What Koji needs to grow and how to provide for its needs

This article sets out to explain what conditions are necessary to grow Koji and how to generate these conditions. An article on the time frame of growing Koji will follow soon. 

What always irked me about instructions on how to grow Koji (and how to make miso) is that they always explained it in a step-by-step way, rather than explaining what the essential factors are in the whole undertaking. I.e. the instructions said “use hot water bottles”, “use x amount of towels on which to let the rice cool”, “set up a bowl of water in the incubation box” etc. but not what the purpose of those actions was.

So, here I will try to summarize what Koji likes, because there are many ways to generate the necessary conditions.

What Koji needs

Pretty much every instruction says that Koji needs temperatures between roughly 28°C and 36°C (and they are right, of course). If the temperature is around 40°C the fungus starts producing spores earlier, which is not wanted almost all of the time). If the temperature is even higher the fungus will die.

Koji will produce more amylases at higher temperatures, and more proteases at lower temperature. So, depending on whether you make sake or miso you can adjust. For the beginning don’t worry about it so long as you are within 28°C and 36°C.

Koji also needs a high relative humidity. In the beginning, the first 24h, 90% are desirable. It’s no catastrophe if it’s 80%, or even 70%, but it certainly works better at 90%.

Some people say that after 24h it is better to lower humidity again, so that the fungus has to burrow deep into the grain in order to find water. If the air is always very humid the fungus can just happily grow on the outside without actually growing much into the kernel. I think there’s truth to that, but I am undecided on how much this is going to affect the amount of enzymes that are produced, which is the whole point. This is an experiment waiting to happen. :)

The Substrate

Many foods can be used as a substrate for Koji. Usually people use rice, barley or soy. If I write “rice” in the following paragraphs it also applies for all other substrates.

The rice should be:
  • Not too wet
    • This is why in all instructions it is heavily recommended that the rice is steamed, after it had been soaking for 12 hours (Barley should soak for 2-4 hours.)
    • Some even recommend keeping the rice in a sieve for 2 hours prior to steaming, to get rid of as much water as possible.
      • In a pressure cooker steaming takes about 20 minutes from the point at which it reached full pressure. In a normal pot it takes about 40 minutes.
        • For steaming, a piece of cloth is very helpful to keep everything together.
      • After steaming, the rice/barley should be spread on a layer of dry cloth or just on a clean table in order to cool down and dry. A lot of moisture will steam off and some will soak into the cloth.
      • Steamed rice will seem strangely dry, don’t worry, it is supposed to be like that. When eating it, it will seem a bit gummy.
    • Why it should not be too wet: If your rice is too wet you are making it hard for Koji to grow, and easy for bacteria (mostly Bacillus) to grow. You will notice as there won’t be much, if any, mycelium visible. Instead there will be a smell of ammonia. To get the water content of your rice perfectly right, you have to steam your rice. Cooking it will not work.
  • Dehulled/polished:
    • The rice should be white, not brown rice. Same goes for barley, it should be pearled barley, if the hull is still there the fungus can’t penetrate the kernel and nothing will happen.
    • Some people do grow Koji on natural rice, but they sprout the rice first. Anyway, if you grow Koji for the first time it is strongly recommended to do so on white rice or pearled barley as they are much easier to work with.

So this is pretty much it. The substrate part is pretty clear, so now let’s talk about the many ways to provide for heat and humidity.

How to provide for it needs

There are as many solutions as there are people making Koji.

Solutions without special equipment

At the most basic, some people use hot water bottles and towels to provide warmth for their Koji, changing them when necessary. Personally that’d be a bit too much of a hassle for me as I like to sleep at night. If you go by that route, there are very helpful thermometers with probes out there that can sound an alarm once temperature goes below or above a certain threshold – this might be helpful with other devices too.

A variation on the hot water bottle theme would be to put canisters/pots with hot water in an insulated box. An insulated box could be everything from one made of carton wrapped with blankets to special thermoboxes.

I am always in favour of using solutions that don’t require (too many) extra purchases. However, if you feel positive that it is going to be a lasting hobby, why not spend a bit of money on it. Or maybe you already have one or more of the following devices:

Solutions with “special” equipment

I have heard people have good experiences with bread proofers, which makes sense because sourdough/yeast like the same temperatures as Koji. By the same token I think there are bread baking devices out there which are meant to do every step of the baking process – if they are tweaked to do just the proofing they might be a good solution too for small batches of Koji.

Another device that seems perfect is an incubation box for chicken eggs. Somebody in one of the miso groups on Facebook talked about it, and it struck me as quite genius, since these boxes (well, the better ones I suppose) not only regulate temperature but also humidity. They can be cheap too – starting from 50€ and you are good to go.

I am sure there are plenty other options out there as well. Stuff that is used for terrariums or aquariums may be very helpful. Heating blankets may be an option too. One person I know makes perfect Koji just with a heating blanket. Ceramic heaters can be used to heat the air in a box. I have used a hair dryer for that purpose too, and it worked quite well! (It just was a bit loud every now and then)

Obviously, for some of these heat sources you will need a temperature regulating device. I use an Inkbird ITC-1000, which works quite well. It comes with a temperature probe, which I usually put directly into the rice. This is better than just regulating the temperature in the box, as the Koji will produce its own heat after some time. For this reason, after the first day, usually no heating is required anymore!

Be creative with your solutions, but make sure to stay safe. My first Koji box was made with floor heating wire, and I think it was not a safe option as the insulation of the wire once melted. Making Koji is fun, burning down your home is not!

Providing humidity

A simple way to provide humidity is to just spray the insides with water every now and then. You can also spray the cloth you are growing the Koji in (as in the photo below, in the tray section).  Probably much better to try this before spending money on a solution that works maybe marginally better than another.

Many people just put a baking tray with water over their heating element. Usually humidity will go up to 70% with that method – which is OK. It helps to put hot water in the tray in the beginning to raise humidity beyond that.

The super fancy solution, however, would be to use a humidifier. These devices are made specifically for humidifying air – perfect. Ultrasonic humidifiers work best. There are devices out there that will switch the humidifier on or off depending on relative humidity – usually they have a temperature controlling option too. The WH8040 is said to be good – it just regulates humidity, however.

I’m sure there are other solutions for humidity out there as well. If you have access to a professional kitchen you might hit the jackpot and there might be an oven that is able to regulate temperature and humidity at levels required for making Koji.

Cory Hughart commented on this article that there is another really easy way to regulate humidity. If you are using an unperforated stainless steel tray (preferably a deep one) as they are common in commercial kitchens, you can put your Koji in the tray and cover it with plastic wrap. Put some holes into the wrap so that your Koji still gets some oxygen. I would also advise to still use a piece of cloth between the tray and your Koji, so that no water is going to pool in the bottom of your tray. More on that in the next section.

Trays for Koji

One thing that really changed the quality of my Koji was the switch from a baking tray to one made of wood. The baking tray obviously didn’t soak up excess water, so the lower layer of rice sometimes got a bit soggy – not good.

