Video Series and Instructions for Making Koji for Sake

What are we trying to do while making koji?

OK, so what exactly are we trying to do when making koji? Well, to examine this we need to consider the role koji plays in Sake Brewing. In sake brewing we use koji to provide a wide variety of products. These include products that provide flavor and aroma elements as well as enzymes which degrade proteins and starches into smaller component parts. For example proteins are disassembled into peptides and amino acids while starches are converted into smaller starches, dextrins and sugars.

Rice starts out with 7% to 8% protein, but the higher polished the rice the less protein will be left. However, even with lower levels of milling we do not focus on koji’s production of enzymes to break down this protein. Rice starch is our main focus and needs to be broken down as effectively as possible into sugars. Koji produces alpha, beta and gamma amylase. Depending on how we culture the koji, we can emphasize protein or starch degrading enzymes. High temperature cultivation, 98°F to 104°F, lead to the production of saccharification enzymes whereas lower temperature cultivation, from 98°F down to 68°F, emphasizes protein degrading enzymes. So to make good koji for sake brewing we must culture the koji at the higher temperature range.

Another important aspect of cultivation is to ensure that koji mycelia reach deep into the grain. When the mycelia work hard to bore into the grain more saccharification enzymes are produced. The primary factor that can prevent the mycelia from boring into the grain is when the grain is too moist and the fungi can get all the moisture it needs from the surface. Under these conditions the fungi will produce a small amount of enzymes which will go to work right away in the moist environment on the surface producing sugar. With the readily available sugar for the fungus there is no need for it to push into the grain or produce more enzymes. Koji produced under these conditions and with these results is called Nurihaze koji.

Tsukihaze koji or koji with the mycelia reaching deep into the grain is produced with rice that has about 38% moisture after steaming and has been cooled such that the surface of each grain is relatively dry. Too dry and the koji-kin (spores) will not stick properly but beyond that it should be dry. Then, cultivating with moist air for the first day enables the koji to get a good start. The lower the seimai-buai, milling rate, of the rice the less humid the air should be. For example, a brown rice would be safer in a more humid environment.  On the second day, moving to dryer conditions helps the koji mycelia to move into the grain.

A koji that is between Nurihaze and Tsukihaze koji is Sohaze koji which is more like Tsukihaze in that the entire surface of the grain is fully covered but unlike Tsukihaze the mycelia do not penetrate very far into the grain. For this reason, Sohaze koji has less saccharification power and is used in circumstances where there is less need to produce sugars; for example, the moto.

Of the three amylase enzymes produced alpha and gamma are the most prevalent but because of the low pH of the mash alpha amylase has a very low activity level. Alpha amylase is well suited for a pH of 5.5 but a sake mash will be closer to a pH of 3. Gama amylase on the other hand thrives at a pH of 3 and produces glucose. The very low temperature of the mash inhibits all of the enzymes which slows the rate of sugar production to a trickle. The slow rate of sugar being added to the mash helps the yeast stay healthy longer than in fermentation where there is a high concentration of sugar at the start. A high concentration of sugar increases the osmotic stress on the yeast cell walls. This increased osmotic pressure causes the yeast to shut down sooner than they might with lower levels. It is, this characteristic of the sake brewing process that allows sake to reach the high alcohol levels it does.

Rice Prep…

Rice preparation consists of washing, rinsing, soaking, draining, packing, steaming, cooling and finally inoculating and then incubating. Let’s cover each of these steps separately.

White rice, whether milled as table rice or milled to a higher degree specifically for brewing sake, has unwanted material on it that we need to remove. This material can simply be the rice flour (Nuka) from the milling process. However, if we are using table rice talc may be added to assist with milling and other materials are often added to enhance or enrich the final product. The later often include several of the following: Folic Acid, Niacin, Iron, Zinc, Selenium and Vitamins B-1, B-12 and E. Washing the rice in cold water removes these particulates. This will remove iron that contributes to bad taste development in sake and surface powders that can cause the steamed rice to be stickier than we would like.

Once thoroughly washed the rice should be rinsed in cold running water to rinse away the particulates that have been washed free. In some cases you may choose to do both the wash and rinse in a single step with cold running water. You know you are done when the water that starts with milky white run off turns clear.

I have used two sets of videos on this page. The older set on rice preparation and steaming was done while making sake and contains some discussion more related to that than to making koji. The second set was specifically made for koji making. For making koji the text and the second video set are most accurate.

Now that we have clean milled rice we want to raise its water content up to 25-35%. Commercial brewers are very specific about how much water they want the rice to absorb. In fact they have different amounts for their various styles and whether the rice will be used for making koji or not. In some cases brewers use a stop watch to make sure the rice does not soak for too long and take up too much water. Anyway, soaking the rice in cold water is the method used. The time needed to reach the desired water up-take level depends on the temperature of the water as well as the type and milling rate (seimai-buai) of the rice.

If the uptake of water is too little the rice will not steam properly leaving a hard uncooked center that the koji mold will not penetrate. On the other hand having too much water uptake will cause the rice to be too mushy and sticky after steaming. This results in a base that is too easy for the koji mold to penetrate and this prevents or lowers the production of transformative enzymes we want. Most rice used for homebrew sake will need to steep between 30 minutes and two hours. As homebrewers we are more often than not more guilty of soaking too much than too little.

