How to make Soy Sauce

This article sets out to explain how to make your own soy sauce, also called Shoyu in Japan.

First off, make sure that you have read the article which explains what Koji needs to grow. In it, you’ll find 80% of the information you’ll need to make your own Shoyu.

Pressed, finished shoyu

What you’ll need

Soy sauce is made of soft wheat and soy beans (and water and salt of course). There are two kinds of wheat berries readily available, durum and soft wheat. Make sure to get soft wheat (it’s the kind that bread flour is made of).
As for the soy beans, I have been getting them from a local farmer who toasts them. I think that had a great effect on the taste of the final sauce.

You’ll also need some equipment, an oven to roast the wheat in, and something to mill the wheat berries with. The wheat needs to be milled as coarsely as possible. Ideally it just breaks into three to four parts or so. I’ve never managed to achieve that and I ended up with much finer stuff, and I think that’s ok. I‘ve always used my coffee mill set to the coarsest setting, which worked well enough. I started out with a small food processor, but working in such small batches got boring quite quickly :)
A temperature probe for keeping track of the koji’s temperature is very helpful! If it has an alarm it’s even better.

The ratio of soy : wheat

You’ll probably wonder on how much of each ingredient to use.

Usually I go with one part soy (soaked in water) and one part wheat (dry), by weight. This is more wheat than is traditionally used. More traditional would be one part soy (dry) and one part wheat (dry).

Generally you can say that, the less wheat you use, the longer the sauce will have to ferment in order to get a satisfactory taste. Shorter term shoyus, like shiro shoyu (meaning white soy sauce) are made with more wheat than soy, and they get a balanced flavor within a shorter time.

In all likelihood you have heard of tamari shoyu, which is made only with soy beans. It’s a matter of taste, but in my opinion miso or shoyu only made from soy are a bit lacking. This is because wheat brings in a lot of carbohydrates, which are converted into manifold other compounds.
By introducing wheat, you’ll get a good amount of lactic acid produced by salt-tolerant lactic acid bacteria, which is important to balance out the saltiness of the sauce. The bacteria themselves also produce other compounds that improve the aromatic profile of the shoyu.
You will also get some alcohol, which is produced by salt-tolerant yeasts. This alcohol is then converted further into esters and probably some acetic acid too. The yeasts themselves also produce a good amount of esters, just like in beer. Possibly at some point you’ll find that your soy sauce smell has inclinations of wheat beer. These are the esters you are smelling!

Wheat also has a different composition of amino acids compared to soybeans. This is probably also a reason why soy sauce made with wheat and soy has a more balanced taste than a soy sauce made only with soy.

The Practical Steps

There are quite a lot of steps, for this reason I broke them up into five sections: “Preparation”, “Cooking”, “Inoculation”, “Incubation”, “Fermentation” and the „final steps“.


Do these things the day before:

  1. Soak your soybeans (toasted or not) in plenty of water. Don‘t worry, you can‘t „oversoak“ them.
  2. Roast the wheat berries in your oven until they are golden brown. Most likely they are going to pop a bit. This is when you know that they‘re soon toasted enough.
    • This step creates a lot of Maillard compounds, the same kind of compounds that people love about grilled meat, fries, even coffee, and generally any browned food (except caramellized food, that is a different set of reactions).
    • I once roasted the wheat until it was dark brown and tasted almost like coffee. It was great, but unfortunately in the process you are likely to get high amounts of acrylamide, which is a carcinogen, so don’t overdo it!


The day you are going to start your Shoyu Koji:

  1. Start cooking your soybeans.
    • In a pressure cooker I’d say it takes about 15 minutes of full pressure until your beans are done. Make sure not to depressurize the pot too fast, otherwise your beans will split open and you end up with a lot of mush. I have started to cook them in a normal pot, so I can check on them more often. They are done when you can squeeze them easily between your fingers. In a normal pot that’s easily going to take 40 minutes, possibly more.
    • With all things Koji, usually it is best to steam your substrate. Here it‘s different! It‘s best to cook your beans, because you are going to mix them with the crushed toasted wheat. The wheat is going to soak up any excess moisture from the beans, and you will then have a substrate with a good moisture content for growing Koji!
  2. While the soybeans are cooking, coarsely crack the wheat in the meantime. Use a mill in the biggest setting or a food processor.
  3. When your beans are done, strain them in a big sieve.
  4. Now you can mix the cooked soybeans with the coarsely cracked wheat.
    • If your mixture seems too wet you will need to add some more of the wheat. Probably you will not feel like roasting wheat again if you don’t have any roasted wheat anymore. You can use some grits instead.
    • You can crush some of the soybeans with your hands, but it’s not absolutely necessary.
    • If your mixture is too dry, spray some water onto it or some more beans.
    • Judging the correct amount of water in a substrate for growing Koji is a tricky thing, which is why I recommend starting out with rice Koji to learn the craft. If you steam your rice, you are bound to get a perfect substrate for Koji, and you will learn about the correct amount of water a substrate needs.


