Shaved katsuobushi (kezuribushi) and dried kelp (konbu) are the main ingredients of dashi, the stock that forms the basis of the Japanese cuisine and enhances the umami of all soups, sauces and dishes in which it is used. The distinct umami flavor of katsuobushi comes from its high inosinic acid content. Katsuobushi is rich in vitamins, minerals and proteins and has been used as a stock base in Japan since the 8th c.
[Block of katsuobushi, hard as wood. Photo from Wikipedia]
The traditional production process is as follows:
- Namakiri (Cutting the raw fish, 生切り). The fish is cleaned by removing the innards and head and filleted into three pieces.
- Kamatate (Boiling, 釜立て). The fish are put into a basket and simmered (if the water boils to hard, the fish will be damaged) for about 100 minutes in a cauldron. The broth of this process can be used as a condiment.
- Honenuki (Removing the bones, 骨抜き). After cooling down, the bones are removed and the fins shaved off. Excess fat may also be removed. After this stage, the fillets are called namaribushi 生利節 (or namabushi 生節) and can be used as ingredients - but they are not yet katsuobushi!
- Baikan (Smoking and drying, 焙乾). Only the undamaged fillets are used (the rest is used for surimi production). The fillets are smoked and dried. Oak or pasania wood is used. Six-hour smoking sessions alternate with day-long rest periods to allow the fillets to dry, and this cycle may be repeated up to fifteen times. The tar from the smoke is carefully cleaned off the surface of the fillets. When this process has been half completed, the fillets are called satsumabushi さつま節. After this process of smoking and drying has been completed, they are called arabushi 荒節. In fact, as the next process is time-consuming and expensive, the hanakatsuo 花かつお shavings (also called katsuokezuribushi 鰹削り節) sold in bags in supermarkets are all of arabushi quality. In other words, this means that most katsuobushi used today is of arabushi quality - the real thing that in addition has undergone the treatment described at point 5 below is only used in top quality restaurants. Arabushi is however seen as a good value substitute. Producing satsumabushi requires about one week and arabushi about one month.
- Tenpiboshi / kabitsuke (Sun drying and injection with mold, 天日干し・カビ付け). After cleaning the fillets, they are sun dried, and after that sprayed with the mold Aspergillus glaucus and left for two weeks in a closed cultivation room. In the warm environment the mold grows. Thanks to the mold, the proteins in the fillets are broken down and the umami element inosinic acid and vitamins are formed. The mold is continually scraped off and the cycle is repeated. After this has been done five to six times, the fillets loose all their moisture and become as hard as pieces of wood. They now retain only 20% of their original weight. Only fillets that have been treated in this manner may officially be referred to as katsuobushi. After repeating the process of mold growth and sun-drying at least twice, the end product is called karebushi (枯節, "dried fillet"); and after this process has been repeated at least thrice the exclusive end product is called honkarebushi (本枯節, "true dried fillet"). When tapped together lightly, the fillets make a metallic sound; and when broken open they are a deep ruby color inside. Producing karebushi takes several months, and producing the rare and very high-end honkarebushi may take over two years. Karebushi and honkarebushi are not only very expensive, but also difficult to find even in Japan - you have to go to a specialty shop, such as the ones around the Tsukiji market.
[Katsuobushi kezuriki, to shave off the flakes from the block of katsuobushi. Photo Wikipedia]
But as stated above, in our present-day convenience culture, katsuobushi is typically sold as shavings in airtight plastic bags rather than the traditional blocks - and this is of arabushi rather than of karebushi or honkarebushi quality. On top of that, these products are usually a mixture of katsuobushi with the shavings of other dried fish as mackerel, tuna or sardines.
There are two types of shavings: large and thick (kezurikatsuo) to make dashi stock and small, thin shavings (hanakatsuo) used as flavoring and topping of dishes on the table.
[Fine katsuobushi shavings (hanakatsuo) used as a garnish. Photo Ad Blankestijn]