I strongly recommend to incubate Koji in a wooden tray. Not only because of sogginess issues, but also because the wood will help regulate the humidity in your box. However, if you don’t have a wooden tray and it’s not easy for you to make one, you can still get some cloth and put two layers of thin cloth or one layer of thick cloth on the bottom of your baking tray or pyrex dish.

(edit March 2019: In the meanwhile, I tried perforated stainless steel trays in conjunction with thick cloth, and it worked quite well too – the key here is to avoid any pooling of water/moisture)

The tray I use

Traditionally in Japan, cedar wood is used for trays and Koji boxes (the boxes, sometimes even rooms, are called “Muro” there). Here in Austria, cedar is hard to get and expensive. In my opinion it’s probably best to use woods that are used in building saunas. So the obvious choice is spruce. It’s cheap and widely available.

Usually trays are made without metal, just with wooden joints. I was a bit lazy with mine and used screws. I don’t see a downside, except that my tray looks less fancy than it could.

Examples of Koji boxes (aka “muros”)

My first setup

Here is was using a dehydrator with a temperature control device. This is not because I think a dehydrator is inherently better, it’s just that I already had one. I put it in a cabinet as shown below.

Doesn't look too professional, I know.
My current setup – a bit of a makeshift solution, but it was alright for the first 20 batches. Now the veneer starts to get loose and wavy.

This is basically an old re-purposed sewing cabinet. The wooden tray with the rice goes on top the wooden rails (more on that later). The pot you see on the right is filled with water and I put an immersion heater in it, it is there to heighten the relative humidity of the air.

Way on the right next to the box you see the ITC-1000, which regulates the temperature. It has a probe attached to it which I always place in the middle of the koji. So depending on the temperature of the Koji, it switches the electricity of the dehydrator and the immersion heater on or off.

It is set to heat when temps fall below 30°C, and to stop heating when they are above 30.5°C. I found it’s better to have a small range of temperature, because the temperature of the Koji will lag behind and the heating phase will result not in a rise of 0.5°C, but closer to 3 or 4°C, but that’s OK.

The next setup

After the sewing cabinet I moved on to a new box, as the veneer of the cabinet started to peel off and the thing got quite gross… so I built myself a box from spruce stock and spruce boards.

My current setup

You can see there are two controllers, one for temperature and one for humidity. The silver thing you see on the bottom right is an ultrasonic humidifier. On the left is the dehydrator. Meanwhile I started to use a hairdryer instead of the dehydrator, as it is small, powerful and made to resist high levels of relative humidity.

The controllers switch the devices on or off, depending on the need of the moment. The temperature probe can be put into the rice, while the probe for humidity is always at the top.

Growing the Koji

Begin by diluting the spores.

Once the rice/barley/etc. has cooled down to about 35-40°C you can spread the spores with a sieve over your grains. Mix the grains well, so that the spores are distributed well.

Line your tray with a piece of cloth and then put your grains into the tray. Keep everything at the desired temperature and humidity for 24h (you can moisten the cloth a bit by spraying some water onto it, but don’t make it too wet). I usually put the thermostat probe into the rice, to ensure that the grains have the right temperature.

After 24h I stir the rice the first time. This helps to better distribute the Koji and also to stimulate it to penetrate deeper into the kernels. If you want fancy looking mats don’t stir the rice again after this point. For better penetration of Koji into the kernels it is better to stir every 4 hours or so.

This Koji has not been stirred again after the first stirring at 24h.
This Koji has not been stirred again after the first stirring at 24h. Note the slight yellowish/green color. This Koji is starting to sporulate and is very much ready for use. More on that below.
This Koji has been stirred a few times after the first stirring at 24h.
This Koji has been stirred a few times after the first stirring at 24h.

When is the Koji ready to use?

The time it takes for your Koji to be ready depends on the type of grain you are fermenting, and also on the strain of Koji you are using. Red rice Koji is ready after 40 hours, in my experience. Barley Koji can take 50 hours or longer.

In any case, if you see that your Koji is producing yellowish green spots, it is starting to produce spores. I recommend stopping the fermentation immediately by cooling the grains either in your fridge or outside if it’s cold enough. Be aware that the Koji may still be producing its own heat, so spread it out. I once just put the tray  into my room to stop the fermentation and after a few hours I came back to some really green Koji.

Heavily sporulated Koji tastes quite bad. It has a strong off-taste and if you make miso with it, the miso will discolor when it gets into contact with oxygen. It does not look good. Don’t worry if there are some yellow/green spots. It only gets problematic if everything is really green.

So the best moment to stop the fermentation is just before it starts to sporulate. I understand it is not so easy to tell when that moment is. It’s best to check your Koji quite often, especially when you make the first few times. With experience you will get a good intuition of when your Koji is ready.

Thanks for reading! If you have any critique, input or questions, please let me know!

This Post Has 108 Comments

  1. Hi Viktor,
    I have been making koji rice successfully but the last few times I made it, I noticed that there were a lot of rice grains left uninoculated. The spores I used are very old could that be the reason? Or is there another?
    I’m going to place a new order because I’ve already run out of the old ones but it’s impressive how resistant they are and continue to work after 2 years. Thank you

  2. Hello Viktor and thank you for the valuable information.

    I have grown my first batch of Koji on basmati rice using light rice koji spores. The resulting product smelled strongly of fresh mushrooms. I made Shio Koji and used 5% of salt. After three days fermenting, and stirring twice daily, a strong blue cheese aroma has developed.

    Having never tasted/seen/smelled koji or shio koji before, I am trying to work out if I should be happy or sad at this point!

    Many thanks

    1. Hi Dylan,
      a strong smell of fresh mushrooms sounds good. Koji can smell like anything between that and fresh fruit (especially apricot and exotic fruit, imho).
      A strong blue cheese smell in shio koji is a bit weird, however. That usually only happens when combining koji with dairy.
      Did you make a 5% brine or is 5% the total amount in the shio koji? If the 5% is the brine, your shio koji now has much less salt in total, which could also explain the off-taste.
      If you have 5% salt in total, and your koji was nicely grown and had no strange spots, you are on the safe side in terms of food safety.

  3. Hi Viktor,

    My koji always starts to sporulate and become green around 36 hours. What can be the reason for this? Too much humidity? Too less airflow? I have temperature quite right.

    1. Hi Maarten,

      it depends on the kind of koji you are making. It sounds like you are either making soy sauce koji or barley koji.
      In the case of soy sauce, it is a sign that the koji was a bit too hot. However, sporulation is quite normal, and not a problem. We are always making our shoyus with sporulated koji.
      In the case of barley koji, it is a sign that the barley was either too wet, or it got too hot. I doubt it was too little airflow.
      As soon as you see signs of sporulation, make sure to remove the koji from the muro and cool it down to stop the growth.

  4. Hi there! I would like to said that you have wonderful website and lot of useful information. Thanks for that. Due to you, i started to try to growth koji first time. After 30 hours at 35 to 28 °c the koji tart to show up on the rice but it’s really stinky. Maybe ammoniac. Is it safe to use it or not? Should i trhow everything?

