Katsuobushi as a block, as bonito flakes or use a shaver: what is Katsuobushi?

                by Joost Nusselder | Updated:  April 12, 2021

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Katsuobushi, also known as okaka is the Japanese name for dried, fermented, and smoked skipjack tuna (Katsuwonus pelamis).

Katsuobushi (鰹節) is a dried, fermented, and smoked skipjack tuna with the scientific name: Katsuwonus Pelamis. Another name for katsuobushi is bonito flakes and this term is used to indicate that a young bonito is used as a cheaper substitute for skipjack tuna.

Young bonito has a similar color and texture and is sometimes used as a cheaper substitute for skipjack tuna, particularly in canned products, however not all countries allow marketing of bonito as skipjack tuna. Katsuobushi on Udon noodles Shaved Katsuobushi and dried kelp – kombu – are the main ingredients of dashi, a broth that forms the basis of many soups and sauces. Here are all of the articles where we talk about Katsuobushi: [wl_faceted_search]

It is called okaka (おかか) when a similar fish is used to make it.

The kombu (dried kelp) and shaved katsuobushi are also the main ingredients of dashi, a broth or soup stock that is at the core of almost every Japanese soups, cuisines, and sauces that give it the savory flavor called umami.

Katsuobushi’s distinct umami taste comes from its high inosinic acid content.

The karebushi, which is a traditionally-made katsuobushi, is intentionally fermented with Aspergillus glaucus fungus during the production stage to remove the moisture from the fish meat as it needs to be dried in order to be useful.

In this Youtube video from Haradaizumi you can see how the katsuobushi is made:

Scientists also observed that katsuobushi exhibits the kokumi (6th a derivative of the 5 basic flavors that the taste receptors in our tongue can pick up) flavor.

However, the tongue receptors cannot actually detect it; instead, it enhances the flavors sweet, salty, and umami.

History of Katsuobushi

Based on historical records, it is safe to assume that the Japanese people have already been using this fish flake seasoning since the late 15th century. However, the fermentation part of making the katsuobushi wasn’t discovered until about a hundred years later.

A famous tale about the katsuobushi is known to all Japanese and it goes something like this:

A man was walking by a fishing village and found a small boatload of katsuobushi lying around which was obviously left by some fisherman. It had been there for quite some time that molds had already grown all around it.

Having found himself starving he was then forced to consume the katsuobushi, but during this time he discovered that the fermentation caused by the molds gave the katsuobushi an even richer flavor than he could have thought.

The tale goes on to say that it was at this point in time that the people of Japan immediately realized the potential of katsuobushi to their dishes. And so they had been using it to make dashi and other cuisines ever since.

Health Benefits of Katsuobushi

The bonito or katsuobushi has a high protein amount plus all the essential amino acids that the body needs to maintain its optimal health. It is also rich in vitamins and minerals, including iron, niacin, and B12.

Health experts confirm and encourage people to consume katsuobushi on a daily basis as it can contribute to the improvement of metabolism and brain function.

It also helps reduce the potential risk of multiple other diseases and ailments such as diabetes, heart disease, and dementia.

Where to buy Katsuobushi

Katsuobushi is probably one of the most – if not THE MOST – versatile seasoning in the world and packs a ton of umami!

The bonito chunks (raw katsuobushi) are sold in just about every convenience store that you can find, in Japan that is.

What is a Katsuobushi block?

A Katsuobushi block is the (Japanese: 鰹節) is the dried, fermented, and smoked skipjack tuna. It comes in the form of blocks and is often shaved down to make bonito flakes often found in Japanese dishes and dashi.

In America you might have to look to your local Japanese store or sometimes some Chinese stores as well (the larger ones).

You can also get it on Amazon here and have it sent to you:

You can take this home with you and shave it to flakes yourself (there are shaving tools for katsuobushi that you can buy too).

Best katsuobushi shaver

If you want to buy a Katsuobushi shaver, you can’t do better than one that’s made in Japan and the Tikusan company imports these now to America.

Favorite Asian Recipes

The shaver is an essential tool if you’re going to buy your katsuobushi in blocks as you need to use the flakes on your Japanese dishes and in your dashi.

