If you've been storing it in the refrigerator, shaving is more difficult and will create more powder. So gently warm it up first, either by allowing it to sit in room temperature for 30 minutes, wrapping it in a warm, dry cloth, or using the natural warmth of your hands and firmly holding it in your palms for a few minutes. Watch the kezuri process here:
You can also watch the whole production process in these three videos. See if you can name each step as it happens!
Where Are Bonito Flakes Made?
The best katsuobushi is made in Japan, the world’s largest producer. The process is deeply rooted in the country’s history and culture, so no outside producers can match their quality.
Perhaps the most renowned katsuobushi-producing city is Makurazaki in Kagoshima Prefecture on the southern island of Kyushu. This site has the perfect climate for drying and curing, katsuo-rich waters, and a long history of traditional methods dating back to the Edo period (1603-1868). The city is particularly known for producing the finest honkarebushi. Other notable regions are Yaizu in Shizuoka Prefecture, Nakiri in Mie Prefecture, and Kochi Prefecture.
Regional variations are also produced in Taiwan, South Korea, Indonesia, and the Philippines. They often use local fish varieties, or bonito itself (not katsuo), and have their own versions of the smoking and drying process. Japanese katsuobushi remains distinct due to the generations of artisans who have passed down very specific knowledge and skills only to their descendants.
What Are the Different Types of Bonito Flakes?
Grades of Katsuobushi (Prior to Shaving)
- Arabushi (荒節)
- Smoked and dried only. Does not undergo fermentation. Takes about 3 weeks. Either sold in lower-grade bonito flake products, or continues on to the following stages.
- Hadakabushi
- Arabushi that has had its rough surface scraped off. This is never sold commercially. It is only a step in between arabushi and the mold application process.
- True Katsuobushi
- Has undergone at least 1 round of fermentation and sun-drying. However, most producers don’t stop there, as karebushi is more desirable. So true katsuobushi is typically found in the form of karebushi at least.
- Karebushi (枯れ節)
- Has undergone at least 2 rounds of fermentation and sun-drying. Takes 2-3 months. Dashi made with karebushi is clearer than with arabushi since the charred layer has been scraped off, and its umami has more complexity.
- Honkarebushi (本枯れ節)
- The most refined katsuobushi. Has undergone at least 3 rounds of fermentation and sun-drying. Takes roughly 6 months to 2+ years.
Next, there are different types of shaved katsuobushi, or kezurikatsuo. These classifications are independent of the above grades of katsuobushi blocks—they only relate to the style of shaving. Here are some of the most prominent styles:
Types of Shaved Katsuobushi
- Hanakatsuo (花鰹)
- The extremely thin, translucent shavings are called hanakatsuo (“flower skipjack”) due to their delicate, light appearance. Hanakatsuo is most often made with arabushi since it’s one of the most prevalent and less expensive commercial bonito flake products. It's typically used as a topping but it's also an economical way to make dashi.
- Hirakezuri (平削り)
- Flat, broad shavings of katsuobushi, typically used for dashi rather than as a garnish due to their larger surface area—their extreme flatness facilitates dissolution. It is most commonly made from true katsuobushi versus arabushi.
- Atsukezuri (厚削り)
- Much thicker than hanakatsuo, nearly resembling bacon strips. Atsukezuri also has more dark meat (chiai), making it a great option for slowly infusing its umami into a decadent soup stock or broth.
- Itokezuri (糸削り)
- Thin, narrow shreds. This form is useful in recipes outside of Japanese cuisine, like pastas and salads.
- Saihenkezuri (砕片削り)
- Tiny pieces of kezurikatsuo, great for a quick topping on everything from tofu to vegetables.
- Konakezuri (粉削り) or Kezuriko
- The powdered byproduct of shaving kastuobushi. This powder can be used to quickly infuse soups, or to make dashi in record time.
What Are the Culinary Uses of Bonito Flakes?
Katsuobushi is one of the most foundational ingredients in Japanese cuisine. It is at the heart of umami, the core of Japanese culinary philosophy. Without it, most dishes would feel severely incomplete.
Katsuobushi is a key component of dashi, Japan’s most essential stock. Dashi is the base of nearly every soup or broth, from miso soup and oden to ramen, udon, and soba. But it isn’t just for soup. It is so prevalent in Japanese cooking because it’s used to impart umami to just about any recipe that requires a liquid. Katsuobushi is also a ubiquitous topping for rice, noodles, salads, vegetables, tofu, shellfish, and beloved batter-based dishes like okonomiyaki and takoyaki (the batter is also made with dashi!). The third primary use is a filling, most notably in onigiri, Japan’s delicious rice balls. Here’s a closer look at some of the most popular uses for this beloved seasoning:
As an Infuser
- Dashi Stock
- Dashi is the soul of Japanese cuisine. The stock is made with katsuobushi and dried kelp, or konbu (often spelled kombu in the West). Sometimes dried shiitake mushrooms are tossed into the mix, but kombu and katsuobushi are the only prerequisites.
