Winter is a time for activities such as koji making.

Koji is the fungus Aspergillus oryzae grown on a grain substrate. It is rich in enzymes used for breaking down soybeans in the production of various kinds of miso and soy sauce. It is also key in saké production.

It takes three days to make each batch. I will go through the process of koji making step by step.

Here’s what you need:
– a heat cabinet
– steam cooker
– cloths for the steamer
– mold growing containers
– pots and pans and strainers etc.


The ingredients:
– rice
– tane koji


I use ecologically grown short grain rice that has been polished. Polishing to a certain degree makes it possible for the mold to penetrate and grow into the kernel of the rice. Tane koji is the starter for the mold which I order from Japan. This is a powder – a collection of living spores of the mold Aspergillus oryzae. The spores last a long time (I have had good tane koji remain viable for more than 30 years), and germinate when the conditions of humidity and warmth become right.

Other kinds of rice or grains can be used, but white rice is the easiest and therefore best to start with. After making koji a number of times, one gains a feel for the right smells, taste, color, humidity and dryness that is necessary for the best quality koji. Then you can go wild experimenting with different grains or other types of substrate.

Step one

The first step is to rinse and soak the rice (here 800 grams) for about 8 hours. In the meantime rinse and clean the equipment from the dust that has accumulated since the last koji making. Sometimes I have had to boil things that have become contaminated with other microorganisms.


Step two

After soaking the rice for a number of hours it is time to take the next step.

First boil the steaming cloths for a few minutes in order to sterilize them.


Put a gauze cloth in the bottom of the steamer and then half of the rice.


Package nicely.


Put over boiling water and steam cook for 20 minutes.

Put the other half of the rice in the second steamer and steam cook after the first is done. I could steam them together but they turn out better when each is done separately.

After steaming let the two portions cool.

Put the steamed rice into a mixing bowl, one portion at a time.


Sprinkle an extremely small amount of tane koji powder and mix it in thoroughly.


Put into a terracotta form and cover with the damp steamer cloth. For rice koji I have found that the terracotta form works best for retaining a just right balance of humidity and aeration. For barley koji I use wooden trays.


Put the forms in the heat cabinet set at 30 degrees centigrade, testing occasionally with a thermometer.

After 12 hours we will open the cabinet and aerate the rice.

Step 3

The morning of the second day

Open the incubator, check the temperature and adjust if necessary. Take out the two containers and mix in air by scraping the rice mass back and forth at least three times.

Break up any clumps that form and get a feel for the dry/wetness of the rice. If it clumps or cakes together, it’s too wet and will have to be aerated more and more often. If too dry, a sprinkling of water while aerating will help.

After aerating, put the dampened cloth lid back on and put back into the incubator, alternating between the top and bottom shelves. Leave to grow.

Next step after about 12 hours.

Step 4

The evening of the second day

Follow the same procedure as 12 hours ago – check temperature, mix air in and observe the conditions of growth. So far there is no difference in what the rice looks like, so no new picture (it would look like the one from this morning). The humidity seems right and there is no clumping. There is a slight change in odor indicating lactic acid fermentation in the rice which is OK.

Next step in another 12 hours.

Step 5

The morning of the third day

Again we do the same as the last 2 steps. Aeration is very important. Everything is developing quite nicely.

We can now see traces of the mold growing. The humidity is just right, and the odor is developing into the sweet, flowery, fruity bouquet characteristic of the Aspergillus oryzae growing on rice.

We’ll have a look after another 12 hours this evening.

Step 6

Now is the evening of the third day

The mold has been growing in the heat cabinet for 2 days at about 27 degrees centigrade. The rice now has a furry covering of aspergillus mold which cakes the whole mass together. The dampness, odor and taste are perfect.

The mold has not blossomed yet but is just starting to. The fuzz of the mycelia is beautiful, and the odor and flavor are wonderful. The enzyme level should be at its very best now, so it is time to harvest.

On flowering it will turn a nice yellow-tan color. Many koji makers let it grow until it gets that color, and perhaps this adds to the flavor and color of the miso, but I seldom let it go that far and haven’t noticed any difference in the miso.

