How to Make Katsuobushi
Katsuobushi (鰹節) is Japanese dried, fermented, and smoked skipjack tuna, considered the hardest food in the world. The months-long process creates blocks that are shaved into flakes (kezuribushi), providing the smoky-savory foundation for dashi broth. The process yields two main types: Arabushi (smoked only) and Honkarebushi (fermented with mold), the latter being the pinnacle of umami development.
Category: Fish & Seafood · Method: Fungal/Mold · Time: 1-6mo · Difficulty: 3/5 · Yield: varies · Temp: 12-18°C
History
Katsuobushi production developed during Japan's Muromachi period (14th-16th century), with techniques refined over centuries. The process spread from Kii Peninsula to other regions. Makurazaki in Kagoshima and Yaizu in Shizuoka became production centers. It remains essential to Japanese cooking.
Ingredients
- 1 whole fish (5-10 lbs) Fresh skipjack tuna (bonito) — Very fresh
- - No other ingredients — Process uses smoke and mold only
Equipment
- Filleting equipment
- Simmering pot
- Smoking chamber with oak/cherry wood
- Mold cultivation room
- Katsuobushi shaver (for finishing)
Instructions
Smoking (Baikan)
Hot smoke the fillets using oak or cherry wood. The temperature is maintained between 70-80°C to further cook the fish, remove moisture, and infuse deep smoky flavor. This cycle of smoking and resting (to allow internal moisture to migrate to the surface) is repeated 10-15 times.
Time: 2-4 weeks
Tip: After this stage, the product is known as 'Arabushi'. It is intensely smoky but lacks the refined depth of fermented versions.
Mold cultivation (Yubushi)
Inoculate the smoked blocks with Eurotium herbariorum (formerly Aspergillus glaucus). Place in a 'muro' (fermentation room) at 25-30°C with 80-85% humidity. The mold consumes residual fats, breaks down proteins into amino acids, and draws out deep-seated moisture.
Time: 3-6 months
Tip: This transformation turns Arabushi into 'Honkarebushi'. The mold must be brushed off and the blocks sun-dried between each of the 4-6 molding cycles.
Fermentation Timeline
- Day 1: Preparation — Fish filleted and simmered.
- Weeks 2-5: Smoking — Daily smoking cycles. Arabushi stage reached.
- Months 2-3: First molding — Mold applied and cultivated. Sun-dried.
- Months 3-6: Repeated molding — 4-6 mold cycles. Hardening. Flavor developing.
- Month 6+: Karebushi complete — Rock-hard, deeply savory. Ready for shaving.
Signs of Success & Spoilage
Good signs
- Rock-hard texture
- Woody sound when tapped
- Reddish-brown color
- Clean savory aroma
- Even mold coverage (during cultivation)
Warning signs
- Soft spots
- Rancid smell
- Green or black mold
- Cracks in flesh
Troubleshooting
- Pathogenic mold growth
- Cause: Incubation temperature too low or humidity too high without airflow. Solution: Maintain a steady 25-30°C. Ensure only the beneficial white/blue-green Eurotium species is present; discard if black or fuzzy green mold appears.
- Won't harden
- Cause: Insufficient smoking temperature (Baikan) or too few molding cycles. Solution: Ensure smoking reaches 70-80°C to denature proteins and drive out moisture. Continue molding cycles until the block is resonant.
- Rancid smell
- Cause: Fat oxidation due to improper mold activity. Solution: Eurotium herbariorum is essential as it produces lipolytic enzymes that break down fats. Ensure proper inoculation and incubation conditions.
Storage
Whole blocks in paper; shavings airtight Keeps Years whole; months for shavings. Shave fresh for best flavor. Blocks keep indefinitely.
Health Benefits
- Extremely high protein
- Rich in inosinic acid (umami)
- B vitamins
- Minerals (iron, niacin)
- Low calorie
- Historic preservation method
Serving Suggestions
- Shaved for dashi broth
- As bonito flakes (okaka) on tofu
- Topping for okonomiyaki
- In onigiri filling
- Over rice with soy sauce
- Base for tsuyu and ponzu
Related Fish & Seafood Ferments
Other Fungal/Mold Ferments
- Miso — Condiment
- Tempeh — Legumes & Soy
- Shoyu — Legumes & Soy
- Tamari — Legumes & Soy
- Doubanjiang — Legumes & Soy
- Gochujang — Legumes & Soy
- Tauco — Legumes & Soy
- Meju blocks — Legumes & Soy