Making Pearled Barley Koji
When you think of Japanese food, what are some of the first flavors that come to minds? The taste of sushi? White rice and pickles? What about that deep flavor of ramen broth? The sweet savory glaze on yakitori? Almost all Japanese food starts with base of umami, coming from either dashi or fermented soybeans. We’re going to talk about the latter, specifically miso paste and soy sauce (shoyu).
Miso and shoyu go through different fermentation process but they share the same two ingredients: soybeans and koji, koji being the secret to these incredible ferments. At its core, koji can be described as moldy rice. Specifically, koji is the end product when you inoculate cooked rice with Aspergillus Oryzae and incubate it, letting the mold grow for between two to three days.
As the Aspergillus Oryzae grows, it produces carbohydrase complexes such as amylase which converts carbohydrates into sugar and protease that breaks down complex proteins into smaller chains of amino acids called peptides. What’s fascinating to me is that protease will release glutamine and glutamic acids, which feeds into another enzyme, glutimase, that the koji produces, which in turn converts the glutamine into more glutamic acid. When you combine koji with a substrate that has a high amount of naturally occurring glutamine, such as soybeans, you end up with an umami bomb as glutamic acid is one of the key chemicals that produces the taste of umami.
The Noma Fermenation Guide, which has been a big point of inspiration for myself, has lead to an explosion of interest in fermentation. This guide is based of their recipe.
Let’s learn how to make some pearled barely koji.
Incubation Chamber
In order for Aspergillus Oryzae to thrive, it needs to be incubated with relatively at a consistent temperature with relatively high humidity. You can grow koji in a fairly wide range of incubation temperatures from 20–40°C, but if you want the optimal growth rate to enzyme production, the koji should be incubated at 30°C. I have a website about building a fermentation chamber with a parts list I regularly update and lessons learned at http://kojichambers.com.
Little Tips
Before you make any koji, you’re going to want to dial in your temperature controller. When your heating element is inside of your chamber, it will continue to produce residual heat even after it has turned off. If your controller turns your heater off at exactly 30°C, you’ll see the temperature continue to raise. I have my heater turn on at 29.5°C and turn off at 29.7°C, keeping my chamber at 30°C ± 0.5°C. When tuning the cut off point, make sure your chamber is already at temp, otherwise your heating element will be on longer and probably be hotter when disabled.
I also found that attaching my hygrometer to side of the chamber was giving me incorrect humidity readings, which makes sense as water tends to condense on the wall. I ended up taping the wire to the top so that the hygrometer was dangling above the koji and got far better readings.
Ingredients
- Pearled Barley, preferably organic and from a local source.
- Aspergillus Oryzae spores. There are a couple of websites selling this but I recommend the folk over at Gem Cultures.
Making Pearled Barley Koji
Before a ferment, spray down your chamber and tray with some star san to sanitize everything.
I normally make koji in 500g batches. To start, you are going to want to wash 500g of pearled barley until the water runs clear. Put the barley in a bowl and cover it with a good amount of cold water, let it soak for 4 hours. After the soaking period, drain the barley.
Steam the barley until cooked. The time really depends on how your steaming the barley. The noma book recommends 15 minutes but I found that didn’t work for my method of steaming, which involved resting a strainer filled with the barley over simmering water and covering it. I steam it for about 45 minutes, mixing the barley around every 10 minutes or so to prevent uneven cooking. The barley is done when it’s easily chewable. When you go to mix your barley, take out a couple grains and try them. You’ll build an intuition on how they hydrate and cook with practice.
Meanwhile, get your fermentation chamber up to temperature by setting the temperature controller to 30°C and the humidity controller to 75% humidity.
Lay out a damp rag on your perforated tray and then spread your barley over it to cool. Run your fingers thoroughly through the barley, breaking up any clumping. When the barley is around 30°C, sprinkle a very light, even layer of spores onto the barley. Mix up the barley, then sprinkle on another layer.
Place your koji in your chamber, insert the temperature controller’s thermometer into the center of the koji, and cover it with a slightly damp towel. After 24 hours, put some latex gloves on and mix up the koji gently by hand. By now the koji should be smelling nice, emitting an almost sweet scent. Make sure the thermometer in back in place and let it sit for another 24 or so hours.
At this point, the koji should have strong mycelium growth between grains, which just means the mold is holding the grains together in a block, and a nice fuzz on top. If there’s a little bit of coloring on the fuzzy growth, it means that the koji has reached sexual maturity. I’ve never experienced a noticeable difference in taste, but apparently it can produce an off flavor. Next time you make koji, pull out the koji a bit earlier before it hits maturity. You’re going to want to stop the growth at this point, so put the koji in the fridge and let it hang out there until it’s cold.
And just like that you have koji! At this point you can use it to make miso, shoyu, shio koji, amazake, croutons in soups, or dry it out and turn it into a fine powder to age steaks.
Here’s a couple of pictures of the finished product. You can see strong growth up close.