We will not need to be as particular as Commercial brewers about the amount of up-take but rather shoot for the general ball park. To hit this ball park using rice with a 60% seimai-buai soak the rice in cold water for one hour. If you are using rice milled as table rice, seimai-buai 90 to 93%, soak for two hours. While these times are close to best, the additional water up-take from soaking for much longer has only a small impact on the sake. For this reason, some homebrewers soak their rice over night to get an early start on steaming in the morning.

As you get better at making koji you may want to be more exacting in the water up-take level. To do this you can add an experiment for the particular type of rice you use. Wash and rinse some rice and divide it into 5 equal portions. Weigh and record the results. Place all portions into cold water to soak. At 30 minute increments remove one portion, thoroughly drain and weigh. The percentage water up-take is the final weight divided by the starting weight minus 1 with the result multiplied by 100. Plotting these five points against their soak time will give you a curve you can used to determine how long you should soak your rice for the up-take you desire.

%water up-take =  ( ((Final weight) / (Starting weight))  – 1 ) * 100

Getting back to the topic at hand, once the rice has soaked for the period we want it is time to start draining the rice. Leaving the rice sit in a colander, strainer or sieve for about an hour will do the trick. The drier the rice the less sticky it will be and the easier to remove all the lumps after steaming. Once nicely drained it is time to prepare for steaming the rice.

To steam the rice we want to ensure the steam has to rise up through our rice to get out of the pot. We control this with the proper packing of our drained rice into our steamer. We want to have an even layer of rice that covers the entire steamer base (or each level of the steamer we will use). Ensure the rice evenly covers the base out all the way to the walls of the steamer so no steam can find a quick path to escape without going through the rice bed. Laying down a layer of cheese cloth or butter muslin before packing the rice will ease clean-up. With the rice packed into the steamer we are ready to steam.

Having drained the rice, we steam the rice for somewhere between 30 minutes and one hour. To tell when the rice has been steaming for long enough, examine a rice kernel, cut it in half, it should be uniformly gelatinized. If you bit into it, it should have a consistent resistance all the way through; firm but not hard. In general, steam the rice for 45 minutes. Be sure to check the water level in your steamer about half way through to make sure you have enough water. Running dry can destroy your steamer, smoke your rice or both.

Once rice steaming is complete; we remove the rice from the steamer and spread it out for cooling. A good place to do this is on a cookie sheet or similar pan with lots of bottom surface area. All the clumps should be broken up. The washing, rinsing and draining steps help here; by removing the outer starchy coating on the rice there is less sticky surface after steaming. This helps with cooling and surface drying and exposes more of the surface area for each grain for inoculation. After you have the clumps broken apart it is time to prepare the koji starter. Koji starter, koji-kin, Aspergillus Oryzae, all names for the same thing, are usually provided as a powder containing the spores that will inoculate the newly steamed rice. Only a small amount of this powder is needed. Because of the relatively small amount of powder, it can be difficult to spread it evenly over all the rice.

A trick I learned from the people at Gem Cultures is to take a small amount of flour and toast it in a dry pan until it is lightly toasted. We can then mix out lightly toasted flour with the koji-kin to double the amount of powder. This makes it much easier to evenly distribute the powder over the rice for a uniform inoculation. The toasting is, in effect, sanitizing the flour to make it safe for use. Without toasting there is a danger that bugs present in the flour could get a foot hold in the koji and cause the batch to go bad. Whether you add the flour or not is up to you since it is just to make it easier.

While the rice is still warm but less than 115F, maybe around 100F is good, sprinkle some of the koji-kin over the rice; about 1/3rd of the total powder. Mix the rice and koji-kin well and spread out again. Repeat by sprinkling the next 1/3rd of the powder and mixing well until all the koji-kin has been mixed very well with the rice. As much as possible we want to cover every grain of rice with a bit of koji-kin. Wrap the mixture in a tightly woven cloth that will breathe but not stick to the rice. At this point we are ready to place the inoculated rice into a warm and humid place where it can grow.

We want an environment between 90F and 95F that is pretty humid for the first 24 hours. An ideal way to create this environment is to use a picnic cooler. These are insulated, cheap and come in lots of sizes. The one I use even has a mechanism (some ICs) for heating and cooling. A heating pad or hot water bottles can also be used to warm the environment. Pre-warm and humidify the environment (could start about the same time as steaming) so the rice balled up in cloth will go into a friendly place. An open glass of warm water is plenty to keep the environment humid.

Place a temperature probe in your rice and place in the pre-warmed cooler. A second temperature probe to monitor the environment temperature is ideal but not required. Check the temperature regularly to ensure the rice reaches and remains in the range of 90F to 95F. At about 12 hour intervals, open the bundle to check and stir the koji. It may have signs of the white fussy mold by the second check (24 hours) or not. By this time you should remove the glass of water so the incubation environment becomes less humid.  The koji will be producing its own heat to the point that you will need to be more diligent about temperature control. Begin 2-3 hour interval checks where you open the bundle and stir the koji. If the koji is reaching temperatures above 110F you will want to perform these more regularly in order to better regulate the temperature.