    1. Hi, if your koji is really stinky, you should throw it away. It is a sign of bacterial infection, which happens when your rice is too wet.

  5. I just wanted to share here the process by which I recently managed to make rye koji. My first attempts weren’t successful, because rye has a thick bran layer that prevents the koji-kin from penetrating the grain. After reading a bit, I decided to crack the rye grains to get around this problem. I used a grain mill set to very coarse (the same setting I use for cracking wheat for shoyu) and passed the dry rye grains through it, twice. The goal was to split in two or three each grain, and it worked well. I sieved off any fine flour generated (which was less than 5% of the initial rye weight). I left any coarse bran that had detached from the grains in, because I think it provides a lot of the rye flavor, and shouldn’t hurt anything once it’s detached from the grain. I then soaked the rye and steamed it (rye soaks and steams quite quickly, like barley: 1h soak, 30min steaming time), inoculated it with spores and let it incubate as usual. I got very vigorous growth and a beautiful koji at 48h.
    Just wanted to leave this here in case anyone else wants to use rye for koji. I like rye a lot in baking, and I can’t wait to find out how the miso I made with this rye koji will taste.

    1. Hi Silviu, thanks a lot for sharing your experiences here! Very appreciated.

  6. Hi :-)
    I searched on Google and read here, but i don’t find this information : do koji spores need total dark obscurity to germinate and grow, or is koji not bothered by light ?
    I ask because I’m going to use a small plastic greenhouse of 50x40cm, electric heated built-in device and precisely thermoregulated, but with a transparent roof.
    Must I cover it or keep it in the dark for good results ?

    1. Hi Ronny! Light doesn’t bother koji. Maybe it would be bad to put it in direct sunlight, but everything else is no problem at all.

  7. Hi Viktor! I have been making koji for years but encountered something strange for the first time: underneath the white layer of koji (after 30 hours or so) became completely brown. The taste is actually not bad, a bit of the sour off-notes that the green sporulated koji has but nothing horrible. Have you had this before? I noticed that the last hours the temperature spiked from 29 to 35 degrees, a bit more than what normally happens…

    1. Hi Lennart, that sounds like the bottom got a bit too wet, and you got some bacterial growth there (hence the sourness from lactobacillus, presumably). Was it slimy too?

  8. Hi Viktor

    I am making Koji for the first time and after 46 hours right now i don´t smell anything sweet but more smokey notes. The pearl barley made a nice cake and everything sporulated according to plan only the smell seems to lag behind. My setup is a plastic container with a layer of water in it and a aquarium heater set on 30 degrees celsius. The towel under the pearl barley remained damp during the whole process and I covered the lid with another towel so that condens would not fall in the tray. I was wondering if I can use this batch or not? thanks in advance for your answer!

    Kind regards

    Joris Holleman

    1. An now that I smell it also a bit like wet laundry which stayed too long in the washingmachine. Thanks again!

    2. Hi Joris,

      it is always hard to say without photos. It sounds OK, but I can’t say without photos. Sometimes people expect a stronger smell, but Koji can have a rather subtle smell too.
      The koji should not sporulate, if you intend to make miso with it. For soy sauce it doesn’t matter, but for anything else, the koji should not sporulate. I recommend to pull koji after about 40 hours.

  9. Hi Viktor, do you have any experience with growing koji on millet or buckwheat? If so – did you soak and cook it? And how long? I’ve tried with soaked, cracked buckwheat – it was directly super wet and slimy and before trying to grow koji on it, I knew already it most probably wouldn’t work. Haven’t tried again since

    1. Hi Clara,

      I don’t have much/any experience with these substrates. You were already on a good track by using cracked buckwheat. As with anything koji, the art of making it lies in getting hydration right. This is especially hard when your substrate is very small. I would recommend to try the cracked buckwheat again, but this time don’t soak it. Instead, weigh how much you have, and then mix in half the weight water. I.e. if you have 800 g of cracked buckwheat, mix in 400 g of water (or 1 kg buckwheat-> 0.5 kg of water). Let it absorb the water and then steam it. This should be much closer to ideal hydration.
      I tried millet once, but I found that the shell is quite hard, and so koji has a hard time penetrating it. But I am sure it is possible, as I know there are people working with millet and koji.

  10. Hi Viktor,

    Thank you for this post! It helps me a lot with my first trial of amazake making from Koji.

    Initially my amazake has quite strong koji-like aroma when it was done being kept for the enzymatic hydrolysis part (i waterbath it for 16h at 57-59’C). However i inactivate the enzyme by shimmering it for 10 mins, and the koji-like aroma also gone, leaving only rice smell.

    I have one question: on the final amazake that I made, there is kind of, something gel-like like nata de coco kind of texture. Im not sure whether its from polysacharide or from aspergillus’ mycellium, but its weird to have something chewy in amazake… theres no off flavor or off taste, tho. Do you have any suggestion or susceptible cause of this?

    1. Hi Scriabin,

      you don’t need to get rid of the enzymes in the end, so if you don’t cook the amazake afterwards, maybe more of the koji aroma will stay.
      I am pretty sure the gel-like texture is a result of the starch being cooked. I like to make amazake-puddings this way. Again, if you don’t cook it afterwards you shouldn’t get this.

  11. Hi Viktor,

    I am wanting to use these spores for a design project where i am looking at pigment producing microorganisms. I was wondering if these spores will produce pigments and if so, what sort of conditions I would need. Your page has already been very informative and it is clear you know your stuff! look forward to hearing back from you.

    1. Hi Anastasia,

      I don’t think Koji is very suitable for pigment production. In this case I would look into bacteria and algae.

  12. Could i make the started with Koji rice ? How much Koji rice do i need per gram of rice ?

    Thank you !

    1. Hi Alberto,

      while in theory that’s possible, it’s not recommended as it is not very reliable or safe. In the process of making koji rice you may introduce other microorganisms which you don’t want in your koji. So it’s better to start off with a pure starter.

  13. I have just finished my second batch of koji using light rice koji spores. My setup is quite simple. I use a seedling warming pad, a wooden tray (filmed under bottom and over top) and a big folded towel for insulation. My only investment has been a steamer.
    I used my ricecooker for the first batch, but the rice were to dry. The result was 50 % koji, 50% dry rice.
    Second batch was steamed. Result > 95% koji. I think, I will supply some extra moisture next time with a damp dishcloth under the top film. The edges were a bit dry.
    I have used the koji for amazake and shio koji (both taste very good) and miso (to be tasted in a couple of months).

    1. Hi Anne,

      happy to hear that you figured out a nice way to make koji :)

  14. Hi, I am planning to do both sake and shoyu. I am fairly confident that I understand about the initial stages, where the koji needs a little air flow to provide oxygen. What is less clear to me is whether the mould stays alive for the subsequent stages, or whether its just the enzymes (amylase for sake, protease for shoyu/miso) that remain active? Should the containers be sealed/airlocked or kept open (cheesecloth with a rubber band to deter insects)?

