Koji Cultures for Soy Sauce

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Koji Cultures for Soy Sauce

Check out our Soy Sauce-making Process


Koji was first used in China (where it is known as qu) in 300 BC, and in Japan in 300 AD. As a fermenting agent, koji was a vital component in food preservation. By 10th Century AD koji was being deliberately manufactured so the foods made with it could be produced in large enough quantities to meet demand. Since then the demand for koji has grown, and its use has diversified from being just a fermenting agent to also being a seasoning in its own right!

Koji is a super star in fermentation and provides the main framework for three major fermented soy foods:

  • Shio Koji - A condiment and marinade
  • Miso (fermented bean paste) and Tamari (wheat-free soy sauce substitute) 
  • Shoyu (soy sauce)
  • Rice vinegars
  • Sake (rice wine)
  • Amazake (sweet, non-alchoholic rice wine)

At Craft & Culture, get our soy sauce koji (麹) cakes to start your ferments! We offer in amounts of 20g

Known scientifically as Aspergillus Sojae, this mould is first mixed with wheat flour and undergoes rapid mycelial growth on grains like soy, and secretes enzymes like amylases to digest carbohydrates into simple sugars when the koji is activated.

Upon addition to brine, a secondary fermentation process then happens, transforming in flavor and texture. It's how soybeans become miso, rice becomes sake, soybeans plus wheat become soy sauce. 

Famed chef David Chang of Momofuku describes it best: 
"Microbes produce enzymes, enzymes develop amino acids, glutamic acid + aspartic acid = umami, umami = delicious."

Here's a sample soy sauce recipe we use:

Soy Sauce Recipe: (makes 600-800 ml soy sauce)
  • 225g dry soy beans (~500g when cooked)
  • 2g soy sauce koji
  • 50g wheat flour (or rice flour)
  • 50g salt
  • 500 ml water
  1. Soak the dried beans overnight and boil in water until they are soft and can be mashed with your fingers (usually 1-2 hours on high heat). Save some boiling liquid and set aside to cool.
  2. Mix the soy sauce koji and wheat flour together. When the beans are at room temperature, toss them to coat with the koji-flour mixture
  3. But the beans into a pan, cover with plastic wrap and allow the mould to develop into a light green-yellow colour before transferring to your sanitized fermentation vessel. This process will taken 2-3 days.
  4. Dissolve salt into hot water and allow to cool. When cooled, pour into vessel with beans and allow to develop and ferment, stirring weekly. In one month, the sauce will be light, but the best flavours take up to 6 months and best if allowed to sit and darken for a year.
  5. Filter out the beans and sediment and heat until simmering. Allow to cool and transfer into sauce bottles. That's it! The process is rather tedious but it's highly rewarding :)


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