It goes without saying that for much of the world, and certainly here in the US, 2020 has been an exceedingly unusual and disrupted year. For many – myself included – March and April were all about sourdough. But I got seriously into another cultivation fixation this year as well: koji.
Koji, a core part of Asian cuisines and the result of culturing the Aspergillus oryzae mold on grains, is effectively a fungal enzyme factory. In contact with fats, koji will produce lipase to break it down into fatty acids; with protein, protease is made to chop that up into amino acids; with carbohydrates, amylase slices long chains of starch into simple glucose molecules. This is how rice is made ready for alcohol production in sake. All this enzyme action liberates amino acids called glutamates, producing the umami flavor that makes so many foods taste so delicious.
I’d considered trying to cultivate it in the past. I have years’ old spore packs in the fridge that, for all I know, would still work just fine. Those things are tougher than we imagine. In any event, in 2019 I ordered some bags of rice koji, or malted rice, on Amazon and used it to coat beef for 48 hours of fridge time before cooking the best steaks I’ve ever made. From there, I played around with some approaches to miso – essentially mixing one part of this storebought koji rice with one part mashed beans (I used chickpeas) and 5% or 10% salt. After some months, this resulted in what was, hands down, the best miso I’d ever tasted.
Fortunately for me, Rich Shih’s and Jeremy Umansky’s book Koji Alchemy was released at the start of May. It’s thoughtful and comprehensive and includes a variety of approaches for making an incubator suitable to culture koji at home. I went with a large cooler, which has also done duty as a beer brewing mash tun, with several inches of water and an aquarium heater, but there are options using sous vide rigs and more. If you live in a warm climate, you may not need special equipment at all. I ordered some fresh packs of koji starter from GEM Cultures and started playing around.
Culturing Koji
Culturing koji is a several day process, but hardly any of the time is active on your end. Here’s the general process:
- Wash and soak rice (or whatever substrate you’re using) for several hours or overnight. When you’re ready to move to the steaming step, drain the rice and let it sit in a strainer for 20 or 30 minutes to dry a bit.
- Steam the rice for 50-60 minutes. Bamboo steamers, with the rice wrapped in cheesecloth, are traditional, but I use a small seafood steamer with the rice in cheesecloth. The finished rice should be relatively dry and starchy and not mushed together the way boiled rice gets.
- Important: Wash your damn hands before proceeding further!
- Transfer the rice, cheesecloth and all, to a clean container. I use various baking dishes I have on hand. Open up the bundle and spread the rice out to cool. When you can comfortably handle the rice, sprinkle the spore powder onto it per the package instructions.
- Mix well. Honestly, my best batches have been mixed by hand, rubbing the rice grains between my hands to embed the spores as much as possible. If you’re concerned about unwanted microbes, you can certainly do this step with a clean/sanitized rice paddle or similar.
- Cover it up and incubate. A lot of instructions call for a damp towel or cheesecloth on top, but I find that my incubator creates enough humidity that this can make the rice too wet. I just cover it with the cheesecloth it steamed in and then, because of all the moisture in my setup, I’ll cover with plastic wrap or beeswax food wrap. Leave some gap for air exchange, but the cover is largely to keep water from dripping onto your humid but not wet grain bed. If your incubator doesn’t have that much moisture, you may not need it.
Inoculated grains heading into the incubator.
- Every 12 hours or so, open up the cheesecloth around your incubating koji and re-mix the rice. It’ll begin putting off heat, usually around 24 hours in my set up, and if you have a lot of rice, or a small container holding it, you may need to mix more often to keep temps from getting out of control. An extra temperature probe can be helpful to keep an eye on that, but again, it’s not strictly necessary.
Unfinished barley koji after incubating overnight.
- It’ll incubate (aim for 30C/86F) for maybe 48 hours, maybe longer. I’ve had fluffy white batches at 36 hours and others at 60. If you notice it yellowing, it’s beginning to sporulate, so stop the process there and refrigerate or dry. The best part of koji cultivation, from my perspective, is the incredible, citrusy aroma the Aspergillus oryzae creates as it grows. Apparently this is unique among Aspergillus species, and scientists speculate that koji may have affirmatively jettisoned genes that produce toxins in order to lean into genes that make this human-stupefying scent. Hey, there are worse ways to earn a meal.
- When complete, you can dry it gently for longer term storage, or bag it up and put it in the fridge for use in the next week or so, or the freezer if it’ll be a bit before you plan to use it.
Use it for what? We’ll get into that in subsequent posts.