  1. As with any other type of Koji, dilute your spores so that they are easier to handle. Typically I sieve out some of the flour that’ll inevitably occur when you crack toasted wheat. That flour can then be used to dilute the spores. Use either the soy sauce spores, the mild soy sauce spores, or A. Sojae spores.
  2. Check if your soybean/wheat mixture has cooled down to 40°C. At this point you can start to spread the spores over your mixture. A tea strainer is very helpful for this process. Mix well.
  3. You can now put your mixture into your muro (incubation box).
    • I have found that a great way to grow this Koji is to use a deep dish (like a pyrex or a gastronorm dish) and:
      • Put a moistened (not wet!) piece of cloth inside your dish, then put your mixture on top of the cloth. Then put another moistened piece of cloth on top.
      • Put cling film over the dish. Put some holes into the cling film so that the Koji doesn’t suffocate (I once didn’t make any holes, you could really smell the CO2, the Koji wasn’t happy!).
      • I like this technique, because you will achieve a really high relative humidity inside the dish and the koji will have an easy time to grow. If you already have a different setup for growing Koji, don‘t worry and use your setup.
  4. Let the Koji grow.
    • The strains for soy sauce are quite different to the miso strains. The soy sauce strains grow like crazy and they overheat very easily, so keep a close eye on the temperature!
  5. After 24h, stir the mixture. Put the cling film back on top, maybe moisten the cloth again.
    • If you find that your Koji is overheating you will have to stir more often.
  6. After 36h you should see a lot of growth. If your Koji didn’t overheat (i.e. it didn’t rise over 37°C for a long duration) it shouldn’t have sporulated.
    • Sporulation is a tricky topic with soy sauce Koji. The growth is so vigorous that everything happens much faster than usual. You should check on your Koji regularly. If you notice any dustiness, yellow or green spots, stop immediately and put your Koji into the brine (more on that later).
    • If you find that your Koji is heavily sporulated, don’t panic. You can still use it, it’s just not as good as it could be. If a Koji that is meant for miso sporulates, I don’t use it anymore, the resulting miso is too bad. But if the Koji is meant for soy sauce, I found that it’s acceptable to use it. Just make sure not to breathe in the spores when handling the stuff. It is going to be very dusty. Either hold your breath or get a mask.
Spreading the spores over the mixture of soy and wheat
Spreading the diluted spores over the mixture of soy and wheat
Diagram of the temperature of the Koji and the Muro. The temperature of the Koji rose to 39°C while the temperature of the Muro stayed at around 30°C.
Here you can see just how vigorous soy sauce Koji can be. Within just 14 hours of inoculation, the temperature of the Koji (green) rose to 39°C! The yellow line is the temperature in the muro, which also was heated up by the warmth the Koji produced.


  1. Prepare a 15% brine.
    • At this point you will have to guess how much brine you will need.
    • Use 176 g of salt per 1000 g of water. This will result in a 15% brine.
  2. Put your Koji into a well-cleaned vessel in which you want to ferment the shoyu.
    • The vessel may be glass, ceramic or stainless steel. I guess you could use food-grade plastic, but alternatives without softeners are easily available, so I wouldn’t use plastic.
  3. Now pour the brine over the Koji until the Koji is covered. Let it soak for one or two hours. Probably the brine level is going to recede as the Koji is soaking up some of the water, so pour over some more brine until the Koji is covered again.
    • Honestly I don’t know if the big producers are using more brine than I am suggesting here, maybe they do. But I figured that if I am going into the trouble of making my own soy sauce, I want to get the tastiest stuff I can make, so I use as much Koji as the brine will be able to accommodate.
  4. Your shoyu is now ready for fermenting.
    • In the first 2-3 weeks it needs to be stirred daily. Otherwise mold or kahm yeast will start to grow on top, the first produces toxins and the latter tastes awful.
    • Your shoyu is going to be very active in this time. The bacteria and yeasts are going to produce a lot of gas, and because of that the solids of your shoyu are going to float on top. You need to push the solids down again, otherwise they will get moldy.
    • Once your shoyu has settled down and is less active, you can start to stir only every second day. Basically, the more aged it is, the less important it is that you stir the sauce.
What it looks like in the beginning…
… and after 6 months.
Notice how the single grains have totally dissolved. They have been “digested” over the course of several months.


After your moromi has fermented for 2-12 months it’s time for harvest. You can use the fermented mash (called moromi in Japanese) just like that, or you can filter and press it. I like to use it unfiltered, I have found that it tastes much fruitier.

