Katsuobushi Or “Bonito Flakes”: How Do They Give Umami?
Bonito flakes are called katsuobushi, the Japanese name for dried, fermented, and smoked skipjack tuna.
The fish is dried, fermented, and smoked. Then pieces are shaved to add to dishes to provide a great umami flavor.
Shaved Katsuobushi and kombu are the main ingredients of dashi, a broth that forms the basis of many soups and sauces in Japanese cuisine, like ramen noodles.
It’s also used as a topping on a lot of dishes like takoyaki and the famous okonomiyaki, making it a must-have staple to cook Japanese.
Katsuobushi’s distinct umami flavor comes from its high inosinic acid content. Traditionally made katsuobushi, known as karebushi, has added Aspergillus glaucus fungus to reduce moisture.
Katsuobushi has also been shown to impart a kokumi flavor.
Bonito flakes are an interesting phenomenon. Because they’re so lightweight, the heat from the food on the plate can cause them to move around.
It is for this reason that many say the flakes dance. Therefore, they’re an interesting addition to cultural dishes.
For culinary purposes, it can also be used as:
- A stuffing for rice balls
- A topping for rice or noodles
- A seasoning for tofu
- A topping for takoyaki or okonomiyaki
- A seasoning for century egg
- A topping for ramen
- A high protein treat for cats
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 usually indicates that a young bonito is used as a cheaper substitute for skipjack tuna.
It’s called okaka (おかか) when it’s used to make a soy sauce base for rice dishes like okaka onigiri.
In this post we'll cover:
- 1 How does katsuobushi get its umami flavor?
- 2 History of Katsuobushi
- 3 Health Benefits of Katsuobushi
- 4 What is Katsuobushi used for?
- 5 How to make Katsuobushi
- 6 Types of Katsuobushi
- 7 Katsuobushi vs Bonito
- 8 How hard is Katsuobushi?
- 9 FAQ around bonito flakes
How does katsuobushi get its umami flavor?
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.
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
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:
- 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.
- 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.
- 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.
- 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:
- Enhanced “Umami”: It secretes essential enzymes like the Proteolytic and Protease enzymes which creates the umami components.
- Dashi is Created Due to the Break Down of Fats: The dashi that is created from the katsuobushi by nature is an animal product, although much of the fat has already been removed during the fermentation process. The good bacteria Kouji also contributes to the breaking down of fats in the dashi as it secretes Lipase and Lipolytic enzymes when the mold grows on the katsuobushi while in the culture room.The Chinese analog of the dashi which is mainly made of beef, pork, chicken or seafood has fats present in it, but the Japanese dashi contains almost no fat as it is made from katsuobushi. The special fish paste or mold is what makes the katsuobushi healthy and provides its unique umami flavor.
- The Unique Aroma that has no Trace of Fish Odor: The Protease and Lipase’s secreted enzymes also give the katsuobushi a unique aroma, but none of the fish stinkiness.
- Anti-Oxidation: The fish fillets of katsuobushi secrete anti-oxidants during the fermentation process, thus it helps protect the surface of the fillets from oxidation even when exposed in the open air.
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.
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.
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) whereas Bonito flakes are the fish flakes made from Katsuobushi shavings, and bonito itself is the live fish.
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.
FAQ around bonito flakes
Are bonito flakes gluten-free?
A gluten-free diet excludes foods that contain gluten such as proteins found in wheat, as well as barley, oats, and rye. Bonito flakes are free of gluten and are, therefore, approved for gluten-free diets.
Are bonito flakes halal?
A halal diet consists of foods that Muslims consider safe to eat. These foods are ones that aren’t considered harmful to their bodies.
Although halal diets usually exclude the consumption of animals, there are certain fish that are considered halal. Bonito is among them.
Are bonito flakes keto?
The keto diet calls for low-carb foods and a good amount of healthy fats. Bonito is low carb and rich in healthy fats, so it’s ideal for a keto diet.
Are bonito flakes vegetarian?
There are some gray areas concerning what a vegetarian can and can’t eat.
However, the consumption of dead animals is never considered vegetarian. Therefore, bonito and other fish are included in the list of things that aren’t considered vegetarian.
Are bonito flakes kosher?
It’s acceptable to make bonito in kosher kitchens. However, the flakes aren’t certified kosher.
Kosher dieters who wish to make recipes that call for bonito will usually substitute the flakes for whitefish.
Do bonito flakes contain MSG?
MSG is monosodium glutamate, which is commonly used to give Asian dishes an umami flavor. Many say it can cause damage to nerve cells; however, this has never been proven.
Others say it’s caused adverse reactions, such as headaches and digestive issues.
In any case, you don’t have to worry about the possibility of an adverse reaction when eating bonito or bonito flakes. They’re both MSG-free.
In fact, bonito flakes are often used in dishes instead of MSG to provide an umami flavor without any possible harmful side effects.
Do bonito flakes expire?
Since bonito flakes are dried food, they last a long time. However, that doesn’t mean that they don’t have an expiration date.
In general, bonito flakes will last 6 to 12 months. However, it’s best to check the packaging to see when yours expire.
What can I use instead of bonito flakes?
If you’re making a recipe that calls for bonito flakes but you don’t have any on hand, shiitake mushrooms and kombu are both good substitutes.
They’re often used in meals as a vegetarian alternative.
Also read: sushi making for beginners
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.