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For those big into fermentation and who are looking to add a new living organism into their rotation, may we recommend reading up about koji? Koji, the microbe that brings those intense umami flavors to Japanese cuisine, can be harnessed to not only ferment liquors and soy sauce, but to quickly and efficiently age charcuterie and cheeses. 

Related Reading: Learn How to Finally Make Kombucha at Home with These Tips

Koji Alchemy: Rediscovering the Magic of Mold-Based Fermentation,” by koji experts Rich Shih and Jeremy Umansky, explores the power of this fermenting microbe and how it’s used around the world by both home cooks and professional chefs. The book is filled with scientific essays and instruction manuals, showcasing a slew of techniques, like how to grow your own koji at home. Armed with this tome, you’ll soon be able to brew your own booze, like koji beer, sake, and shochu, and dry cure meats, like coppa and steak. 

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Ahead you’ll find an introduction to what, exactly, koji is, for a foundational understanding of this beloved organism. When you’ve proven educated on the subject, you can move on to attempting some of your own koji alchemy, like fermenting amino paste (aka miso), which only requires three key ingredients—koji being the main one. These amino pastes can be added into a number of things—from chicken noodle soup to tomato sauce, hummus, and even chocolate ice cream—amplifying flavors with that extra umami hit.

Like other fermentation projects, you’ll need to map out a few weeks, and up to a few months, to allow the fermentation to properly click into place, but the final result is well worth the wait.

The following excerpt is from Shih and Umansky’s new book Koji Alchemy: Rediscovering the Magic of Mold-Based Fermentation (Chelsea Green Publishing, May 2020) and is reprinted with permission from the publisher. 

What is Koji?

Koji is an amazingly transformative and seemingly magical ingredient that has bewitched many people over thousands of years. One of the many things koji does is turn complex carbohydrates into simple sugars via powerful enzymes it produces in order to feed itself. It is a type of mold used in the production of many foods such as miso, soy sauce, sake, jiang, douchi, amazake, makgeolli, meju, and tapai just to name some. Koji has been used for millennia throughout Asia and most recently, in the past 150 years or so, has been slowly conquering the rest of the world in ways that the people who first domesticated it could hardly conceive. Take the charcuterie that Jeremy makes at Larder Delicatessen & Bakery. After the meat is cured and inoculated with koji, the drying time is cut by as much as 60 percent. Imagine being able to make a prosciutto in six months instead of two years. 

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Koji is an extremely powerful organic technology that has not only shaped the foods of various peoples but also ingrained and transformed their very cultures. Actually, virtually every culture that encounters koji or a food made with or from it becomes entranced by its transformative power. The Japanese have declared it their National Mold and have even created comic books in which it is featured as a cartoon character! We feel that in order to truly understand what it is and what it’s capable of, we must know a little about how, where, when, and why it came to be. When investigating these matters, it’s always best to start at the beginning in order to give a complete understanding. That beginning would be koji’s evolution. 

The Origins of Aspergillus oryzae (aka Koji) 

The koji mold, Aspergillus oryzae (or, as we will refer to it going forward, simply koji), has a bit of mystique surrounding its origins. Due to rigorous scientific research, we know that koji evolved when it was domesticated from the highly toxic A. flavus. Dr. John Gibbons at Clark University in Worcester, Massachusetts, is currently leading the way in research related to how koji evolved away from its toxic ancestor, by identifying the traits and genetic changes that accompanied the domestication of A. oryzae. To address this topic he and his team sequence and compare the genomes of A. oryzae and its toxic progenitor species, A. flavus. They then use computa- tional genomics, evolutionary biology, and population genetics to pinpoint genetic differences between domesticated and wild genomes. When the genetic differences are present in genes whose functions are known, they design laboratory experiments to test how these genetic differences change the characteristics of A. oryzae. They’re essentially attempting to use biology to understand the traits that ancient artisans selected for when they domesticated A. oryzae. These findings have evolutionary, cultural, historical, and applied significance, which makes this system so exciting to many of us. 

Why would an individual decide to conduct research on something so specific as koji? Well, when Dr. Gibbons went to college, he wasn’t fully aware of filamentous molds and their uses. He had always been a big-picture person and applied to graduate school knowing that he wanted to study genomics, indifferent as to what his specific organism would be. After interviewing with labs that studied fruit flies, humans, yeast, plants, and molds, Gibbons ended up joining Dr. Antonis Rokas’s lab at Vander- bilt University, where one of the major research areas was Aspergillus (the koji genus) genomics. Gibbons was given a stack of papers to read when he started at the Rokas Lab so that he could see which areas would be of most interest for him to research. One paper he read completely blew him away. He had assumed that only plants and animals had been domesticated by humans, but a number of papers called A. oryzae “domesticated.”1 One particular paper detailed how the publishing group used a combination of chemistry and archaeology to determine the contents of a nine-thousand- year-old pottery jar from China. They were able to show that the pottery held a fermented drink composed of rice, honey, and fruit, and that this type of fermentation required a mold that was really good at breaking down starches into sugar. It confirmed that humans have been making rice-based alcohol for nine thousand years through the help of filamentous fungi! The biology and genomics, cultural aspects, and applied side of this topic were exciting for Gibbons. 

