How Artisanal Katsuobushi is Made - Matoba Suisan

How Artisanal Katsuobushi is Made - Matoba Suisan

In the Autumn of 2016, we ventured down to the southern tip of Kyushu in Kagoshima prefecture with one purpose in mind, finding the best katsuobushi (dried skipjack tuna). Our journey led us to Matoba Suisan in the port town of Makurazaki.

A building at Matoba Suisan

Matoba Suisan

Why is katsuobushi important? Because, along with konbu, katsuobushi is used to make dashi, which is the foundational stock of Japanese cuisine. The umami that dashi brings to so many Japanese dishes is really one of the central flavors of the cuisine. Let’s use miso soup as an example. A long time ago when Greg first tried making miso soup he boiled water with tofu, seaweed, and added miso. He tried it and just felt like something was “missing". It didn’t taste quite like it did in Japan. He later found out what was missing was dashi made with konbu and katsuobushi. In fact, you’ll quickly find that katsuobushi lends its unique flavors to countless Japanese dishes. And it is indeed these flavors that make so many classic Japanese dishes truly Japanese. There is no substitute. From foods like a simple miso soup to ramen stock, katsuobushi is really not something you can find a substitute for and without it, you’ll always find that something is “missing". To us, katsuobushi is what makes Japanese food Japanese.

What is katsuobushi? It is cooked, smoked and sometimes fermented skipjack tuna loins. The whole process can take up to six months. The fish becomes so hard, when you tap two finished loins of katsuobushi together, they give off a metallic clink. They are so hard you need the equivalent of a wood shaver to shave off flakes. To see the production process up close & personal is incredible. We had never seen something so fascinating.

The morning we arrived was sunny with a nice chill to air that was perfumed by the sea. There we met the president of Matoba Suisan, Shinya Matoba. He explained to us his company started as wholesalers of katsuobushi in 1956, but in 1975 they began to make their own katsuobushi to keep up with customers' demands. Over the years, Matoba-san has been refining his products to reflect the true taste by having most of the procedures performed by hand. Matoba-san is serious about sticking to tradition. In his mind there is a reason why katsuobushi has been made one way for hundreds of years.

When we got to see the katsuobushi production at Matoba Suisan, it was completely mind blowing. To begin, they receive whole skipjack tuna which they inspect for quality. Then they remove the head, gut the fish and cut it in half to remove the spine. Once removed, the two fillets are cut in half again, which yields four fillets - two dorsal and two ventral. Then the sectioned loins are carefully arranged on trays. It was mesmerizing watching the Matoba craftspeople cut and process these fish in such an efficient manner.

Prepared fish and poaching

First steps - preparing and poaching

The trays are then lowered into a hot water bath that is just below boiling for 60 to 90 minutes. After cooling, the small bones are carefully removed by hand, then a half to a third of the skin is removed from each section. We were surprised that with all these raw and poached fish in this part of the factory, it smelled not ‘fishy’ but of the ocean.

Skilled craftspeople work on the fish; almost ready for smoking

Careful hand work to prepare poached skipjack tuna for smoking

Now they “shape” the sectioned loins by using a skipjack tuna paste to fill in cracks and smooth out irregularities. This improves the ultimate shape of the finished product. This method also helps prevent any mold from forming below the surface. Now they are ready to be smoked.

The skipjack loins are smoked using oak in one of two large smoking rooms. It was surreal when Matoba-san invited us to step into one of those big rooms because they were three stories tall. The loins spend two days being smoked on the first floor, close to the fires. They are then moved up to the second floor for a week and finally the third floor for another five days. Matoba-san, however, can alter these time periods depending on the customer and application.

Firewood for smoking the skipjack tuna and entering the smoking room

Left: Firewood for smoking the skipjack tuna
Right: Greg and Takehiro Wada enter the giant smoking room with Matoba-san

At this point the loins are called Arabushi, meaning rough timbers. Any tar or fat is carefully scraped off the surface. And for the vast majority of the smoked loins, this is basically the end of the process. The only step left is shaving the Arabushi. The resulting Hana-Katsuo shavings are ready to be sold for making dashi.


Left: Arabushi right out of the smoking room
Right: Finished Arabushi

But for a very small number of smoked loins, their time at Matoba Suisan has just started. These lucky few will now go through a fermentation process. Don’t think of a wet fermentation process like for beer or wine. In this case they are inoculated with koji spores and placed in a humid fermentation room for 2 to 3 weeks. This mold helps break down remaining fat and makes the product more delicious. Next, they are dried in the sun before being put back into the humid fermentation room again. This cycle is repeated 3 to 4 times.

After about 6 months of exacting work the fermented katsuobushi, now called Karebushi, are ready. The fermentation process has reduced the moisture level in the Karebushi to less than 20%. This is why when you tap two of them together, they give off a metallic clink. And when you split one open, the inside shines like a ruby. It is an almost miraculous transformation from what amounts to sashimi to this magical jewel of an ingredient.

From raw fish to jewel (finished honkarebushi)

Left: Starting point - raw skipjack tuna
Right: Finished product - jewel-like Karebushi

The flavor of the fermented katsuobushi is even deeper with umami. Dashi made with Karebushi is clearer than that made of Arabushi. Both are full of umami, but dashi made with Karebushi has a deeper, rounder, more nuanced umami.


The penultimate stop on our tour was to the shaving room where the finished loins are made into shavings (like you would use for making dashi) or flakes (like you would see “dancing” on top of Okonomiyaki). The katsuobushi are first washed and then steamed. If they are to be thick shaved, they are also roasted at a high temperature for five minutes. Using drum shavers, Matoba-san then shaves the katsuobushi. His commitment to customer service is evident in this step as he can customize the thickness of the shavings and flakes depending on his customers’ desires. The katsuobushi shavings are then packed up & ready for shipment.

Like many of our company visits, we ended up in a meeting room where Matoba-san filled our heads with more katsuobushi facts. Amongst the things we learned were:

• The loin from the back of the skipjack tuna has a more refined taste than the belly loins
• Leaner fish produce better tasting katsuobushi, but climate change is making for fattier fish
• The market in Japan is 90% Arabushi and 10% Karebushi

He even presented us with a new product offering they had developed – skipjack tuna chunks simmered in a soy-based sauce and then covered with cheese. It was an…um…acquired taste. What wasn’t an acquired taste was the lunch Matoba-san treated us to at nearby restaurant that specialized in, you guessed it, skipjack tuna. It was amazing and to this day Greg still dreams of the salt cured skipjack tuna liver.

Skipjack tuna with cheese and skipjack tuna lunch

Left: From the R&D lab - skipjack tuna with cheese
Right: A skipjack tuna lunch to dream about

Fast forward five years to late 2021 and here we are finally introducing Matoba-san’s artisanal katsuobushi to all of you. We blame the delay on government red tape (now solved). Thank you (and especially you, Matoba-san!) for sticking with us and being patient. We are over the moon with joy to now be able to offer this incredibly important part of Japanese cuisine.

This really makes us want to make some dashi