Koji Mold Growing


Photo Courtesy of New Society Publishers

Koji Charcuterie

Koji charcuterie is a method of preserving meat that relies on Aspergillus oryzae, or koji mold, grown directly on the surface of the meat. This mold is a filamental fungus (as is P. nalgiovense), which might seem weird, since most people think of fungus as a typical Mario Brothers mushroom. The truth is that fungi come in many shapes, sizes and colors, and the “mushroom” you picture is just the fruiting body of the dynamic fungus – its way of getting its “seed” out to the world. If you think about it, this isn’t too crazy. The familiar apple, for example, is really just an ovary, holding the seed of the apple tree. Likewise, there is more to fungus than its fruiting body. What more? Well, the mycelium, which you can think of as the fungus’s “roots.” Mycelia are highly networked, forming mats and webs, and are responsible for incredibly dynamic metabolic activity in the life of any fungus. Understanding this may help you recognize surface molds such as penicillium and koji as fungi indeed. In warm, moist environments rich in oxygen, koji can grow on the surface of nearly anything, and what you’ll see is a literal mat of filamental white, yellow or pale-green mycelia, growing all over the substrate. I’ve heard of koji mold being used to break down plastic (seriously), and using the same metabolism, it can work its magic on meat as well.

The science of how koji works is a bit more complex than we have room to explore, but the main thing to understand is that its mycelial mat produces many enzymes, which work to break big molecules into smaller ones. The bigger molecules we’re talking about here are starches, carbohydrates, proteins and fats, and they are being reduced to simpler sugars, amino acids, fatty acid chains, etc. With what you know about fermentation and curing so far, you might be able to guess that these smaller molecules are prime nutrition for some other microorganisms (like our friend Lactobacillus), and in this way, koji lays a spectacular groundwork for natural fermentation processes to unfold. But, in tandem with other microbes, koji’s enzymes have their own added effects. For example, it has been found that typically tough cuts of meat can be cultured with koji spores; once the koji populates their surface and releases its enzymes into the meat, it radically tenderizes the cuts. Additionally, meat that is cured using koji has been shown to cure in at least a third of the time that meat cures using traditional charcuterie practice, due to the ongoing activity of koji’s enzymes during the curing process . It ‘s truly amazing.

I’m not an expert on koji charcuterie, and have only recently been introduced to the power of koji across all of its applications, from miso to soy sauce to sake and vinegars. I’m extremely excited about the applications, however, and am now happily growing koji like a fiend, right next to my desk. I grow it on everything from rice to bar­ley to pork loins, after the advice of Chef Jeremy Umansky, the leader in koji charcuterie, using methods he developed at his restaurant in Ohio. Chef Umansky has contributed his own recipe to this chapter, so you ca n get a sense of how the experts are working with koji and meat. I’ve also included my own koji experiment, a recipe I am developing for a local restaurant here in Asheville, NC. Umansky is working on his own books and is totally open sourcing his projects online. Do yourself a favor and check out his restaurant, Larder, and the social media associated with the exciting work he is doing.

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Growing Koji

Like any mold, koji prefers warmth and moisture. Temperatures of roughly 80-95 degrees Fahrenheit and high humidity levels are ideal for koji to thrive. Since this is decidedly not the ideal environment for your home, you’ll have to rig up a small incubator for your koji projects. My incubator is made from a 12-x-24-inch plastic tub about 6 inches deep, with a lid. I fill it about a third of the way with water, and in that water, I place a roughly $40 aquarium heater, capable of heating water up to 90 degrees. You can find these anywhere they sell tropical fish. The aquarium thermometer is plugged into the wall beside my desk, and then run into the water and suctioned to the bottom of the plastic bin. I crank it all the way up to 88 degrees, then invert a couple of small loaf pans in the water, allowing me to place a 9-x-13-inch glass casserole pan on top of them so that the casserole pan is submerged in the water but not loosely floating. Then whatever I am koji culturing can hang out in the casserole pan, covered in a towel, and happily form sweetly fragrant koji mold on its surf ace. I typically cover whatever I am culturing in a tea towel, which I change out daily. This prevents any condensation from drip­ ping consistently on the food. While koji likes high humidity, I find that it helps to keep whatever you are culturing from getting down right soaked.

So, how do you get the koji on there to begin with? The answer is, you’ll need to buy a starter culture. I know I kind of scoffed at this earlier, but it is important to understand that koji is relatively difficult to conjure from the wild. Research into ancient Asian methods for doing this show they involve making strange cake-like concoctions from as many as twenty different native wild plants, and allowing these to ferment wrapped in leaves until the mycelial mat forms on their surface. Assuming you don’t have the flora of a Chinese mountainside at your disposal, it is best to start by buying koji spores from reputable independent sources. My favorite provider is GEM Cultures. There are several types of koji, and they are grown on different grains. My favorite is barley koji, but you can choose what you want. Once you’ve picked it out, it will be mailed to you in a little bag with instructions for use. It looks like olive green powder.