The katsuobushi shaver is called a “Kezuri” and was an essential tool in making bonito flakes after 1670 when the Japanese added mould to the fermentation process.

Using the mould, the fish would be able to be preserved for even longer than before, but it also took out all of the water and fat from the fish, thus making the katsuobushi block as we know it now as hard as stone.

Prior to 1670 a knife would be used to shave down the blocks into shavings for consumption, but after the making process was changed, the specifically designed Kezuri shaver was introduced and became a household item.

You can shave the dried fish block over the top of the shaver like so:

Check out the Tikusan shaver here on Amazon

Buying Katsuobushi in pre-ready bonito flakes

Of course, you can get the shaved down flakes online as well (here the best quality for the lowest price):

They are sealed in plastic bags and are sold at a very low price.

What is Katsuobushi used for?

The katsuobushi is one of the only 2 major components in creating the dashi soup stock (kombu is the other ingredient) – which provides the umami flavors to so many amazing Japanese recipes.

When it isn’t used to make the dashi or other sauces, the bonito flakes are then utilized as a simple but delicious topping for the okonomiyaki, pickled vegetables, or tofu (flavorful Japanese pancakes).

Katsuobushi has also earned the moniker of “dancing fish flakes.”

This is because when they are sprinkled on top of a sizzling dish like the okonomiyaki, for instance, the grill’s heat causes the flakes to react and move around as though they are dancing, thus the moniker.

Katsuobushi is also used in some other popular rice dishes mixing it with the Unagi Hitsumabushi Grilled Eel Rice Bowl, Onigiri, or Chimaki Chinese Style Glutinous Rice Balls in order to enhance its flavor.

You can easily find katsuobushi packs sold in Japanese supermarkets and convenience stores as well as in online stores like Amazon and Japan Centre.

Something as significant and popular such as the katsuobushi it would be odd if you can’t find any to buy at a physical store or in virtual stores.

How to make Katsuobushi

dried fish

Katsuobushi, dried bonito, is an essential ingredient in Japanese cuisine. By dehydrating fresh fish creates a highly condensed umami in its body, this in turn – when dried – becomes the basis for the dashi broth which is used in making the miso soup and soba dipping sauce as well as dozens of other Japanese recipes.

When it is not used to make the dashi stock, it is used as a topping. Typically the katsuobushi shavings are sprinkled over boiled vegetables or tofu.

Freshly shaven bonito flakes are preferable; however, there are good pre-packaged flakes that you can buy too!

The traditional method of making Japan’s honkarebushi is labor-intensive, and takes about 6 months to complete; needless to say that it is the highest-quality katsuobushi in the market today.

The basic steps are as follows:

  1. Making the katsuobushi starts with removing the head, internal organs, tail, and excess flesh from the freshly caught bonito fish; then it is sliced lengthwise into 4 equal parts of fillets.
  2. Once the fillets are ready, then they are placed in metal baskets and submerged under a large cauldron of water which also sits atop a stove or open flame grill in order to boil the water to almost its boiling point (around 80-90℃) for about 90 minutes. After that, the fillets are allowed to be cooled down, and then deboned, as well as removing much of their skin and fat. The fillets will have lost about 32% of the water in them at this stage.
  3. The fillets are placed in wooden-lidded baskets and wood-smoked for about one hour, then allowed to cool. Smoking and drying the fillets is repeated around 10 – 15 times, and then they are laid out in the open to allow the sun’s heat to further dehydrate them. The fillets will have lost another 40% of the water in their bodies at this stage.
  4. The fillets are washed clean with fresh cold water and then laid out to dry again in the sun for a day or so. A fish paste coat is applied to them and afterwards, they are placed in a culture room and allowed to be fermented for around 2 weeks. After that, the special mold (fish paste) is removed and the fillets are laid out in the open once more for dehydration. This molding/drying process may take up to several months before the honkarebushi fillets of dried bonito can be considered ready for use and sold in the market. By this time the fillets contain about less than 18% of water and are the best kind of fermented katsuobushi.

The Power of Eurotium Herbariorum

The Japanese call the bacteria responsible for fermenting the katsuobushi fillets “Kouji” and it is obvious that it is rooted in their food culture.