For pressing you will have to improvise a bit. I used a big sieve and a piece of cloth. Put the cloth into the sieve, pour the moromi into the cloth, fold it and put something heavy on top. Let it press overnight. Oh and don’t forget to put the sieve over a pot to catch the shoyu ;)

In the morning you can go ahead and press the cloth a bit more, sort of like when you wring out a towel.

If you have a cider press or something like that, count yourself lucky :) Just pour your moromi into layers of cloth (maybe even bags of cloth) and then go ahead and press them.


Make sure your bottles are well cleaned. It doesn’t hurt to sterilize them in the oven – just put some aluminum foil over the opening and keep them at 160°C for half an hour, let them cool down overnight. Also boil the caps in some water.

Heat your Shoyu to 90°C. The heating is important to kill off any yeasts or molds. If you don‘t boil your shoyu, you will get a really yeasty taste after some time. By yeasty taste I don‘t mean the esters they produce, but the taste that you get when the yeast cells die and autolyse. It tastes sort of like biting in a cube of fresh yeast.

Pour your Shoyu into the bottles and then close them with the caps.


Of course you do not have to use wheat and soybeans. You could also use, say, oats and lupines. Or Einkorn and chickpeas. Go crazy :)

However, I always recommend to start with the tried and true before starting experiments. If something goes wrong, you can be sure it is not because of the ingredients you chose.

Thanks for reading! I hope this article is of help to you! If you have any questions, please ask in the comments section :)

This Post Has 75 Comments

  1. Great timing on the soy sauce article! Here’s my feedback:
    * Mention explicitly whether the 50:50 ratio of soy/wheat is by weight or volume (I assume weight).
    * “a manifold” -> “manifold”
    * Is the lactic acid you mention wheat providing due to the activity of lactobacillus or is it some other reason?
    * Consider pulling the example math for 15% brine into a footnote.
    * Same for the note on sporulation.
    * Consider breaking “The practical steps” section into several subsections: Perhaps “Preparation”, “Cooking”, “Inoculation”, “Incubation”, “Fermentation”. It’s really long, and a bit tricky to navigate in present form.
    * Is aerobic fermentation recommended for the last stage, or, since I have airlocks, would it make sense to use them?
    * Did you inoculate with any yeasts or lactobacillus for the last fermentation, or just rely on atmospheric?
    * Why did you boil the soy sauce at the end?

    Higher level note: What I love about your other articles is that the describe not just what to do, but help build an understanding of the why, which helps the cook recognize and correct any issues, makes it easier to adapt the recipe to constraints, and provides a more fulfilling home cooking experience. This article goes into a lot of detail on what to do, which is great, but more insight into the “why” would make it much more informative.

    1. Thanks a lot for your input, it is highly appreciated! :) I will work through the list to bring this article up to par.

      * Mention explicitly whether the 50:50 ratio of soy/wheat is by weight or volume (I assume weight).

      yes, by weight

      * “a manifold” -> “manifold”


      * Is the lactic acid you mention wheat providing due to the activity of lactobacillus or is it some other reason?

      yes, it’s due to the action of various salt-tolerant lactobacillus.

      * Consider pulling the example math for 15% brine into a footnote.

      good idea

      * Consider breaking “The practical steps” section into several subsections: Perhaps “Preparation”, “Cooking”, “Inoculation”, “Incubation”, “Fermentation”. It’s really long, and a bit tricky to navigate in present form.

      That was one of my concerns, will do that for sure :)

      * Is aerobic fermentation recommended for the last stage, or, since I have airlocks, would it make sense to use them?

      I think it is important to submerge the stuff that floats on top every now and then, you can’t do that without introducing air (at least not without getting quite technical,..). Probably the introduction of oxygen does bring the fermentation forward, or if not, I am sure there’s no harm.

      * Did you inoculate with any yeasts or lactobacillus for the last fermentation, or just rely on atmospheric?

      I’ve done both. Generally, with shoyu you can easily rely on atmospheric, but I have found that it’s nice to add a bit of miso to ensure a balanced “ecosystem” of microbes.

      * Why did you boil the soy sauce at the end?

      To stop any fermentation. The concern is mostly with yeasts and molds. The former keep on working and that can lead to an unappealing yeasty taste. Mold is very much unwanted, too, since you can’t be sure if it’s Koji or a toxin-producing cousin.

      Thanks again :)

      1. Thanks very much! I soaked my soybeans last night and am going to start steaming today! I’ll be using the soy sauce koji I got from you awhile back. Now that I have a precisely controlled incubator, growing koji is extremely easy.

