I don’t know what we expected when we tasted koji fermented coffee. What we got was a cup of coffee. Acidic, fruity, bitter, a decent espresso that wanted to be showcased alone and not in milk. Adjectives like “strong” and “flavorful” come to mind, but it was not so different that we could confidently point to the cup and say, “Ah yes, the koji has entered the cup.”

In a way, that makes the story more interesting. Because the question is not simply, what does koji coffee taste like? The better question is: how would we know what koji changed?

Coffee is already a moving target

Coffee can taste wildly different before koji ever shows up. A washed Ethiopian, a natural Colombian, a Kenyan, a dark-roasted Brazil, and a funky anaerobic coffee can all taste like they belong to different beverage species. Coffee can be floral, chocolatey, nutty, citrusy, winey, earthy, smoky, berry-like, fermented, you name it. The Specialty Coffee Association’s Coffee Taster’s Flavor Wheel exists because coffee professionals need a shared vocabulary for a huge range of flavors, and the SCA describes it as an industry-standard tool developed with World Coffee Research.

So when a koji-processed coffee tastes savory, that does not automatically mean it’s the “koji” note. Coffee can already have savory elements. When it tastes acidic, that does not automatically mean “koji.” Coffee can already be acidic. When it tastes funky, strange, or fermented, that also does not automatically mean “koji.” There’s already a coffee for that.

This is the first problem with tasting koji coffee: coffee already has so many varieties, processing methods, and flavors in play that it’s hard to isolate what the koji actually changed.

What koji is supposed to be doing

Koji coffee usually refers to processing of coffee with Aspergillus oryzae. In coffee experiments, the mold is often applied during post-harvest processing, on coffee cherries rather than roasted beans. Early attempts to apply koji directly to green coffee were difficult because green coffee has relatively little starch available for koji to grow on, while applying koji to coffee cherries produced more promising results. As we know, Aspergillus oryzae can produce enzymes that break large molecules into smaller, tastier, more fermentable pieces. In rice, this is dramatic. The clearest example is in amazake where starch becomes sugar. Coffee cherries do not act like rice. Coffee is a seed inside a fruit, processed through an array of microbial, agricultural, and roasting decisions before reaching the mug mug. Koji is doing something, but the question is whether the tongue can pick it out of all the possible variables.

Koji coffee’s origin story

Koji coffee’s origin story starts with the question “can koji save old coffee?”

Christopher Feran, a coffee Q grader working with chef and Koji Alchemy co-author Jeremy Umansky and Koichi Higuchi of Higuchi Matsunosuke Shoten, an Osaka koji-spore producer, had been experimenting with koji on green coffee as a way to manipulate the flavor of aging coffee. The results, they claim, were fascinating. Feran described some of those early cups as “brothy, shoyu-miso-umami bombs,” with kombucha-like aromatics and an “uncoffeelike character.”

Then Finnish barista champion Kaapo Paavolainen asked a more useful coffee-world question: could koji be used not to make coffee taste wild and strange, but to make it taste better by specialty-coffee standards? In other words, rather than striving for novelty, the goal became: could koji change sweetness, aroma, structure, or acidity while still letting coffee taste like coffee?

Some advocates describe koji processing as increasing sweetness, mouthfeel, fruit aroma, or acidity refinement. Perfect Daily Grind quotes Christopher Feran and collaborators discussing koji’s ability to produce fermentable sugars, amino acids, glutamates, esters, and aldehydes, while also noting that one producer framed the effect less as creating new flavors and more as enhancing existing components in the coffee.

Because if koji enhances what is already there (like rice’s sweetness in amazake, soybean’s umaminess in soy sauce), then it may not taste like “koji.” It may just taste like a slightly louder version of that coffee, which is right in line with our experience.

The missing control cup

A proper comparison would need a control cup with the same level of sameness: the same farm, same variety, same harvest, same cherry ripeness, same drying conditions, same roast, same brewing recipe, and ideally a blind side-by-side tasting. That level of control matters because studies of coffee quality repeatedly show that variety and processing interact in complicated ways, and that the same processing method can amplify or reduce attributes depending on the coffee variety. The aforementioned steps all leave their own fingerprints onto the final taste of the cup of coffee. Without that, we are not tasting koji coffee versus non-koji coffee, but rather one coffee with a koji backstory.

Unfortunately, fresh coffee cherries are not something we can just pick up at the local supermarket, and so we could not produce koji-fermented coffee ourselves in a way that would make for a fair comparison. Even if we could source the coffee cherries at a store, Claudia Victoria Alzamora Moreno, a Panamanian chef, explained that the process is even more delicate than we naively thought: “as soon as the fruit is separated from the peduncle, enzymes are released and biochemical changes start to occur - affecting freshness, structure, and the overall condition of the coffee.”

In other words: once the cherry is picked, the fruit starts to change and the countdown begins. Sugars, enzymes, microbes, moisture, temperature, and time all start to transform the cherry.

So instead of pretending we could run a proper controlled experiment from our kitchen, we did the next best thing: we tasted what we could, read the available methods, and spoke with someone who had actually put koji on coffee cherries.

A coffee cherry does not behave like rice

Christopher Feran has been open about how his koji coffee process works. In his writing, he describes the production method in detail, calling it the Koji Supernatural Process. The protocol uses the koji spore strain from Higuchi Matsunosuke Shoten, selected for strong saccharifying activity and high amino acid production.

The process happens while the coffee is still in cherry form. Feran describes controlling temperatures between 25 and 30°C and using a spore ratio of 1 gram of spores to 1 kilogram of coffee cherries. This is five times higher than what might be used for typical rice koji, which is already a clue that coffee is not koji’s dream substrate. Unlike rice koji, where the rice is steamed to gelatinize starch and prepare it for mold growth, coffee cherries are fruit wrapped around a seed, with skin, pulp, mucilage, moisture, acidity, basically a much less cooperative structure.

Apart from that major difference, the process still resembles koji making: inoculate, control temperature, manage moisture and monitor growth. Once the koji stage is complete, the coffee needs to be dried back down to a stable moisture level. Feran describes a target of around 12.5–13% moisture, after which the coffee can continue through more familiar coffee-processing steps: resting, storage, roasting, grinding, and brewing.

Claudia’s experience followed the same general problem, but from the perspective of practical R&D rather than a fully standardized industrial process. Apart from Feran’s public protocol, there are not many detailed sources explaining how to make koji-fermented coffee, so Claudia had to build from her own experience growing koji by trying out different materials.

The biggest challenge, she explained, is the cherry itself. Coffee cherries have high moisture content and a dense skin. That makes cultivation and penetration difficult.

As Claudia described:

“One obvious difference is that the mycelium does not compact into a solid block the way it can when growing on grains. Instead, the colonization appeared more scattered, almost like it was ‘painted’ across the cherries in different spots. I also noticed that the koji tended to search for small cracks in the fruit. Even though we worked with whole cherries, some of them inevitably get slightly damaged during transport or handling, and the fungus seemed to take advantage of those small openings.”

Koji may be domesticated, but it is still a fungus, and fungi are opportunists. Give them a crack, a crevice, dampness, food, a little warmth, and they start wedging their way in.

Getting a spot on the shelf

There are several debates about koji coffee that go beyond its flavor.

The first is economic. Coffee competitions and high-end auctions can dramatically affect the reputation and prices of specific farms and producers. But access to those spaces is not evenly distributed. Feran has argued that one reason for publishing the koji protocol openly was to give more producers access to a method that could potentially create competition-level coffees, rather than keeping experimental processing locked behind the same small circle of celebrated farms and consultants.

That is the optimistic version: koji as a tool for access, differentiation, and maybe better prices.

We all know that just having access to a protocol doesn’t give you a product. For producers, the question is not simply, “Is koji interesting?” It is, “Why would I choose this over the processing methods I already know?” Koji fermentation adds cost, labor, knowledge, risk, and infrastructure needs. Producers need access to spores, training, controlled fermentation conditions, careful drying, and buyers willing to pay enough to justify the extra work.

Claudia’s results also point back to the missing control cup. She tested different coffees and saw different outcomes:

“The results were mixed. In the case of the Pacamara, the coffee felt noticeably more full-bodied in the cup, even when brewed with relatively high ratios. However, it also became slightly more bitter. The Geisha from the other farm behaved quite differently. It was very clean in the cup, with light fruity characteristics, essentially resembling a good washed Geisha. So in that sense, one result convinced me more than the other. But I believe this had more to do with the inherent characteristics of the coffee varieties themselves rather than the intervention of the mold.”

If koji enhances what is already there, then the coffee’s quality matters enormously. The mold is not a magical wand. It may be nudging sweetness, body, aroma, acidity, or mouthfeel in directions that depend on the variety and condition of the cherry. In one coffee, that nudge might feel like more body. In another, it might bring out bitterness or even an imbalance.

This is where koji coffee becomes less like a recipe and more like a collaboration between mold, fruit, farmer, processor, roaster, and barista. Sounds like most fermentation processes, right?

For roasters, koji-processed beans may also behave differently from more familiar washed or natural coffees. Changes in density, moisture, surface condition, or chemical composition can affect how the coffee responds to heat. That means roasting may be less predictable, especially if the roaster has little information about the processing method.

