If you don't know what koji is and what it does then you're in for a treat. An extremely useful edible mould that has the potential to help solve a lot of global problems like, hunger, malnutrition and effective organic farming.
In this post, I will show you how to grow your own koji at home or in a professional kitchen. If you're savvy you could even turn your new fermentation and koji growing knowledge into something useful that will make you money.
I wrote an in-depth article for no-reply-mag about the relationship between sustainability and responsible consumption using the wonders of koji.
If you would like to follow a more responsible omnivorous diet then go read that. It's to-the-point and very informative.
Otherwise, stick around and learn what koji is, how to grow it and ideas on what to do with it.
What is koji?
Aspergillus oryzae. The biological name for the species of mould responsible for giving us koji. It's a filamentous fungus that can be grown on many substrates like rice, barley, vegetables and anything else rich in carbohydrates.
It's been used in Asian countries for centuries in the making of soy sauce, miso, douchi, and alcoholic drinks like amazake(low alcohol), sake(medium alcohol), and Shōchū(high alcohol).
Koji's usefulness lies in the fact that it produces a huge range of enzymes when grown on a substrate. Up to 50 different enzymes have been found.
The most useful to us being amylases which break up carbohydrates into it's building blocks, sugars, and proteases that break up proteins into it's building blocks, amino acids.
Examples of how these work are, miso and sake.
In miso, the soybeans have a high protein content and when mixed with koji, salt, and water the soybeans disintegrate because the amylases cleave the carbohydrates and the proteases the proteins.
A once bland and indigestible ingredient gets turned into one of the most delicious umami-rich, nutrient-dense foods known to mankind.
When making miso, a mould strain producing high protease is selected, and grown at a specific temperature, to promote high protease development instead of amylase.
With sake, the opposite is done. A high-amylase producing strain of mould is selected and the mould grown within a specific temperature range to promote amylase production.
The amylase then cleaves the carbohydrates in a carbohydrate-rich ingredient, like rice, into simple sugars, which the yeast in sake brewing can consume and turn into alcohol.
The mould produces these enzymes in order to free up the building blocks it needs to survive and eventually sporulate.
Most of the time we stop the process at the time enzyme production is at it's highest. Other times you might choose to let the mould spore in order to harvest more spores for next time you want to grow koji.
In order to grow, it needs a specific environment. And, as we have seen, different temperatures yield different results depending on what we want to make with it.
Let's look at what you'll need to do this at home.
How to make a fermentation chamber
You need a little incubation set up to properly make koji. You could wing it but chances are you will probably mess it up and give up altogether, which is not the desired result.
Don’t worry, all you need is the following:
- An insulated box - Could be a small wooden cabinet, Styrofoam box or even an unused fridge or freezer.
- Thermostat and humidity controller – Here are the ones I use.
- Heating mat - Like this one.
- Small humidifier - Like this one.
- Clean linen cloth - Any will do.
- Tray to grow the koji in - Either flat or perforated to allow for airflow.
The point to all this is to create an environment where the temperature and humidity can be kept constant.
To set this up plug your two controllers into a power socket and then connect your heating mat to the thermostat and the humidifier to the humidity controller.
This is all very easily done. I barely passed math at school so I’m sure you will manage it too.
Jumping ahead but, sometimes we ferment or age an ingredient at 60C. Your heating mat won’t reach that temperature. I insulated my fridge doors with aluminium foil and use a small fan heater to reach and keep that temperature.
It doesn't consume too much electricity once the temperature is reached and very little energy to maintain the temperature when well insulated.
For home use, you could use a rice cooker or slow cooker to ferment at higher temperatures. It’s what I use when doing small batches.
Simply set your thermostat to 59C and then plug the rice cooker or slow cooker set to keep warm into the thermostat. More on that another day.
You need mould spores to grow koji. I list a few places I've bought from before at the end of this article.
- 1000g Pearl barley
- 4g Koji tane (I always use more than suggested on the packet in case the potency of the spores have gone down a bit)
You either need the pure Aspergillus Oryzae spores or Koji tane. A white powder which is spores mixed with rice flour or blended dried rice koji that has fully spored.
If you buy pure spores you need to mix it with lightly toasted white flour that's been cooled down.
We toast the flour to sterilise it and mix the spores in flour to ensure even distribution when inoculating a substrate.
How to grow it
The process is very simple. However, you will need practice to get it perfect. Like anything in life.
- Steam the barley for about 45 minutes or until fully cooked. Do not boil it as it would ruin the process and drown the mould.
- Sterilise all your utensils and hands. Also, boil or steam the linen cloth. This is to make sure no bad bacteria gets involved.
- Once your barley is cooked, cool it down in a separate sterilized tray or bowl to about 35C. Sprinkle over the Koji tane and mix well. This is to inoculate the barley with spores.
- Line your perforated or flat tray with a slightly damp cloth(not wet) and spread the inoculated barley out and cover with the cloth completely.
- Place into your incubation setup. Place the thermostat needle into the barley and let the humidity controller sensor dangle close by.