  2. I tried this, and it has been incubating for 24 hours. One thing that would be helpful is more discussion of getting the moisture level right — I tried to follow this as is, with 50:50 wet soy to dry grain, but for some reason it ended up too dry, and I had to add some moisture at the end. I *think* I got it reasonable, but I have barely seen much growth in that 24h. I know it’s an art not a science. One thing is that I steamed my soybeans, I did not boil them. I think that maybe if I had boiled them, and they’d soaked up more water, the dry toasted flour would then have put the moisture into a good range. The recipe does mention steaming as a way to cook them, but I think that it may require moisture corrections.

    Anyway I think it will probably be ok; I added a (very small) bit of water and covered with a moist towel, and the soybeans did have a bit of white fuzz on them. But it’s not like the last batch of mixed grain I did (for black vinegar; soy sauce koji) which was fully covered in 24h with thick white fuzz.

    I’ll update how it ends up going if I remember.

    1. Maybe 16 hours after I added the additional moisture, and the flour is covered in mycellium. A few of the soybeans do have green spots of sporulation, but I think it should be ok. Not bad for a first attempt. Probably shouldn’t have started with 1kg, but it’s easier in bulk.

      For anyone else reading this: Let me just reiterate how fast the soy sauce koji grows…you really, really need to keep an eye on this stuff!

  3. Bread flour is made from hard wheat. Cake and pastry flours are made from soft wheat.

    1. Probably there are regional differences, around here in Austria soft wheat is used for bread.

    2. In North Italy bread is made with soft wheat, in the South with hard wheat. It depends. I personally make bread with einkorn, for ex

  4. Hello,

    I emailed a question about my homemade soy but have not received an answer.

    1. Hi Mike,
      I replied to your email. Please check your spam folder (and please mark it as non-spam, that’d be very helpful for us, thanks!)

      1. Thank you! I will keep skimming. She already taste amazing after a month and a half!

  5. Great article. How much soy/wheat (total weight) would you need to produce 4 liters ( little over 1 gallon) of soy sauce?

    1. Hi Rocky,

      This is actually a quite complicated question! I am going to assume you want 4 liters of pressed soy sauce, not 4 liters of mash. Calculating 4 liters of mash is harder – also, your mash is going to need some headroom, since it’s going to rise and fall with the fermentation.

      I usually go with a ratio of 1.65 of dry stuff to brine. That means, I multiply my dry ingredients by 1.65, and the result is the amount of brine (15%) I need.
      So for your that’d mean that you’ll have to start with 4 kg / 1.65 = 2.42 kg of dry ingredients, assuming that 1 L equals 1 kg, which is wrong of course since soy sauce is denser than water, but let’s keep it as simple as possible.

      A recipe I usually go with is two parts cooked soybeans (by weight) and one part roasted and crushed wheat.
      Soybeans will weigh 2.2 times more when cooked. So, for ease of calculation, I’d just soak 2.42 kg / 2 = 1.21 kg of soybeans, and I’d roast 1.21 kg of wheat.

      I hope that helps.

      1. Hi Viktor thank you for the reply. Thanks for the info gonna give it a shot as soon as my koji spores arrive from Japan. I’ve seen ratios of approximately 1 : 1.1 , soy:water so that seems to line up pretty well. Keep up the great content!!

      2. Hi Viktor,

        I read the recipe and this comment and I am a little lost on the dry/soaked ratio and the quantity of substrate that you can do with one bag of spores :
        If I want to use the whole bag of diluted spores to make 5kg of substrate how much dry ingredients do I need ? and then how much brine? Sorry if my questions seem a little dumb…


        1. Hi Paul,

          sorry for the late reply, I was on holiday :)

          It’s not a dumb question at all!

          It is a topic that we needed some time to get a feeling for it. With soybeans, the ratio of dry weight to cooked weight is about 2.3x. So if you want to get 2.5 kg of cooked soybeans, you will need to soak and cook a bit more than 1 kg of dry soy beans.
          The weight of the wheat can be used as is, that is to say you can just go ahead and roast 2.5 kg of whole wheat. It will lose some weight because wheat is not 100% dry. To offset the weight loss, you could just roast 2.6 kg of wheat.
          If you then go ahead and mix the cooked soybeans and the crushed wheat, you should receive about 5 kg of mixture. It is not necessary to be terribly exact. So if you get 5.4 kg of mixture, don’t worry, the spores will do just fine on a bit more.

          Hope that helps!


  6. Hey, I started making my soysauce after your recipe end of January and at the beginning everything was fine. But for about 4 weeks now there seems to be white mold growing on top of it. Has anyone experienced something like that?
    Thanks for your help.

    1. Hi Tim,

      that’s not good. Have you stirred your sauce regularly? It’s very important to stir every day for the first 10-14 days. Later on you don’t have to stir so much, but you should do it at least weekly, no matter how old your sauce is.