Scrape the mass onto cloth lined drying baskets and spread it out.


These baskets go on a rack in the furnace room to dry for 2 or 3 days.

The next and last step will occur in about 2 days when I check for dryness, package and save for later miso making.

Now is the time to put rice to soak for the next batch. I will make up to ten batches of rice and barley koji during this winter season.

Step 7

The evening of the fifth day

It is time to package the koji that has been drying for two days. In plastic bags it will keep for years in the coolness of the food storage room in the cellar. I will probably use it up within a half a year.


The 800 grams of rice has now become 700 grams of rice koji full of enzymes – amylase which catalyses the breakdown of starch into sugars, lipase which facilitates the breakdown of fats and protease for the breakdown of proteins – perfect for making soybeans more palatable as in miso and soy sauce fermentation.

This 700 grams of koji will make as much as 3 kilos of miso. It can also be used to make amazaké rice pudding and saké rice wine.

And that brings us to the end of one koji making cycle.

In the meantime, the next batch of rice koji has been growing these last two days and is ready for harvest. And the third batch will now be put to soak. This succession of procedures will continue for the next few weeks.

I have a bigger heat cabinet and could make one big batch all at once, but I prefer the slow steady pace of making a series of small batches over a longer period of time.


Brown rice koji

Making brown rice koji is much more difficult than polished rice koji. More often than not I have failed. I thought I should try again when I noticed a bag of ecologically grown brown rice that looked like it might work (Italian, long grain). I washed and soaked 750 grams, which is less than usual but easier to manage. I then broke up and inoculated the rice with the same tane koji I use for the other rice cultures.

I put it into the terracotta trays.

Then into the heat chamber as usual.

After the first day growing, the smell seemed ‘off’ – as if a bacteria growth was going to take over and cause a bad culture that would have to be thrown out on the compost like many times before. With extra aeration and spreading out, the mold took hold again, and it turned out fine.

After two and a half days growing.

Spread out to dry.

Brown rice has a covering that is polished off when making white rice. This barrier hinders the koji mold from growing into the kernel. The trick is to soak and steam the rice just enough, so as to break this shell. That way the mold can get in. At the same time one must not let the rice get too soggy where bacteria thrive. Another method is to find a rice that is slightly polished but can still be considered brown rice. A little rice polishing machine would be good to have. I could polish it just right and throw in the polishings.

Brown rice koji making is for the experienced koji maker and whole foods enthusiast. It is more difficult to keep the mold growing ahead of the bacteria. It is also less efficient in enzyme production because the mold doesn’t get into all the grains.

So, I recommend starting out koji making with white or polished rice, which is by far the easiest, while learning the procedure, the look, the smells, the consistencies, etc. Then move on to experiment with brown rice and other grains.


Barley koji

The procedur for making barley koji follows the same general flow as for making rice koji, but there are some differences.

Use pearled barley that is well hulled and slightly polished so that the mold can grow into the kernel.


Steam each portion of soaked barley 30 minutes instead of 20 as for the rice.

Use tane koji that is made for barley koji. I’m sure the tane koji for rice will work too, but is not optimal.

I use wooden trays for growing the mold rather than the ceramic ones used for rice koji. The barley needs to be spread out more in order to not get soggy.


Barley koji ripens and sporulates sooner – the middle of the second day.


I let it grow until 48 hours have passed before harvesting it. Harvesting can raise quite a cloud of spores, so be careful.


Otherwise follow the same instructions given for making rice koji.


Tane koji

I have previously bought tane koji (koji starter) from suppliers in Japan, but this last time I bought a package (along with starter for barley koji and tempeh) from a company in Lakewood Washington USA that I found on internet. It is so easy to find and contact these companies using internet now days.


If you have any questions, suggestions or otherwise, please feel free to contact us at:

By the way, we are a planning a three week trip to Japan in April. We hope to visit some small-scale ecological gardens and traditional food production outfits. If anyone out there has any tips on places to visit, let us know!