Peter Larson

With the promise of potential research ahead, Gibbons dove in on a quest to unlock the how, why, when, and where of koji’s domestication. For more than ten thousand years, humans have been taming plants and animals for particular characteristics. For example, domesticated plants usually produce more fruits or seeds than their wild progenitors thanks to selective breeding. Domestication has a profound impact on the genome of any given organism, and koji is no exception. Specific mutations underlie many of the traits selected for in domestication. For example, a single change in the genetic code of maize (corn) from its progenitor teosinte led to “naked grains” as opposed to the nearly impenetrable kernels of teosinte that are encased with silica and lignin. These mutations were shaped by selective breeding over long periods of time; when you simply compare the phenotype (essentially the way something looks) of teosinte with that of maize, you can easily observe these changes. And while plants and animals primarily shape our collective knowledge of the genomic and phenotypic effects of domestication, a number of bacteria, yeasts, and molds were also domesticated. 

We’ve read some of Dr. Gibbons’s papers about koji and its pathway to domestication, and they are nothing short of fascinating! To under- stand koji’s impact on various cuisines and cultures, we felt it important to establish an understandable timeline for its evolution and domestica- tion. Dr. Gibbons points out that we define domestication as “the genetic modification of a species by breeding it in isolation from its ancestral population in an effort to enhance its utility to humans.” As we’ve noted, the domestication of koji occurred at least nine thousand years ago. Noncoincidentally, according to Dr. Gibbons, this is roughly the same time rice was domesticated (the two often go hand in hand). It makes sense that as rice was domesticated, the mold that eats it, koji, would follow suit in its new agricultural home. He also points out that people have been selling koji dating back to the thirteenth through the fifteenth centuries in China, a considerable amount of time before Western science even knew what microbes were.2 To put this into relative perspective, it would still be roughly three hundred years before Robert Hooke would first observe dead plant cells under a microscope, followed by others observing living organisms. 

The exact answers to the questions surrounding koji’s evolution and domestication are yet to be found, and the process is quite puzzling due to the fact that koji and its toxic ancestor, Aspergillus flavus, share 99.5 percent of their genome. But the important point is that koji has been used in food production in China since at least 7000 bce, making it one of the oldest domesticated foods on the planet. 

Basic Amino Paste Recipe

When it comes to applications, amino pastes have way more potential than has traditionally been explored. We’ve put them into chicken noodle soup, burgers, tomato sauce, pierogi, hummus, cookies, pies, jam, and chocolate ice cream, to name just some of the successes. An all-time favorite of ours is a compound butter made with amino paste, which we use for everything from sautéing vegetables to schmearing on a bialy. The beauty is that the paste is so concentrated and has so little moisture that you don’t need to adjust a recipe in most cases. There are reasons that miso has become ubiquitous around the world: It’s versatile, relatively inexpensive, and scrumptious. The key is to think of amino pastes as salt with a greater depth of flavor. 

This is the master recipe that we use for nearly all our amino pastes, whether we make them from soybeans to beef heart. We’ve kept it simple and straightforward so that you can easily memorize it. It can be scaled up or down as you desire by either multiplying or dividing the ingredients. You can make 20 pounds (9 kg) just as easily as you can make 2 pounds (900 g). Try to take into account how much of the paste you plan on using and adjust the measurements appropriately. For both light and dark basic amino paste, fresh koji is preferred, but if you’re using dry koji, mix in 25 g (about 1 fluid ounce) of lukewarm water into the koji in a small bowl and allow it to hydrate for a couple of hours at room temperature. If you don’t want to wait, process into a rough paste. 

Note: For ferments applications, we recommend using grams to measure rather than their US equivalent. This assures an accurate salt percentage for food safety.

Basic Amino Paste

  • Light (2 weeks–3 months): 250 g koji
  • 25 g kosher salt
  • 250 g protein
  • Dark (6 months–1 year+): 165 g koji
  • 65 g kosher salt
  • 330 g protein
  1. Add the koji and salt to a medium mixing bowl. With clean hands, mix the koji and salt together so the latter is evenly distributed. Now combine mixing and squeezing the koji and salt together to break down the koji into a paste as much as possible. Don’t worry too much about making it super fine or missing some grains; the pieces will have the opportunity to break down fully during the fermentation process.
  2. If the protein is in a solid form and cannot be simply mixed into a paste, process accordingly. Most ingredients can be cut up into chunks and run through a food processor.
  3. Add the protein base and mix thoroughly. Pour the contents into any non-reactive pint container. A mason jar is preferred. Store the jar at ambient temperature for the specified time for either light or dark miso.

Header image by Andrew Wang.

Amy Schulman is an associate editor at Chowhound. She is decidedly pro-chocolate.
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