  7. Hi Viktor,
    All recipes I found for making soy sauce are using wheat berries. But is it possible to use barley or other grains instead? How would barley (for instance) affect the taste of the soy sauce?

    1. Hi Marnix,

      Basically, the most important function of wheat is to provide starch, which is broken down into sugars, which are fermented into lactic acid. In other words, wheat is important to give your soy sauce a sour taste (and to make it more stable, due to the low pH). But it also brings proteins which have a a lot of glutamic acid.
      You could replace it with barley. In fact, the first shoyus were made with barley, but at some point wheat was preferred.
      As for other grains, I haven’t experimented much with different grains for shoyu. We have one Einkorn shoyu that seems promising! Other than that, it’s on you to find out about other variations :)

  8. Hello, great article. I made my Koji mixture and inoculated it in a dehydrator for what turned out to be just about two days. It was showing no spores after 24hours but by 30-35 it started ‘clumping together. I kept stirring until about 48hrs when I realized I think I left it too long. It has turned green and dusty. Not a dark green, or a yellow green, just a light green fully coating the wheat and soy. I’m making soy sauce so felt a lot better after reading your comment of leaving it too long should be fine. After I combined it with the brine now it’s really green … lol…. do you think it will be ok? Will I be making a new green soy sauce ? I’m trying to decide if I chance it and put six months into green soy sauce or I should start again.
    Any insight would be great.
    Side comment: the green color is very similar to the colour of spores I started with.

    Stay healthy and safe!

    1. Hi Emily!

      Soy sauce is much more forgiving if your koji has sporulated. I’ve made shoyu with very sporulated koji, and it turned out to be perfectly decent shoyu. Don’t toss it for sure! :)

      If your koji for miso ever sporulates, I recommend not to use it for miso. I tried that as well, and it was pretty bad.

  9. Hi Viktor,
    do you have any tips how to deal with massiv heat spikes? The temperature of my koji (sojae spores) rises up to 47°C even if I put everything in my fridge. To keep the temperature at least a little bit I have to to break up break up my koji every half hour. The heat increases already after the first 12 hours.

    1. Hi Elias!

      I have been struggling with this too. The only thing that was a lasting solution for me was to make thinner mats, about 1-2cm max. What we also do, we continually lower the temperature in our muro over the course of growth. I.e. we start out at 30°C for 18h, and then when the heat starts, we lower the temperature continually.

  10. Greetings! I am attempting to make my own soy sauce and I have been following your instructions. I don’t see a picture of what Koji should look like when it is ready for fermentation, or what it looks like sporulated, so I have a question: I never saw a coating of white fuzz of my soybean/wheat mixture and it is now day 5 of inoculation. I tried my best to keep the temperature between 85-98* F, though it did fluctuate quite a bit within that range. However, around day 2, there was a dusty coating of green a similar color to the spores I initially used. Does this mean it has already sporulated and past use? Also, what might be the reason there never developed the white fuzz? Thank you for any insights you have.

    1. Hi Joanna,

      soy sauce koji is not as visually flashy as the other types. But you should definitely see some growth. That you saw a dusty green coating is a sure sign that your koji was done. Generally, koji should not take longer than 3 days to finish. I am happy to keep it going for 40h without turning completely green :) (Sporulation is almost a none-problem with soy sauce koji though. In Miso it’s a no-go).
      I will make sure to upload some pictures when we start making soy sauce again! Thanks for the input.

  11. hi, im at about 8 months and noticing the liquid is much lower and the brew is getting saltier as a result. Can i add more water to counter this process or maybe during pasteurization?

    1. Hi Laurel,

      you could add some water to offset the loss, but honestly I think it’s OK to lose some water, as it will intensify the taste of your sauce. If the loss is really high, I would first try to press the sauce, and once that is done, I would add the water to the solids that are left after pressing. This way you can extract some more flavor.

      Kind regards,

  12. Viktor greetings from Brazil.
    I am very happy to have found your site and to be able to read the information you share, it is gratifying to meet people like that, congratulations on this.
    Comments and interactions also reflect how people like what you write.
    One idea would be for people to put up their websites so we can see the results too.
    Soon I will follow all your recommendations and start my handmade soy sauce, study the world’s cuisines and put them into practice is fantastic.
    Thank you again.
    Rubens (@rubens.fogs)

  13. I make my own soy sauce. However, my soy sauce don’t have fragrance of typical good soy sauce. I did some research and thought of adding some yeast (S. rouxii or Candida). Where can i purchase this yeast? Most of the yeast in market asre baking yeast.

    1. Hi Steven!

      I wouldn’t go out and buy pure cultures, I think it’s sufficient to add some unpasteurized miso to get some good yeasts into the moromi. (I actually found that most miso is unpasteurized, even if it doesn’t say on the package).