Then there is the regulatory and consumer side. Depending on the market, green coffee has standards around defects and foreign material, and anyone working commercially would need to understand how koji processing fits within those rules. This is worth checking carefully before publication if you plan to mention EU regulations specifically.

And finally, there is the public relations “mold” problem. Most consumers are not familiar with koji. Say miso, soy sauce, sake, amazake, and shio koji all rely on mold, and some people lean in with curiosity. Others might block out everything that comes after “mold”. A barista may have to explain that koji coffee is not “moldy coffee” in the spoiled-food sense, but coffee processed with a carefully cultivated fungus used in some of the world’s most beloved fermented foods. But this is more of a linguistic issue. Maybe instead of explaining koji coffee as “moldy coffee”, we could say “cultivated coffee”? Sounds like a $30 bag of coffee to us.

So where does that leave koji coffee? Probably somewhere niche, but it could still be a serious processing tool for some producers or competition coffee. We like it nonetheless.

So did the mold do anything?

Probably. Maybe. We’re not sure. We wouldn’t have been able to tell you that koji was in the cup in a blind test. But we like that uncertainty. Koji coffee is not interesting because it recreates what coffee can taste like, but it is interesting because it asks a better question: how much of flavor comes from the microbe, how much from the material, and how much from the story we were told before we took a sip?

Special thanks

This article was made possible with the collaboration of Claudia, aka. “fermentnation.pa” on Instagram, who provided us with an interview session on this topic and shared her experience with koji coffee.

See more of her koji research by checking out her account: https://www.instagram.com/fermentnation.pa/

Sources:

1. Christopher Feran. 2021. Coffee, Koji and Kaapo’s WBC Routine (or: the Koji Supernatural Process). https://christopherferan.com/2021/10/23/coffee-koji-and-kaapos-wbc-routine/

2. The Latest on Koji Fermentation. October 24, 2022. https://sucafina.com/na/news/the-latest-on-koji-fermentation

3. Jong | 三浦宗民 . Miura Munemitsu. 麹（Koji）でつくるコーヒーの話. The story of coffee made with koji. February 7, 2023. https://note.com/jongminjemi/n/n8e9215db9850 .

4. Liu K, Su R, Wang Q, Shen X, Jiang B, Yang L, Li Z, Zheng J and Li P (2024) Interaction and dynamic changes of microbial communities and volatile flavor compounds during the fermentation process of coffee flower rice wine. Front. Microbiol. 15:1476091. doi: 10.3389/fmicb.2024.1476091

5. HERNANDEZ, Carlos Eduardo; MENCÍA-GUEVARA, Alejandra; ROJAS-ROJAS, Katherine. Young coffee leaves biotransformed by aspergillus oryzae in enriched source of caffeic acid. Coffee Science - ISSN 1984-3909, [S. l.], v. 16, p. e161863, 2021. DOI: 10.25186/cs.v16i.1863.

Sourdough ruined ordinary yeasted dough me for. Once I got used to that mild tang and that moist, open crumb, there was no going back, not even for sweet breads. It isn’t just the taste, either. Sourdough tends to sit better with me, while straight-yeasted dough often leaves me feeling bloated.

Naturally, I assumed this was as good as bread could get. Then I met sakadane (酒種), literally “sake seed.” People often call it “Japanese sourdough,” which is useful as a rough comparison but not a very precise one. Like sourdough, sakadane can be built through repeated refreshments to cultivate a stable population of yeasts and microbes. But where sourdough relies on wheat flour and water, sakadane swaps in rice and koji, which gives it a very different character!

Where sourdough leans crusty and tangy, sakadane bread has a thin crust, a soft and moist shittori texture with delightful sweet notes. It’s well-inline with the flavor and texture profile of Japan’s fluffy fuwafua shokupan or the red-bean bun, anpan. That raises a bigger question: what exactly is sakadane, and why does it taste so distinctly Japanese? To understand sakadane, we have to learn a bit about sake and bread making in general. This article will be a hodgepodge of science and history. Next time I’ll get into my own experiments and experiences making sakadane bread.

Bread and Sake’s Meet-Cute

When we think of Japanese bread, we think of soft, fluffy, white shokupan. It seems to be true that this kind of bread is what sparked Japan’s bread culture.

Bread first came to Japan in 1543 via Portuguese traders and missionaries and thus Japan borrowed the word “pan” (パン) from the portuguese word, pão. Bread didn’t become a staple yet, mostly because the hard bread that survived the seatrip from Portugal to Japan and made it into the mouths of Japanese were probably not very attractive to the palate if you have other food at your disposal and are not a starving marin. And of course, Japan closed its border soon after that so there wasn’t much time for a bread culture to take hold and develop. Fast-forward 300 years later, bread was mass-produced by a Japanese military science researcher as a convenient ration for soldiers.

Kimuraya makes bread feel Japanese

Bread was introduced to the masses a few decades later under sweeter conditions, after the Meiji restoration where Japan opened its island to the outside world again. At the time, Western-style bread was being introduced to Japan, but it was largely unpopular. The bread of that era was typically leavened using hops, which resulted in a hard texture and a bitter taste that did not appeal to a population accustomed to the sweetness and moisture of rice.

In the late 1800s, the samurai-turned-baker, Kimuraya had a new mission: develop a bread that was more suitable to Japanese palettes. With baker’s yeast hard to come by, he drew inspiration by sake-manju, a traditional Japanese steamed bun that was leavened using a sake-based fermentation process. Whereas sake-manju creates a one-use starter from sake kasu, the lees from filtering sake, Kimuraya found that if you take its base ingredients, rice, koji, and water you can cultivate a uniquely Japanese sweet and natural yeast that would last multiple bakes. And so in 1874 when the old-school anpan bakery came out with the adzuki-filled sakadane anpan. 150 years later, the original starter is alive and bubbling today where it can cozy up in its “sakadane Room” kept at exactly 27°C and 70% humidity, managed by only a few designated “Seed Masters” (Taneshi).

Kimuraya’s achievement was not just inventing a successful starter. It was making bread feel less foreign. By building leavening around rice and koji rather than hops or wheat alone, sakadane produced a loaf that made more sense to Japanese tastes: softer, sweeter, and closer in spirit to existing fermented foods. That is also why sakadane should not be treated as merely “Japanese sourdough.” It may occupy a similar role in breadmaking, but it works through a different fermentation logic.

Sakadane vs. Sourdough

Both starters leaven bread, but they are built on different raw materials and follow different fermentation logics. Sourdough is a flour-based culture shaped largely by wheat or rye and the microbes that come with them. Sakadane is a rice-and-koji culture, where koji enzymes begin converting rice starch into sugars early on, creating a sweeter and more readily fermentable environment for yeast.

In mature sourdough, lactic acid bacteria usually dominate, with yeasts working alongside them, and the balance of lactic and acetic acids helps shape flavor, structure, and keeping quality. sakadane can also acidify and select for yeast over time, but it is not simply sourdough made with rice. Its sugar economy is different. Flour-based sourdough gradually unlocks sugars as fermentation progresses, while sakadane starts with koji already doing a good part of the digestive work.

Why sakadane dough tastes different from sourdough

Koji’s enzymes give sakadane a boost. Anyone who is friends with koji will be familiar with amylase, the two enzymes are the catalysts that break down starches and proteins, famously making sweet amazake (more amylase) or that umami-rich soy sauce (more protease). Whether working with sakadane or not, bread baking also relies on these two enzymes, among others, but sakadane brings extra along.

In bread, amylases break starch into fermentable sugars, which can support yeast activity, browning, softness, and moisture retention. Proteases break down proteins, which can make dough more extensible and the crumb more tender. That helps explain why sakadane breads are so often described as soft, moist, fragrant, and slow to stale.

Sourdough has enzyme activity too from flour and microbes, but when you use sakadane, you aren’t only adding fermentation microbes, you’re also adding koji’s enzymes that influence dough properties. This extra enzyme dose from koji in sakadane often accounts for faster browning, a softer crumb, and sometimes more dare slackness if the fermentation is warm and long.

Where the “sake” in sakadane comes from

The “sake” in sakadane points to its lineage. When Western-style bread began taking hold in Japan, bakers drew on sake-making logic, specifically mizumoto (水酛), meaning “water origin”1, a starter logic as a way to create reliable fermentation using materials already close at hand.

Anyone familiar with doburoku making might be familiar with this approach. The mizumoto method starts with a clever pre-step: you first create a soyashi-mizu (そやし水) literally “starter water”, which is allowed to acidify and become microbially selective toward lactic acid bacteria. That prepared liquid is then used to build the main ferment with steamed rice and koji. In other words, like sourdough, a starter is not built in one step. It begins by preparing an environment where the right microbes are more likely to thrive.

That soyashi-first step matters because acidity helps protect the ferment, while koji simultaneously breaks starches and proteins into sugars and amino acids that support yeast growth. So sakadane is a starter shaped by both microbial selection and enzymatic pre-digestion.

Balancing acidity and temperature

Acidity and temperature are the two main variables to keep a close eye on. In sourdough, pH drops as lactic acid bacteria mature the culture. sakadane tends to taste less sharply acetic than many sourdoughs, in part because its rice-koji environment and fermentation style tend to favor a gentler acid balance.