From 40 to 54 hours the koji should complete its process. While stirring the koji, you can begin to check it for completeness. Cut a grain of koji in half to see how far the koji mold has penetrated the rice kernel. It should cover about half the diameter of the kernel. Once complete the koji should be spread out and cooled to room temperature. Once at room temperature, koji can be bagged or placed in some container to be refrigerated or frozen depending on how soon you want to use it. If storing for a month or more, freezing is the way to go.

And there it is, are you ready to give it a try?


Summary of Equipment used / needed:

  • Wok and bamboo steamer
  • Bowl for washing and steeping rice
  • Flat bottom pan for cooling and mixing
  • Cloth with tight weave for wrapping
  • Cooler to function as an incubator
  • Thermometer (I like those with a probe that can be in the rice while the monitor is outside and easily visible)
  • Temperature control, one of:
    • Controller with heater
    • Jars or bags that can be filled with hot water to control the temperature
    • Heating pad


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90 thoughts on “Video Series and Instructions for Making Koji for Sake”

  1. Thank you for the great content.

    What is the size of the oven pan that you use for the 2.5 lbs of rice?

    1. Hi Daniel, I’ve been reading this article too and happened on your comment by a reverse link search. In case you are not on the Sake makers Discord, I very much encourage you to join! It would be great to discuss koji making in more depth there.

  2. Hey Will,
    Thanks for keeping this site, Fred’s recipes and the superb videos!
    Your info interested me into trying my hand at SAKE one day soon and am in Japan atm trying to track down some TANE-KOJI online. When I do and have it back at home in Oz, I’ll let you know how I go (I intend to try KAN-ZUKURI so I may have to wait a while for the weather to cool a bit.)
    Best regards, Matt

        1. Hey Larry,

          I don’t know of any. In the US the best source of small batch Sake Rice is You can check out what they have and make your own koji.


  3. I just watched your videos on making the koji rice .I purchesed the koji kin form your page and will be making my koji rice .. I will be making miso with it as the price for miso is very high for a very small amount …and will be very economical I will be nice to get started and will keep you in formed on the process thanks Brenda Findlay

  4. Hello Will,
    thanks for the great post and instructions!

    I tried to make my first koji batch last week, everything was going very fine until the 24h mark, after that it looked like the diffusion of koji had kinda stopped, and although the smell was very nice they were not producing heat on their own anymore and there was no visual spreading of the molds.
    I think the problem might have been due to too much humidity after the first 24h, as the rice still looked kinda wet. So I would like to know if you have any average humidity values (before the 24h mark and after) to suggest, so to monitor humidity with a hygrometer and try to keep much more balanced during the entire process.

    Thanks a lot in advance!

    1. I don’t have precise values for humidity. The koji shouldn’t look wet though. In fact if the rice has been steamed it will be sticky and soft but not wet. Then keeping it wrapped up generally holds most of the moisture.


  5. Hello to all,

    I have a problem growing koji. I am using a Coleman cooler for an incubator with a Ranco temperature controller. My rice / koji spore mix is sitting in a Rubbermaid take along container. It is not wrapped in cloth.
    I wash and soak my rice, getting about a 30% weight gain. My rice is steamed for about an hour. It is fully gelatinized. The cooked rice is transferred to two sanitized cookie sheets where it dries for about 8 hours before it is inoculated with a generous amount of Vision spores.

    I have been using an incubation temperature of around 100 deg f (based on the earlier Homebrew range of 98 to 104). I place a glass of water on the heating pad located in the bottom of the cooler for the first 24 hours.

    The humidity in my incubator is in the 95+% range for the first 24 hours and reduces to about 80% after the glass of water is removed for the second 24 hours.

    Before I stir the rice every 12 hours, I rinse my hands with Star-san and let my hands dry.

    It seems like every time I make a batch of Koji, I start getting a little ‘alien’ mold growing in the rice sometime after the first 24 hours.

    There is not a lot, but there are some gray-ish looking fibers in a few spots, and there is a little yellow-ish looking fibers in some other spots.

    I cannot seem to grow pure white mold. Any ideas would be greatly appreciated.

    1. Hey Devin,
      A few suggestions that may help. First, I would not dry the rice for 8 hours after steaming. The rice will be a better host for koji-kin much sooner after it has been steamed. Just make sure the rice is cooled to about 100F and apply the koji-kin. Foregoing the 8 hour exposed drying period might also help to limit a possible source of contamination. With this in mind the ‘alien’ mold may not be alien at all. However, if it is not it is quite early (24 hours in) for the koji to develop yellowish tints. Second, I would drop your incubator temperature down to around 90F. The koji will get warmer than this but the environment should not be the reason. Third, I would wrap the koji in a cloth for at least the first 24 hours. This helps the koji take hold. Some people watching videos of koji making see non-wrapped koji being turned or stirred and think that it should not be wrapped. But what they are seeing is just the second stage of the process. In the first stage it is wrapped.