    1. Hi Oliver,

      once you start making something with the koji, it will die. So just the enzymes will remain active. I would advise against airlocking your shoyu, as you need to stir it often. The mass of wheat and soybeans will float up like a sponge because of all the CO2 that’s produces, and you need to push it down every now and then. I recommend to stir every day for the first two weeks. This also helps to prevent wild mold growth, as the surface is disturbed every day. After these two weeks, your shoyu will have a lower pH, so the likelihood of mold growth will be less, and you can start to stir every two to three days. Stirring also brings in oxygen, which will help with darkening the sauce. In between stirs, I just put a lid on, but you can also use a cloth with a rubber band.
      I have never made proper sake, so I am not sure how it works there to be honest.

  15. with wich instrument do you arrange the temperature?i havent understood.i just have recieved your koji spores and programming my equipment.if you could help little more!
    the miso poppyseeds btw was supertasty!!!

    1. Hi Stergios,

      I recommend to get an Inkbird ITC-308. It is already wired up and user friendly.
      Happy to hear you liked the miso!


  16. Hi Viktor, thank you for the thorough explanation of how to grow koji. My question is how to keep the rice from overheating in hot weather. Even when I break up and stir the rice, after about 30 hours it’s generating so much heat that it quickly climbs back towards 40 degrees. I’ve tried floating the tray in a container of ice water but it’s a bit difficult to get the temperature right. Any suggestions? Normal daily temps here are 29-35 Celsius (great for the first day of incubation, but not after)

    1. Hi Nick!

      That’s quite warm ambient temperatures. Do you have any spot in your home where it could be a bit cooler? I think it’ll be very hard to get the temp right otherwise.
      If you don’t have such a spot, it could be an idea to get a fridge, put the thermostat probe into the rice and make the fridge cool down the rice to 33°C.

  17. Hi Viktor
    I wish I have found you guys earlier.
    I have this strange situation with my koji. It has now been growing nicely on the steamed rice for almost a week and it is till not turning green. It is beautifully cream-white with what i can describe as crowns on top of the stalks/fiber and has been like that for a few days. the aroma is very pleasant. But, it is just not going green. Is that normal? Are there Koji types that have white spores?
    It is residing in the oven with oven light on and a tray of water so the the humidity should be around 70% with around 39 degrees celsius.

    1. Hi Peter,

      there are spores that are white! Was your starter white or green?
      It sounds to me that the rice dried out, and the koji couldn’t produce spores in time.

      Generally, I think it’s not a good idea to make your own spores, as it is hard to keep a pure culture in a private setting. Some foreign molds produce toxins that accumulate in the liver and elsewhere. That being said, make sure to only make your own spores once. I.e. don’t keep on propagating your propagated spores.

  18. Hi Viktor
    I’m struggling to get strong growth on my Koji rice or barley.
    I would greatly appreciate some help.
    I’m either using long grain white rice (white koji spores) or pearl barley (barley spores)
    I dilute the spores into 29 g sterile rice flour as suggested.
    Rice is soaked over night, barley for 4 hours.
    Rice is steamed in a rational oven 100C for 1 hour on a perforated tray wrapped in muslin cloth. Barley for 45 minutes.
    The substrate is cooled at room temperature and is cool and dry before inoculating.
    The substrate is wrapped in muslin, approx 2.5 cm thick in a gastro oven tray and wrapped in cling film with a few holes.
    The tray is put into a themo box with a heat mat connected to a pid controller and set at 30c. The probe is put into the substrate.
    I mix after 24 hours (have tried dampening the muslin) and leave until the full 48 hours.
    The koji comes out better and at best is all chalky white with a good sweet smell and taste but no growth on top and sometimes slightly cakey.
    The barley at best smells good and tastes slightly sweet but is not cakey and is little to zero visibility of growth.
    Do you have any suggestions?

    1. Hi Duncan,

      please accept my apologies for not getting back to you earlier.

      We usually steam our rice in the rational oven for 25 mins, it’s long enough. 45 mins for barley is good! I see in the email that you are actually using Job’s tears? That’s what they used in Japan originally instead of barley, if I am not mistaken :)

      Did you make holes in the cling film? The last customer who had trouble growing koji used the cling film method too. Once he tried without it, it worked much better. Maybe your Koji is suffocating? I would recommend to try again without the cling film, and making sure that the cloth stays damp. How high is the gastro tray you used? Maybe there was not enough air in it.

      Let me know if this changed anything if you try again.

  19. Hi Viktor! I have a brewery in Quebec and I want to incorporate koji in my sour mash. I want to do a starter with my pure koji. This is my questions.

    – Can I use malted barley with koji to do my starter?

    – I saw that some brewers( they are not a lot and there are not a lot of information on it) that use Koji Rice in their sour mash (lactobacillus production to get lactic acid) at 65 celcius to accelerate the process.

    – Which kind of acid the Koji secrete (lactic acid???, kojic acid?? )

    – The koji is aerobic or can be anaerobic

    – Do you know the Ph of the koji rice at the end approx

    1. Hi Mike!

      You can kojify barley malt. Maybe you will have to crack the barley a bit since Koji can’t grow through the hull.
      Strictly speaking, Koji Rice does not have much to do with lactobacillus. With Koji Rice you are supplying additional sugars and enzymes.
      Normal Koji does not produce acids in quantities worth mentioning. But you could try to use Aspergillus Luchuensis – it produces citric acid. So you could make a sour mash with it, which would have a more fruity touch.
      Koji is a mold, so it needs to breathe oxygen in order to be able to digest all the sugar and amino acid it is eating :) if you put it in a closed thing, it will suffocate. You can really smell the CO2 when you do that.
      I don’t know the pH, sorry. My guess would be around a pH of 6.

      For your application, I would kojify pearled barley with A. Luchuensis and use that. Making a mash with pearled barley only is problematic for lautering, but as a supplement I can imagine that it’d work quite well.
      If you prefer to have lactic acid instead of citric acid, it’d be probably best to look out for lactic acid bacteria for beer. I am sure it’s possible to buy pure cultures.

      Hope that helps!

  20. Hi Viktor,
    This is my first time making koji.
    Im currently at 64 hours in my koji rice fermentation.
    I haven’t seen the white mold fiber forming other than really small pieces.
    It smells really alcoholic now and has this broken white/ darker yellow with no sign of mold any where.
    I stirred every 12 hours and the temp kept rising to 40 degrees Celsius.
    I don’t know if its bad or still usable.
    Can you help me?

    1. Hi Michael,

      you should see white stuff at around hour 24. It sounds to me that your substrate is too wet. Can you please send me a picture to office -at- fermentationculture.eu?

  21. Thank you for sharing your thoughts and experience regarding koji rice. There is actually this guy on YouTube that showed how to make your own koji-kin from koji rice. https://www.youtube.com/watch?v=tE1-Q0wskfk&t=521s He let it spore until it’s totally green, and then he powdered it. He said it’s related to the white koji-kin. However, you mentioned that the greenish spores have an off taste. I’m pretty doubtful myself, and I’d like to hear your thoughts on this.

    1. Hi Catherine!

      My honest thought on this topic is that it’s not worth it to propagate your own spores, the risk far outweighs the gain.
      I know what many people may think when I say that, “of course, you sell them after all”. So, I may be in a bit of weak position to make my point, but I wouldn’t ever propagate my own koji.