Temperature matters here too. Warmer conditions speed up both fermentation and enzyme activity, which can be helpful up to a point, but can also push the dough toward excess softness and slack dare if things go too far.

Broadly speaking, sourdough and sakadane both raise bread, but they do not get there by the same route. Sourdough is mostly a flour-and-acid story. Sakadane is a yeast-and-enzyme story shaped by rice, koji, acidity, and temperature. Rather than thinking that sakadane is a “koji sourdough”, a better mental model is that sakadane is a pre-digesting rice-koji starter that can make bread beautifully soft and aromatic!

Eating and Making sakadane

Eager to taste a bite of this dough-y bliss? There are bakeries scattered around Japan that specialize in this treat making anything from sakadane shokupan to sakadane baguettes. If you aren’t in Japan, well…you’ll just have to make it yourself. In the next article, we will shift from understanding sakadane to working with it, exploring several methods for preparing the starter and how it can be incorporated into bread recipes. Feel free to make some koji to prepare while you wait.

Want more? Check out episode 29, “when sourdough and koji meet” from the Fermentation Cast.

Sources

• Akiyama, Y. (1980). Mizumoto ni kansuru seitaigakuteki kenkyu [Ecological studies on mizumoto]. Journal of the Brewing Society of Japan, 75(4), 314–319. https://doi.org/10.6013/jbrewsocjapan1915.75.314.

• Akiyama, Y. (1983). Mizumoto to sakadane pan [Mizumoto and sakadane bread]. Journal of the Brewing Society of Japan, 78(12), 925–927. https://doi.org/10.6013/jbrewsocjapan1915.78.925.

• American Society of Baking. (n.d.-a). Amylase. https://asbe.org/article/amylase/.

• American Society of Baking. (n.d.-b). Protease. https://asbe.org/article/protease/.

• Ando, S. (n.d.). Sakadane ni tsuite no ohanashi [About sakadane]. Panpedia. https://www.panpedia.jp/lesson/pdf/71-7.pdf.

• Chowdhury, M. A. H., Sarkar, F., Reem, C. S. A., Rahman, S. M., Mahamud, A. G. M. S. U., Rahman, M. A., & Ashrafudoulla, M. (2024). Enzyme applications in baking: From dough development to shelf-life extension. International Journal of Biological Macromolecules, 282, Article 137020. https://doi.org/10.1016/j.ijbiomac.2024.137020.

• Gänzle, M. G., Loponen, J., & Gobbetti, M. (2008). Proteolysis in sourdough fermentations: Mechanisms and potential for improved bread quality. Trends in Food Science & Technology, 19(10), 513–521. https://doi.org/10.1016/j.tifs.2008.04.002.

• Kawai, H. (1996). Nihon no pan-dane—sakadane—no kigen to sono hakko tokusei [The origin and fermentation characteristics of the Japanese bread starter sakadane]. Journal of the Brewing Society of Japan, 91(5), 311–317. https://doi.org/10.6013/jbrewsocjapan1988.91.311.

• Kimuraya Sohonten. (n.d.). Kimuraya no ayumi [History of Kimuraya]. https://www.kimuraya-sohonten.co.jp/ayumi

In Japan, we can find special labs that will test our koji and provide us with a nicely detailed description of the quality of the koji and how to improve it if needed. For the majority, however, this is not a viable option and we need the tools to train our senses. We will build our own internal ‘lab’ looking at haze, timing, color, and form of the final rice koji.

Haze: the clearest visual clue

Haze is the visible mycelium (hyphae) growing on and into the grain. In practical terms, haze is our best “at a glance” indicator that the mold is active, reflecting active enzyme production.

There are two main places haze shows up:

• Surface haze: growth on the outside. It shows up first and is easiest to spot.

• Internal haze: growth inside the grain as the mold penetrates the surface of the substrate. It develops later, and is often what makers are aiming for when they want stronger, more even enzymatic development across the batch.

Once we understand those two “where” categories, we can peek deeper to see how haze is distributed, and whether it’s desirable for our purpose.

Koji Haze Cheat Sheet (patterns + quality terms)

Location terms

• Haze-mawari (破精廻り): surface spread of mycelium

• Haze-komi (破精込み): internal penetration into the grain

Coverage / style terms with cross-sections

High-performing koji

The following tend to deliver strong enzymatic activity and consistent results across most applications. If your koji cross-section looks like this, total bragging rights.

• Sō-haze (総破精)

  • Look: strong overall coverage with good internal growth

  • Taste: Often more α-amylase-leaning, so sweetness is a tad delayed (maltose-first)

  • Used in: Junmai sake for full-bodied notes

  

• Tsuki-haze (突き破精):

  Look: patchy surface but strong internal penetration

• Taste: Often more glucoamylase-leaning, so it can taste sweet immediately

• Used in: Ginjō/Daiginjō aiming for lighter, cleaner profiles

  

Koji seeks out moisture. If the rice surface stays moist, growth favors the surface. If the surface is relatively dry, hyphae “drill” inward to find moisture.

Underperforming koji

If your koji looks like any of the following, stay positive and consider it a learning experience.

Nuri-haze (塗破精)

• Look: thin “painted” surface coverage; glossy or wet - like the growth won’t stay

• Taste: Weak taste; more like plain rice than sweet, chestnut-y koji

• Reason: too much surface moisture, insufficient draining, too-high humidity, or not enough airflow

• Risk: encourages bacterial growth and can suppress healthy filament formation

  

Haze-ochi (破精落ち)

• Look: weak or incomplete growth

• Taste: Like hard steamed rice

• Reason: temperature stress, drying out mid-run, uneven mixing, or microbial/environmental competition

Baka-haze (馬鹿破精)

• Look: Can first appear impressive and fluffy, but it is over-agressive overgrowth that can collapse and degrade quality

• Taste: Overpowering flavors

• Reason: bed too thick, poor cooling, too high incubation temperature, delayed mixing

Timing: “aesthetic” isn’t always “powerful”

Modern koji culture loves photogenic results: bright white, spotless bricks that look like they belong in an art gallery. But “Instagram-perfect” doesn’t automatically mean “high-performing.” As mentioned with haze, looks can be misleading: a batch can be very white on the outside, yet not be deeply penetrated. The opposite can also happen, where the substrate seems less “perfect” but performs beautifully.

Loose grains evenly coated with white growth often allow better internal penetration (haze-komi), which can support more uniform enzymatic development. That said, loose grain isn’t automatically a sign of quality either, as it can also reflect weak binding, handling issues, or uneven growth. The point is, don’t judge by one cue alone.

Timing matters because haze development generally progresses in a predictable direction:

1. surface haze appears first

2. internal penetration ramps up later (often peaking around 40–44 hours in many rice koji schedules)

3. if it keeps going long enough, the mold may shift into sporulation

Stopping too early can put a break on enzyme potential. Letting things run too far can push into sporulation, the mold shifting into a reproductive phase. Sporulation which can be desirable in some ferments, like shoyu (soy sauce) and undesirable in others, like amazake.

Color: what stage you’re in and what your koji is cut out for

Color is the most obvious marker, and tells you what stage you are at in koji production.

• White haze: usually signals active growth

• Green coloration: generally indicates sporulation

For miso, heavily sporulated koji is often avoided because it is said that it can contribute bitterness or harshness, which could be a disaster if your heart is set on a sweet, mellow miso.
For shoyu, sporulated rice koji has historically been used and even intentionally pushed green, partly because “green” made it obvious the koji had reached a late stage. Many modern producers don’t need to rely on full green as a marker anymore, thanks to improved control, monitoring, and a clearer understanding of when koji has reached the maker’s preferred endpoint.

If the koji doesn’t seem perfectly suited for your initial use, don’t sweat it. You can still turn it into another delicious creation. If the rice koji goes too green for miso, it may still shine in shoyu. And if your koji didn’t develop enough haze for miso, it might still be great for something like amazake. Don’t automatically throw it out, but match it to a fermentation where its current stage makes sense.

Ita koji vs. Bara koji

Koji commonly shows up in two forms, encouraging a different haze expression.

• Ita kōji (板麹): “block koji,” where grains bind together into a mat

  • tends to develop heavier surface mycelium that binds grains together.

  

• Bara kōji (バラ麹): “loose koji,” where grains remain more separate

  • often supports internal penetration and more grain uniformity.

Outside Japan, ita koji often gets extra love because it photographs well. Traditional Japanese production, especially in sake, commonly favors the loose, bara koji. Bara koji promotes internal haze, leading to better enzyme development, while block koji forms when the mold grows more on the outside, binding the grains together. For this reason, bara koji is generally considered superior.

Practically, block, ita koji holds more moisture and spoils faster, while bara koji is drier, stores longer, and is easier to distribute in commercial settings. Regional methods also play a role, Japanese makers often use higher temperatures (around 42 °C) for internal growth, while many Western makers favor cooler conditions (around 30 °C), which tend to produce more external mycelium and brick-like koji.

Nevertheless, there’s a time and a place for both. For home makers, this difference is usually less important than basic fundamentals (good inoculation, temperature/humidity control, mixing, and timing), so pick whichever catches your fancy. In professional settings, form and haze pattern can matter more because producers need repeatable performance and consistent flavor outcomes.

