Aloha, to celebrate our first nattokimchee blog we will show you how to make koji, which is the beginning and first step of umami.

Koji is rice (or any grain) inoculated with a mold called aspergillus oryzae. It is the fundamental building block for many food in Japanese cuisine, including miso, soy sauce, and sake. Although it is a mold, it is harmless and it enhances the flavor by creating umami. The enzyme actually breaks down protein into amino acids and starch into sugar.

Koji kin, which is the starter for koji, can be purchased on amazon named as sake kit. (Search Koji kin) It comes in powder form.

There is also miyako koji, in the blue package, which is rice that has been inoculated with the mold.

If you want to skip the step of inoculating your own koji you can buy the miyako koji. They also sell koji at local Japanese grocery stores; the product from Cold Mountain works great.

But there’s just something about growing your own koji fungus and seeing the beautiful fluffy white cloud on the rice. And smelling the irresistible sweet chestnut aroma. I would have never thought in my life that I would fall in love with a fungus or a mold.



All equipment should be sanitized by pouring boiling water and let sit for a minute.

You can also use a paper towel slightly dampened with alcohol and water.



Incubator (cooler & heat pad, dehydrator, or yogurt maker)


Cheese cloth

Strainer (large and small)







Koji Recipe

400g rice

2g-3g koji-kin (more koji kin = faster growth)


1.       Gently rinse the rice changing the water couple times. Soak overnight.


2.       Strain the rice and let drain for one hour. This is important to make sure rice separates evenly to avoid clumps, resulting in poor growth of koji. Shake off excess water gently making sure not to break any grains.



3.       Cover rice with cheese cloth, steam for about one hour. Rice should be firm to touch but able to smash between fingers with no core. Check water level in 30 minutes and add water if necessary. If the steamer is small I would recommend doing two batches, so the rice cooks evenly.


4.       Place cooked rice on tray, spread out in even layer. Make sure rice is cooled to 36-40 C (96-104F) before sprinkling koji to make sure it won’t die from the heat.



5.       Using a small strainer, evenly spread koji kin on the rice. Gently mix and cover with cheese cloth.



6.       The optimal temperature for koji growth is 32-36C (89-97F). You do not want to go over 43C (109F) or the koji kin will die. If you have a dehydrator, make sure you cover the koji with damp towl and wrap in plastic to prevent drying and use the lowest setting. I use an incubator that I purchased in Japan, but a proof box for bread or a yogurt maker also works well. My first incubation chamber was made by a cooler box and a heat pad that I bought from the pharmacy. The only down fall was that I had to reset the timer every two hours. I also poured hot water in a plastic bottle and kept that inside to keep the temperature high. Whatever the method, the key is to keep that constant temperature of 32-36C (89-97F) with medium to high humidity.




7.       After 18 to 20 hours from the inoculation, check temperature of koji to make sure it is around 36-40C (97-104F). Mix rice with clean hands making sure all grain is separated evenly. (First Mix) The aeration allows the koji to grow evenly and rapidly.



8.       After 6 hours, mix again with hand making sure temperature is between 36-40C(97-104F). (Second Mix)

9.       After 8 hours, mix again with hand. (Third Mix) The temperature should be slightly higher between 38-40C(100-104F).

10.   After 8 hours, (total 42-48 hours) the rice should have a sweet chestnut aroma. It is ready when you see white fuzzy strands from the rice.


On our next episode we will show you the different uses of koji.