  14. This has been my dream for decades, now I have time to pursue it. I have not seen a recipe that advises how much (sea) salt to add per batch. I see a specific gravity, but is there a more laymen measurement ? I have not seen a recipe that mentions ratio of
    (soft ground) wheat or Koji spores to soy beans. AND, can shoyo be aged in wooden barrels like wine and whiskey ?
    Thank you from Hawaii

    1. Hi Robert,
      in my opinion it’s best to prepare more salt-water than you’ll need. I recommend 15% of salt. You can just weigh 850 g of water + 150 g of salt, or do a multiple of it. Put your finished koji into the vessel, and then you can put in the saltwater until it’s all submerged. Keep the rest of the saltwater, because as the koji is soaking up the water, you’ll have to add some more after some time (a few hours or the next day).

      I always use 1 part crushed roasted wheat and 1 part cooked soybeans.

      It can be aged in wooden barrels, but care must be taken that it doesn’t start to grow mold – by stirring a lot and wiping the edges of the barrel.

  15. Hi Viktor!
    I wonder about stirring during the inoculation. Do you have an idea, what happens if you stir every hour or so?
    (This would help to control the temperature and the moisture.)

    1. Hi Ingo!

      This is what I did when I first started out at home. It’s a good way to control the temperature, but it can be a bit much to do it at night, too :) Usually I stirred a bit when I had to go to the toilet at night.

      Now, in our production, we can’t do that anymore, so we make very thin mats. This helps a lot. Also our thermostat is lowering the temperature in the incubation box as the koji grows.

  16. Hi Viktor

    Was really impressed with your article, it is so full of useful information! One question I have is, how do I get my shoyu to be the classic dark brown/black colour?

    I’ve started by making the yellow pea shoyu recipe from the Noma Guide to fermentation, and have just pressed and bottled it. I’m very happy with the flavour (although it is more mellow and subtle than shop bought stuff), but it is a pretty light colour. Are there any steps I can take to darken it? Should I leave it longer? Or is it the ingredients I used?


    1. Hi Will!

      thanks a lot :)

      The colour is achieved by a few things:

      • Ingredients: a higher content of soy/peas compared to wheat
      • Starter: it’s a bit of a factor as well. Using a Sojae strain will result in a lighter shoyu, compared to an oryzae strain for shoyu
      • Fermentation time: the longer the darker. The reason is, the color is a result of the maillard reaction. In a frying pan it happens very quickly, but in shoyu it’s at a snails pace
      • Oxygen: also helps to speed up browning. If you stir it often to aerate, your shoyu will get darker more quickly
      • Light: If you put your pressed shoyu into glass vessels and then put those into the sun, they will become noticably darker
  17. Hi Viktor! I’ve made my soy sauce for more or less 1.5 month with yogurt machine. I stirred it for the first weeks, actually for the first month (I dont know if I was right or not but there was a part of shoyu on the boottom of the jar that was more liquid and with pieces floating in)… so I preferred to make it more homogeneous stirring it. Now I’ve not stirred it for one week and the upper part, let’s say the substrate, is darker. Is this just oxidation or something different I should worry about? Moreover, everytime I stir it, I should use sterilized spoon, shouldnt I? Thanks :)

    1. Hi Cecilia!

      Are you making your shoyu at a higher temperature? Just interested :)

      don’t worry about darkening on the surface. It’s a normal process, oxygen (and light) speed up the darkening process, nothing to worry about.

      You don’t need to sterilize your spoon every time. Especially after some time of fermentation, your shoyu will have a robust microbiological community, which will outcompete any intruders easily :)

  18. Hi Viktor,
    Thank you so much for this wonderful guide, I just received my koji-kin and will be starting the journey soon. I had a question about salt, I saw that you use a 15% brine however does it matter what salt you use? There are a lot of variations but some are way saltier than other. I was thinking of going the safe sea salt route but I would like to have the best quality when I start this long process. Another question I had is about aging (which is a long time from now for me), after pressing the soy is it possible to intensify the flavor of the soy sauce by not boiling it and letting it sit in the bottles for even longer?

    1. Hi Thijs!

      Thanks :)

      In my opinion the salt hardly matters. We made some triangle taste tests with different salts, and nobody could detect a difference. Just make sure to get uniodized salt!
      The perceived saltiness of something is influenced much more by acidity than anything else. Your sauce will taste very salty in the beginning, but it will mellow out, because it will be more sour, thus balancing the saltiness.

      Yes, I generally recommend to let the pressed sauce sit in a container for at least two weeks, to make sure that all the available sugars are fermented out, and then bottle it. If you’d bottle it right away, you run into the danger of carbonating your shoyu :) (or exploding bottles worst case)
      I have exclusively bad experiences with boiling shoyus. I know it’s traditional to do it in Japan, but I find it loses complexity, and if the shoyu gets burnt (on the side of the pot for example if you’re using gas), the whole batch is ruined. So I would recommend not to boil it, or maybe just a small part of it, to learn which difference it makes.

