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ENPL

Koji & Miso Fermentation

Cultivate koji mold and ferment soybeans into umami-rich homemade miso

creativecraftyintellectual$ lowa weekenddifficulty 4/5

Grow koji (Aspergillus oryzae) on rice or soybeans and ferment it with salt to create miso paste. Journey from 2-week koji to 6-month+ aged miso.

How to start

  1. 1
    Order koji spores (koji-kin) or use white miso as your koji starter culture
  2. 2
    Make koji first: steam rice/soybeans, inoculate with spores, maintain 77-82°F with high humidity for 40-48 hours
  3. 3
    Mix koji with salt (13% by weight) and paste into jars for fermentation phase
  4. 4
    Learn different miso types: white (2-3 months), red (6-12 months), or longer aged varieties
  5. 5
    Monitor fermentation for signs of good progress: smell should shift from raw to savory-umami over weeks

What you'll need

  • Incubation setup (yogurt maker, heating mat, or oven)
    Essential
    ~$30
  • Koji spores (koji-kin)
    Essential
    ~$15
  • Glass jars for fermentation
    Essential
    ~$15
  • Thermometer/humidity monitor
    Essential
    ~$20
  • Rice cooker (optional)
    Nice to have
    ~$40

Where to learn more

Plot twists

Ways to spice this up when the basics get boring.

  • Make chickpea miso using the same technique with legumes
  • Create black bean miso with garlic and ginger additions
  • Blend finished miso with other ingredients: miso butter, miso caramel
  • Make liquid koji (shio koji) for quick umami paste in 2-3 weeks instead of 6 months
ADHD notes

Two distinct phases: active koji growing (2 days) then passive fermentation (months). Initial koji phase is short and engaging; fermentation requires patience but minimal active work.

Fun fact

Koji is one of Japan's 'National Fungi'—without it, there would be no miso, mirin, sake, or koji amazake. It's essential to Japanese fermentation culture.

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