Simple Koji Applications
This is part of a series on Koji, the magical fungus behind miso and a powerful transforming agent for just about any food. If you haven’t yet, I recommend reading this Intro to Koji first.
Koji’s popularity in fine dining is slowly spreading into home kitchens, meaning both dried koji and koji spores are available with a bit of searching. Below are a few recommendations for where to buy dried koji (koji-kin). If you’re interested in growing your own koji and are looking for a place to buy spores, check this post.
In the US, Miyako, Cold Mountain, and Cultures for Health all sell ready-made koji-kin for your next fungus-fueled fermentation project. Writing from Germany, I have not been able to try any of these but they are positively regarded and should certainly do the trick.
In Germany, I strongly recommend ordering a package of koji barley or rice from mimi ferments, a local shop taking a dedicated, artisanal approach to all things koji. Mimi ferments offers a range of dried koji, koji products like miso and shoyu, and workshops. They’re truly a bastion of koji craft and fermentation culture and well deserve your support.
Once you’ve procured your dried koji, you have your choice of short- and long-term applications. I suggest doing one of each, to familiarize yourself promptly with the flavors and features of koji, as well as a long-term investment to look forward to several months down the road -- for example a jar of shio koji, a bit of ricotta koji, and a larger jar of miso paste.
The ideas below are widely cited and permeated through the koji forums I’ve been haunting lately, so I can’t cite one single source. If you do want to learn more about koji and its applications, I strongly recommend the Shoyu and Miso chapters of The Noma Guide to Fermentation. In addition to the koji sections, you’ll enjoy the brilliant chapters on vinegars and lacto-ferments with creative pairing ideas and heaps of helpful color photos.
Koji Alchemy has become something of a bible for home koji enthusiasts in the US. The title truly captures the jaunt of the book: a handbook to see koji as an agent for performing alchemy on a wide range of ingredients. It is slightly more ‘in the weeds’ than the Noma Guide, so I would recommend getting the Noma Guide first due to its breadth of fermentation methods and clearer recipes.
Shio Koji (5 days)
Shio koji, or salt koji, is a simple combination of koji, water, and salt, left to sour at room temperature for a few days. The resulting concoction is a powerful marinade, salty, sweet, and sour with a rich arsenal of enzymes.
Shio koji is highly flexible, but I’d recommend coating chicken breasts or thighs in koji and leaving for up to 4 hours in the fridge, then simply frying at medium-low heat with a neutral oil in a pan. Commit fully to the theme by preparing a vegetable marinade of equal parts shio koji, lemon juice, and soy sauce, tossing with bell peppers and onions sliced broad and thick, and roasting at 200C / 400F until a few brown spots emerge and the peppers just begin to lose their crunch.
1 part water (by volume)
1 part koji (by volume)
Weigh mixture and add 10% of combined weight in salt
Then, cover the mixture with a bit of cheese cloth or a loose lid and let sit, stirring daily, for 5-7 days until pleasantly sour. It’ll keep in the fridge for a few months after that, retaining the enzymatic activity of the koji with the extra funk and acidity from the room-temperature lactofermentation.
Below are two quick weeknight dinners — on the left, chicken breasts marinaded in shio koji in the fridge for 2 hours, then cooked in a pan and served with some roasted onions and peppers coated in shio koji and lemon. On the right, steaks marinated in koji for an hour and then butter-basted with garlic.
Koji Ricotta “Parmesan” (4 weeks)
Another brilliant use of koji’s enzymatic activity is to take a soft, young cheese like ricotta, mix well with koji, and let sit in the refrigerator for a few weeks. The resulting mixture is spreadable like ricotta, but with an umami depth like a well-aged parmesan. I like it as is, stirred into soups or spread on a piece of crusty bread, but some will press the finished cheese to achieve a crumbly, parmesan-like texture, per the recommendation of Rich Shih, an author of Koji Alchemy.
1 part ricotta (by weight)
1 part koji (by weigth)
Weigh mixture and add 5% of combined weight in salt
Miso / Amino Paste (3 months)
Miso is a combination of soybeans, koji, and salt, with the salt content varying based on how long you intend to age the miso. Soybeans are ideal for miso as they have high proportions of both protein and starch (30% carbohydrates, 36% protein).
Miso making is an ancient art with thousands of years of history. A white American guy who barely made it through two semesters of Japanese in college is not going to be any source of truth on the matter. What I can do is say that it’s well worth its own rabbit hole, noting and following Japanese sources that have perfected this tradition. I’d recommend a post on Chopstick Chronicles, How To Make Miso as a starting point.
More broadly, the basic premise of miso-making can be applied to a near-infinite range of ingredients that feature starch and protein. The Noma Guide features recipes for pea-so with yellow peas and bread-so with Danish rye bread, and koji forums and blogs are filled with recipes of misos with defatted nuts (to avoid rancid flavor from full-fat nut meals) or squash. In fact, the ricotta “parmesan” above is something of a miso itself, though used at a younger age and only developed under refrigeration.
Shoyu / Amino Sauces (3 months)
The malty roundness and dark hue of soy sauce come from deeply toasted wheat. Soy sauce and miso follow similar pattern and salt content, but soy sauce is obviously more liquid, aged with whole soybeans and deeply-roasted and roughly ground wheat. Traditionally, the koji is grown directly on the wheat and soy and then that blend is added directly to a brine (of 15-20% salinity), but ‘amino sauces’ more broadly can spring forth from nearly any protein- and starch-rich substrate, much like miso.
Like miso, soy sauce is a complex ingredient with thousands of years of tradition. I’m 2 weeks in to my first batch, so don’t have much guidance to offer other than another nudge to the Noma Guide and Koji Alchemy.