      I hope you find this helpful,

  6. Thanks for your response Will , your advice is very helpful for me, you recommend to mix ready cooked rice to the saccaryfication stage , I was thinking to cook crushed rice in water and enzymes like the maltodextrin production process , when the desired sugar level is reached cool down the mix and add the yeast and some koji as I like to use enzymes activated at high temperature only.i ll try both systems anyway .Many Thanks

  7. Hi there,
    I was reading the posts for a while, iam from Italy, want to try sake here because making wine so boring generally.
    I have some expertise in hydromel and wine too but sake is new for me.
    I want to try using amylase and protease to cook the rice first then add a very small amount of koji rice for flawour and white wine yeast for some kind of “western fermentation” , I know it isn’t a real Japanese sake way but want to simplify it in a more wine like process.Any suggestions?Is my suggested method or symilar currently usedto make sake in a novel way?Thanks from Italy

    1. Hey Diego,
      Some sake brewers will add enzymes to the rice at the very beginning to speed up the initial release of sugar but then they continue with the regular process.

      I don’t recommend doing this but if that is what you want to do I’d love to hear how it terns out.

      Beginning with cooked rice, some water and enzymes mix and let them do their thing for a few days. Strain out the solids, add your yeast, koji. This my be done within the week.

      Check the beginning sugar levels to make sure its not too much for the yeast you choose.

      Good luck!

  8. After looking around some more I believe the answer is to start over. It appears it is not a good idea to use the rice once propagation of the Aspergillus oryzae has begun. I’ll have to be more attentive at the 48 hr mark.

    1. Mike, Hi,

      If the koji has just a very light tint it is OK, more than that and you can keep going for that life time supply.


  9. Hi Will,

    After following you’re excellent guide here I was very successful in making my own koji rice on my first attempt….except 1 small problem, maybe?
    At the 48 hour mark the rice definitely had growth. Since this was my first time I thought I would let it go just a little longer because it just didn’t seem
    to look like enough mold coverage. So I let it go to 51 hours…oops mistake.. its now has a slight lime color. I quickly covered and stuck in the freezer.
    Question if you don’t mind.
    Can I still use this to make Sake or should I just have let it bloom out and had a everlasting supply of spores?

    I am looking at it now after an hour in the freezer and it definitely has a slight green tint


  10. Hey Will! Haven’t spoken in a while so I have a few things. First, were having a NYC fermentation festival this Saturday February 25, 2017 from 11 to 4. If anyone is in the area contact us at for details or search online. It’s at the Brooklyn Expo Center and it’s kid friendly. It’s a big deal, especially because a lot of people that count themselves as your fans will be there. Including us of course.

    We have our first kura and sake company in New York @brooklynkura and a lot of home and start up brewers will be presenting, sampling and even selling along with beers, kimchee, etc. it’s a benefit for @JustFoodNYC so it’s just twenty bucks and we’ll be answering questions regarding lactofermentation and yeasts, along with a brewing expert. I’m bringing your sake book with me so people know where to get it and the stuff you sell.

    Anyway don’t want to make this too long but we have a FB group called culturesgroup. There’s three actually if anyone wants to join. I’m posting about the results of the junmaidaiginjo koji and the junmaidaiginjo rice we got from you for our first test and the result was good. We made a sake where we replaced the water with honeydew juice, and we also made our own yeast mix from goji berries. A pale green and a pale pink, both quite good!

    Question: is there a way to replace or repair fans on the Koolatrons? No response from them after many attempts. Also, the sake yeasts from Wyeth I believe come in numbers like 701 and 901. These are non foaming yeasts that really are convenient if they prevent constant wiping down of primary incubators. Do you know anything about these?

    Thanks. Ken and @culturesgroup

    1. Hey Ken,

      That all sounds terrific!

      I can’t help with Koolatron issues, don’t really know anything about the company itself.

      It has been some time sense I looked into it and I am not sure I am remembering correctly (can’t find the correspondence with WhiteLabs). I think that their sake yeasts are of the foaming variety. I think the same is true of Wyeast’s. Mostly this issue is about having a vessel that is large enough to handle the foam.

      Wishing you the best for your event,

  11. Thanks for the response Will! I ended up doing my additions before seeing your response, and adding extra koji to the recipe for each addition (adding about an extra 3/5 of koji altogether). Am interested to see how this will affect the final sake. Fermentation has certainly picked up and the brew is bubbling away quite vigorously at this stage. Taste is decent so far. Thanks again.

  12. Upon a closer look and count, my estimate for colonization was off. Over 90% of the kernels are colonized, with varying degrees of penetration.



    1. Hey Mike,

      Your koji should be just fine for sake. Taken to the extreme this produces slow conversion of starch to sugar which can slow fermentation, but I don’t believe you are close to this.

      I’m not sure about the slow fermentation in this case. I don’t believe it has anything to do with your koji. Be patient and see how it goes.


  13. Hi Will! I have a question regarding koji and one regarding yeast. I recently made koji following your procedure and did not get as good colonization and rice kernel penetration as I have previously. I think part of the problem is that my koji-kin was a year old (Gem recommends within 6 months for full potency). I am wondering if I can still use this koji to make my sake. Would it be recommended to increase the quantity of koji used depending on success of colonization? Is there some kind of metric for that? I would estimate that 80% are fully white and penetrated about 1/5 of the kernal. Rough estimate. Fyi in case you are interested, using exact same set up as seen in your videos, and pulled out at about 61 hours because I was afraid the koji might start turning.

