Making Koji - a Foundation of Fermentation

Koji is a magical food. It is the result of carefully cultivating a mold called aspergillus oryzae on a starchy substrate like rice, barley, soybeans, even vegetables and old bread. Koji is a foundational ingredient for all kinds of ferments, including soy sauce, sake, miso, teriyaki - and you can even eat it on its own as an umami-packed, gut-healthy snack. Koji contains a marvelous array of beneficial enzymes that support the immune system by helping the bacteria that live in our gut. Two particularly useful enzymes in koji are amylase (which breaks down carbohydrates into simple sugars), and protease (which breaks down proteins into amino acids), making both of these nutritional components easier to digest... and not just in our own guts, but also in the fermentation of other foods. For instance, when brewing sake (an alcoholic drink made from rice), the amylase in koji helps break down the rice's carbohydrates into simple sugars, which the brewing yeast can then easily digest and turn into alcohol. Or, when used as a meat tenderizer, the protease in koji-based marinades breaks down the proteins in the meat, making it softer and easier to eat.

For this Instructable I will show you how to cultivate a batch of koji on a substrate of barley, and from there you can use it in whatever fermentation or snacking adventure you crave next :)

500 grams pearled barley or polished rice

4 grams aspergillus oryzae spores (koji kin)

Strainer

Steamer

Glass mixing bowl

Clean cloths or very fine cheesecloth/butter muslin

Fermentation box, which includes the following:

• Insulated box - this can be an old wine fridge, a styrofoam cooler, or in my case an old cabinet left over from remodeling my kitchen, lol
• Heating pad/warming mat
• Thermostat
• Humidifier
• Humidistat
• Perforated tray for containment and air flow (I use a giant pasta strainer)

**Make sure all your equipment is thoroughly cleaned and sanitized, including the inside of your fermentation box!

1. Rinse your grains of choice several times to remove any bran, dirt, or other contaminants leftover from processing (you can see how cloudy the water is for the first several washings - keep washing until the water is clear)
2. Soak the grains for 12 hours in the fridge - this will help loosen the grain structure and make it easier for the aspergillus oryzae spores to penetrate and take root. **While your grain is soaking, you can take advantage of the down time to set up your fermentation box in Step 2 below...

1. Set up the fermentation box (see photos):
2. I mounted the control panel for the humidistat and thermostat on the front of the box for easy reference, and I ran the cords for the thermostat and humidistat probes through a hole in the bottom of the box, so the lid could close completely
3. Place the humidifier in one corner, so it doesn't spray directly on the koji when it's time to put it in the box (my humidifier is the white cylinder in the left rear corner of the box)
4. Mount the humidistat probe on the opposite side of the box so it's reading the furthest point from where the humidifier is, and will kick on if that area starts to dry out. This will keep the entire box humid, not just the area near the humidifier (my humidistat probe is the little black rectangle mounted on the right hand side of the box)
5. Place the warming mat on the bottom of the box (my warming mat is the large black-and-clear striped rectangle in the picture)
6. To promote air flow, place a wire rack inside the box over the top of the heating mat, so air can flow below and above where the koji tray sits. **As the koji grows, it will begin to generate its own heat and you don't want it to burn, so maintaining air flow between the heating mat and the koji tray is important
7. To start, set the thermostat to 82 degrees F, and set the humidifier to maintain a 70% humidity. Close the lid and let your box start warming/humidifying (we will decide on our exact temperature in the next step, but this will let the box start to prepare itself)
8. Decide which type of enzyme you want to encourage most in your koji (this is important, and will determine the temperatures we choose).
9. If you would like to use your koji for fermenting high-carbohydrate foods (like the rice used for making sake) you will want a koji high in amylase. If so, set your thermostat to maintain a temperature between 86 and 92 degrees F, because amylase develops best in this range.
10. If you would prefer to use your koji to ferment high-protein foods (like soybeans used for making miso, or for a marinade to tenderize meat) you will want a koji high in protease. If that is the case, set your thermostat to maintain a temperature between 82 and 86 degrees F, because protease develops best in this range.
11. **If you plan to simply snack on your first batch of koji, your taste preferences can also help you decide which kind to make. Koji high in amylase will smell and taste sweeter, similar to dried apricots, while koji high in protease will be more nutty with a smell and taste similar to mushrooms. I prefer the flavor of high protease koji, and I like to use my koji for making miso, so I will be aiming for a koji high in protease.

