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Katsuo Bushi

Updated on April 10, 2014

Katsuo Bushi


Katsuo Bushi In Detail

To be a little more precise, katsuo bushi (aka OKAKA) is made from Skipjack tuna. If you look in a Japanese / English dictionary, Katsuo is translated as dogfish tuna, so I am guessing that Skipjack tuna and Dog fish Tuna are the same. Please feel free to correct me if I am wrong.

Katsuo Cleaning

The Making Of Katsuobushi - Catch, Clean, Boil

According to Japanese culturists, the tuna fish are beheaded, gutted, filleted and cleaned after they have been caught. Tuna fish have a distinguished layer of fat around the belly and fat generally doesn't preserve well. It tends to go rancid much quicker than meat, so this layer of fat is nearly always trimmed off.

The filleted fish are then placed in to baskets and thrust in to vats of boiling water. The water is then reduced to just below boiling (to simmering point) and the fillets are simmered for an hour or an hour and a half. The bones are removed after the fillets have been boiled and cooled for a time. Unlike most other preserved fish products, Katsuo is completely cooked before being preserved. It is now after the fish have been boiled that they are preserved by way of smoking and then drying.

Smoking Katsuo

The Making Of Katsuo - Smoking

Smoking fish generally only takes a couple of hours. I have smoked fish at home in my garden and the results were amazing. It did not take long either. 3 maybe 4 hours in total.

This is not the case when it comes to smoking Katsuo fillets.

Katsuo fillets are smoked for a very long time. The process can be as long as a month. The wood that is used to produce the smoke is traditionally Japanese Oak and they are smoked according to a specific schedule.

They fillets are smoked for 5–6 hours in the first smoking session (the first day). They are then left to cool for a whole day. During this cooling time much of the moisture in the fillets will rise to the surface and evaporate. The fish are then smoked for 5 to 6 hours again on the second day, and the third and so on. The entire smoking cycle is repeated from 12 to 15 times.

The result is very hard fillets of Katsuo (Skipjack Tuna). These fillets are completely coated with a build up of tar from the smoke. This build up of tar is removed from the surface with a grinder. The dust is fragrant and at this stage of the process the fillets are called aragatsuo. (Ara) comes from the Japanese word ARAI and it means coarse and / or rough, so at this stage the katsuo fillets have not yet reached the end of the preservation process. Pieces of aragatsuo are still shaved and sold in stores. They are not true Katsuobushi yet, because they have not been subject to the final fermentation stage of the preservation process, but it still tastes great and is a cheaper alternative to real Katsuobushi.

Fermenting Katsuo Bushi

The Making Of Katsuobushi - Controlled Fermentation

The last and final stage when making katsuobushi is to allow the fish to dry completely. The drying is generally done out doors on hot dry sunny days. Thus the fillets are traditionally sun dried.

The fermentation is caused after the fillets have been dried and then sprayed with Aspergillus glaucus. This is a culture that causes the fish to grow mold. After being sprayed, the dry fillets are left for 2 weeks in a closed temperature controlled cultivation room. The mold ferments the fillets and the heat from the fermentation process helps to siphon out any remaining moisture that is left.

During fermentation, the mold is periodically scraped off, and with further sun-drying of the fish the fillets so hard that they almost resemble a piece of wood.

At this stage, each fillets weighs less than 20% of its original weight. By definition, it is only fillets that have been treated in this exact process and manner that can be referred to as a true katsuobushi. They are ruby red on the inside and so amazingly fragrant and full of flavor, the result of centuries of perfection.

© 2014 Lucas Uren


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