      1. Thanks for the reply, very helpful. I also just saw that the Koji kin I bought is for making Sake, does that matter a lot?

        1. Yes, it matters, since strains for sake are specifically bred to produce as little protease as possible (and as much amylase as possible). Free amino acids are unwanted in Sake since they produce bad sensations.
          I recommend to get a starter for soy sauce before putting any effort in.

          1. I knew I should have checked before I bought this… cost me 20 euro’s as well haha. Guess I will also be making some Sake in the future then lol

            1. Well, you are just 7,50€ away from a proper soy sauce starter ;)

  19. Hi Viktor!
    What an amazing and comprehensive article! I*m writing from Sweden and have ordered the spores from a local farm and now looking into a glass container, which seems to be quite difficult to find. What did you use in your picture? Is it a 5 Liter jar that you have? or would you, from your experience, suggest getting a 10L jar? Thanks!


    1. Hi Gyps!

      Ikea has brilliant 3.3L glass jars. They are also great for miso.
      I wouldn’t get bigger glass vessels, they are heavy and break easily.
      If you want a bigger vessel, I recommend to get a food-grade plastic bucket.

  20. Hello! I don’t have access to wheat berries, but instead, i have rolled oat and whole wheat flour. Is it possible to replace wheat berries with one part rolled oat and one part whole wheat flour?
    Also, I only have one strain of A. oryzae. The label mentioned that this strain is used to make miso, sake, and amazake. But I don’t find shoyu :(
    I’m thinking to mix some tempeh or R. oligosporus starter to increase the amount of protease.
    How do you think? I think I’m ready to experiment.

    Thank you

    1. Hi Anthony,

      it’s possible to use oats instead of wheat.
      You can use the strain, it should work, but better would be to get a dedicated shoyu strain of course. I would not mix in tempeh spores.


  21. It looks like you’re using a lidded jar. In Japan, the vats are completely open throughout the process. All the books and websites on making shoyu I’ve read skip over this part, instead focusing only on the stirring regimen. So what say you?

    1. Hi Adrienne,

      In a home setting, I strongly recommend lidded jars. Or at least a jar with a cloth covering it. Homes are much dustier than shoyu production facilities. This means there are more mold spores around, and eventually they’ll settle and grow in the shoyu. Also, shoyu producers won’t forget about stirring, private people will, it happens to everyone.

  22. Hi Viktor

    I have some of your Soy Sauce Koji Spores as well as some of the Mild Soy Sauce Koji Spores. I see in the description for the mild spores that they are bred to avoid overheating. I also see in the description for the “regular” spores that they are suited for “long-term dark shoyus”

    Question 1: Obviously the heat properties of the mild spores are desirable but that aside, do you have any observations on flavor impact between the two types of spore?
    Question 2: Given the “regular” spores are directed for long-term shoyus, would you say the 1:1 dry soybean to wheat ratio is suitable for this strain of spore or would you lower the wheat proportion? If so, do you have any recommendations?
    Question 3: Not related to spores, but I note that your 15% brine is among the lowest I’ve seen in recipes. Elsewhere, most recipes I’ve seen appear to run from 16-20%. Is there a reason you recommend 15% or considerations to be aware of?

    1. Hi Reuben,

      ad 1) I have not yet directly compared the two. In my opinion, both can make perfectly good shoyu. Mild Soy sauce koji will produce a bit less enzymes, so it will take a bit longer to get the same result.

      ad 2) You are correct, 1:1 is indeed a lot of wheat for a long term shoyu. If you plan on ageing it for longer than 10 months, you can use 1,5-2 parts soy and 1 part wheat .

      ad 3) 15% is the lower point for brine concentration. I had good experiences with this ratio, the shoyus come out quite balanced and more sour than usually, both of which I like and value. Generally, with koji fermentation, the higher the salt concentration, the “cleaner” the product will taste. The lower, the more funky notes/sourness you will get. With miso I prefer a cleaner taste (i.e. I never go below 7%), but in shoyus, I’ve found that 15% is good.

  23. Hi Viktor,

    I was hoping you could give your opinion about my soy koji. I left it fermenting for about 48 hours, it became a little bit green, do you think it has started sporulating already? If I understand correctly it’s not a really bad thing, and I can still use it. But it would be helpful for next time to know what is normal or not.

    Thanks so much!

    1. Hi Leon!

      Looks great! Sporulation doesn’t really matter with shoyu making. Some even seek it out to get a certain flavour in the final product.

  24. What should the temperature be during the fermentation process?

    1. Hi Isabella,

      room temperature is good.