1. Boil the cloths you intend to use (I used two pieces of fine mesh cheesecloth) to sterilize them, and set them aside
2. When the 12-hour grain soak is finished, take the grains out of the fridge and allow them to drain for at least an hour (I bundled mine in one of the cheesecloths and hung it from my sink arm). **You want a very even draining, because concentrations of dampness will cause the grains to steam inconsistently in the next step and can cause problems with koji growth
3. Once drained, steam the grains as evenly as possible. If you're using pearled barley, steam for 45 minutes; if using rice, steam for 20 minutes. **Don't boil the grains or they will become too mushy and wet, and will drown the koji spores
4. Place your steamed grains in a clean bowl and allow them to cool to 112 degrees F. Once cooled, sprinkle them with the aspergillus oryzae spores or koji tane; this is called inoculating or "seeding" the grains. Mix well, distributing the spores as evenly as possible (the act of stirring will also help cool the grains down toward our target temperature)
5. Once mixed, wrap the grains in one cloth, flip upside down, and wrap in the other cloth (see photos). **You want the cloths slightly damp so they don't wick away moisture from your grains, but you don't want them wet or they will drown the koji spores

This is where some finesse is involved, and why making koji successfully requires some art along with the science...

1. Stab your thermostat probe into the center of your grains, making sure it is completely submerged (I had to make a small hole in one of the cloths to get the probe through), and place the sack on your perforated tray
2. At first, your thermostat will likely read higher than your set target temperature, because the grains are likely still warmer from the steaming. Don't worry, they will cool off eventually
3. Make sure your humidifier is full of water
4. Close the door/lid to your fermentation box, and the ferment will begin. Over the next 48 hours, we are going to watch closely for temperature fluctuations and intervene if the temperature either drops too low, or rises too high.

**As the aspergillus oryzae begin to grow and populate throughout the grains, they will start to form a network of mycellium that knits them together, and the koji will start to generate its own heat. That's a good sign the koji is healthy, however we have to prevent it from getting hotter than our target temperature range or the enzymes we are cultivating will die.

1. When you notice a spike in temperature, you will need to open the fermentation box (working quickly so it doesn't cool down too much), unwrap the cloths, and use your hands to break up the koji so it can cool off. Break up large chunks and spread them out again on the cloth in the tray, reinsert the temperature probe, and cover with the other cloth again (you don't need to bundle them up in sacks anymore, just keep them covered and keep the cloths slightly damp). **I have attached a chart in the photos for this step that shows an example of how one koji company, Kawashima, monitors their koji production - you can see how the temperature rises as the koji grows, then falls after they break up the grains, then rises again... over and over, maintaining the koji in their desired target temperature range.
2. At each spike in temperature, simply repeat this process. **These are also good opportunities to check your humidifier water level, and wipe up any excess water that may be pooling in the fermentation box or even in the koji tray
3. **During this batch, I noticed the humidity was holding at a much higher range than I wanted, so at the end of day 1 I had to prop the lid open a bit to let some of the moisture out... I was concerned this would allow the temperature to drop too much, but thankfully the temperature inside the koji held steady. These are the kinds of adjustments you may have to make along the way

1. After 48 hours (or I like to think of it as four 12-hour cycles to make it feel more manageable), you should have a tray of barley coated in beautiful white koji
2. Give it a taste, did you end up with the kind of koji you were shooting for? High-amylase or high-protease?
3. These are some of the things you can research recipes for, and make using your koji:
4. Amazake (sweet sake) - amylase koji
5. Shoyu Koji (shoyu sauce) - amylase koji
6. Miso paste - protease koji
7. Shio Koji (meat marinade and tenderizer) - protease koji

The process for making koji can seem a bit intense at first, and it can be tricky to keep an eye on the temperature fluctuations - but once you get the feel for when temperature spikes usually happen it becomes easy to anticipate when you'll need to intervene.

I hope you enjoy making koji and using it to make all kinds of wonderful things!