The Complete Koji-Making Process for Honkaku Shochu

(2025 Master-Class Level Detail – From Spore to Perfect Seikiku)

Koji (麹) is the single most important step in shochu, sake, miso, and awamori production.

In honkaku shochu, the quality of the koji determines 70–80 % of the final flavour.

Every distillery guards its exact method like a state secret, but the fundamental process is the same everywhere in Japan.

Here is the full 48–72 hour journey, step by step, as done by the best distilleries in Kagoshima, Kuma, and Okinawa in 2025.

1. Rice Selection & Polishing (精米 – Seimai) – Day –2 to –1

• Only short-grain Japonica rice (usually from Kyushu or Kumamoto).

• Polishing ratio: 60–90 % remaining (10–40 % polished off).
  → Higher polishing (60–70 %) = cleaner, more elegant koji (Kuma-style rice shochu)
  → Lower polishing (80–90 %) = richer, oilier koji (sweet-potato shochu)

• Washed, then soaked 4–12 hours until moisture reaches exactly 36–40 %.

2. Steaming (蒸米 – Mushimai) – Day 0, 06:00–09:00

• Rice is steamed in large wooden or stainless koshiki (steamer) for 50–70 minutes.

• Goal: 100 % gelatinised starch, 38–42 % final moisture, firm outside, soft inside.

• Over-steaming = mushy koji → sour off-flavours

• Under-steaming = hard grains → incomplete saccharification

• After steaming: spread on steel tables to cool to 35–40 °C.

3. Koji Spore Selection

Three main strains legally allowed for shochu:

Type	Strain name examples	Acid production	Flavour profile	Famous region
White koji	Kawachi, Shochu-ko No.1	Medium citric	Clean, pineapple, peach	Kagoshima, Miyazaki
Black koji	Okinawa black, Shochu-ko No.2	High citric	Funky, tropical, earthy	Okinawa (awamori)
Yellow koji	Sake-type (e.g., #9, #7)	Low citric	Floral, elegant, sake-like	Kuma rice shochu

Spore dosage: 0.05–0.2 g per 100 kg steamed rice (≈ 1 billion spores/g).

4. Inoculation (種麹付け – Tanekiri Tsuke) – Day 0, 12:00–14:00

• Cooled rice moved into the koji room (麹室 – kojimuro): temperature 30–35 °C, humidity 70–90 %.

• Spores are dusted by hand or machine while workers mix with wooden shovels.

• Traditional method: two workers sing rhythmic chants while turning the rice to ensure even distribution.

5. The 48–60 Hour Koji Dance – Hand-Made (Tejime) vs. Machine

Traditional hand-made koji (te-koji) is still used by >70 % of premium distilleries.

Day 0 – 14:00 Seed koji (種麹)

• Rice piled into small heaps, covered with damp cloth

• Temperature rises naturally from respiration to 36–40 °C

• First 8–12 hours: “keep warm and quiet” – no touching

Day 1 – 06:00 First turning (一番手入れ – Mori)

• Rice spread thin on wooden trays (koji-buta)

• Mycelium just visible as tiny white spots

Day 1 – 12:00 Second turning (二番手入れ – Niban)

• Re-piled into higher mounds to raise temperature

• Goal: 38–42 °C peak for enzyme production

Day 1 – 20:00 Breaking (割り込み – Wari-komi)

• Rice broken apart and flattened again to cool and prevent overheating

• White “hair” now clearly growing

Day 2 – 06:00 Final shaping (出麹準備 – De-koji)

• Temperature allowed to drop slowly to 30–35 °C

• Koji smells like sweet chestnuts and fresh mushrooms

Day 2 – 10:00–14:00 Finish (出麹 – De-koji)

• Koji removed from room when:
  → Mycelium completely covers every grain (snow-white for white koji)
  → Light green spores just beginning to appear (for white/yellow)
  → Pleasant sweet aroma, no sour or ammonia smell
  → Hand test: grains stick together lightly but break apart easily

Total time: 48 hours (black koji), 50–54 hours (white), 54–60 hours (yellow).

6. Quality Grades (2025 Distillery Internal Grading)

Master koji-makers grade every batch:

Grade	Appearance	Enzyme activity	Use in shochu
Tsuki-haze	Perfect snow-white, long mycelium	Highest	Top premium lines
Standard	Even coverage, slight yellowing	High	Regular honkaku
Tama-haze	Some broken grains, green spores	Acceptable	Blended or chu-hi base
Failed	Sour smell, dark spots, ammonia	Low	Discarded or sold as animal feed

7. Modern Machine Koji (Rare in Premium Distilleries)

• Automatic trays with temperature/humidity sensors

• Takes 44–48 hours, more consistent

• Used by large brands (Iichiko, Kuro Kirishima mass lines)

• Traditionalists claim it lacks “soul” and depth.

8. Enzymes Produced (Why Koji Is Magic)

Final good koji contains:

• Amylase → starch → glucose

• Glucoamylase → glucose polymers → glucose

• Acidic protease → proteins → amino acids (umami & flavour)

• Citric acid (black koji) → prevents contamination, adds fruity notes

• Lipase → fats → aroma compounds

Bottom Line – 2025 Reality

Making perfect koji is still 90 % human skill.

Even with sensors and lab testing, the master koji-maker (kōji-mori) decides by nose, hand feel, and 40 years of experience when to pull the batch.

In Kagoshima they say:

“Rice shochu is made in the distillery.

Sweet-potato shochu is made in the koji room.”

One millimetre too much mycelium or one degree too hot and your $200 bottle of 25-year aged shochu becomes vinegar.

That is why great honkaku shochu will always be limited, expensive, and worth every yen.

It starts with 50 hours of people singing to fungus in a hot, humid room — and somehow that becomes liquid art.