Introduction: Koji Propagation

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Koji can be purchased online or in asain markets. but it known to be best when used fresh, which clearly sitting in a plastic bag for weeks on a store shelf does not ensure freshness.

Or if you buy it online from amazon, it comes in an ordinary package, shipped without insulation or cooling in the back of a mail truck for days... also sub satisfactory in the freshness category.

So in search of a way to brew sake at home, I found my options for imported koji to be less than satisfactory... it was also rather expensive! amazon has it for $15/200g. most of that weight is the rice the koji was inoculated into!

This instructable is here to help those homebrewers to get the best quality Koji available to them, even in remote locations where 98% of the people you meet would never know even what "Koji" is, or what it's used for...

Step 1: Little Background Information

Koji is a mold, scientific name of Aspergillus oryzae. This mold is inoculated into rice, and then let to mold over.

Once you have a solid block of infected rice, while it is still white, you can then either use it immediately or refrigerate as is to keep it fresh for a few weeks, or even dry it, then freeze it in containers to keep it fresh for nearly a year! it's been used to make Sake, Miso, and Soy Sauce for hundreds of years. And it's also known to be a great marinate ingredient for all sorts of foods.

while it is possible to buy koji, then mix it with prepared rice to get more koji from your original purchased source, my suggested method and the one we will be walking thru together here is starting from Koji-kin, powdered spores of Aspergillus oryzae

Step 2: What Your Going to Need

These are merely suggestions and guidelines. my backwoods approach is not nearly as good as what a commercial operation is going to create with lab-style sanitary conditions and temperature control. But seeing as this has been done LONG BEFORE refrigeration and even electricity, i'm going to trust that it can do what it needs without too much scientific process.
  • Rice of preference ( enough to satisfy your immediate requirements, this batch is made with 6cups of rice)
  • Koji-kin (2g per Kg/8 cups of rice)
  • cheesecloth
  • steaming pot
  • thermometer
  • food safe sanitary containers to inoculate in
  • insulated box (suggested but optional)
  • sanitary solution (i use star-San sanitizer)

The rice can be white, brown, short, long, etc. But short grain highly polished sushi rice is supposed to be best. just note that the hulls of brown rice stop the fungi from infecting the core, and you will need to de-husk the brown grain rice so that ii is atleast partially broken or scratched

The Koji-kin can be sourced online if you have no local sources. a 1Lb brick of koji-kin can make a whopping 200kg/440 lbs of rice, barley, or soybeans. and is reportedly good for 6-12months from time of shipment if properly cared for (dark, cool location like your fridge).

Step 3: Day 1

  1. rinse with rice water till the runoff is no longer milky white. we want as much of the small particulate matter washed away. if using brown rice remember to Hull it first
  2. Immerse the rice in water, cover, and let it soak for 18hrs in the fridge, or 12hrs if room temp.
  3. Steam the rice, 45min or till "al-dente"
  4. let the rice cool, breaking up the clumps with clean, sanitized hands.
  5. once the rice is 100F, spread out in a thin layer and evenly disperse the Koji-kin over the Rice. this stuff is a fine dust, be careful to not let it blow away!
  6. using some strength, mix this all together and place into the food safe container. I use ceramic crocks and jars, but zip lock bags or turkey basting bags would work just as well if you wrapped the rice in cheese cloth to maintain high humidity levels.
  7. Since it's summer, i just cover the jars and set them in the sun, then just bring them in and put them in an insulated box at night. the more technically inclined folks can choose to put the filled and covered container into an insulated box and turn on a low heat source (Edison style bulb). mist some water into the container to help maintain a humid atmosphere
  8. maintain temp as much as possible between 86-104F closer to 104 will give more sugars and temps closer to 86 will give more amino acids. For Sake, we need those sugars. 110 is too high and your going to need to mix it up to bring that temp down.
  • this is your Zero hour. Know it well...

Step 4: Day 2

  • if your rice starts to go >109F, remove, stir, repack, and expect a solid 20F drop in temp from mixing.
  • As the mold grows, it creates it's own heat. This is noticeable at ~hr20 from inoculation. if it didn't start getting warmer than the ambient temp by now, something went wrong and you should look back thru your notes, or more simply start over.
  • at the 38hr mark, start lowering the humidity (open the box, stop misting the interior) this signals the flowering stage and urges the mold to penetrate as deeply into the rice grains as possible.

at 48hr mark your koji can be harvested, or it can continue for up to 55-60hrs. if it starts to turn yellowish, finish it. that means it's about to turn to spore, which is not the desired state of the mold for fermentation purposes.

Step 5: Finishing the Koji

You now need to finish the Koji. Do so by breaking it up into small pieces, almost granular in nature which is now good for:

  1. Immediate use
  2. Immediate refrigeration for use within the next 10 days
  3. Immediate freezing for use within the next month
  4. drying into small clumps/individual grains for long term freezer storage. (less than a year)
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