- Quick & Easy Dashi Recipe
- Soak a piece of kombu in 4 cups of water for 30 min.
- Bring it to a boil, then remove the kombu.
- Drop the heat below boiling.
- Toss in some katsuobushi shavings (about a handful).
- Let it sit for 5 minutes, then strain the hot dashi stock.
- Ingredient in Tare (Sauces)
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- Katsuobushi plays a crucial role in enhancing the complexity of tare, the flavor-rich sauces used as bases for famous Japanese dishes like ramen, yakitori, and gyoza. The beloved citrusy sauce ponzu is a great example, which is typically made with soy sauce, vinegar, yuzu juice, and dashi.
As a Topping
Okonomiyaki
Okonomiyaki is a savory pancake made in various creative ways. No matter how it’s made, it’s almost always coated with criss-crossing okonomiyaki sauce and mayonnaise, and topped with aonori (seaweed flakes) and bonito flakes.
Okonomiyaki
Okonomiyaki is a savory pancake made in various creative ways. No matter how it’s made, it’s almost always coated with criss-crossing okonomiyaki sauce and mayonnaise, and topped with aonori (seaweed flakes) and bonito flakes.
Takoyaki
This is a very popular, very delicious street food. Takoyaki balls are typically filled with diced octopus, pickled ginger (beni shōga), and green onions (negi). They are drizzled with takoyaki sauce and mayonnaise and sprinkled with aonori and bonito flakes.
Hiyayakko
Hiyayakko is a refreshing chilled tofu dish that places silken tofu in a little puddle of soy sauce or ponzu, often sitting on a shiso leaf. While there are many ways to season it, grated ginger (shōga), green onions, sesame seeds (goma), and katsuobushi almost always make the cut.
Hiyayakko
Hiyayakko is a refreshing chilled tofu dish that places silken tofu in a little puddle of soy sauce or ponzu, often sitting on a shiso leaf. It is then seasoned with grated ginger (shōga), green onions, sesame seeds (goma), and katsuobushi.
Agedashi Dōfu
In this dish, silken tofu is deep-fried until golden and crispy and served in a warm dashi broth. It's often topped with grated radish (daikon), ginger, green onions, and katsuobushi. It's a favorite appetizer or side due to its intriguing textures and toppings.
Rice
Neko manma, or "cat rice," isn't just for cats. It's a delicious snack made by simply seasoning hot rice with dried bonito flakes and soy sauce—a combination known as okaka.
Rice
Neko manma, or "cat rice," isn't just for cats. It's a delicious snack made by simply seasoning hot rice with dried bonito flakes and soy sauce—a combination known as okaka.
Noodles
When cooking ramen, udon, soba, or any type of noodle for that matter, a sprinkling of katsuobushi always helps amplify the dish's umami.
Sushi Rolls
While more of a Western take on Japanese cuisine, bonito flakes can add a key savory touch to many sushi rolls. Their smokiness especially complements rolls with stronger flavors like oily fish (salmon), savory sauces (unagi sauce), and creamy or spicy components.
Sushi Rolls
While more of a Western take on the cuisine, bonito flakes can add a savory touch to many sushi rolls. Their smokiness especially complements rolls with stronger flavors like oily fish (salmon), savory sauces (unagi sauce), and creamy or spicy components.
As a Filling
- Okaka (おかか)
- Sometimes katsuobushi itself is colloquially called okaka, but the term also refers more specifically to a mixture of katsuobushi and soy sauce. Okaka is commonly used to stuff onigiri (rice balls) and temaki (hand rolls), where its smoky, salty depth pairs perfectly with the soft rice and light crunch of nori. Okaka also works well as a secret ingredient in various soups, stir-fries, noodle dishes, and cat rice, as we've seen.
By Itself
- Snack
- We mustn’t forget that bonito flakes make a quick, tasty snack right out of the bag!
- Pet Food
- Cats and dogs love katsuobushi too. You can give it to them straight as a little treat. The strong aroma is inviting, and it can be a healthy, protein-rich topping to get them to eat their dry food as well. Be sure to exercise moderation though due to the high sodium content. It should be a treat.
Are Bonito Flakes Healthy?
Katsuobushi is rich in protein, omega-3s, Vitamin B12, iron, potassium, magnesium, and phosphorus.
Bonito flakes provide deep savory flavors without adding significant calories, fat, or salt. Here are some key elements of their nutrient profile:
- Turning fresh skipjack into katsuobushi concentrates its nutritional profile, increasing its protein content threefold to 75% by weight.
- They contain omega-3 fatty acids like EPA and DHA, which are crucial for heart and brain health.
- Bonito flakes are also rich in amino acids like histidine, which supports immunity, digestion, and sexual function by promoting the production of histamine.
- They are an excellent source of Vitamin B12, essential for neurological function. They also deliver key minerals, including iron, potassium, magnesium, and phosphorus, all of which play important roles in the body.
- Finally, the smoke-drying and fermentation process breaks down collagen into gelatin, which promotes gut health, joint health, and skin elasticity.