Now the real fun starts.
Depending on the purpose, we need the Koji to produce either more protease or more amylase. This means that we need to maintain a temperature of 28C(82F) - 30C(86F) for protease production and 30C(82F) - 34C(93F) for amylase production.
For that reason:
- Set your thermostat to maintain a temperature of either 28C(82F) or 32C(89,6F). Set your humidistat to 70% and makes sure the humidifier is switched on and has enough water.
- Place a buffer like a bowl or wire rack in between the warming mat and the tray with barley so that there is some circulation and the barley does not directly touch the heating source.
- Close the incubation chamber and keep an eye on the temperature. You can connect the thermostat and humidistat to your phone via Wi-Fi so that it tells you when things are changing.
- We now start a 48-hour cycle. Over the next 12 hours, the koji will start “infiltrating” the barley. At some point, it will start to form a mycelium and the koji will produce its own heat. When this happens we have to break it up and cool it down.
- We want the temperature to stay within range. So, break it up and spread it out when the temperature jumps. Don’t worry if the temperature goes a bit above the maximum limit. Just don’t let it stay there for too long.
- Keep this up until 48 hours are finished and the barley is covered in a thick mycelium of white mould.
You now have fresh koji. Taste it. It's delicious just like that.
If you made koji to produce protease, it should have a mushroomy flavour, a bit like the rind of camembert cheese. If you made it to produce amylase, it will have a sweeter aroma and flavour, a bit similar to very ripe apricots.
Once you have tasted koji you can not un-taste it. You will immediately be able to identify it in naturally brewed soy sauce, miso, and sake.
To store for later use simply store airtight in the freezer. Otherwise, you can dry it out for longer storage or store in the fridge for up to a week.
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You don't have to grow koji on barley or rice. It can be grown on many substrates. For instance, when making soy sauce you grow it directly on soybeans and toasted cracked wheat, or a combination of others. Here's a list of just some of the substrates you can also use.
- Bread - One of the more creative ways to use up old bread. The Noma fermentation book has a wonderful rye miso recipe you could follow. In my kitchen, I use Borodinsky bread or sourdough leftovers from the previous day. Any other bread will work.
- Sweet potato - Vegetables are also a great substrate to grow it on. The book, Koji alchemy, concentrates on that a lot.
- Peeled beans - Make sure the beans are fully cooked but not mushy and peel the outside skin off. Otherwise, the mould will not be able to break through the tough skin and start growing.
- Buckwheat - Tricky but doable. Good for those that love a challenge.
- Split peas - Instead of using barley or rice to grow it on for miso, try growing straight onto split peas(green or yellow) and then mix with more cooked split peas, water and salt to make stunning miso.
- Lentils - Lentil shoyu(soy sauce), is one of the things I made that always surprises my clients most when doing tastings for them. I use a mixture of different lentils blended with toasted crushed wheat and grow aspergillus sojae on it. It then goes into a salt brine and ferments for months.
- Quinoa - Also one for the brave but, miso and soy sauce made from quinoa is absolutely outstanding.
What to do with it
Ones you have grown it the possibilities of what to do with it are almost endless. Below are a few traditional and non-traditional products to make with it.
- Soy sauce - Once you've made your own, you won't ever use store-bought soy sauce again.
- Miso - One of the easiest most versatile koji ferments to make.
- Sake - Made by using rice koji and extremely tricky but, very rewarding when done.
- Shio koji - A cure or marinade made with salt, koji and water. Used to briefly marinate beef, chicken or fish.
- Flour - Dried and ground up into a fine powder. Used in bread making and baking.
- Amazake - Lightly fermented low alcoholic drink.
- Koji milk - Dried koji blended with water and strained.
Where to buy spores
Here are a few companies I've used in the past to buy it. They are all slightly different but they are all very helpful and good at what they do.
- Fermentation Culture - They also produce their own shoyu, miso and other ferments. (non-affiliate)
- Good old Amazon - This strain is best for making soy sauce. (affiliate)
- Organic cultures - They stock tons of others mould and interesting spores too. Also, has great information and how-to section. (non-affiliate)
- Bio'c (product site) - This is the best quality I've bought. It's a longer wait than the others though, and the dealing with the post etc is a bit of a pain. But, worth the effort. (non-affiliate)
Useful equipment for this recipe
Helpful books and resources
You can read a lot on Wikipedia and the sites mentioned above. It's where I learned most of what I know today about the subject.
Below are also a few interesting books on fermentation I own and recommend. There are hundreds of others but these are the most well known and most understandable.
The Art of Fermentation by Sandor Ellix Katz - Amazing book on fermentation of all sorts.
The Noma Guide To Fermentation by René Redzepi and David Zilber - Deals with a few topics on fermentation and very well written and understandable.
Koji Alchemy by Jeremy Umansky and Rich Shih - Dedicated to koji and how you can use it.
Miso, Tempeh, Natto & Other Tasty Ferments by Kirsten K. Shockey and Christopher Shockey - Variety of moulds used and also very informative.
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