In December of 2020, after a long year of dashed plans, I asked myself the question “how exactly is soy sauce made and I can I make it myself?” I wanted to try something new. Again. It was 2020, after all.

A small amount of searching revealed that soy sauce is made with soybeans, wheat, a specific kind of mold, and at least a year’s worth of time. I followed a recipe I found online and put the results in a jar where, as of March of 2021, it sits to this day.

Some more research revealed that there are quite a few different kinds of food products that can be made using this mold. I decided to try sake next because, due to shipping issues, I got a packet of yeast along with the koji spores. That experiment ended unsuccessfully with a sake that had all the charisma of rubbing alcohol and burning metal.

Obviously, something went wrong. I decided that I would do some research in order to better understand how to grow and use koji first before I attempted to make something again. After reading one book on the subject, I had a much better idea of how I had failed and how to do better in the future. I also got several ideas for way to modify existing recipes of mine to make new and interesting variations of the food I already eat. Since then, I’ve had much more success.

What follows is documentation of each and every one of my experiments with koji, how it went right, and how it went wrong. My biggest frustration with the sake recipe I used was that it told me what to do without giving me any hints about the consequences of not following the instructions. I’m going to write down everything I’ve learned not to do as a part of this process, both for my benefit and for anyone following in my footsteps.

Batch NumberTimeGoalOutcome
112/20 – 6/21Soy Sauce + LearningNo soy sauce, learned a lot
21/21Sake + LearningLots of learning, no sake
32/21Amazake + test new equipmentEquipment works. Methodology doesn’t
42/21AmazakeSuccess
52/21-4/21Ricotta Cheese MisoTBD: March 27, 2021 taste test was good
62/21Small batch amazakeFailed. Poor distribution and sporulation
74/21Small batch amazakeSuccessful. Technique improvements worked.
84/21Small batch amazake (other spores)TBD: Currently soaking the rice

Koji Growing and Experiment Logs

Experiment 1: Soy Sauce

This was my first ever attempt at growing koji, so I did not know what to expect. I followed the recipe linked above to prepare the soybeans and used wheat flower instead of wheat berries because other sources online said that flour would work as well. I’m going to use the wheat berries next time.

My incubation method was to put the incubation tray, a deep aluminum foil tray like the kind you can cook turkeys in an oven with, into my oven and try to regulate the temperature with warm water bottles and the oven’s interior light. This did not work very well at all, mainly because I didn’t know what to expect. The temperature probe I used showed that the tray was way too cold for most of the first day. The temperature stayed at 24 °C for far too long, indicating that the koji was not growing.

At about 30 hours in, the temperature had reached 27 °C, which indicated that growth was finally starting to happen. The temperature fluctuated a lot because I wasn’t changing out the water bottles quickly enough. Eventually, the internal temperature reached the right threshold, but it was more than a day later than expected.

I don’t believe that I let the koji grow enough. The conditions weren’t favorable. Part of the problem is that I like to keep my apartment’s thermostat at 66 °F during the winter. The cold ambient temperatures made it that much harder to maintain warm temperatures inside the oven. The consequence of not growing the koji enough is that not enough enzymes were produced. Those enzymes are what break the soybeans down into the sauce. Not enough of those means very slow sauce development.

Progress Update: February 2021 (t + 2 months)

The brine mixture I made has been developing very slowly. It’s possible that the reason is because of the colder ambient temperatures in my apartment, but now that spring is coming I’m not seeing an increase in development. I suspect that this sauce isn’t going to turn out, but it doesn’t cost me anything to keep it. It might mature nicely if I’m patient enough.

Experiment #2: Sake

I had yeast, and I had koji spores, so why not make sake? It can’t be that hard, right?

It turns out that brewing sake requires a lot of care and understanding of the process that I did not have at the time. To be clear, this was my first ever attempt at brewing alcohol of any kind. I got advice from more experienced homebrewers, but in the end I had to learn from my mistakes.

To be clear, the recipe I used is not at fault for my unsuccessful brewing attempt. I should have done more research ahead of time. Instead, I used my naive computer programming mindset and decided that the lack of documentation in the recipe meant that the instructions were merely guidelines that I only had to try to follow. Surely, the consequences wouldn’t be that bad, right? This was truly the wrong mindset for the problem and I paid for it with my inexperience.

I used a slightly better method of temperature control in my oven when I made the koji rice for this project. Instead of hot water bottles, I boiled water using an electric kettle and put it in a pot situated underneath my incubation tray. This kept the internal temperature of the oven much higher, but it still wasn’t nearly consistent enough. This, as in the soy sauce experiment, resulted in underdeveloped rice.