    Second question is regarding yeast. I only had whitelabs 705 on hand, as my local brew supply was not carrying any #9, so I went ahead using that yeast with the intentions of following your recipe exactly. To me it seems that fermentation is happening very slowly. Unlike the foaming and heavy bubbling i seem to recall using #9, I am only noticing a slow bubbling with lots of fizzing when i stir it. It was slightly more active day two of yeast mash, but now at day 5 has subsiding quite a lot. I am wondering if this is due to the koji I used being not so good, or owing to different characteristics of the yeast #7, or both. I am all about experimentation, and I’d like to continue the fermentation, however as I am doubling the recipe, that might entail wasting quite a few kilograms of specialty rice not to mention time, as this may be destined for failure. Hence I am looking for a bit of guidance!

    Sorry for the long post. I’m looking forward to any insights you might share about this!

    Best regards,


  14. Will,

    Good to hear that I didn’t totally screw up. I was looking for that fuzziness by the 48hour mark. Next time I’ll let it go a little longer and watch out for the color to change.

    I’m currently in the process of doing some tweaking to my system. As mentioned earlier, I’m using the same type of cooler as you. The cooler does have the ability to both generate and extract heat from the cooled area. I want to experiment on the results of reducing the heat and even extracting the heat as thermal runaway occurs. Basically monitoring the koji temp and ambient temp and then controlling whether the cooler is in heat, cool or off mode based on the temperature of the koji. I noticed at about the 30 hour mark that the cooler temp kept rising even though the cooler was off. This meant that the koji was producing more heat then the cooler would release on its own.

    My next challenge after that will be to automate the mixing of the koji while still in the cooler.

    Sorry… Can’t get the egghead out of me and I’m tired of getting no sleep on koji nights. I figure, if I can keep the koji cool enough and mixed I might be able to get some good night sleeps.;)

  15. One last side note. After the 48 hour period the koji was still thermally active and generating heat. Not as much as earlier but still rising from around 90 degrees to 100 degrees within 1.5 hours with an ambient temp air temp of around 90 degrees.

    1. Some brewers take this process out to around 72 hours. You can’t go that long if the koji starts turning greenish yellow. I don’t know the differences in their process but the point is that it is not strickly tied to 48 hours.


  16. OK, my first attempt at making kome-koji was less then ideal. I have the same cooler setup as you and used that as an incubator.

    I started the process on Tues evening. The rice used was a Japanese short grain table rice polished. After washing the rice in a large strainer I soaked 4 cups of rice in room temp water until it was about 5.5 cups in volume. Took about 1 hour to achieve this. Steamed the rice in a stainless steamer covered with butter mulsin cloth to keep condensation off. After cooling to about 90 degrees, I inoculated the rice with one complete pack of GEM spores using a very fine sifter. I added 1/3 of the spores and then blended the rice. I did this three times to complete the full inoculation. Each time I made this addition I was left with some white material that would not pass though the sifter. I did mix this material back into the rice when completed. Once completed I put the rice, rolled up in a moist mulsin cloth into a 1 gallon tupperware container (with no lid) into the preheated cooler (set at 95 degrees F) along with a glass of water at around 11:00pm

    The next day (8:30 am)it was at 101 degrees according to the digital thermometer in-bedded in the rice mass. The temp controller was reading 95 degrees hanging outside the rice in the incubator. I stirred the rice mass to cool it off, breaking up any clumps, and put it back into the incubator. At 3:00pm I checked the incubator and the temp had again risen to about 104 degrees. I again stirred the mass and returned it into the incubator. I continued the process over the next few hours. At 11:00pm I stirred the rice and removed the water glass. I found the start of the white fungus forming. I ended up sleeping in the room with the incubator. I set the temp alarm at 101 degrees and woke up every 1 to 1.5 hours with the alarm going off. Gradually I reduced the incubator set temp from 95 degrees to 89 degrees but the mass of rice kept generating more heat so the incubator never turned on during that night. After 7 wake-ups and turning it was finally morning. Now at around the 30 hour mark I was not seeing any significant growth beyond the 24 hour mark. I continued this process until the 48 hour mark. At the end I had some growth but no fuzziness covering the rice. The rice tastes very sweet with a nutty after taste.

    Any idea what may have gone wrong? Is this usable to make sake? The rice has some covering of white with no off colors, is relatively dry and not clumped. I have since dried and vacuum packed the rice and placed it into the refrigerator. On a side note I did wash my hands each time I stirred the rice using anti-bacterial soap and a star-san solution. Could I have damaged the spores by mixing it too much with some residual sanitizer on my hands?

    Sorry for being so long on this post but I really need to figure out what I did wrong. There must be an easier way to make the kome-koji without having to wake-up every 1 to 1.5 hours.

    Very tired now.

    1. Julius, Hi,

      I think you have done very well. There are three categories of koji quality with the worst and best having spotty fuzzy coverage. I think you have hit on the best, tsukihaze koji. Full coverage of the rice by koji, sohaze koji, is good and has the best aesthetics but not really the best for brewing sake.