Seeing beyond the surface

Koji visuals are more than aesthetics: haze, color, and texture can tell you a lot about stage, readiness, and likely performance. Watching the shift from surface haze to internal penetration (and recognizing when the batch is drifting toward sporulation) helps us choose timing and intended use with more confidence.

Of course, a lot is occurring on a microscopic level, and getting a cross-section of a koji grain is not in the future of many home koji-makers. So, I turned koji’s growth, heat and enzyme activity into sound (sonification) and motion, to represent the koji process. I sketched the melodies; Duncan Geere at Loud Numbers handled the sound design, sonification, mixing, and mastering. Since we cannot smell or taste digitally, this video attempts to use the other two senses, sight and sound, to playfully unravel what is going on when koji is incubating.

Just as the video and sonification is imprecise and perhaps a bit ambiguous, it’s important to stress that we still don’t have universal, absolute rules for koji making. Different strains, grains, bed depths, airflow, temperature curves, and handling can change what “good” looks like. Even research can disagree across conditions. The best approach is part observation, part record-keeping, and part experimentation. Because koji is alive, we have to hand over some amount of control. So use your senses!

Sources

1. KojiWiki. Glossary of koji terms. http://www.kojiwiki.com/index.php/Glossary

2. The Society for Nada Sake Research (SNSR). Haze. http://www.nada-ken.com/main/en/index_h/132.html

3. Ito K, Gomi K, Kariyama M, Miyake T. Quantitative evaluation of haze formation of koji and progression of internal haze by drying of koji during koji making. J Biosci Bioeng. 2017 Jul;124(1):62-70. doi: 10.1016/j.jbiosc.2017.02.011. Epub 2017 Mar 31. PMID: 28373030.

4. Sakemove. 唎酒師への道（18）ー 製麹（麹造り）その③　酒質設計との関わりー (The Path to Becoming a Sake Sommelier (18) - Koji Making (Part 3) - Its Relationship with Sake Quality Design) http://sakemove.com/2017/06/30/seigiku3/

The result is a tea with the roasted smoothness of Hōjicha, layered with deep, malty sweetness and a subtle fruity funk from fermentation. It’s complex but not heavy, rich but not earthy, and entirely unique in the world of tea.

Why This Belongs in The Koji Collection

Most fermented teas rely on bacterial fermentation—heicha, Pu-erh, and similar styles develop their deep flavors from a mix of microbes breaking down the tea over time. Yamabuki Nadeshiko does something different. Instead of an unpredictable microbial community, this tea is fermented in a controlled process using koji mold, a long-trusted workhorse of Japanese fermentation. That connection alone makes it a perfect fit for The Koji Collection.

A Modern Approach to an Ancient Tradition

While the fermentation method might suggest something ancient, Yamabuki Nadeshiko is a 21st-century creation. It was developed by the Japanese company Riverson in 2007, with a patent granted in 2011. The fermentation method was designed by Denbei Kawamura, a key figure in Shizuoka’s ginjo sake industry and a major influence on modern sake brewing.

The tea itself is grown by organic farmers in Haruno-chō, Hamamatsu City, Shizuoka Prefecture, using a blend of three cultivars—Yabukita, Benifuuki, and Surugawase—at elevations of 300–500 meters.

Its name, Yamabuki Nadeshiko, is inspired by two flowers:

• Yamabuki (Kerria japonica), a yellow Japanese rose.

• Nadeshiko (Dianthus superbus), a delicate pink carnation.

A poetic name for a tea that’s anything but ordinary.

How It’s Made: The Fermentation Process

The production method borrows techniques from both Pu-erh tea and koji-based fermentations like sake and shochu. The process follows a carefully controlled sequence:

1. Freshly picked tea leaves are sterilized and moistened.

2. Black koji spores are introduced, triggering fermentation.

3. As the tea ferments, it naturally generates heat and must be mixed multiple times a day to keep conditions optimal.

4. Once fermentation is complete, the tea is sterilized again to halt further microbial activity.

5. The leaves are dried, evaluated, and packaged.

Unlike traditional Pu-erh, which relies on a mix of bacteria and fungi working together over months or even years, this process is precise, clean, and centered entirely around koji mold.

What It Tastes Like

If Hōjicha, brown sugar, and dried fruit had a meeting over a cup of sake, this tea would be the outcome. It’s roasted and malty, with layers of barley, dates, fermented plum, and treacle balanced by a hint of koji-driven umami.

What Makes It Special?

Beyond its flavor, Yamabuki Nadeshiko is a scientific curiosity. Researchers found that it has higher levels of gallic acid and citric acid than conventional green tea, plus two newly identified polyphenols—Teadenol A and Teadenol B—which have been studied for their potential to suppress diabetes-related enzymes.

There’s also a sustainability angle: this process works well with second-flush tea leaves, making use of harvests that might otherwise go to waste. By transforming these leaves into something high-value, it offers tea farmers an economically viable and environmentally friendly option.

A New Chapter in Koji-Fermented Foods

Koji has already transformed Japanese cuisine through sake, miso, soy sauce, and shochu. Now, it’s doing the same for tea.

With its unique flavor, health benefits, and sustainability perks, Yamabuki Nadeshiko pushes the boundaries of tea fermentation in an exciting new direction. It’s a must-try for tea lovers, koji fanatics, and fermentation geeks alike.

For anyone looking to explore the evolving world of koji, this tea proves that fermentation and koji innovation is still full of surprises.

Sources:

1. FAO - Tea.

2. Kawamura D.; 河村傳兵衛. Functional fermented tea and method for producing the same. JP2008263831A, November 6, 2008. https://patents.google.com/patent/JP2008263831A/en?q=(riverson+koji)&oq=riverson+koji .

3. Yamanashi H.; 山梨宏之; Kawamura D.; 河村傳兵衛. Semi-fermented tea and manufacturing method of the same. JP2014054219A, March 27, 2014. https://patents.google.com/patent/JP2014054219A/en?q=(riverson)&oq=riverson+

4. www.y-nadesiko.jp.

5. Osada, N. Yamabuki-Nadeshiko Tea : Organic Tea Farm in Haruno Town.

6. Koji Plum. Mei leaf. https://meileaf.com/tea/koji-plum/?srsltid=AfmBOopROhixnC2C8az-YHaIVMj4P163dGgO4W-UoeVlBbNyu0agHcWM

7. Soil Society of Japan 2013. Part 4. Organic cultivation technology of tea. Pages 394-395. http: www. japan-soil.net/report/ h24tebiki_04.pdf

8. Lin, M.-L. “Technical Development of Production and Products In Organic Tea Farming”. International Journal of Tea Science, Vol. 12, no. 01, Page 80. May 2016.

“I used to hate amazake,” she admitted. “Too funky. Too weird.”

Then she started making it with a special strain of koji spores, one bred specifically for amazake. And suddenly, she was hooked. No more earthy mushroom notes. No lingering koji funk. Just pure, creamy, chesnutty, rice sweetness.

Turns out, in Japan, koji makers often use different spores for amazake than they do for miso or soy sauce. Meanwhile, in the West, we tend to lump all "rice koji" together, missing out on the fine-tuned magic of specialized strains. The origins of this particular amazake spore were top secret, but Max was told she could get her hands on some—delivered discreetly in a plain package, as if it were a black-market treasure.

And honestly? It kind of is.

If you’ve never tried amazake, think of it as Japan’s ancient, fermented answer to a sweet rice pudding—except it’s a drink. Amazake is one of the purest expressions of koji’s enzymatic magic. When rice meets koji, starches transform into natural sugars, creating a drink that’s naturally sweet, thick, and almost impossibly comforting. Whether you sip it straight, cook with it, or just marvel at how rice and water can turn into something this good, amazake is worth a taste.

Let’s dive in.

Amazake is a traditional Japanese drink with a history that goes back centuries. Though hard to compare to anything else, its unique flavor is derived from rice koji, creating a subtle sweetness that must be experienced to be fully understood. If you haven't yet tried this delightful beverage, it's time to give it a sip and taste a part of Japan’s rich culinary heritage.

Amazake (甘酒) translates directly to "sweet sake," yet this drink is typically non-alcoholic and is made using only a few simple ingredients: rice, water, and koji. Served hot or cold, it can be consumed as a refreshing drink or used as an ingredient in a variety of dishes, from baked goods to sauces. With different preparation methods, amazake can range in consistency from smooth and liquid to thick and porridge-like. Additionally, amazake made with koji contains no alcohol, while versions made with sake kasu (sake lees) have some alcohol content, making it a versatile drink suitable for almost anyone.

What Is Amazake, Exactly?

Amazake (甘酒) literally translates to "sweet sake," but don’t let the name fool you—most amazake contains zero alcohol. The classic version is made with just rice, water, and koji, though there’s also a variation made with sake kasu (sake lees), which does contain some alcohol.

Depending on how it’s prepared, amazake can be thin and drinkable or thick and porridge-like. It’s enjoyed hot or cold, straight-up as a soothing drink or as an ingredient in everything from baked goods to sauces.

Amazake isn’t new—it’s been around for centuries, showing up in religious ceremonies, Edo-period street stalls, and even modern-day health trends. Thanks to its mild sweetness and easy digestibility, it has long been given to children, the elderly, and anyone in need of a quick, nourishing pick-me-up.

