Making Shoyu (Soy sauce)

How to make Shoyu (Soy sauce) at home?

This is Koji to make Shoyu.

Look like….mud.

Shoyu (Soy sauce) is made from “soybeans”, “wheat”, “koji bacteria” and salted water.
Both steamed/cooked soybeans and roasted wheat are mixed with Koji bacteria in the special Koji room called Koji muro (麹室).
This is the one shown as above photo.

For home made Shoyu, you can start from this process by purchasing this prepared Koji for Shoyu.
Once you get this Koji, the making process not that hard.
What you need is LOVE to look after your shoyu, and TIME for slow process.

With this prepared Koji + Salt + Water + fermentation period = Your Soy sauce!! Yeah!

Prepare….Koji, salt, water and a big jar.
In the big jar (My one is bit too small …. difficult to put  hand. Bigger one is recommended)
First, decide how long you want to ferment your Soy Sauce.
(From 6 months to 12 months)
Depend of the fermentation length, you can calculate how much salt you need to your  Soy Sauce.
(From approx 18% to 22 %)

Prepare salted water.


Then pour the salted water to the jar.


Mix them well by your hand in the jar.
(That’s why you need a big jar)


At first, Soy Sauce Koji doesn’t want to be mixed with salted water,
but after while you are mixing it, they become friend with salted water 🙂

This is how it looks at this moment.


Wipe the jar, keep it clean.


Place the jar in the dark + cool place.


Mix Shoyu every day for the first week.
After the first week, mix like this once a week for 6 months to 12 months.


This is the surface of the second day.
Can you see little bubble is coming to the surface?
It’s alive Shoyu, fermenting now ~~.
Taste ? Sharp saltiness.


It is a slow fermentation process.
That’s why it is good ♪
That’s why it has a great flavor ♪
That’s why it has many nutritious benefits ♪

This is the photo of 4 months age.
Surface looks different from the first day, doesn’t it?

Taste already good, but I want to wait few more months to grow.
Looking forward to have my own Shoyu soon !!!

18 thoughts on “Making Shoyu (Soy sauce)

  1. Hi,

    your Shoyu making process is interesting – since there are not so many “ready to do” sources available. However, I wonder how much brine (in relation to your koji) you used. I had seen other recipes using brine up to 40% (I think that is a little to salty).

    Another question – I asume you used 50% soy and 50% wheat koji? Did you prepare it yourself?

    Thanks for your help. All the best.

    • Hello, Chris.
      Thank you for your comment.

      Salinity concentration of my brine was 20% of this batch.
      (As I mentioned in the blog, you can chose from 18% to 22% depend on the length you would like to ferment. If you want long term, them you need to put more salt)
      Also, this is the ratio of Koji and salted water.
      Koji : Salted water = 1:1.2

      No, I didn’t prepare koji for shoyu by myself.
      I got it from one of the Shoyu-gura (醤油蔵)where makes shoyu.

      As far as I know, in case of dark soy sauce (regular one), ratio of “soybeans” and “wheat” is 1:1
      Depend on kinds of soy sauce, the ratio will be changed.

      These are the steps to make Shoyu koji.
      *Soybeans will be soaked in the water and will be steamed/boiled.
      *Wheat will be roasted and will be crushed,
      Then, both steamed/boiled soybeans and crushed wheat will be mixed in the special room called Koji Muro (麹室)
      In this room, “koji bacteria” will be sprinkled over the mixture of above mentioned soybeans and wheat. Then all will be mixed well.
      This become Koji for making shoyu (Shoyu koji).

      I would love to try this steps,
      but I need to make Koji muro first.
      Temperature and humid control is essential.
      If you try, please let me know!

      By the way,,,,
      “Koji bacteria” is called Tane Koji (種麹)and there are different kinds.
      Some are good for making sake, some are good for making shoyu.
      Some are good for making miso.
      Using these “Koji bacteria” (Tane koji), people make Koji,
      which is known as Rice koji, Wheat koji and Shoyu koji etc.