Courtesy of New Society Publishers

I like to do about 4 cups of organic pearled barley at a time. That ‘s about 2 pounds. The package instructions may suggest to soak or rinse the barley, but Jeremy says not to do either, as koji is a saccharifying mold, meaning it seeks out starch and breaks it down. So the more starch, the better. Steam the barley. I use a bamboo steamer for about 45 minutes, until it is cooked and sticky. After cooking, I’ll turn it out onto a towel and break up the clumps, allowing it to cool slightly. Jeremy suggests temping it during the cooling process, aiming for 90°F. While it is cooling, I toast about 1/4 cup of flour in a cast iron skillet, to sanitize it, then mix it with about 2 tsp of koji spores. If I am using koji from a previous batch, I’ll use double this amount, simply because part of the barley from the last batch is in there as dry matter, and it isn’t straight koji spores that I’m adding to the mix.

Once you’ve mixed the toasted flour with the koji spores, you’re ready to add them to the cooked barley. I usually sprinkle about half of the flour and koji mix onto the barley, then mix it around with my hands. It should smell good, like a meadow wildflower. Once I’ve moved it around to coat the grains as much as possible, I’ll sprinkle the rest of the flour/ koji mix on and combine again, using my hands. After all the mixing, I bundle the koji up into the towel, leaving a slight opening at the top. Then I’ll put the bundle into my casserole dish and place the dish into the incubator, close the lid and leave it alone for a bit.

I like to check the temperature of my koji every few hours. It will take 36-40 hours at 88-90 degrees before the barley gets its fluffy white mycelial mat. For the first 24 hours, I keep the barley bundled in the towel, temping it with a meat thermometer every few hours to ensure it is keeping around 85-90 degrees. After 24 hours in the towel, I pull it out and dump the barley directly into the casserole pan, spreading it into an even layer. At this point, you may want to make a couple of furrows in the barley, to prevent the mix from overheating. Cover the pan with a towel and put it back in the incubator; then when you check the temperature every few hour s, you can move the fur rows to different places.

What you are watching for is a thick, fluffy, white or slightly yellow coverage of mold. After about 24 hours it will look lightly dusted, and after 36-48 hours you will see the thicker coverage. Leaving the koji to incubate longer will cause it to mature to the point where it wants to produce spores. You can tell this is happening if the mold begins to turn olive green. If you want to use it for miso or sake, try to harvest it before it gets to this point. If it does start to turn green, that’s OK. You can still harvest it and use it to seed a future batch of grain.

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To harvest, just pull the barley from the incubator and spread it out to let it dry and cool, then put it into a nonreactive container and store it in the fridge. Most recipes that use koji to ferment will have you pulverize the barley with the mold on it before adding it to other ingredients.

So what does all this have to do with meat, again? Well, now that you know how to grow koji on grain, you simply use the same principles to grow koji on meat. I’m not even kidding. The first time I did this, I was absolutely sure it was going to rot, but it didn’t. The process is outlined in more detail in the two recipes for koji charcuterie included in this chapter , but the basic process is to salt cure the meat, adding any other flavorings you want, just as you normally would. After the meat has cured in salt, you’ll dust it with a flour/ koji mix just as the barley was, and then place it in the casserole pan in the koji incubator. It might see m incredibly wrong to be putting a piece of meat into a 90 degree bin, but trust me, it works. The koji will colonize the meat ‘s surface, and when you’re satisfied with the mold growth you see, it ‘s time to weigh the meat, record the weight, and then hang it in your charcuterie cabinet . It will hang there until it has lost 40-50 percent of its weight. Jeremy’s work over the last two years has shown that it will reach this finished weight in drastically less time than a piece of meat you’ve simply salt cured and hung to dry.

With all this info at your fingertips, you may well ask, Why do anything BUT koji charcuterie? Well, to that I have a few answers. First and foremost, koji has its own complex and distinctive flavors, and just as you wouldn’t want every cured meat project to include anise or paprika, you may not want every project to include koji. Additionally, it may outcompete other microbes that you’d like to favor, so doing projects without koji from time to time can enrich diversity in your cabinet and your biological arsenal. That being said, koji is addictive. I won’t lie. The first time you smell its sweetness you may be inclined to disagree with me.

Cover Courtesy of New Society Publishers

More from Pure Charcuterie:

  • Five-Spice Koji Lomo Recipe
  • Nduja Recipe

Reprinted with permission from Pure Charcuterie by Meredith Leigh and published by New Society Publishers.

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Ethan Smith is a seasoned marine veteran, professional blogger, witty and edgy writer, and an avid hunter. He spent a great deal of his childhood years around the Apache-Sitgreaves National Forest in Arizona. Watching active hunters practise their craft initiated him into the world of hunting and rubrics of outdoor life. He also honed his writing skills by sharing his outdoor experiences with fellow schoolmates through their high school’s magazine. Further along the way, the US Marine Corps got wind of his excellent combination of skills and sought to put them into good use by employing him as a combat correspondent. He now shares his income from this prestigious job with his wife and one kid. Read more >>