Amazake Through the Ages

Amazake-like beverages have been fueling people for over a thousand years. It likely traces back to ancient China, where a similar fermented rice drink called "Li" was consumed. In Japan, it appeared during the Kofun period (circa 300 AD) and evolved into the amazake we know today.

By the Meiji period (1868–1912), amazake had become a popular street food, sold by vendors carrying large barrels through town, shouting “Amaii! Amaai” (“Sweeeeet! Sweeeeet!”) like the old-school version of an ice cream truck. Some sellers even had a special tall kettle, heated over charcoal, to warm the amazake before serving it—cold amazake on one side, hot amazake on the other. A simple but effective way to serve it year-round and for all tastes.

It’s also been intertwined with rituals and festivals, like the "Amazake Koboshi" ceremony in Chichibu, where people pour amazake over each other to ward off misfortune. (Because clearly, if you’re drenched in fermented rice, bad luck can’t possibly touch you.)

From sacred legends to street stalls, amazake has been a constant presence in Japanese food culture—quietly persisting through centuries, evolving, and adapting.

Health Benefits of Amazake: Nourishment in Every Sip

Amazake isn’t just delicious—it’s packed with nutrients. Thanks to koji’s enzymes, it’s rich in:

• B Vitamins – Great for energy production and cell regeneration.

• Glucose – A natural brain boost, making it the original energy drink.

• Amino Acids & Probiotics – Good for digestion and gut health.

It’s also easy to digest, meaning kids, elders, and anyone with a sensitive stomach can enjoy it. You might even call it a "drinkable IV drip" because of how quickly the nutrients absorb.

Different Types of Amazake

Not all amazake is created equal. The base ingredients and fermentation methods can change the sweetness, texture, and acidity. Here are a few key variations:

Koji Amazake – The classic, non-alcoholic version made with rice koji, cooked rice, and water. Smooth, naturally sweet, and porridge-like.

Koji Amakoji – A more concentrated version made without added rice, using only rice koji and water. This results in a less sweet, deeper koji flavor, making it especially suited for sour koji strains.

Sake Kasu Amazake – Made with sake lees (a byproduct of sake brewing), this version has a slight alcohol content and is often served warm in winter.

Black Amazake – Fermented with Aspergillus luchuensis, which gives it a darker color and a tangy, citrusy kick. (Elad’s favorite)

Sour White Koji Amazake – Fermented with Aspergillus kawaii, this variation has a milder citric acid flavor than Black Amazake but retains the white koji color and a subtle brightness.

Sour Amazake – Left to ferment at room temp, allowing lactic acid bacteria to create a refreshing tartness. (Side note: Yes, "ama" means sweet, so calling it "sour amazake" is a bit contradictory, but language is weird like that.)

In Japan, 600+ manufacturers produce over 1,200 types of amazake, ranging from homemade to high-end craft varieties.

How to Make Amazake and Amakoji at Home

Making amazake is easier than you think, and the method you choose affects the final flavor:

Amazake Ingredients:

1 part rice koji : 1 part cooked rice : 2 parts water

Amakoji Ingredients:

1 part rice koji : 1 water

Instructions:

1. Combine everything in a container.

2. Keep it warm (~55°C) for 6–8 hours to ferment.

3. Once sweet and thick, refrigerate or dilute to taste.

Tips:

• Use dry or frozen koji for convenience.

• Make it overnight—it’ll be ready by morning

• Add fruit, substitute pumpkin for rice and experiment!

Not Just a Drink: Other Applications

Amazake is way more than just a drink—it’s a fermented sweetener that can be used anywhere you’d use sugar, honey, or even cheong.

Max’s top 3 uses:

• Amakoji + chestnut flour → crepes

• stirred into overnight oats with miso

• As a natural sweetener in marinades (but be careful, it burns quickly!)

Elad’s picks:

• Using amazake lees in sugar cookies

• Mixing amakoji into bread dough for extra depth

Final Thoughts: Why You Should Try Amazake

Amazake isn’t just a drink—it’s a cultural time capsule, a health food, and a secret weapon in the kitchen.

It’s also one of our all-time favorite koji products. Max likes it mixed with kefir, kinako goma, and miso, while Elad swears by citrusy black amazake. However you try it, amazake is proof that fermentation is pure magic.

So, what are you waiting for? Go ferment some rice.

Sources:

1. Hiroshi, F.; 藤井 寛. 甘酒のほん: 知る、味わう、たずね. Amazake book; 山川出版社, Yamakawa: Japan, 2023.

2. Hiroshi, F.; 藤井 寛. 元気をつくる!麹の甘酒図鑑; 主婦の友社, 2023.

3. H.T. Huang. Science and Civilization in China Vol.6 , Biology and Biological Technologies. Part 5: Fermentations and Food Science; Cambridge University Press, 2000.

4. あまざけ.com

5. Shurtleff, W.; Aoyagi, A. HISTORY OF AMAZAKE AND RICE MILK (1000 BCE to 2021); Soyinfo Center, 2021.

6. Oguro, Y.; Nishiwaki, T.; Shinada, R.; Kobayashi, K.; Kurahashi, A. Metabolite Profile of Koji Amazake and Its Lactic Acid Fermentation Product by Lactobacillus Sakei UONUMA. J. Biosci. Bioeng. 2017, 124 (2), 178–183. https://doi.org/10.1016/j.jbiosc.2017.03.011.

7. Kurahashi, A. Ingredients, Functionality, and Safety of the Japanese Traditional Sweet Drink Amazake. J. Fungi 2021, 7 (6), 469. https://doi.org/10.3390/jof7060469.

Note: This guide assumes you’re already familiar with koji basics—like what Aspergillus oryzae is, and how koji spores work. If not, head over to our "What is Koji?" article first.

What Koji Needs to Thrive

• Temperature: Most strains of Aspergillus oryzae like temps between 32°C and 37°C. Higher temps push spore growth, while lower temps hold it back a bit. For home-growing, stick close to 30°C and you’ll be golden.

• Oxygen: Koji needs airflow. Without it, the mold gets suffocated and growth slows. Regular stirring and maybe even a small fan can help.

• Humidity: Keep things humid to prevent drying out, but not too wet. Koji loves a well-moisturized environment but doesn’t want to swim.

• Nutrients: A nutrient-rich substrate like rice is perfect. Finer grains grow slower, so choose wisely depending on your project.

Essential Equipment for Koji Growing

Creating the perfect koji habitat can be as high-tech or low-tech as you like. Here's what you'll need:

• Heater: To keep that cozy 30°C.

• Humidifier: For steady moisture.

• Temperature Controller: To stay on top of the heat.

• Humidity Controller: Because koji likes it humid but not too damp.

• Chamber: You can get creative here. A Styrofoam box is a solid home option for holding in heat and humidity.

  Temperature Guidelines for Koji Cultivation

  The ideal growing conditions depend on your substrate (rice, beans, etc.) and what you want to make. Here’s a quick cheat sheet — these are by no means rules, just common patterns:

For now, we’re keeping it simple with what we think is the most straightforward method: 30°C with rice as a substrate. This beginner-friendly technique is versatile and works for most koji-based products. Once you’re comfortable with it, we’ll tackle more advanced methods and sprinkle in some Japanese terminology to expand your knowledge.

Step-by-Step Guide to Growing Koji at 30°C

Step 1: Prepare the Rice

• Soak rice overnight, rinse, and steam it until just done. The grains should be soft but not soggy—think "al dente" for rice. Over-steaming can lead to too much moisture, which spells trouble for your koji.

• Once steamed, let the rice cool down to around 28°C (82°F). Hitting exactly 30°C can be tricky at home, so aim for 28°C—by the time it’s all mixed, it should even out.

Step 2: Inoculate the Rice

• Spread the cooled rice on a tray, then sprinkle your koji spores evenly over the surface. Get in there (with gloves, of course) and mix it thoroughly, making sure every grain gets some spore love.

• Smooth the rice into an even layer and cover it with a cloth to maintain moisture.

Step 3: Set Up the Chamber

• Place the tray in a chamber (a DIY setup with a heater and humidifier works just fine) at 30°C and 75% humidity. You’re officially on koji watch duty now! Here’s a typical timeline:

Monitoring Timeline

• Hour 0 (Day 1, 20:00): Rice is mixed with spores and tucked into the chamber. Follow the spore packet’s instructions on quantity—about a tablespoon usually does the trick.

• Hour 24 (Day 2, 20:00): Stir the rice and reshape it into a mountain range-like formation to improve air circulation. You might notice a faint koji smell, which is a good sign!

• Hour 36 (Day 3, 08:00): Check for growth. You should start seeing some white fuzz creeping in.K

• Hour 42 (Day 3, 14:00): Keep an eye out for overgrowth. White is what you want—green, not so much. If there’s some green, don’t panic; just scrape it off. If the rice looks fully covered in white mycelium, your koji might be ready.

• Hour 48 (Day 3, 20:00): It’s koji time! The rice should be covered in a beautiful white mycelium. Use it immediately or store it in the fridge for up to a week. For longer storage, freezing is an option, especially if you plan to make sake.

You may think of those hour marks as a must check period and anything more from it you should judge by yourself if any more checkups or mixing is needed. For example if the koji is overheating for some reason another mixing is needed.