      The problem is that nobody can work cleanly enough at home to ensure that no other species takes hold. Maybe it’s safe to do it one time. But it’s definitely not safe to keep on propagating your own culture, as other species may take hold.

      Many molds produce powerful toxins, which do not poison right away (which causes people to think it’s fine), but the toxins accumulate in vital organs, causing cancer years down the line. Many people underestimate this problem. Saving a few euros is just not worth the risk to me. Also, the rice or barley also cost something + the work involved.

      Apart from that, the propagation will change the behavior of the starter, as genetics change.

      Also, when propagating, the rice is not powdered afterwards, the spores are sieved off the rice.


    2. Hi Viktor and thanks for the fast delivery of the white koji spores !
      I made my first attempt with a. Oryzae on pearl barley that last week.
      all looked great after 48 hours (I pushed the humidity to 80, 85 % as the grains looked a bit dried at the beginning, even then on the top) and the temperature moved from 30 to 38 degrees during the last 24hours. I just mixed the barley one time after the first day. The mycelium had a really early and great development.
      My problem is , after tasting it at hour 48, there’s absolutely no taste in it, no sugar or simply not any aroma.
      i cut the culture in half to let one part in the fridge and decided to pushed the other in same conditions to see what happens.
      Finally the part I put to the fridge failed, it just taste like plastic.
      The other part that i let 12 more hours in the fermentation room was finally better even if the « Whooa » effect were not really there.
      I took some fresh grains that I mixed grossly to marinate shio, and that was still weak in term of aromas. Not zero but not crazy. I dried quickly the same grains from the marinade to grill them in oil then, and that was finally and strangely pretty great.
      Then I put the main part to dehydrate and it smelled strongly something like cheese or mushrooms when i mixed it to powder, but then again the aroma was a bit low when I tried a bouillon with it. (And I put a lot).

      I would love to know your opinion about it, as a beginner i’m a bit lost in my conclusions, i thought It could come from a barley which is not enough polished or a problem with low humidity

      thanks a lot,

      1. Hi Johann,

        it is hard to judge the quality of a koji without pictures. To me it sounds like you were expecting an explosion of taste, but the taste of koji can be quite subtle!
        Generally, I think koji shouldn’t take longer than 48 hours. If the koji tasted like plastic, I would say it’s the fault of whatever you put the koji in.
        If it smells like mushrooms that’s a good sign, but it shouldn’t ever smell like cheese, that’s a sign of a bacterial problems.


        1. Thanks a lot Viktor , as it was my first try, I think I was simply too much around the box to disturb the process^^
          All is going well now,
          Greetings, J

  22. Dear Viktor, thank you for your article!

    Since three weeks I am experimenting to make Barley Koji. I have Koji spores, pearl barley from seeberger, and I made a nice fermentation chamber out of wood, equipped with a thermostat and humidistat, a little humidifier from beurer and a little bathroom heater.

    The first two times my main error was to follow the times badly (from another tutorial) and letting the Koji grow a lot of spores (24h longer time!), that produced bitter green koji… and very separated koji.

    I just finished my third try, after more research: the Barley soaked maybe a bit longer (short night), then steamed 30min. nicely (was chewy), inoculated at 30 in a stainless steel tray (with holes on the bottom and a lightly damp cloth), first 24h at good temperature and humidity (30° / 75%-80%), when I took it out for the first stir it was looking nice and quite white (not completely), with a fruity smell and quite bound together… I broke it apart and put it in the chamber again. During the following 24h the temperature went up more at first (34’max), humidity also a bit higher (85° max), and the smell developed further (the fruits sweeter almost too ripe, and a somehow cheesy smell – by hour 36 ca.). When I took it out today (after ca.46h from inoculation)… the aspect/color was basically the same as 24h earlier, but the barley didn’t bind together at all, I barely saw a clump. and the smell was decreased… I tried it and the flavour is “boring” really, nothing interesting going on.

    I have never tasted Koji before so I am a bit running blind… what should I try doing different next time? Why could it be that it is
    always so “separated”?

    Every hint, suggestion, recommendation is very much appreciated…
    Thank you again for your site, best regards. F

    1. Hi Filippo,

      It sounds like you are doing quite well already. To me it sounds like the koji dried out in the last 24h of your process. The measurements of the humidity can be a bit misleading, as the sensor also picks up on the humidity that is leaving your koji :) so it’s drying out but the sensor thinks everything is alright.
      I would suggest for your next batch, to put a damp towel also on top of your koji (and make sure to keep it damp), and don’t stir it this time, then you should get a nice mat. Also, I think the ideal time to pull your koji is at about h 40-44, I wouldn’t leave it any longer.

      Hope this helps!

  23. Hallo Viktor, irgendwie ging meine frage nicht durch denke ich.

    Denkst du es ist möglich in einem Konvektomaten Koji zu fermentieren, da könnte ich Temperatur und Luftfeuchtigkeit genau einstellen.

    Und denkst du weiters es is möglich dinkel, roggen oder gestern koji zu machen.

    vielen dank, lg

    1. Hallo nochmal,

      wegen dinkel, roggen und gersten koji: Gerste funktioniert bewiesenermaßen ganz gut zum Koji machen :) wichtig ist halt, dass es gerollte Gerste ist. Dinkel und Roggen funktionieren sicher auch, aber auch die müssen gerollt sein. Das Schwierige ist da immer, den Feuchtigkeitsgehalt richtig zu erwischen. Gerollter Dinkel sauft sich sehr schnell an meiner Erfahrung nach.

      Auch sind diese Körner oft unterschiedlich stark geschliffen, weshalb manche Gerste recht lange braucht bis der Feuchtigkeitsgehalt stimmt, während wieder andere stärker geschliffen sind und nur die halbe Zeit benötigen.

      Falls du noch nie Koji gemacht hast, würde ich empfehlen mit Reis anzufangen. Da kriegt man ein sehr gutes Gefühl dafür, wie viel Feuchtigkeit im Korn sein solle (gar nicht so viel nämlich!). Beim Reis kann man weniger falsch machen. Einfach über Nacht in kalten Wasser einweichen und dann 25-30 min dämpfen. Der Reis kriegt so eine ganz eigene, relativ harte Konsistenz.

  24. Hi Viktor,
    I keep a sourdough starter and use it constantly and was curious if a koji culture could be kept like sourdough? Like, how you half the sourdough and then continue to feed it and keep it alive in order to constantly use it? Would you separate some of the koji and let it sporulate?

  25. Do you know if light affects the growth of Koji. I made an incubator from a wine fridge with a glass door and can’t seem to get consistent batches.

    1. Hi Vince,

      I am not aware of any bad effects of light on koji. In all likelihood your problem is somewhere else, but you could always just put some cardboard on your glass to be sure.

