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2020, May, 10

Katsuo Bushi :​

​Is it fermented?


Katsuobushi is one of the ingredients which is essential for Japanese cuisine. It's made of Katsuo fish (bonito or skipjack)and looks like a piece of wood. It's known as the hardest food in the world. We shave a block of Katusobushi for making Dasi (Japanese broth) and also use it as a topping such as savoury pancakes, noodles and also cooked green veggies with soy sauce. Our food culture has a strong connection with Katsuobushi.


However, we don't know well about how it is made, what kinds are fermented or not and the differences in products. I like Katsuobushi but sometimes choosing the product according to only its price. As a person who loves Japanese cuisine and introducing its culture overseas, I thought it's good to learn more about Katsuobushi. 


1st chapter of

getting along well

with Katsuobushi.


One day, I found a good old Katsuobushi shaver at my grandma's house. The shaver generally has two layers. The top is a blade to shave Katsuobushi and the bottom is a drawer for catching the shaved ones. I was quite excited to find this old tool because I've seen this only on TV. So, I posted a photo on Facebook and some friends went like ' Oh, my mom used to use this for shaving Katsuobushi.', ' It was my task to shave it when I was a kid.',
' The freshly shaved ones are the top!!' It seemed like s
ome of the friends older than I kept some good memories of home shaved Katsuobushi. Then I realized that I didn't have any memory of Katsuobushi.


Most of the Japanese buy ready-shaved Katsuobushi flakes from supermarkets these days. My grandma says her mom used to buy a block of Katsuobushi and shaved it every morning to make Dashi because there's no ready shaved Katsuobushi in the past. After packaging method improved and people have no time to shave it at home, this kind of culture became disappearing.

Although I found the Katsuobushi shaver, for making freshly shaved Katsuobushi I needed to buy a block of Katsuobushi and it's not sold at general supermarkets.

This experience made me thought about visiting a Katusobushi maker. To know how it's made and to buy a block of Katsuobushi. I just wanted to get along with Katsuobushi more than before. So my 1st Katsuobushi journey was about to start in 2019.

Yaizu, a Katsuobushi city.

There're some regions that produce Katsuobushi. The famous one is Makurazaki, in Kyushu but it's far from my place, Yokohama. Then I found one in Yaizu which were used to be the top region of Katsuobushi.


(The photo is from the museum of fishery in Yaizu. People are driyng Katsuobushi in the sun.)


Yamajyuu Masuda Shyouten.


Yamajyuu Masuda Shuouten is one of the Katsuobushi makers in Yaizu. They do a factory tour in Japanese and you can buy the products at the shop next to the factory. I visited Yamajyuu with some friends to learn how Katsuobushi was made. (2019, March, 20)

When we visited the factory, the workers were simmering skipjacks and deboning them. They willingly explained the process to us. I'll share with you what I've learned here.




1, Defrosting and filleting.


Firstly, defrosting and filleting skipjacks. Yamajyuu process a ton of bonito every day and they fillet all by their hand. The photo on the right is the cutting board of Yamajyuu. You can see the people's works have been carved on the board. 




2, Shimmering.

Shimmering the fillet skipjacks in 95℃ water for a while. This process slows the degradation of the meat.

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3, Deboning.

Deboning the cooked skipjacks and take some parts apart to shape them closer to the final product. This process is done in the water. After this process, the products are called Namaribushi






4, Tebiyama smoking. 

Then the Namaribushi are smoked and dried. 


Yamajyuu has been following the Tebiyama smoking method for more than a century. This method used to be the main method of smoke-drying Katsuobushi since from the Edo era (From 1603 A.C. to 1868 A.C.) but it needed much time and efforts. So, nowadays only a few Katsuobushi makers follow this method. 

Placing the Namaribushi on a special tray and pile some trays up on the smoking stove then smoke-drying them with woodfire. Switching the layers of trays sometimes and smoking the Namaribushi well. It's said that theTebiyama smoking method has a stronger aroma of the smoke compare to nowadays methods and it influences the flavour and the quality. 