The rice should display the characteristic white mycelium growth without over-sporulating. Once it reaches this stage, the koji can be used or preserved for later use.

Is Your Koji Ready?

You’ll know your koji is ready when:

• The rice is evenly covered in mycelium. The color depends on the starting spore and if haze is desired for your application (more on this in the advanced series).

• It smells sweet and fragrant. The aroma should be distinct, like a cross between mushrooms and freshly baked bread.

• Bonus test: Split a rice grain in half—if you see mycelium all the way through, your koji is in great shape. Surface growth is nice, but internal growth means your koji is really thriving.

This guide walks you through a simple, effective method for growing koji at home. In future articles, we’ll dive into advanced techniques, alternative substrates, and the art of getting creative with your koji chamber setup.

Sources:

1. Murakami, H. Koji Studies (麹学); Japan Brewing Association: Tokyo, 1986.

2. Yamashita H. Koji Starter and Koji World in Japan. Journal of Fungi. 2021; 7(7):569. https://doi.org/10.3390/jof7070569

3. 務望月. 麹と味噌の品質. 日本釀造協會雜誌 1966, 61 (8), 682–686. https://doi.org/10.6013/jbrewsocjapan1915.61.682.

4. Yu, A. C. Haze - Japanese Wiki Corpus. https://www.japanesewiki.com/culture/Haze.html

5. Haze types - Koji Wiki. http://www.kojiwiki.com/index.php/Haze_types

6. Matsunaga, K.; Furukawa, K.; Hara, S. Effects of Enzyme Activity on the Mycelial Penetration of Rice <I>koji</I>. J. Brew. Soc. Jpn. 2002, 97 (10), 721–726. https://doi.org/10.6013/jbrewsocjapan1988.97.721.

7. Matsunaga, K.; Furukawa, K.; Hara, S. Effects of the Digestibility of Steamed Rice on the Mycelial Penetration of Rice <I>koji</I>. J. Brew. Soc. Jpn. 2003, 98 (7), 526–529. https://doi.org/10.6013/jbrewsocjapan1988.98.526.

8. Wisman, A. P.; Tamada, Y.; Hirohata, S.; Gomi, K.; Fukusaki, E.; Shimma, S. Mapping Haze-Komi on Rice Koji Grains Using β-Glucuronidase Expressing Aspergillus Oryzae and Mass Spectrometry Imaging. J. Biosci. Bioeng. 2020, 129 (3), 296–301. https://doi.org/10.1016/j.jbiosc.2019.09.016.

9. Sudo, S.; Koseki, T.; Kizaki, Y. Factors in the Formation of Haze. J. Brew. Soc. Jpn. 2002, 97 (5), 369–376. https://doi.org/10.6013/jbrewsocjapan1988.97.369.

10. Tatsurokuro, T.; 京都大学名誉教授栃倉辰六郎編著. 新増補 醤油の科学と技術. (Science and Technology of Soy Sauce); Japan Brewing Association: Tokyo, 2011.

11. https://www.nihonjouzou.co.jp/en/maruhuku/

Introduction Part 3: Koji’s Origins

Koji’s origins are a puzzle—a story pieced together from ancient records, culinary traditions, and a lot of educated guesses. To understand how this mold became the cornerstone of Japanese cuisine, we need to travel back to China, where its ancestor, qu, first emerged.

What is Qu?

Qu (pronounced “chu”) was the Swiss Army knife of fermentation in ancient China. Made from grains or legumes inoculated with a chaotic mix of molds, bacteria, and yeasts, it was a one-stop shop for brewing alcohol, making vinegar, and crafting fermented sauces. Qu’s microbial diversity made it versatile, but also unpredictable—you couldn’t always predict the outcome, but it usually led to something delicious.

The origins of qu are a little fuzzy (no pun intended). Archaeological evidence suggests it was first used between 5,000 and 3,000 years ago, but without modern documentation, pinning down the exact timeline is tricky. What’s clear is that qu played a crucial role in shaping fermentation traditions that are still alive today.

Where Did Koji Come From?

Despite its unpredictability, qu’s transformative potential didn’t go unnoticed. As trade routes blossomed and ideas flowed between cultures, qu made its way across borders. By the Yayoi period (300 BCE–300 CE), it had reached Japan, where it met a new climate, new ingredients, and a new culinary philosophy.

Once in Japan, qu began to evolve, shaped by the country’s unique climate, ingredients, and culinary philosophy. What started as a chaotic microbial mix transformed into something far more refined, that we now know as koji: a mold-based starter that became central to Japanese fermentation traditions.

First Mentions of Koji in Japan
According to scholars, the first recorded mention of koji in Japan could date back to around 725 CE. Of course, historical records around food can be a bit scarce, so who knows how long koji was quietly shaping Japanese cuisine before anyone thought to write about it. Hishio, a fermented product that could take the form of either a sauce or a paste, even makes a poetic entry in the Man’yōshū, Japan’s oldest surviving poetry anthology (compiled between 315 and 760 CE). However, it is unclear whether at the time this product was made with qu or koji as we understand it today.

醤酢尓 蒜都伎合而 鯛願 吾尓勿所見 水ク乃煮物

醤酢に蒜搗き合てて 鯛願ふわれにな見えそ水葱の羮

I long to eat sea bream with a hishio, vinegar and garlic sauce.

Do not show me that water scallion soup.

Man’yōshū, Volume 16, Poem 3829, (686-707) by Nagano no Imiki Okimaro

By the 10th century, koji was firmly established as a cornerstone of miso production, and by the 13th century, it was central to soy sauce-making. However, tracing koji’s history gets a little murky because the terminology wasn’t consistent. The Japanese used the word “koji,” while the Chinese referred to a similar concept as qu (or chu). The terms often overlap in historical texts, leaving historians with a linguistic puzzle that’s as complex as the fermentation process itself.

Refining the Mold: From Qu to Koji

A critical moment in koji’s evolution was the domestication of Aspergillus oryzae, a mold native to East Asia. Over generations, Japanese fermenters carefully selected strains of A. oryzae for their remarkable ability to produce enzymes that broke down starches and proteins with precision. If qu was a microbial symphony, A. oryzae became the soloist—a mold that could deliver consistent, reliable results. This refinement made koji an ideal tool for fermenting soybeans, rice, and other staples of Japanese cuisine.

Separating A. oryzae from qu’s diverse microbial cast was no small feat. Early Japanese fermenters used wood ash to create conditions that encouraged A. oryzae to flourish, effectively isolating the mold. Though the exact origins of this technique are hazy, its impact was profound, allowing fermenters to improve the quality and predictability of their koji.

Diverging Philosophies: Complexity vs. Precision

While qu in China retained its rich microbial diversity, embodying a philosophy of complexity and adaptability, Japan’s culinary traditions took a different path. The isolation of A. oryzae was made possible by the ingenious use of wood ash. This simple yet effective technique created conditions that favored the growth of A. oryzae over other microbes, allowing Japanese fermenters to refine their process and produce koji with remarkable consistency. By mastering this method, they unlocked the full potential of their ingredients and elevated koji into a tool of precision—an essential element of Japan’s most iconic fermented foods.

The Birth of an Industry

In the early days, koji spores were made at home—a craft deeply tied to everyday life and tradition. By the Muromachi period (1336–1573), this practice began to shift. Historical records suggest the emergence of dedicated spore producers who provided fermenters with reliable, high-quality koji spores. This marked the beginning of a more specialized industry, making koji production more accessible while further enhancing its consistency and quality.

By refining koji and embracing a deliberate, focused approach to fermentation, Japanese fermenters transformed it into an indispensable culinary tool. From miso to soy sauce and sake, koji’s role in shaping Japanese cuisine is a testament to the art and science of its evolution.

Wrapping it Up

Koji’s story is one of remarkable ingenuity and endless mystery. Long before Aspergillus oryzae was formally named in 1729, early fermenters had already mastered the art of isolating this mold—using techniques like wood ash to refine koji without the aid of modern technology. Their resourcefulness transformed koji from a humble starter into a cornerstone of Japanese cuisine.

Yet, much of koji’s history remains shrouded in ambiguity. Its journey from qu to koji, from a microbial mix to a precise fermentation tool, is a testament to the interplay of culture, environment, and human curiosity. So much has been lost to time or reinterpreted through shifting perspectives, leaving us with tantalizing fragments of its past.

As we explore these mysteries, one thing is clear: koji’s journey is not just a testament to fermentation, but to the boundless curiosity and ingenuity of the people who shaped it.

Sources

1. Anonymous, Manyoshu Translation. "The Manyoshu Anthology of Japanese Poetry." Web Archive, https://web.archive.org/web/20060519145719/http://etext.lib.virginia.edu/japanese/manyoshu/AnoMany.html (Accessed December 29, 2024).

2. Aoyagi, A.; Shurtleff, W. History of Koji - Grains and/or Soybeans Enrobed in a Mold Culture (300 BCE to 2021): Extensively Annotated Bibliography and Sourcebook.; Soyinfo Center, 2021.

3. H.T. Huang. Science and Civilization in China Vol.6, Biology and Biological Technologies. Part 5: Fermentations and Food Science; Cambridge University Press, 2000.