Beyond their direct nutritional content, some studies have demonstrated that katsuobushi-flavored dashi may help reduce anxiety and fatigue and improve mood and vigor.
What Are the Best Substitutes for Bonito Flakes?
When a recipe calls for bonito flakes, you really should just find them. Their umami-rich, smoky profile is too unique to replicate. Dashi is not the same without them. They are also not hard to source, as any Japanese market and most Asian grocery stores will almost always carry some variety. And you can easily get them online. However, if you can’t get them in time for your meal, just want to try something different, or have dietary restrictions, you do have the following options:
- Furikake with Bonito Flakes
- If you can’t find bonito flakes, this popular Japanese seasoning comes in many forms, some of which contain bonito flakes. It is best used as a topping versus making dashi.
- Dried Shiitake Mushrooms
- Dried shiitake mushrooms also offer deep umami flavor to dashi. Rehydrate and simmer them to release a savory taste that can stand in for bonito flakes when combined with kombu.
- Konbu (Dried Kelp)
- Konbu, or kombu, is another key ingredient in traditional dashi. On its own, it can create a flavorful broth with a different but still rich umami profile. It's especially suitable for vegan and vegetarian recipes.
- Dried Anchovies or Sardines
- For non-vegetarian options, dried anchovies or sardines offer a slightly similar fishy flavor. They are often used in Korean cooking to prepare broths. However, they lack the deep smokiness of the katsuobushi-specific umami.
- Dried Shrimp
- Dried shrimp adds some similar oceanic notes, but it’s more briny and less smoky.
- Shredded Nori or Aonori
- Various seaweed seasonings work well as a topping in the same way as bonito flakes, often adding a similar lightly smoky and savory saltiness.
- Shōyu (Japanese Soy Sauce) or Tamari
- These fermented soy sauces add a salty, umami complexity, but obviously can’t be used as a topping.
- Miso Paste
- This fermented soybean paste can also be used to add umami depth when cooking stock, broth, and soup, but it has a different taste and a more pronounced saltiness.
- Umeboshi (Pickled Plums)
- Umeboshi is not a direct substitute, but it can impart a complex savoriness to rice dishes or sauces.
- Yeast Products
- Yeast extracts and nutritional yeast are popular vegan options that can add umami with a cheesy, nutty character. They work well both as a topping and as an infuser.
Where to Buy Bonito Flakes
If you have a local Japanese or Asian market, you will most likely have no issues acquiring a bag of pre-shaved flakes. The Asian aisle of a regular grocery store might also carry them, and they are available from many online retailers.
Of course, there are levels to it. Sourcing a premium honkarebushi block vs. a generic bag of “bonito flakes” is more difficult outside of Japan. Still, many online stores now specialize in authentic Japanese ingredients and kitchen tools, making it easy to order both whole blocks of honkarebushi (the highest grade of katsuobushi) and a quality kezuriki (the necessary shaving tool). These options from Nihon Ichiban are sourced from Tenpaku, one of the most well-respected katsuobushi companies in Japan.
Just as spices are at their best when ground whole, katsuobushi is best when freshly shaved because it quickly loses flavor when oxidized. Japanese chefs have a saying that you should only shave katsuobushi when you can see the guest's face. This is because the only way to truly experience of the essence of katsuobushi—bringing the fullest flavor to life—is through the traditional manual shaving process. It's a lot of fun too. The pleasant smell, sound, and feel of the shaving is hard to match.
In Japanese, the phonetic word "katsuobushi" can also be written 勝男武士, which means "victorious samurai." Because of this fun play on words, katsuobushi has always represented good luck, the spirit of a triumphant warrior. Thus, in addition to the wedding gift symbolism mentioned above, katsuobushi blocks are also the perfect gift for someone embarking on a new endeavor or recovering from an injury or illness.
How to Store Bonito Flakes
Storing Pre-shaved Flakes
Flakes are often sold in small packs to be used fully in one sitting. This is because they lose their desired wispy shape and color relatively quickly once exposed to oxygen. They also typically come in a larger, resealable bag, but they should be used as quickly as you can, or stored in the refrigerator or freezer in between uses if you’re expecting a gap in between uses.
However, in terms of sheer preservation, bonito flakes are highly resistant to spoilage. The smoking, drying, and fermentation processes remove bacteria and block new pathogens from forming. So as long as you keep them in an airtight container in a cool, dry place, they can keep for 6 months to a year. However, they can only be considered “fresh” for a few weeks after first use. Be extra careful in humid climates as their extreme thinness and dryness makes them very sensitive to any moisture.
Storing Katsuobushi Blocks
Whole, dried filets keep much longer than the flakes. Storing a “block” is all about keeping it dry and airtight. Vacuum seal if you can, or at the very least, tightly wrap it in plastic wrap. You can also place the plastic-wrapped block into a larger ziplock bag with a silica gel packet. Once you’ve started to shave it, it spoils more quickly, so use the above methods and keep it in the refrigerator. A block that’s properly stored can last up to four years.