The soy sauce or “shoyu” is often listed with a product name of “Kouji” too just like the bacteria.

Eurotium Herbariorum is the scientific name of the Kouji bacteria that is used to create Makurazaki Honkarebushi (katsuobushi).

The benefits of Eurotium Herbariorum (Kouji) include:

Types of Katsuobushi

There are different kinds of katsuobushi that have varying degrees of use and for different purposes.

You can spot and identify the best katsuobushi by its light pink or beige colors and they will slightly glint when exposed to the daylight.

Hanakatsuo (花鰹; はなかつお)

These katsuobushi or bonito flakes look alive because they are thin petals that look like large wood shavings in those woodworking or carpentry works you see (some may have dark meat coloring).

Shaved Karebushi (削り枯れ節)

The bonito flakes of karebushi have lighter-colored shavings and may or may not have dark meat in some of the flakes.

The light-colored flakes are ideal for making clear dashi with flavorful and aromatic soup stock.

Whereas the darker ones can be used for making miso soups simmered dishes and dressings.

Shaved Arabushi (削りあら節)

This type of katsuobushi is very common in the United States and is ideal for making soups like miso, dipping sauces such as the ponzu sauce, and dressings.

If you want your soup recipe or dipping sauce recipe to have a stronger flavor, then use those bonito flakes that have darker meat in them.

Arakezuri (粗削り)

This katsuobushi has thicker shavings compared to the other bonito flakes types and it has more dark meat to it too! This makes it essential in making braised dishes.

Itokezuri (糸削り)

The katsuobushi with the thinnest shavings and is suitable as a garnish for salads and tofu.

Take the time to read my post on these different kinds of Japanese dishes if you have the chance

“Usukezuri” – Thin shave

This bonito flakes have a shaved thickness of less than 0.2mm but have a significant larger width compared to the itokezuri.

The usukezuri flakes are easy to extract the umami flavors from, especially when you make dashi and it can also be used as a garnish.

“Atsukezuri” – Thick shave

It has the same shaved thickness as the usukezuri does of 0.2mm and has a large width as well.

It is great for making a braise with fully seasoned rich flavored dashi.

“Soft Kezuri” – Soft shave

This bonito flake is called “soft,” because it has been shaved vertically to cut against the grain.

When you’ll eat the kezuri in any of the favorite dishes prepared by the Japanese restaurant chef or a home-cooked meal, you will notice its tender texture when it melts in your mouth in just a few seconds.

The umami flavors are also easy to extract from the kezuri as it quickly secretes the enzymes in it once it comes in contact with water and the kombu in making the dashi soup stock.

“Saihen” – Cracked shave

Shaved parallel to the grains then crush into small pieces, the saihen or “cracked usukezuri” provides excellent aroma and flavor when you use it to make a seasoning for various Japanese recipes.

The tiny – almost looking like wood grain – katsuobushi is similar to potato chips crumbles, except that it tastes better and is healthier by comparison.

“Funmatsu” – Grinding

The term “funmatsu” is used when describing this fish fillet is when the katsuobushi or bonito flakes are shaved and then grounded into an orange-brown powdery substance.

And just like the saihen it is also used for cooking or flavoring as a seasoning.

It provides your dishes with great aromatic elements and rich flavorful umami plus a lot of health benefits that you never knew you needed!

Katsuobushi vs Bonito

Katsuobushi is essentially the same as bonito, although Katsuobushi is often used to refer to the dried and fermented fish blocks (the fish as a whole) where Bonito are the fish flakes made from Katsuobushi shavings.

How hard is Katsuobushi?

The dried and fermented fish blocks known as Katsuobushi are hard as a rock. This is because of the fermentation process and mould which extracts all of the water and fatty tissue. So hard in fact, that you need a specialized shaver to get the fish flakes you can use in your dish.

Also read: sushi making for beginners

Ever had trouble finding Japanese recipes that were easy to make?

We now have "cooking Japanese with ease", our full recipe book and video course with step-by-step tutorials on your favorite recipes.

Joost Nusselder, the founder of Bite My Bun is a content marketer, dad and loves trying out new food with Japanese food at the heart of his passion, and together with his team he's been creating in-depth blog articles since 2016 to help loyal readers with recipes and cooking tips.