4. Machida, M.; Yamada, O.; Gomi, K. Genomics of Aspergillus oryzae: Learning from the History of Koji Mold and Exploration of Its Future. DNA Res. 2008 Aug;15(4):173-83. doi: 10.1093/dnares/dsn020. PMID: 18820080; PMCID: PMC2575883.

5. Murakami, Hideya. 麹学, Koji Studies, 1986. 6th edition published in 2018.

6. Sato (1963, p. 29). “Documents on Fermented Black Soybeans, Chiang, Miso, and Shoyu.”

7. Shogakukan. Man’yōshū, Volume 5 (Annotated Edition). Showa 61 (1986). Shogakukan, Tokyo, Japan.

8. Shurtleff and Aoyagi (1983). The Book of Miso, 2nd ed., p. 219.

9. Yamashita, H. Koji Starter and Koji World in Japan. Journal of Fungi. 2021; 7(7):569. https://doi.org/10.3390/jof7070569

10. Yokotsuka, T. (1986). Soy Sauce Biochemistry. Advances in Food Research, 195–329. https://doi.org/10.1016/s0065-2628(08)60350-x

For anyone venturing into the world of koji fermentation, you’ve probably heard the same two names tossed around: Marika Groen’s Cozy Koji and Nakaji Minami’s Koji for Life. Both are excellent beginner-friendly resources. But if you’ve mastered the basics and want a book to help you go deeper — or if you’re a total newbie with the ambition to dive headfirst into the craft — Nakaji Minami’s second book, 麹づくりと発酵しごと (Koji-Making and Fermentation Work), might just be the one.

While this book is currently only available in Japanese, don’t let that stop you — the pictures alone are worth the price. Even if you’re not fluent, it’s easy to follow along, thanks to the clear step-by-step instructions and stunning visuals. It’s the ultimate starter pack for anyone wanting to dive into koji, offering just the right mix of inspiration, guidance, and practical know-how to get you started and running.

What Makes It Special

Minami doesn’t just tell you how to make koji — he shows you. The detailed, step-by-step photos are one of the book’s biggest strengths, walking you through processes for rice koji, sour white and black koji, barley, shoyu, and even brown rice koji. Fermentation is a deeply sensory experience, and while a book can’t offer smells or tastes, Minami makes up for it by providing clear visual cues and instructions to guide you. Each chapter is concise, intuitive, and thoughtfully designed with color cues to split up sections, so you’ll feel confident following along, no matter your experience level.

I also love how Minami lowers the barrier to entry by emphasizing tools and methods accessible to most Japanese households. You don’t need a professional incubator or a ton of specialized gear to get started. All you need is a clean plastic bag, rice, spores, and a pocket to tuck your rice-filled bag in for warmth. And yes, I’ve tried it — it works!

The book doesn’t stop at methods. It includes “key recipes” in the back for each type of koji, highlighting Minami’s favorite ways to use them. These recipes range from simple applications to more ambitious projects, giving you something to strive for once you’ve mastered the basics.

Finally, the size of the book deserves a mention. It’s compact but dense, packed with enough information to keep you experimenting for months. Minami has managed to create a beginner’s guide that feels anything but basic.

A Few Challenges

No book is perfect, and 麹づくりと発酵しごと has its quirks.

For one, the constant references to other pages, footnotes and sections can be a bit distracting, particularly if you’re using a Kindle where flipping back and forth isn’t as easy.

The other notable gap is the lack of “why.” Minami doesn’t dive into the science behind his methods. Why start with 300g of rice? (My guess: it fits comfortably in the tools he recommends, but it’s not explicitly stated.) Why raise the temperature to 38–42°C during certain types of koji fermentation, only to lower it again in the final hours? If you’re the curious type — and let’s face it, fermentation tends to attract the curious — you’ll find yourself asking these questions.

To be fair, this book isn’t trying to demystify the science of koji. It’s a how-to, not a “why-so.” If you’re the kind of person who needs to know why things work, you’ll want to dig into other resources — and that’s exactly where The Koji Collection plans to step in.

Why I Bought It

I’ll admit, I’m a sucker for koji books — if it’s about koji, it’s probably already on my [virtual] shelf. But this one had me especially excited because I loved the aesthetics and clarity of Minami’s previous work. Beyond that, I’ve been eager to explore making bread with koji and natural yeast, a topic he explores here in depth.

What I love most about this book is how it moves beyond shio koji basics to showcase a more modern and inventive side of koji-making. Minami’s approachable methods and clear, thoughtful documentation have set the standards and been an inspiration for The Koji Collection books.

While I don’t know if we’ll ever match the stunning photography in his books, I hope we can address some of the gaps, like those pesky “why” questions, to make the art of koji-making even more accessible.

Final Thoughts

Whether you’re a total beginner or someone looking to expand your koji repertoire, 麹づくりと発酵しごと is a fantastic resource. Equal parts inspiring and practical, it’s the kind of book you’ll keep coming back to as you dive deeper into the endless possibilities of koji. Approach it like a cookbook: start by following the recipes and pictures exactly as shown. Once you’ve mastered the process, the real fun begins—experimenting, innovating, and uncovering the “why” behind the “how.” That’s where The Koji Collection comes in to guide your next steps. If you can get your hands on this book, don’t hesitate—it’s a worthy addition to any fermentation library.

Max Graze

Book Details

Author: Nakaji Minami

Print length: 96 pages

Language: Japanese

Publication date: November 14, 2024

Table of Contents

(translated from Japanese)

• Introduction

• Basic materials and tools

• Rice Koji (Kome Koji)

  • Making rice koji

  • Making rice koji (large quantities)

• Chinese steamer/stainless steel steamer

• Ziplock plastic bag

• Glass bowl

• Yogurt maker

• Extra: Pocket koji for small quantities

• Barley malt (Mugi Koji)

  • Making barley koji

• About Koji Mold

  • Three types of koji molds essential for Japanese fermented foods

• Black Koji and White Koji (Kuro Koji · Shiro Koji)

  • Making black and white koji

• The Story of Koji

  • A fungus cultivated and selected over a long history

• Brown rice malt (Genmai Koji)

  • Making brown rice koji

• Soy sauce koji (Shoyu Koji)

  • Making soy sauce koji

• About Koji Mold

  • How to use the ever-evolving koji mold

• Making soy sauce

  • The difference between artisanal soy sauce and raw soy sauce

• Various uses for Koji

  • Making sake yeast bread

    • Step 1: Brewing sake yeast and soyashi water/main brewing

    • Step 2: Sake yeast bread

  • Making miso

    • Sweet miso

    • Brown rice miso/barley miso

  • Making Amazake

    • Sweet rice sake

    • Black Koji Amazake, White Koji Amazake, Brown Rice Amazake

  • Sea bream sushi

  • Salted sweet sake pickled egg yolk rice / Yuzu-scented koji natto

  • Dried squid marinated in sweet sake / Fermented takara-zuke

  • Making soy sauce using sweet sake

  • Sweet sake peperon sauce / Umami miso gochujang / Sweet sake mala sauce

  • Garlic toast salad / Peperoncino

  • Tomato spicy tofu / Cucumber and chicken with spicy sauce

  • Boiled pork with gochujang / Bean sprout namul / Gochujang rice ball

• Making fermented seasonings

  • Soy sauce koji / Onion koji / White koji ponzu

  • Making dashi soy sauce

    • Dashi soy sauce

    • Tomatoes simmered in soy sauce / Lightly pickled avocado

    • Lightly pickled cucumber / Tuna and egg yolk rice bowl

• The Story of Koji

  • The Koji Tane Shop that Protects Japanese Food Culture

• Where to get tane koji

• Koji making Q&A

• Conclusion

Types of Fermentation: Microbes Doing Their Thing

Here are some of the big players in fermentation:

• Alcoholic Fermentation
  Yeasts like Saccharomyces cerevisiae are the sugar munchers behind alcoholic fermentation. When yeast cells dive into glucose, they pump out ethanol (the fun part) and CO₂ (the fizzy part), all while creating a cozy, low-oxygen environment they thrive in. This process doesn’t just create alcohol—it adds layers of flavor and texture, giving bread its soft crumb, beer its refreshing sparkle, and wines and spirits their nuanced aromas. Without yeast, many food and drink traditions would be a little flatter, a little duller, and definitely less lively!

  

  .

• Lactic Acid Fermentation
  This is the “sour” ferment that bacteria like Lactobacillus are known for. When they get involved, they convert sugars into lactic acid, creating that beloved tang you find in yogurt, sauerkraut, kimchi, and sourdough. Lactic acid acts as a preservative, dropping the pH to keep unwanted microbes at bay while adding complexity to the taste. So when you dig into a bowl of kimchi or spoon up some Greek yogurt, thank these bacteria for that irresistible mix of tangy, creamy, and downright mouth-watering flavor.

  

  .

• Acetic Acid Fermentation
  Acetobacter bacteria are specialists in turning alcohol into acetic acid, transforming a wine into vinegar, or cider into apple cider vinegar, with just a little time and oxygen. These bacteria require an open-air environment, making this type of fermentation a bit different from the airtight setups of many others. It’s a slower process, but the reward is a vinegar with complex notes of fruitiness, sweetness, and a whole lot of zing—perfect for preserving, pickling, or just drizzling on salads.