5,  Second smoking.

After smoking with the Tebiyama smoking method, the skipjacks are smoked and dried more in a smokehouse. In that house, there're 4 floors which the smoke and the heat from the ground floor can easily reach all the skipjacks of all layers. And it's possible to change the layers according to the condition of skipjacks, so all conditions of the skipjacks can be smoked at once.  


It will take nearly a month to get them dried. The amount of moisture has to be lower than 26 % of the final product. The smoking process in this smokehouse takes for a month but the wood fire isn't always on. 

Yamajyuu thinks it's important to moist the skipjacks sometimes not only just keep them drying for a month. It's difficult to see it only from the photos but the place for simmering skipjacks and the smokehouse isn't divided. So when the factory simmers the skipjacks, the smoke-drying skipjacks also get an influence of humid. Loosen and tighten, Loosen and tighten. Then the skipjacks get dried well from its inside.   

The role of this process is to evaporate the moisture of skipjacks, bring abundant aroma to the product and prevents oxidation of fat. 

Then the resulting products are called Arabushi. Thinly shaved Arabushi is called Hana-katsuo(means like skipjack flower) and Katsuo-kezuribushi (means thinly shaved skipjack.) that we can find in supermarkets.


Some ferments lovers may have wondered when was the fermenting process or I may have forgotten to tell it. Well, thank you for waiting. We'll soon come to the molding process.

6, Scraping.

So, after Arabushi is beautifully done, the well-shaped ones and well fatty ones are chosen then they're shaved for taking out tar from the surface. After this process, the skipjacks are called Hadakabushi then they move on to molding. The well fatty Arabushi makes more beautiful mold compare to the ones have less fat or too much fat.





7, Molding.


Molding process takes 4-6 months by repeating spraying Katsuobushi mold, incubating in the molding room and drying them in the sun. When the bonito has molding process for twice, they are called Karebushi (Kare means withered) and after taking three or four processes they're called Hon-Karebushi (Hon means very or truly.).

The water content of Hon-karebushi is 13-15% of the products and the weight has reduced one-sixth of the Namaribushi.  

Then thinly shaved Hon-karebushi is called 'Katsuo-karebushi Kezuribushi'. The name always confuses me because in general, the Japanese call all kinds of thinly shaved skipjacks as Katsuobushi and most people didn't mind if it's fermented or not. So, I didn't think about the differences between Katsuo-kezuribushi and Katsuo-karebushi Kezuribushi for a long time but actually they have huge differences. The process, the time, the quality and the effort. When you see the word 'Kare' on the package of Kastuobushi, it means processed by mold and people put much effort and time. I wish they had shorter and easier names so that anyone understands it.  






The mold of Katsuobushi. 

So, why do we have two kinds of Katsuobushi even major society call both of them Katsuobusi for short.  It's obviously Karebushi are dryer and more preservable but since we use a fridge it seems like it doesn't matter these days. ​To get the good answer we need to know a bit of history of Katsuobushi.


When the Tebiyama smoking method was the main method, it's in the Edo era, people hadn't discovered the molding method on Katsuobushi. It was ok to sell and buy Arabushi on the small scale of business but it was difficult to ship them far because the products easily got bad mold because of the high humidity.  So then, around the year 1700 one producer in Wakayama Pref. found the technic of molding to preserve Katsuobushi longer.

' To suppress the unwilling mold, why don't we attract good mold first?'


That was an idea. And then the people got tagged with Katsuobushi mold. This method spread some regions of Katsuobushi and then Karebushi became popular. 

So, here let me deepen about the Katsuobushi mold. When I searched on the web, it seemed like there're some kinds of mold were used depending on the factory. Some said the first mold belongs to Penicillium and the others belong to Aspergillus. Some said it's Aspergillus glaucus and some said Eurotium repens and Eurotium herbariorum. It seemed like Aspergillus repens is the main mold but I wasn't really sure about it. Because as I the person who never studied about fungi I can't tell who's right or wrong or everyone is right. However, I understood that all are a beneficial mold for making Katsuobushi. Please allow me to carry on by calling them Katsuobushi mold for now. 


