Miso (Koji to Soybean Ratio)

1 part by weight (baseline)

Cooked soybeans — Pressure-cooked to complete softness; cooking liquid reserved and used to hydrate the final paste to correct consistency

1–2 parts by weight

Rice koji or barley koji (Aspergillus oryzae) — 1:1 for long-aged red miso; up to 2:1 for sweet white miso (shiro miso) made in 3–6 weeks

10–13% of combined (soybeans + koji) weight

Non-iodized salt — 10% for sweeter, faster ferments; 13% for long-aged miso where protection over months is needed

Soak dried soybeans 12–18 hours, then pressure-cook until completely soft (they should crush between fingers with no resistance). Reserve the cooking liquid. Cool to below 35 °C. Weigh cooked soybeans and koji. Calculate salt as 10–13% of their combined weight. Dissolve salt into the koji, then mash soybeans into a smooth paste (a meat grinder or food processor works well). Combine salt-koji with soybean paste. Add reserved cooking liquid if needed to reach a consistency like stiff peanut butter. Roll into balls and pack tightly into a crock, pressing out all air pockets. Smooth the surface, dust with extra salt, lay a sheet of plastic wrap directly on the surface, and weight with a stone. Ferment at room temperature for the appropriate period (see variations). Skim any surface mold (white or tan mold is benign; black or pink mold indicates contamination requiring discard of that section).

• Temperature during fermentation matters enormously — above 30 °C accelerates enzymatic breakdown but risks off-flavors from competing microbes; 20–25 °C is the sweet spot for balanced flavor development.
• The miso ball packing technique — rolling paste into dense balls and throwing them firmly into the crock — removes air pockets that would allow anaerobic spoilage organisms to proliferate.
• Tasting every 4–6 weeks teaches you the trajectory of your batch; pull early for sweet miso, let it run for depth.
• Tamari — the liquid that pools on top — is a byproduct of miso pressing and a premium condiment; don't discard it.
• Iodized salt kills or inhibits Aspergillus oryzae; use sea salt, kosher salt, or pickling salt only.
• A layer of sake or mirin on the surface plastic, rather than just salt, prevents surface mold formation in humid kitchens.
• Miso salt percentage is calculated on total combined weight, not on soybeans alone — a common beginner error that under-salts the batch.

• Shiro miso (white miso)

  2:1 koji to soybean; 10% salt; 3–6 weeks at mild room temperature; pale yellow-cream, sweet, low umami

• Shinshu miso (yellow miso)

  1.2:1 koji to soybean; 11–12% salt; 2–3 months; balanced sweetness and savory depth; Japan's most common everyday miso

• Aka miso (red miso)

  1:1 koji to soybean; 12–13% salt; 6–18 months or longer; deep reddish-brown, complex, intensely savory due to extended Maillard reactions

• Mugi miso (barley miso)

  Barley koji replaces rice koji at 1:1 ratio; earthier, grainier texture; common in Kyushu; ferments 6–12 months

• Hatcho miso

  All-soybean koji (mame koji) at 1:1 with soybeans; 20% salt; aged 2–3 years under stone weights; extremely dense, dark, intensely savory; used in Nagoya region dishes

• Chickpea miso

  Non-traditional variant substituting chickpeas for soybeans at identical ratios; milder, nuttier; popular in grain-free and allergy contexts

• Shio Koji (Salt to Koji Weight)

  Uses the same koji but as a marinade paste rather than a fermented substrate; far shorter process

• Garum (Salt to Protein Weight)

  Western enzymatic fermentation analog — achieves similar proteolysis via different microbial/enzymatic pathway

• Kimchi Paste Ratio

  LAB fermentation rather than mold-driven enzymatic breakdown; both rely on precise salt control

1. 1.The Book of Miso — William Shurtleff & Akiko Aoyagi (Ten Speed Press, 2001)
2. 2.Koji Alchemy — Jeremy Umansky & Rich Shih (Chelsea Green, 2020)
3. 3.The Art of Fermentation — Sandor Ellix Katz (Chelsea Green, 2012)
4. 4.Japan: The Cookbook — Nancy Singleton Hachisu (Phaidon, 2018)

Confidence: high