  25. Can I use a patent glass jar to ferment my moromi? Or should the moromi be able to breath?

    1. Yes, that’s possible.
      In my opinion, the breathing process of the shoyu through the wooden vessel or whatever is overrated. Just make sure to stir it often.

  26. If I use soy sauce koji to make soya sauce, then which color should my beans get when the inoculation process is done?

  27. I saw in a comment that for making long term shoyu is 1:1 ratio of soybean and wheat too much. I wasn’t aware of this and it is the second day of my soybeans inoculation whit a 1:1 ratio. Should I left some wheat behind when I transfer my koji to the glass jar?

    1. I would go for it nonetheless. The traditional recipes have a different ratio, but you will still get a good shoyu this way.
      Also, in my opinion, shorter soy sauces are very good as well. Longer fermentation does not always automatically mean better.

      1. Thank you very much for your quick answer!

        Then if I decide to make a short-term fermentation, how long would it be?

        1. About 5-8 months.

  28. Hi!
    I’m now on my second week of stirring my moromi. But I noticed that after about 5 days, it didn’t seem like the beans are floating to the top anymore. They’re mostly staying under the water level. You’ve mentioned that there’s a lot of activity the first three weeks and that stirring helps to push the beans down and prevent them from molding. So now I’m just wondering if something went wrong along the way. Thanks in advance! / gyps

    1. Hi Gyps!
      If they are not floating up it mustn’t mean that your batch is bad. Sometimes real activity starts after one month, sometimes there’s not as much activity (but the shoyu still turns out good!). It depends on many factors, like ambient temperature, on how well the beans were cooked and so on.
      Just stay with it, and in all likelihood it will turn out very nicely! Just make sure not to get surface mold, that’s the only thing that can go wrong at this stage :)

  29. Hi Viktor!

    I am now 6 months in and have pressed a few spoons of the mormori just to sample the taste. It has a complex flavour but it is intensly salty, especially compared to a Kokkoman Tamari (the only other sauce I have at hand currently). What can I do to make the salty taste less overwhelming at this point? Ferment it for longer? Or skim some of the salt water off the top to have more of the mormori when pressing?

    Thanks a lot for your effort and this guide! :)


    1. Hi Mike!

      It sounds a bit like you used too much brine for your koji. Usually there isn’t much if any salt water on top which you could ladle off (at least when we make shoyu). You could add some more Koji, or maybe just some roasted and crushed wheat. The enzymes will break down the wheat, and lactic acid bacteria will produce lactic acid -> Salt is balanced by acidity.
      So you could try to taste your shoyu with a drop of lemon juice to see if it helps, and if it does, maybe that’s a way forward. Ageing the shoyu for longer will certainly also help.

      Did you make a 15% brine or a stronger one?

  30. Hello again!

    Now I’m going on one month of fermenting a moromi in a big 5 liter glass jar. Yesterday I noticed there was greenish mold growing on the sides of the jar and I wiped it off. And in a smaller jar I picked out a soybean with mold growing on the surface of the moromi. Is that ok? And how can I prevent the growth of mold on the glass jar?

    Thanks so much! Again!

    1. Hi Gyps,

      Mold on the sides of the jar can happen every now and then. To avoid it, I recommend to clean the sides of it after stirring. If you removed it, it’s OK generally.
      Mold on top of the shoyu is different, as possible toxins may leach down into the shoyu. If it was a small spot, just generously remove it and make a commitment to stirring more often :) The more the shoyu is stirred, the less chance molds have.

      I have also found that a solid lid helps a lot more than a piece of cloth. Some people worry about not enough oxygen reaching the shoyu with solid lids, but in my opinion it doesn’t matter. You’ll get a great shoyu with or without oxygen. It’s just that it will be of a lighter color when less oxygen reaches the shoyu. If somebody really wants the typical dark color, I recommend to age the pressed shoyu in glass bottles in a bright spot at home.

  31. Thank you so much for this article! I was making the koji and starting to notice a little yellow-ish color developing at hour 31 and decided to pull it and make the shoyu based on your article. I also appreciate the explanation of the reason for doing many of the steps, as this information is hard to come by. Thanks for taking the time to do this!!

    1. Thanks for letting me know, it’s appreciated :)

  32. Hello! After just 1 month old, my soy sauce mixture suddenly get a lot of bubble and form some liquid kinda soy sauce at the bottom of the jar (usually it is not that active). I don’t know why it suddenly bubbles, it did smell nice and not alcoholic/sour, just nice soy sauce smell, but it definitely produces huge amount of bubbles. I’m afraid of contamination happened in my soy sauce. What do you think?

    1. Hi Anthony,

      that’s perfectly normal and no need to worry! It happens often that a shoyu is not very active and suddenly it starts to ferment vigorously.

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