      Good job!

  17. Will,

    I’m putting all the pieces together for my first run of sake making. I’m going to make the kome-koji from scratch using the spores from GEM that I purchased from you. What I haven’t seen is a figure on how much rice I need to make the required 2.5lbs of kome-koji. Is it basically a 1 to 1 ratio of rice = kome-koji? I know that I can make more then needed and store it but I would like to make sure that I’m making enough for my first sake batch. I was thinking of using 5 lbs of rice and the entire package of koji spores. Use what I need and freeze the rest for my next batch. I may also allow some of the kome-koji to turn to spore and use that for my next batch of kome-koji.

    1. Pablo, Hi,
      This would take 15g of the GEM koji-kin for 5lbs of rice. Other koji-kin types might have different amounts that are needed.

  18. Curious as to why you don’t use the temp controller probe inserted into the rice to better control the actual rice ball temperature as opposed to maintaining ambient temp? Would seem that it would reduce the risk of overheating the Koji.

  19. Very easy instructions on how to make Koji rice. I found link on Amazon to sell Koji rice.

    Is it any different than the one you made? I’m thinking of buying Koji rice from Amazon and skip these steps and processed with making Sake.

    1. Stavrose, Hi,

      Yes, all of these koji are different. Most are focused on food applications rather than sake BUT will work fine for Sake. Check the price per ounce and overall amount as this varies product to product. Cold Mountain Koji is often used for sake and has a good following.


  20. Figured it out. I had an older Flashplayer version in the cloud that my desktop was accessing instead of the later version on it’s hard drive.

    I think today will be an exciting day! Stuff getting delivered from you guys! When I think about it I should have resolved my serious refrigeration space issues by buying a huge cooler and storing it in my bedroom closet. There’s no reason why the Koolatron or any other heater/cooler can’t be used in that manner, right? A 52 quarter says it can be used as a cooler and a heater (if you reverse the plug?)

    These youtube videos greatly compliment the book! Great book!
    Thanks Will (and family!) Ken

    1. Ken, So glad to see you figured it out. I wasn’t seeing anything on this side.

      Keep in mind that the active cooler will dump heat around wherever you have it and so might heat up a closet more than you’d like. Have fun and enjoy.


  21. Hello! I am currently just researching making sake and stumbled upon your site. I live in CA and have access to fresh local rice from Lundberg. I was curious, is there an ideal type of rice for making Koji? I am familiar with cultivating fungus, so I figured there was an ideal nutritional balance….. I am thinking about making my sake from their black rice……should I grow my Koji on the type of rice I will use to make the the sake?

    1. The koji should be grown on the best rice you will use for the sake. The best rice used in Japan are short grain rices but in the US we mostly use medium and short grain rices. Calrose is a common choice. Lundberg medium grain rice should also work well but I am not familiar with their black rice.

      Good luck,

  22. Hi Will,

    I am growing the koji in wood boxes(koji buta) and since I am doing so, I get the yellowish color. At least not that white as before! I guess it is because the wood. Do you think it is infected by the wood? Can I used it?

    I read that if it turns Green it means that is infected, but I am not sure.

    By the way, how do you clean the Wood? Do you use any special soap?


    1. Humbert,

      I don’t have any experience with making koji in wood, however, many small kura use wood without issues. I wouldn’t worry about small changes in color over the complete cycle. If you are only getting the yellowish color near the end then it could be related to a change in the rate of maturation. There is a transition in the koji growth to creating spores which is where the color change comes in. It will go from white to yellowish to greenish.

      I don’t believe any special type of soap is needed.


  23. Thanks for the answer Will. When I asked that question was not documented enough about the issue …. I now understand that yeast is an ingredient that wants added later, in the final stage of fermentation … I know the koji-kin converts starches into sugars that serve as food to yeast … now I am of the opinion that if we do the sake we must carefully follow the precise method, because we have to do the sake and not something else …. now I want to ask if I buy the koji-kin, you can it grow again in the form of spores? or if I will have to buy it every time … how do you “grow” the koji-kin in the form of spores, at home? and I want to ask you: if you do not use powder koji-kin, does sake ferment anyway successfully? Thank you so much ..I I’m documenting more and more about each specific stage of the process

    1. Ugo,

      I should probably write a post on making spores from koji-kin because this keeps coming up and I have answered it in a number of places. However, readers really have no way to find these comments.

      Anyway, if you follow the standard directions for making koji from koji-kin you will be 95% of the way there. When the standard directions tell you it is time to stop incubation, don’t stop but rather keep it going. The koji will turn green, yellowish green. These are the spores coming out. Once they have fully changed to the greenish color carefully spread them out and dry them. When completely dry you can place them in a shaker (like a salt shaker or powdered sugar shaker). When ready to make your next batch of koji shake the shaker over the fresh steamed and cooled rice and then follow the standard instructions.

      That’s all there is to it.