I did the two week fermentation process in a borrowed glass carboy. For the first week and a half, the mixture had the right smell to it. It actually smelled like wine. Towards the end though, it developed a strong and unpleasant smell. That smell only got worse when I bottled it. The process did result in an alcoholic fluid as expected, but a lot of other things got produced that made the mixture as a whole smell downright nasty.

Lessons Learned

I asked various people I knew what sake was supposed to taste like and got wildly different answers, so I decided that I would just have to buy some from the grocery store and try it myself. Yes, I attempted to brew sake without even though I never tasted it before. It took a few weeks to find some in stock, but when I was able to buy a bottle I tried it and found the drinking experience to be enjoyable and not reminiscent of a toxic metal file. A small quantity of sake, served heated, is quite pleasant.

What went wrong? After reading Koji Alchemy and doing some online research, I came to the following conclusions:

  • When they say “rinse the rice until the water is clear”, they really mean it. Koji Alchemy says that the process can take up to 30 minutes to do correctly. I didn’t wash the rice nearly enough beforehand. Here’s why you can’t afford to slack off when rinsing the rice:
    • The starch you don’t rinse off the rice has a negative impact on the flavor of the sake. I knew this, but didn’t really appreciate it at the time.
    • Starch causes your steamed rice to stick and clump together. Koji can’t grow if it isn’t exposed to air, and sticky clumps of rice deny it that air. Slower koji growth means fewer enzymes and worse results overall.
  • I don’t think I steamed the rice in my Instant Pot enough. I don’t remember the exact time I programmed in, but it couldn’t have been more than 20 to 30 minutes. I’ve had more success since then with 45 minutes to an hour.
  • My oven approach to incubating the rice was not nearly effective enough. I just wasn’t able to control the temperature well. In addition, the rice was far too wet. Koji can’t grow on really wet surfaces either, so that also negatively impacts yield.
  • I stirred the mixture in the carboy too frequently. My method was to take a wooden dowel I bought from the store, sanitize it with rubbing alcohol, and use that to stir the mixture. Either bad sanitation or repeated opening of the carboy’s airlock had the potential to allow unfriendly microbes into the mixture.
  • I let the carboy be exposed to direct sunlight multiple times. I’m so used to getting no direct sunlight in winter that I put the carboy somewhere where afternoon sunlight could hit it. We had several days here with clear skies while I was fermenting the sake. I should have hidden the container away somewhere else just to be safe.
  • I don’t regulate the temperature of my apartment very strictly, so the apartment got too warm during the sunny days. 66 °F is the ideal temperature for this recipe, so I thought leaving my thermostat set there would be enough. It’s not. Even in the winter, my apartment can get into the mid-seventies and that is well outside the recommended temperature range for the sake recipe.

I will attempt to brew sake again in the future, and next time I will take the process more seriously.

Experiment #3: New Equipment Test

  • Time: February, 2021
  • Result: Unsuccessful

The biggest takeaway from my sake experiment was that I needed better climate control during the koji inoculation and growth phase of a recipe. I built an incubator using the following parts:

  • 30 quart drink cooler
  • Inkbird temperature controller
  • 100W aquarium heater
  • 10W aquarium pump and air stone

I’ll write a dedicated post describing this incubator in the future sometime.

In theory, this would let me maintain the temperature and humidity inside the cooler very accurately. I made a batch of rice, taking extra care to rinse it well, prepared it, and put it in the cooler.

Too much water is bad

The experiment was unsuccessful because I filled the cooler too high with water, to the point where it contacted my growing tray. I though that having more water would improve the temperature stability inside the cooler. I was right. My assumption that having the pool of water contacting the tray would help prevent the tray from overheating was also correct.

What I didn’t expect was that having the cooler being filled mostly with water meant that the relative humidity of the air in the cooler was way too high. The high humidity caused excessive condensation on the cooler’s lid and the surfaces in the tray. The condensed water pooled in the tray and covered the lower layers of the rice. Koji doesn’t grow on submerged rice.

The final result was that most of my rice was wasted. However, the few patches of rice that weren’t inundated with water sported really good looking koji growth. Seeing this growth made me realize that I was heading in the right direction. The results in these limited patches were far better than in the oven method. All I had to do was control the humidity better.

Experiment #4: Amazake for marinading chicken

  • Time: February, 2021
  • Result: Success!
  • Recipe: From Koji Alchemy

I repeated the same steps from experiment #3, except I used about a quarter of the water.

Midway through the incubation process, I discovered one improvement for my specific incubation setup that differed from the recommendation in the Koji Alchemy book. I started by setting the aquarium heater’s target temperature to 30 °C as recommended. However, I found that, for my specific setup, this meant that the temperature of my koji substrate was too low.