  26. Hallo Viktor,

    Ich haben in meiner küche einen kombi ofen, und würde gerne darin koji fermentieren, denkst du das geht, weil dort könnte ich die luftfeuchtigkeit und die temperatur genau einstellen,

    ich hatte an roggen, gersten und dinkel koji gedacht,

    lg johannes,

    und vielen dank

    1. Hi Johannes!
      (I’ll be replying in English, so that more people can read it)
      (Also, sorry for taking so damn long to reply!)

      The question was if a combination oven can be used for koji-making.

      I think, in regards to humidity, it doesn’t work, since these ovens make steam by heating water. That alone will heat up everything a bit too much, and the ovens are generally not made to keep such low (30°) temperatures reliably. At least that’s my experience with older models, you would have to try yours with a test run. Maybe get a thermometer with a cable to see what’s the temperature you have within the oven.

      Since you seem to be working in a proper restaurant kitchen, maybe you have a holdomat? These should be able to keep the desired temperature a bit more reliably.

      You could also get yourself a thermostat (like this one) and hook it up to a plate warming cabinet. Instant Muro :) This works great in my opinion.

      As for humidity in the last two cases, I’d recommend going with the plastic-film technique. This works very well in my estimation. Some of the nicest, fluffiest koji I made was using this technique.

  27. Thank you Viktor, will follow your advice :)

  28. Hi Viktor,
    You right , the barley was a bit soft ,
    I never made koji with rice before , what type of rice should i buy ? can i still use the barley koji or i need to buy rice koji?

    1. Rice that is intended for rice-pudding or sushi works best. We always use Originario.
      The barley koji will also work on rice.

  29. Hello Viktor , need some guidance…. my first barley koji
    So, for my set up
    I am using a styrofoam box , seed heater mat , metal gastro ( without hole ) , ink bird temperature controller , humidity controller and humidifier and clean towels .

    I soaked the barley for 24 hours , then steamed it for about 2hours until the barley was cooked .
    Set up the box at 30degree and 90% of humidity
    Cool down the barley until 30degree then put the barley koji ( the one i bought on your website and followed instructions on the package )
    Mix it very well to make sure that all the koji is on the barley.
    Put in the towel then in the gastro with 5cm thickness
    Put into the box with the temperature stick in the barley
    24hours passed and nothing happened…….. then i put an other 24hours nothing happened , just a nice smell when i open the box
    I would like to know what mistake i made….
    If you could guide me :)

    1. Hi Laura,

      it sounds like you are doing everything correctly, except for maybe one thing. Try to soak your barley for a shorter period, about 5-6 hours, and steam it for 1h.
      Was your barley super soft, or did it still have some bite? The duration of soaking depends on how polished your barley is, but I imagine that 24h is too long either way.
      Have you made koji with rice before? I recommend learning the craft with rice, because you can’t really oversoak it. You’ll get a good feeling for what is a good moisture level.


  30. Hi Viktor
    I’m using an egg hatcher that has max 70% humidity – hoping that’s enough. You mention reducing the humidity after the first 24 hours – any thoughts about how much to reduce it?

    1. Hi Lorel,

      if your max. humidity is 70%, I’d recommend using a moistened dish towel to put on top of your koji. In the duration of the fermentation you can moisten it every now and then. After 24h-30h you could then stop moistening it and open the towel on top to expose the koji to the 70%rh air.

  31. Hi Viktor, I have read your post and they are so brilliant I came to you thanks to Flavio from Bologna that explained so well the Koji world and he introduced us your website. I hav got a question after Koji is ready, as you wrote up here, if I want to make a let’s say sake, even if you could not call like this because all the procedure and religion behind that, but if I blend let’s say Koji rice with water, could I leave it to ferment like this to create a kind of fizzy beer, or do I need to put yeast different from Koji inside that mixture?
    I am asking you this because I read a book about sake and they do a kind of PARALLEL fermentazion, where they mix Koji rice water sugar and yeast? I have to inoculate with a yeast or for example I can put pieces of fruit so they can provide they spontaneous yeast?

    Thank you

    Kinds regards

    1. Hi Mirko!
      Thanks for the kind words!

      When I made sake, I just put the koji rice into water without blending it. I think if you blend it it’ll be very hard to filter. The starches will go into solution anyway, and you are left with “empty” rice so to say, which you then can separate much easier.

      Also, I added some bakers yeast to start the process. You could also try to rely on wild yeast as you say, by adding pieces of fruit.

      So while the enzymes are breaking down the sugars (in my case at room temp, probably between 15-18°C is best), the yeast is consuming the sugar and producing alcohol –> it’s, as you say, parallel.

      All that being said, I don’t have that much experience with sake, all I know is that I got a rather decent result in the way I described above. If you want to go deeper into the topic, this rustic style of sake is called “Doburoku”.

      Hope that helps!

      Kind regards,

  32. Hi,
    Thank you for your koji breeding process in detailed.
    I am living in Iran and have no access to Koji seed.if possiple it would be appreciated if you could write me procedure of Koji making without Koji seed or Koji kin.

    1. Hi Tajaldin,

      sorry for the long delay in answering you.
      Making Koji without starter is very dangerous, because you can’t know what species of Aspergillus you are growing. Many types of Aspergillus produce powerful toxins.

      Kind regards,

  33. Hi Victor! Thanks for the reply. You’re right, I think they dried out. I need to improve the humidity in my incubator. At that time I only have a bowl of water beside the tray. I stopped incubating them at hour 48 (I didn’t see your response in time), there was already bit of matting at the bottom, but the dried grains were hopeless. I blitzed everything into a powder to use as koji flour in my home cooking, and will try again this week. Thank you again!

  34. Hi Viktor,

    Thank you for this very helpful site! I am now on my 44th hour of making koji and while majority of the rice is white, there are some grains that aren’t–maybe the spore couldn’t attach itself to them? They are also not yet “matted” or in the form of a “cake”, and none of the sweet aroma of koji. Do I incubate longer?

    1. Hi Mabi!

      It sounds like those grains dried out before the Koji could take hold of them. The ones that aren’t white, do they just seem dry or do they have any other color?

      Usually, if it hasn’t worked by hour 44, there is little point in continuing the fermentation. Better to try again with higher humidity.

  35. Hi,

    does posible to get koji without steam? Does that realy nesessary?

    Thank you.

    1. Hi Dusan,

      steaming is absolutely crucial. There is hardly a way around it.

  36. Hello there viktor,
    Just wanted to thank you for putting together such an informative site about Koji. As you can see I’m a newbie in this whole thing but greatly interested. I’ve just placed my first order of Koji spores and looking forward to making my firs Amazake drink and may be Miso.
    charles K.

  37. Hi Victor,

    Ich habe eine Frage, die ich im Internet nicht beantwortet bekommen habe: deckst Du den Koji mit dem Handtuch zu oder liegt das Handtuch nur unter dem Koji und oben ist offen? Vielen Dank & liebe Grüsse

    1. Hi Philipp,

      ich decke ihn meistens schon zu. Ich mache das Tuch (ein Geschirrtuch ist besser als ein Handtuch) auch etwas feucht mit einem Wasserzerstäuber. Dadurch ist dann auch eine richtig hohe Luftfeuchtigkeit gegeben. Kann man hin und wieder dann mal checken ob es eh noch nicht ausgetrocknet ist, und bei Bedarf wieder befeuchten.