  24. other worlds,is there a way to create the koji-ki powder at home or something as an alternative that leads to the same result? .. thanks

    1. Ugo,

      I’m not sure I am getting all of your question but I think you are asking if there is something else you can use rather than koji-kin. The answer is really no. Koji-kin is Aspergillus Oryzae spores that is a starter for the mold we want to grow on the rice. This mold produces enzymes that we need to brake down the rice starch into sugar for the yeast to convert to alcohol.

      Koji-kin comes in two forms: mold covered rice (let your koji go beyond the white stage used for sake and it will turn greenish yellow with spores) and the powder which is just the former ground up.

      The yeast used for cooking can be used to replace sake, wine or brewers yeast but will have its own flavor and aroma contributions. I’m not sure of the amounts that would be needed for this substitution.

      I hope this covers your question.



  25. Hi, my name is Hugh and are Italian, I was impressed by your method and I would get the complimenti.Vorrei ask you something ….. I would try for the first time to do the sake and I’m documenting … I want to ask , since I have the Japanese koji to sprinkle on the rice, you can use Quach else as an alternative that does not significantly change the flavor of the final product? such as yeast to make pizza and bread or malt, and if you can, how many grams of dry yeast (Italian) I could use for about 2 kilograms of rice (3.5 lb)? Thanks again and congratulations

  26. I’m at hour 54 and it smells good, but hasn’t changed visually at all. It got too hot (120 F) at hour 20 (ie sometime in the 7 hours it went unchecked while I slept). was the mold dead at that point? Since it still smells good, could it still be useful/edible?

    1. Not sure. I’d be surprised if it died but looks and smells the same. I would guess that it is still good. Generally, if it goes too long the koji will turn greenish yellow. Turning greenish yellow is a sign that it is creating spores and is not usable as koji. It can be used for Koji-kin when this happens.



  27. Thanks for the instructions.. I have a question. Does the incubator come with a temp control module? What is the Koolatron model did you use?

  28. Very good instructions, much better technique than what I normally use.
    I go for least-contamination and do not use flour (always had bad luck but then I did not toast it first) and try not to move the rice too much. I steam in a pressure cooker (without pressure) and then use the same container for cooling – put the whole cooker into a bowl of cold water and check with an infra-red thermometer. Works reasonably well but I am not as careful.

  29. I tried my first attempt at koji this week. I used an incubator at the production kitchen I work in. The temperature never got above 90 but I believe we let it go too long and it became a pale, earthy green, which seems to be a cue to not use it in further fermenting. I plan on starting a new batch but I am wondering if there is any use for the koji when it has gone that far or if I should just throw it away.
    Thank you!

    1. Yes, you are correct that it has gone to far for use in sake. However, if you let it keep going and turn more fully greenish and then dry it you can put it into a shaker and use it to inoculate your next batch.



  30. I own a bamboo steamer like your and did that process the same using cheese cloth. I left it in there with a bit of water in a big round pan under it. I poked a thermo in the top of the bamboo lid and monitored the situation. I use an electric stove, so I turned the burner on barely~ and was able to maintain A steady temp of 86-90 degrees. The lid keeps it dark and I have moisture and proper heat. I am checking it at regular intervals and it’s doing great!.. I just thought I should share my methodology for those fellow ” electric stove ” users…

  31. Question, my koji always turns mostly yellowish/white but some have a dark yellowish color to them. Everything taste good and smells good but just wondering if its ok to use. I noticed Davids post above mentioned his turned turned a pale yellow/mint green color.

    1. John, I would start to cool the koji a bit sooner than you have been. It would be best to arrest its progress a bit sooner while it is still all white. Going from white to yellow to green is where the spores are coming into being (i.e., the koji-kin).

  32. Hi Will,
    Reading your book ” Brewing sake” at one point you mention that the optimum temperature for getting amilases is grow the koji between 98 and 104 F, but as I understand in this post you recommend that the temperature during koji making needs to be between 90 to 95 F. Which should be the correcte temperature? Does this temperature should be the same during all the koji making process?

    1. Humbert,

      Sorry for the confusion. This represents a bit of a change in my thinking about what should work best for the reader. Both temperature ranges will work well but I think it is safer to start with lower temperatures and move to the higher temperatures as you get the hang of making koji. The higher range is a little better for producing the saccharification enzymes.

      Also, in truth, each type of koji will have its own characteristic temperature profile; where it produces enzymes to break down proteins and where it produces enzymes for starches. In addition, very skilled koji masters will use temperature, humidity and time to very the characteristics of the resulting koji to make specific types of sake.


  33. Hi Will
    I did a post on your forum the other day, but i think this was the appropriate place.
    I am more confident after browsing the instructions here for the koji process, also i have a copy of your book on order, which is in stock in the uk.
    I wonder if i will have some good sake ready for my wife to take back to Japan next month for my father in law?
    Thanks for your great site

    1. Chris,

      I’m glad you are feeling more confident. It does sound like you are moving in the right direction. However, one month for good sake is a pretty short time. That would be pretty cool for her to take some good sake that you made to her father!



