【Step 1: Steaming Beans—Heat Control Is Critical】
Soak soybeans for 12 hours
Steam until tender yet intact when pinched
Undercooked → fermentation stalls; overcooked → sauce turns bitter
【Step 2: Making Koji—The Invisible Workers】
Naturally inoculate with Aspergillus oryzae
Monitor temperature, humidity, and turning rhythm
After 3-4 days, beans sprout yellow-green spores
This isn't industrial-grade instant koji.
It's the “air fermentation” passed down by elders.
【Step 3: Mixing the Paste — The Salt-to-Water Ratio】
Brine concentration ≈ 18%
Place koji and beans in vats; rake, pound, and scrape the paste
Stir once daily for the first 30 days
No preservatives added.
Relying on salt, sunlight, and diligent work.
【Step 4: Sun-Drying — Time is the Key Ingredient】
Open-air fermentation vats: sun-dried by day, sealed by night
Covered during rain, uncovered under clear skies
180 days, from summer sun to winter chill