      Liebe Grüße,

  38. Hi Viktor,
    your site is amazing and very informative, thank you so much. I am super new to the whole koji concept but extremely into it.
    I am looking to buy spores and give koji a go. I live in Cyprus, an island that has desirable temperatures and humidity levels for koji, but I am not sure whether I should try growing it outside?
    Another thing I don’t understand is if it’s possible to multiply koji ? is there a way to make a mother koji and stop buying spores?
    Also, I checked the koji products I can buy on your website: are these ready to be spread on soya beans or meat for example or they are good for spreading them on rice/barley to grow koji?

    looking forward to hearing from you.


    1. Hi Maria,

      thanks for the kind words :)

      I think that growing koji outside is not very easy. A stable temperature at 28-30°C is really important. This may be possible by day (in the shade!), but at night it probably cools down too much. If you are certain that you will enjoy making your own Koji and Miso, it’d probably best for you to invest in a thermostat (there are readily wired ones by inkbird) and a heating blanket or some kind of bread proofer or egg incubator. Anything to keep a stable temperature.

      If you decide to still make koji outside, put your koji in a pan or pot, with a piece of cloth between the metal and the rice. Close this vessel with cling-film, to avoid any other molds to enter.

      It is possible to make your own spores, but I do not recommend it. There is the very real likelihood that in the process you are introducing a mold that produces toxins (many of which are super potent) – and there is no way to know whether or not that is the case. In a home you can’t work cleanly enough to avoid such a contamination.

      The spores are meant to be used on any substrate. I have successfully grown koji on meat, but felt a bit unsafe :)
      For beginners I recommend to grow the white koji on rice, it is the easiest. If you feel you achieved that, you can try to grow them on barley, etc.. There is an article that explains the differences between the strains.

      Kind regards,

  39. stefano novellino
    Hi Viktor i just found your site with all those great info you want to share and i am so happy !
    thanks a lot !!!
    best regards, stefano

  40. Hi Viktor

    Could you help me with some advice about how to build a wooden koji tray? I am building a fermentation chamber like the speed rack type in Noma’s Guide to Fermentation, and all I need now is a tray for the koji. I tried finding a perforated sheet tray, but it was not possible to get one at a reasonable price where I live.

    Any advice about how to build a woode tray would be greatly appreciated!

    1. Hi Håvard,

      best/easiest way to do it is to get a three-layer wood panel (https://www.putzer.com/bilder/produkte/gross/Dreischichtplatte_1.jpg) from a woodshop/hardware store. Here you can buy custom sizes. Then you get a board of solid wood, about 6-10 cm high. You can then cut the lengths (or have it cut for you at the store), to fit the perimeter of your panel. Then just screw the boards and the panel together.

      Kind regards,

    2. I am experienced in making Natto and have got my equipment together to make my first rice Koji.
      Does it taste nice just as rice ‘cakes’?
      By that I mean, turning several times early, then allowing it to bind together in small cakes.
      I will try for the upper temperature range to encourage more sugar production.

      Secondly, has any research been done on health benefits of Koji?

      1. Hi Tony,

        I don’t know rice cakes, but I can vouch that rice koji tastes absolutely wonderful. It’s mushroomy, fruity, flowery.
        I think you could try not turning it at all if you want to achieve tightly bound cakes. Just make sure to not make it thicker than 3-4cm, or else the center will overheat/suffocate.
        If you are using higher temperatures your koji will be finished earlier, so keep a close eye on it in the last 30-40 hours. You really want to avoid sporulated koji, as spores makes the koji look unseemly and they impart a bitter taste.

        I am sure there is research out there – but I am not in it for health reasons, my approach is culinary :) So I can’t say much about health topics regarding koji.

  41. Hi Viktor,

    Thanks for all the information here, it’s been very helpfull!
    I’ve been growing koji on oats to make amazake. But it has sporulated so much that I cannot use it anymore. I’d like to use it to inoculate a new batch of oats. Is this possible? Can I just mix some of it in there? Or maybe dry it, blend it and then sprinkle it on top?

    1. Hi Jan!

      it is possible to do that, but I would advise not to do it. The spores that are sold here are pure, single-species spores.
      If you continue to make your own spores from previous batches, you might easily introduce species of mold that are not as benign. I think if you do it once (i.e. to take spores from a batch that was made with pure spores), in all likelihood you’ll probably be fine, but don’t take spores from a batch that you have made from harvested spores already.

  42. Thanks for the advice. At 40 hours it has a nice coating and it looks pretty ready can I pull it now and call it done? I don’t be home to monitor it so this might be a better option.

    1. Yes, it’s probably better.

  43. I’m a little late in responding but I’ve just discovered koji and I’m currently about 40 hours into a koji ferment of wheat and soy (to make shoyu) unfortunately the temperature spiked overnight and I woke up to a temperature of 45°C I am wondering if this will have ruined my koji. It has not sporulated yet and I stirred and cooked it to 27°C. I’m hoping that I can still use it for the moromi. Any advice?

    1. Hi Laurel,

      I think it should be fine for moromi. It’s not ideal of course :) but it should work fine. Make sure to keep a close eye on it. If it starts to get kind of yellow/green or if it starts to “dust”, get it out of your box and make a moromi with it.

  44. I took a class offered by the amazing Jeremy Umansky, and his solution for keeping the humidity at the right mark just blew my mind. Now, he uses a commercial dehydrator to keep the temperature constant, so how does he keep it humid? Plastic wrap! A simple stainless steel tray with plastic wrap covering and 4 holes poked. I had developed a whole temp/humidity system with an Arduino and sensors, but instead I tried his method with a humidity probe inside the tray—and what do you know, perfect 90% humidity! I kinda feel weird giving away this amazing secret, but I don’t think he would mind (I hope).

    1. Hi Cory,

      that’s a great tip, thanks a lot! The easiest solutions are often not the most obvious ones! I will definitely put this into the article.

      Kind regards,

  45. Trying to grow Koji on a mix of grains meant for my chickens… I see the spores favor the cracked corn first… Its been over 50 hours and not quite ready to harvest… have you had similar results?

    1. Hi Nick!

      Is the Koji meant for the chickens or for you? :D
      Generally I find it much, much easier to grow Koji on one thing only at a time. I.e. only on rice, only on barley, etc.
      The time it takes depends on the strain. I can’t remember right now which strain it is, but one of them can go on for a long time without starting to sporulate. If you notice that bits and pieces are starting to get yellow/green spots you should stop the Koji right away as it is starting to produce spores, and you don’t want that, they bring a bad side taste.

      Kind regards,

  46. Hello Viktor, very informative thanks for sharing!
    I have setup very similar to yours, just not made of wood. The issue I’m having is regulating the humidity. I have a humidity controller and a humidifier. When I start the process everything works as it should, and when I reach the desired humidity the controller stops power to the device. Problem is when the humidity lowers again, the controller turns on power to the device, but the device does not actually run. I would then have to manually turn on the humidifier every time, defeating the purpose of the controller. Does the model of humidifier you have turn on automatically when power goes on? Any suggestions? or do i just need to buy one that starts when plugged in?