  34. Hello Will…
    Well, your advice and instructions have convinced me that sake is a great addition to my brewery! I followed the instructions and thou I had some concerns the outcome might be short of the mark, I pushed onward only to find the end product delicious and having measured the ABV at 21% was shocked at the level of alcohol produced!!! Thank you for opening a new frontier in brewing for all of us out here on the web…
    My next quest is to experiment with the Koji in brewing beer. Have you ever tried it? Just curious…
    Do you know of a source for dry sake yeast here in the U.S.? I used K1V white wine yeast on my first batch and it was delicious and quite fruity fermented at 50F. I wanted to use the #7 yeast but would rather use dry if available….
    Again, many thanks for all the great content on your site and as they say…. Kampai!

    1. Hey David,

      I’m glad that you had such a good experience! I don’t know of any dry sake yeast that is available. I have heard of people using koji with beer but I have no details. I think Boston Brewing has successfully experimented with this type of thing.



  35. A quick question… My Koji turned a pale yellow/mint green color. The aroma was great and it was nutty and sweet tasting but somewhat softer than I thought it should have been. Do you think it would still be good for brewing? Love the site and videos… My first attempt at sake but been brewing beer and mead for years. Hope my first attempt is drinkable…. 🙂
    Thanks for any help and advise.

    1. David,

      If the hue is only slightly off white it should be OK but much more than that and you are getting into iffy territory.


  36. Hi Will,

    You have awesome instructions and love your videos online. Thanks for posting them.

    I have been doing Sake for a couple of years, but I do not have access to polished rice, and can’t make myself to spend the shipping from FH Steinbart. Have you or someone you talk on your forums tried any home appliance rice polishers? I have seen them in Japan. So I am not sure if they can polish the rice well. I was wondering if anyone was successful polishing rice at home with those tools or any other tools.

    Thanks and have a nice day,


  37. Thanks Will. Yeah, it was pretty humid in there! I used a big glass for the water. Also, I had a lot of cloth wrapped around the koji and I think the cloth retained a lot of moisture after the water was removed.

    Despite the excess moisture, it was growing pretty well, but slowly. It had not covered and penetrated the rice as much as I thought it should by 50 hours, so I let it keep going. Bad decision. At about 60 hours, it started turning green, and it was apparently ruined. In hindsight, the koji might have been sub-optimal but OK if I had just cooled it off and stored it at 50 hours.

    Next time, less moisture in the beginning, less cloth wrapping and more ventilation.

    1. Jeff,

      It sounds like the tweaking has begun :-).

      As a side note: The green koji, if let go all the way and then dried and stored can be used for koji-kin (tane-koji). After dried, it can be put in a shaker to disperse the spores when ready.


  38. Hi Will,

    This weekend I tried making koji for the first time. Your instructions are a wonderful resource, thank you!

    This batch didn’t turn out, but I’m learning and have an idea about what may have been the main thing to go wrong. I used a setup very similar to yours, but my cooler doesn’t have a built-in heating/cooling element like yours does. Instead, I used a small heater attached to my temperature controller.

    The problem with my setup, I think, is that after I removed the source of humidity (glass of water) after 24 hours, there wasn’t enough ventilation to let the koji dry out properly. It was still very moist even after 48 hours, and the cooler had lots of condensation inside.

    I’m starting to think about how to revise my setup. Getting a cooler like yours would probably be the easiest solution.

    Just wanted to pass along this word of warning so others don’t repeat my mistake. Thanks again for this great resource!


    1. Hey Jeff,

      Every system is a bit different and they all need some tweaking. I wouldn’t get a new cooler for this. Next attempt just prop open the lid a little after removing the water. This will let it dry out a bit. Once it is dry enough, if it gets dry enough, you can close the lid all the way again.

      I wonder if you had it a bit too moist during the first 24 hours.

      It takes most people I talk to several tries to get it right.

      Good luck with your next batch,


  39. Thanks. I just saw the stuff on the main page and didn’t go to the product page.

    I have access to 30% milled rice, so not quite gingo grade but close enough. For a trial, I’ll likely just buy that rice locally and order the GEM spores. If I like the results, I’ll order all the gingo grade stuff from you because I don’t know where to find true gingo grade rice locally. I know it would be easier to get your ready made koji rice, but I’m all for trying to do it all myself.

  40. Hi Will-

    First off, what an amazing resource. Thanks!

    My LHBS usually stocks a Vision Brewing “kit” which amounts to koji-kin spores and a set of instructions for $13. They have been out of stock for some time now. I don’t see the spores you said you were going to sell here. Can you offer any advice on using miso koji? My local asian grocer has this: (link went bad).

    Can I use that to make Kome koji or is it not the right stuff. Any idea on when you will sell the spores yourself?

    1. Kurt,


      The koji-kin that I sell is at: the product page

      This page has two types of koji-kin. One that is more general from GEM Cultures and the other is specifically for ginjo grade sake. All the other ingredients I sell are represented on this page as well. They both come with instructions :-).

      On the recipe page are some additional instructions as well.

      The Cold Mountain Koji (your link) can be used just as the fresh koji I sell.

      Thanks, Will

    1. Hey Tony, I am not sure of the condition of the koji. If it is a “sticky mess” then it is possible that the rice was over cooked or steams and so was too soggy. At 30 hours I would keep it warm so that it will continue to grow and give it a good stir / mixing every couple of hours. Remove any source of humidity and give it some more time.

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