Hadakabushi (The Katsuobushi which has smoke-dried and scraped the surface.)still has a bit of moisture. So the Katsuobushi mold utilizes the moisture left inside of Hadakabushi to grow. The enzyme called lipase brakes down the fats of Hadakabushi then produce mild flavour and Umami. And also it influences the colour of Dashi. When we cook meat or fish in the water, it produces scum or foam on the surface of the water but Katsuobushi doesn't. So thanks to the Katsuobushi mold it just makes clear and Umami-full soup. This is the beauty of Dashi.


There are many scientists studies about the science of Katsuobushi. I'd like to introduce one of the great doctors of fermentation in Japan here. He is Mr Takeo Koizumi. Let me roughly translate what he described the Umami of Katsuobushi.



The mold which grows on Katsuobushi needs to reach the moisture which remains inside of the Katsuobushi to survive and grow. Thanks to their work Katsuobushi drys more and becomes harder than Arabushi (the smoked ones) and preservable. The lipolytic enzyme of the mold breaks the fats of Arabushi and prevents deoxidation of the fats and degradation of the product. And also the proteolytic enzymes of the mold breaks the protein of Arabushi then produces Amino acid which is the source of Umami. It's called Inosinic acid. It's known that Umami is maximized when they meet other Amino acids (such as glutamic acid of Kombu seaweed and Miso and guanylic acid of Shiitake mushroom). So, that's why Katsuobushi can produce unbelievable elegant but powerful taste. 

【Takeo Koizumi:  Jpn. J. Med. Mycol. Vol. 42. 1-5. 2001    ISSN 0916-4804   P3】

I'd like to add that Arabushi also has much Umami. The Dashi made from Arabushi is also wonderful. Because the component of Umami also extracted when the bonito simmered in the hot water. So every Katsuobushi is tasty. To make things precise, Umami of Karebushi is more condensed, the Dashi is more clear and more preservable. 

So let me make things clear about how the Japanese choose the product. If you want to make clear Dashi with mellow flavour Honkarebushi or Katsuo Karebushi Kezuribushi is the best but costs you more. And if you want the smokey flavour, mild taste and to use without minding the price, Arebushi or Katsuo Kezuribushi is the best. I can't explain more about the difference in the taste yet but now I can explain why we have some kinds of Katsuobushi. The reason is to have more choice in Japanese cuisine according to how the cook wants to create the flavour or the colour. However, I think we should have easier names for showing the differences.

​Further information about Yamajyuu. 

Thanks to Yamajyuu Masuda Shouten, I learned a lot about Katsuobushi and now I can explain the process and differences better than ever. I hope my article helped you understand the process of Katsuobushi somehow.

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Yamajyuu has the reserved factory tour on weekdays when they are open. So if you want to learn about Katsuobushi please visit them. And if you need an interpreter and a private guide please send me a message. :)

Here are the HP, Instagram and the Youtube video of the process of Katsuobushi at Yamajyuu.


Yamajyuu Masuda Shouten (ヤマ十増田商店)

〒425-0031 5-4-9 Ogawashinmachi, Yaizu City, Shizuoka Pref.TEL : 054-628-3677 / FAX : 054-626-3654 (9:00-17:00 of weekdays)


(This is a wrapping paper of Yamajyuu. The drawings show all the process of Tebiyama smoking method. Isn't it pretty? )




A postscript about the Katsuobushi mold.  (2020.May.19)


I asked about the Katsuobushi mold to Yamajyuu and found that Eurotium mold are used for making Honkarebushi at Yamajyuu. There's a Katsuobushi union at Yaizu and the factories belong to that union are using the same mold which developed at the Union. However, one generation back, Yamajyuu used to use Aspergillus. So there might be a factory which follows inherited way of making Katsuobushi and still uses wild Aspergillus which thrived in the molding room.   For those who understand Japanese here're more to read about Katsuobushi mold.


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