  47. Hello Viktor, very informative thanks for sharing!
    I have setup very similar to yours, just not made of wood. The issue I’m having is regulating the humidity. I have a humidity controller and a humidifier. When I start the process everything works as it should, and when I reach the desired humidity the controller stops power to the device. Problem is when the humidity lowers, the controller turns on power to the device, but the device does not actually power on. I would then have to manually turn on the humidifier every time, defeating the purpose of the controller. Does the model of humidifier you have turn on automatically when power goes on? Any suggestions? or do i just need to buy one that starts when plugged in?

    1. Hi Alexander!
      I had the same situation once. I sent back the humidifier I bought and went on to look for another one that would turn itself on when it gets electricity. I found that it works with the Medisana humidifier. I am not a huge fan of the thing, but it does work as it should now. I kept my eye open to find a humidifier with a mechanical knob.

    2. Hi, I know it has been a long time since you posted this, but I get around this problem by tightly taping a coin to the ‘on’ button of my small humidifier.

  48. Hello Viktor,

    I’m very new with this but I have a lot of interest to lean about it. It is posible to grow Koji if I do now have spores, I mean can I create the atmosphere to grow it. For example at the begging of the year I was trying to make vinegar but suddenly I realized that a scoby was growing in my base so I made kombucha.

    Kind regards

    1. Hi Alejandra,

      I suppose you mean to ask if you can make Koji without spores.
      You will need the spores, it is the only way to make sure that the mold that is growing is not producing any toxins. Wild molds, like Aspergillus niger for example, produce super toxic compounds. So getting the right spores is the only way to make sure that you get a safe product.

      Kind regards,

  49. Hi Victor,

    I am about to build my first ever box for koji, an this page has been incredibly helpful! I was wondering what your newest setup is like, and how it is working out for you.

    Thank you!

    1. Hi Kal,

      I am quite happy with the new box!

      However, there are two things that I am not entirely happy with:
      1: when the door gets wet, the wood expands and I can’t close it completely anymore. Not a big deal.
      2: The upper rungs are often warmer then the lower ones. This is because after 24h the Koji starts to produce its own heat, which then of course rises up. Maybe a small fan on top would solve this problem.

      Kind regards,

  50. Hi Victor

    Thank you for this information. Once the koji is produced, is it possible to dehydrate the rice for longer storage?

    1. Hi Ellen,

      yes that is possible! But you need to be careful with the temperature. If it is too high, you will destroy the enzymes. So it’s best to dehydrate it at 35-40°C.

      The koji rice stays good in the fridge for one week. You can also freeze it, instead of drying it.

      Kind regards,

      1. Hi Viktor!

        Regarding the temperatures harmful for koji and its useful products, I was wondering:
        Koji produces amylase and protease enzymes (A. is useful for breakdown of starches, whereas P. breaks down protein chains).
        In beer brewing, amylase from the malted grain is essential for the conversion of starches into sugars and is most active at relatively high temperatures of around 65°C (and therefor I assume doesn‘t denature until somewhere above this temperature). Is koji amylase any different from malt amylase in this regard?
        I‘m not sure at which temp protease denatures. Do you have any information on this?
        As you note, the koji spores themselves die somewhere above 40°C.
        So, do I conclude correctly, that if you are dehydrating koji exclusively for later us as a starch converter (as in sake and amazake), one could do so at higher temperatures (up to approx. 60°C)?

        Btw, thx for your really informative website!

        1. Hi Hjalti!
          Sorry for not replying earlier =)

          You are right, in beer brewing the temperatures can be quite high. However, if I remember correctly, the mash can be kept at 35°C for the protease phase (which usually done if the mash is destined for yeast propagation. Holding 35°C will result in bad foam stability due to a lack of proteins).
          So I am assuming that higher temperatures will denature the proteases. It is for that reason that I recommend a drying temperature of 35-40°C. Probably higher temperatures are possible, but just to be on the safe side it is probably better not to use too high temperatures.
          I have not yet found much about the proteases that Koji produces, so I am assuming them to be similar to the ones in malt.

          Another interesting thing is that the guys from Noma make their beef garum at 60°C. So, surely, some protein degradation must be happening.

          So, I guess you can dehydrate your Koji at 60°C as well, but I think it’s still best to do so at 35-40°C, as the stuff itself isn’t that wet after all. I think the enzymatic potential will be higher/better if you dry it at 35-40°C.

          Kind regards,

  51. Hello Victor,
    Thank you for your articles.
    I’m an Italian house miso maker and I do my job with a very primitive sysyem: a bulb lamp into the incubator connected to a thermostat.
    What I don’t understand in your article is:
    1) what a dehydrator is for?
    2) heating the water in the pot you obtain humidity for the environment, but also you obtain the necessary heat for incubating, right?
    Thank you

    1. Hi Marcello,

      the dehydrator has the same function as your lightbulb, to warm the box. The idea with the warm water was meant to heighten the humidity, but frankly I have soon stopped with this idea. I built a new box, which I am going to describe in this article in a few weeks (hopefully).

      Kind regards,

  52. Hi Viktor!

    Thank you for the great articles. I would like to know how the koji after being grown on the rice should be stored? As well, how the spores should be stored and how long they last for.

    Do you also have the suggestions how one should try and make miso from soy, barley and chickpeas and what the actual miso would need.
    One last question, isn’t tamari the liquid coming out of the miso not soy sauce?

    Thank you in advance!


    1. Hi Shalom!

      The Koji Rice can be stored in the fridge for up to two weeks. You can also freeze it, but it will decrease its potency somewhat.

      The spores are viable for at least a year. If they are older than one year, you can just use a bit more than usual and you will still have good results. Mold spores are made by nature to persist for a long time, after all :)
      They should be stored slightly below room temperature in a dark and dry place.

      I am planning on writing an article on how to make miso soon! You can follow either my facebook or instagram account to get the update once the article is online! :)

      When speaking of Tamari, usually the liquid coming out of a miso is meant, but it can also be a type of Shoyu, which is made from soybeans only. The latter is a bit of an artifact of the commercial marketing of soy sauce in the west.

      Kind regards,

  53. Hey Viktor!
    Danke fuer deinen Beitrag, und ich als Koji-Beginnerin bräuchte vor allem einen Artikel darueber, welches Koji ich fuer welches Projekt verwenden kann.

    Ich stehe ein wenig hilflos vor den 6 angebotenen Kojis und weiss nicht, was das Richtige ist.

    Daher meine Frage oder Bitte: Schreibst du mal was darueber? Welches Koji fuer was in etwa geeignet ist? Danke – beste Gruesse aus Köln, Sylvia

    1. Hey Sylvia!

      Danke für deine Anregung! Ich wurde gestern schon mal zu dem Thema gefragt, also habe ich nun einen Artikel geschrieben in dem die Unterschiede erklärt werden. Ich hoffe er ist hilfreich für dich! :)
      Which Koji should I buy?

      Liebe Grüße,

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