      • Hi Happa, making koji at home is easy once you have made an incubator. Mine is an old but very clean dead fridge with a lightbulb set in the base for heat . The bulb is connected to a thermostat set to precisely 31 degrees. I also have a digital indoor outdoor thermomerter with humidity function set up so i can check the condition without opening the door. To keep oxygen flowing through i also put in a fish tank pump.. The tube runs up the drain hole in back of the fridge.
        Koji tane spores are the mold aspergillus oryzae which can be obtained online from several suppliers in small packs suitable for home. It lasts forever sealed well in the fridge. I have some very special koji spores that are still viable after nearly thirty years in storage.
        Growing your own fresh koji for either miso or shoyu takes three days and is such fun like gardening. Cook soybeans not too soft or wet…if using rice soak and steam it….cool to 30degreesc then add a a half teaspoon of spores per kg of grain bean mix or rice and put 3cm thick in a sterilised tray. Cover the tray with a scalded cloth and put in your incubator, keep the cloth damp over the three days so the koji does not dry out while it grows a nice white furry mycellum like a fur coat. As you see it start to sporulate take it out and freeze it or dry it in a dehydrator or use it same day. It goes a tinge of olive green when it sporulates.
        Be very very careful with hygiene as you can also accidentally incubate some very very nasty bacteria.
        Is it goes slimy or you see colours other than the olive green then throw it out and sterilise all your equipment start again with more care with hygiene.
        I also use my incubator aka the fridgcubator to make yummy tempeh

  2. Hi my name is Ed I have been trying to make koji for some time, and it all ways comes out a light greenish yellow. Is this ok or is it bad, and what am I doing wrong. please advise. thanks

    • I have so limited information about how you make koji, so I cannot really tell if you are doing right or wrong.
      I don’t even know what type of Koji you are making, and I’m not even koji making specialist. Sorry!
      All I can say at this moment is…Rice-Koji colour will can be different, depending on the Koji-bacteria/asperigillus oryzae you use.
      Pure white, creamy, yellow….
      Koji to make soy sauce was kind greenish, muddy colour.

  3. Hi, I have question regarding soy bean to wheat ratio.

    The ratio I assume, based on googling, is per weight. Is the weight of the soy based on its dry state? or should I measure the weight after I soaked it overnight?

    I have 1 kg dried soy and 1 kg wheat. The soy beans I soaked overnight and it more than tripled in volume and god knows how much more they weigh now. The amount of wheat is minuscule compared to soy at this point. Getting a little confused.

    Sorry to bother you and thanks.

    • Hi Chipmunk,
      We normally weight soy beans before soaking, so it means under the dried condition.

      Are you trying to make Shoyu koji (to make Soy sauce?) from scratch?
      Or are you trying to make Soy Sauce.
      Either way, good luck and have fun xx

      • Looks like I’m on the right track then! Thank you.

        Currently the hydrated soy is being boiled and I just finished roasting the wheat, by the end of today I’ll have them inoculated with A.oryzae.

        I’m not very hopeful at this point, since the more research I do, the more I realize the necessary things I don’t have. But hopefully, by the end of this year or next summer, I’ll have something that sort of taste like soy sauce that won’t get me sick or dead.

        Again, thank you for your help.

  4. Hi. For the 18-22% salt, is that the percentage of salt in the salt water mixture? Or are you including the weight of the koji mixture as well?
    I’m guessing the 18-22% is salt percentage in water, then the ration of 1:1.2 of the koji to salt water.
    I have koji bacteria that I use for making miso, so I’m going to use the same koji to make the shoyu.

    I love your website. I showed my mom some of your recipes. She thought it is cool too (she is Japanese…I’m Happa), and she is always making different tasty japanese pickles.

    • Yes, the % is the salt in the water.
      Koji bacteria for Miso and Koji bacteria for soy sauce is actually different,
      but it worth to try with what you have. Let me know how it goes!
      Thank you for your complement, hopefully I can post more next year.

  5. Hi, I have some soy sauce fermenting ( about two months now) for the first month everything was good and the smell and taste were amazing. In the second month an acetone (nail polish remover) smell developed, it has got slightly less strong but is still there. I’m assuming this isn’t normal and wondered if it had ever happened to you in your experience. Love the site, Rob.

    • It never happened to my soy sauce, but my advice is mix it very well (every day) until the smell goes away. By just doing this, it should go away. Also, you can add a bit more salt to solve this problem.

      • Thanks, I’ll let you know how it turns out. Wish I could go to your workshops but I’m in the UK. Have you ever thought of filming them and selling a video package?

    • Thank you! It’s all similar meaning in Japanese, so when I use these words in English, I am confused. Thank you for your advice! It helps! I’m sure there are more these mistakes in my blog, your advice would be most welcome !! Thank you x

  6. Hi, any sugesstions for the pressing method? I have tríed a sussage stuffer with a coarsley woven sack but it failed miserably. Regards from Querertaro

    • I use a cloth bag (I sewed by hand) or a cheese bag (I bought at organic food store), both works all right. I tend not to press too much, to get clear liquid.

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