I suspect that this is because my incubation tray rests at the top of my cooler because the cooler is relatively small. The illustration in Koji Alchemy shows a much bigger cooler that trays can rest in. Their approach was very good. All I had to do was tweak it a small amount for my specific setup.

Setting my heater to its maximum temperature of around 33 °C raised the temperature of my substrate from around 25.5 °C to around 29.5 °C. This sped up the growth of my rice koji noticeably. It did take about 12 extra hours to grow though.

In the end, I got very nice looking rice koji. I used it to make amazake that also turned out well. In turn, I used some of that amazake to marinate chicken for some chicken fajitas. The fajitas turned out spectacularly.

Experiment #5: Ricotta Cheese Miso

  • Time: February to April, 2021
  • Outcome: TBD
  • Recipe: From Koji Alchemy

Making amazake was part 1 of a larger goal of mine. I want to see if cheese miso can be used as a substitute for parmesano reggiano in an alfredo sauce. If it can, then I can make a fusion Japanese/Italian version of fettuccine chicken alfredo pasta. It would be the most unique food I’ve ever made.

I used the cooler incubator again, except this time I set the aquarium heater to its maximum temperature at the beginning. The higher starting temperature meant that it took much less time for the koji to grow into the rice.

One note from the steaming process: I wasn’t happy with the way that my rice stuck through the holes in the steamer basket and got wet, so I put a layer of paper towel underneath the rice. This was a bad idea. The paper towel absorbed water and soaked even more rice than before. It wasn’t enough to ruin the whole basket of rice, but I will not be steaming rice that way ever again.

As of February 27, 2021, I am about to pull the rice out of the incubator and mix it together with the ricotta cheese. I’ll update the post after the process completes in about two months. Wish me luck!

As of April 10, 2021, the process still looks to be going well. The one month taste test on March 27 was good. The miso developed distinct parmesan-like taste and smell. It reminded me somewhat of those expensive parmigiano reggiano cheese blocks that you can buy from the grocery store. That’s a good sign because those expensive cheeses are exactly what I’m trying to replace with this.

Batches 6-8: Small-Batch Amazake

  • Time: February to April, 2021
  • Outcome: Variable. The goal was to try new techniques and improve my process
  • Recipe: From Koji Alchemy

Batch 6: Every change made the product worse, but that’s OK

Now that I knew I could make amazake, it was time to start trying out new techniques to improve the process. For batch 6, I tried several changes:

  • Put a layer of paper towel underneath the rice while steaming it. This resulted in making the bottom layer of rice even more soggy than before. Bad idea.
  • Cut slits into the pan I used to hold the rice while it was being incubated. Also a bad idea for the same reasons as before. Water vapor from the brine got into the paper towel and saturated it causing the koji to not grow properly. Also, I had to buy a new pan.
  • Did not disperse the spores from the starting kit in flour before mixing them into the rice. This resulted in very uneven growth on the rice that was dry enough to support koji growth.
  • Kept the incubation process running for longer than when I did in the previous batch to try to compensate for the poor growth. This led to excessive spore production in the few areas where the koji grew well.
  • Used the spores I got from the sake making kit. I need to complete experiment 8 to know how this affected the results.

As you can see, every change I attempted for batch 6 made the end product worse. This is fine. Half the fun of this hobby is being able to try new things without fear of consequences for messing things up. I don’t have that luxury elsewhere.

Batch 7a: How to break your Instant Pot in 1 easy step

Batch 7 got interrupted when I broke the sealing ring in my instant pot trying a new technique for reducing the amount of rice that got ruined during the steaming process. I put a trivet in the instant pot, put a small plate on top of that, and then put the steaming basket in. The goal was to create a physical barrier that stopped boiling water from splashing on the lower layers of the rice. That goal was achieved very nicely.

Unfortunately, the stack inside the instant pot was too tall and I couldn’t seal it. I was able to force the lid to close, but steam started leaking out of the pot when the pressure built. It was because I had damaged the seal in the lid while forcing the lid closed.

Batch 7b: Everything works this time

In this batch, I made the following improvements based on my successes and failures from the previous experiments:

  • Took a spare foil pan and cut out a section to place between the trivet and the steamer basket. This protected the rice from splashing water and did not break my instant pot. Very little rice got over-soaked this time.
  • Dispersed the spores from the kit in flour before mixing them into the rice. It turns out that, at least for me, this step is not optional.
  • Used the spores from the previous successful amazake experiment and stopped incubation early before spores could be produced.

Incubation did take a little bit less time than in the past. It was about 40 hours instead of the expected 48. I guess that’s because I was using smaller quantities of rice.

Batch 8: Batch 7b but with the sake kit spores

I am repeating the technique from the previous batch exactly but with my original kit of spores. This should answer once and for all if the other spores are viable or not.