  

• Mixed Fermentation
  Sometimes, it’s a team effort — this is where Aspergillus oryzae (koji mold) comes in! In foods like soy sauce and miso, there is a fermentation assembly line. Koji enzymes break down grains and legumes, unlocking sugars and amino acids that other microbes can feast on. Then, lactic acid bacteria and yeasts get to work, adding layers of flavor, umami, and complexity. The result is an intense, savory depth that’s only possible through this collaborative fermentation.

  

  .

A Thought to Chew On: Isn’t it curious how we carefully cultivate specific koji strains, but often leave yeast and bacteria to chance, letting the environment decide which ones show up? It’s a reminder that fermentation is as much about what we control as it is about letting nature do its thing.

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Koji: The Catalyst of Fermentation

Once koji mold grows on a substrate (like rice, barley, or soybeans), it releases enzymes that break down starches and proteins into simpler components. It’s the catalyst that puts everything in motion, creating fermentation-ready ingredients that evolve into rich, complex flavors. This transformation also makes the food easier to digest and more nutritionally accessible.

• Amylases: break down complex carbohydrates (starches) into simpler sugars like glucose and maltose. In sake brewing, amylases convert rice starches into sugars, which yeast then ferments into alcohol. These sugars don’t just keep the yeast happy—they also add subtle sweetness and depth, giving sake its delicate, layered flavor profile and amazake its sweetness.

• Proteases: focus on breaking down proteins into smaller peptides and amino acids, especially glutamate, the amino acid key to unlocking that rich umami flavor. In foods like miso and soy sauce, koji’s proteases break down soybeans to release this savory glutamate, creating that deep, satisfying taste we crave in these ferments.

The Bottom Line

Fermentation is a hands-off process that transforms food, and koji is one of its key players. By breaking down starches and proteins, koji’s enzymes perform culinary magic—from the rich umami of miso to the smooth sweetness of sake. Understanding how koji works is like holding the keys to unlocking some of the most iconic flavors in Japanese cuisine—and beyond.

But koji’s story goes beyond flavor. Its journey spans centuries, from ancient China to its essential role in shaping Japanese cuisine. In the next section, we’ll dive into this fascinating history, tracing how a humble mold became a cornerstone of food culture.

Sources:

1. Encyclopaedia Britannica. (2024). Fermentation | Definition, Process, & Facts. Encyclopedia Britannica. https://www.britannica.com/science/fermentation 

2. 発酵のきほん . みんなの発酵. https://www.hakko-blend.com/study/ 

3. Zeng, C., Tagawa, Y., Yoshizaki, Y., Wang, T., Yamaguchi, M., Kadooka, C., Okutsu, K., Futagami, T., Tamaki, H., & Takamine, K. (2021). The expression profiles of acid-stable α-amylase and acid-labile α-amylase of Aspergillus luchuensis mut. Kawachii effect on the microstructure of koji and alcohol fermentation. LWT, 139, 110580. https://doi.org/10.1016/j.lwt.2020.110580 

4. Devanthi, P. V. P., & Gkatzionis, K. (2019). Soy sauce fermentation: Microorganisms, aroma formation, and process modification. Food Research International, 120, 364-374.

5. Yamashita, H. (2021). Koji starter and koji world in Japan. Journal of Fungi, 7(7), 569. 

6. Allwood, J. G., Wakeling, L. T., & Bean, D. C. (2021). Fermentation and the microbial community of Japanese koji and miso: A review. Journal of Food Science, 86(6), 2194-2207.

7. Oguro, Y., Nishiwaki, T., Shinada, R., Kobayashi, K., & Kurahashi, A. (2017). Metabolite profile of koji amazake and its lactic acid fermentation product by Lactobacillus sakei UONUMA. Journal of bioscience and bioengineering, 124(2), 178-183.

8. Diez-Simon, C., Eichelsheim, C., Mumm, R., & Hall, R. D. (2020). Chemical and sensory characteristics of soy sauce: a review. Journal of Agricultural and Food Chemistry, 68(42), 11612-11630.

9. Ito, K., & Matsuyama, A. (2021). Koji molds for Japanese soy sauce brewing: characteristics and key enzymes. Journal of Fungi, 7(8), 658.

Koji might seem like magic, but it's actually just a humble mold. Still, watching it transform simple ingredients into rich, complex flavors? That’s about as close to wizardry as you can get in the kitchen. This unassuming mold, Aspergillus oryzae, has been quietly shaping Japanese cuisine for centuries. Today, chefs and food enthusiasts around the world are tapping into its power to ferment, break down, and deepen flavors. Odds are small you have never tasted one of its products –from miso and soy sauce to sake and amazake—koji has been subtly making your meals tastier for years. 

But what does it actually taste like?

Koji’s flavor profile is unique. It’s often described as a gentle sweetness with a hint of nuttiness and a touch of umami. If you want to experience it firsthand, try sipping on some amazake or sake, and let your taste buds sort out the subtleties.

In this introduction, we’ll explore the origins of koji, how it works its moldy magic, and why it’s a staple in both traditional and modern kitchens. By the end, you'll not only understand what koji is, but also why this humble mold is making waves far beyond the sushi counter.

Discovering Koji

Koji refers to both a specific type of mold, Aspergillus oryzae, and the substrate (often rice, barley, or soybeans) that’s been inoculated with it. The mold works its magic on the grains or beans, breaking down their complex components—starches and proteins—into simpler ones, like sugars and amino acids, that give food deep, rich flavors and wonderful aromas.

Here’s where things can get a little tricky: since koji didn’t originate in English, the terms we use don’t always have perfect translations. It’s a bit like playing culinary charades—we generally know what we mean, but the terminology doesn’t always land neatly. The good news? You don’t need to know Japanese to talk about koji; just understanding how it works is enough.

• Koji: 麹 (kōji) – This is the general term for Aspergillus oryzae or other similar molds that ferment grains, beans, or starches. These molds break down complex ingredients into simpler, tastier components.

• Tane-koji: 種麹 – Think of this like koji’s “seeds,” or spores. Just as basil seeds sprout into a plant, these spores grow into koji when sprinkled onto a starchy base like rice, barley, or beans.

• "___ Koji": The fill-in-the-blank model for koji substrates. When you’re being specific, follow this format: rice koji, barley koji, oat koji, etc. It’s like saying “bread” without specifying if it’s sourdough, rye, or focaccia. Every type has its own character, but they all fall under the same fermentation magic of koji.

So, when you’re talking about koji, keep in mind: if it’s general, stick with “koji.” If you’re talking about the little mold-makers themselves, say “koji spores.” If you’re specifying what koji’s growing on (like grains or legumes), use the "___ koji" format. It’s a useful shorthand that helps us navigate the world of koji without tripping over too many language barriers.

In the end, what matters is understanding how koji works. Whether you’re talking about the spores or the finished product, the magic lies in its enzymatic breakdown. And don’t worry too much about the language—what really matters is how koji works its magic. Focus on the process, and enjoy the incredible flavors it creates.

The Role of Aspergillus oryzae

Aspergillus oryzae is a key player in the world of koji. This mold has been domesticated over centuries for its ability to produce a variety of enzymes, such as amylases and proteases, which do the heavy lifting in fermentation. These enzymes break down starches into sugars and proteins into amino acids—essential for creating the umami-packed flavors we associate with miso, soy sauce, and sake.

Don’t worry—you don’t need a microbiology degree to grasp koji’s magic. In simple terms, Aspergillus oryzae makes enzymes that break things down during fermentation, creating those mouthwatering final flavors. It has various strains, and your koji spore supplier will often describe them by the specific food or fermentation process they’re best suited for.

It’s also worth noting that while Aspergillus oryzae is the main koji mold, it’s not alone. Other strains like A. sojae and A. luchuensis play their roles in different fermentations, but A. oryzae remains the go-to for most traditional Japanese ferments. Depending on the strain, your koji may yield a slightly different flavor profile, which is why some koji makers get real nerdy about which spores are best for which foods. You can usually find detailed information online from suppliers about the specific strains you're working with and how to use them.

Wrapping It Up

In the end, koji is more than just a mold—it’s a bridge between simple ingredients and complex flavors, a humble kitchen tool that unlocks the hidden potential in everyday foods. Whether you’re crafting miso, brewing sake, or just experimenting with a new way to transform rice, koji’s enzymatic magic is there to guide you. So dive in, get messy, and let this remarkable mold show you just how tasty science can be.

The real fun begins when we get into fermentation, where koji’s enzymes really start to shine. In the next section, we’ll dive deeper into fermentation—how koji breaks down starches and proteins, the science behind those umami-packed flavors, and how you can harness this process to transform your own kitchen experiments.

So keep fermenting, keep experimenting, and most importantly—keep having fun with it. Koji is just the beginning!

Sources: 

1. Murakami, H. Koji Studies (麹学); Japan Brewing Association: Tokyo, 1986.

2. Declartion - Recognizing Aspergillus Koji as Japan’s National Fungus. https://www.jozo.or.jp/gakkai/wp-content/uploads/sites/4/2020/02/koujikinnituite2.pdf . 

3. 醤油の科学技術 (Science and technology of soy sauce); 好学, 2022.

4. H.T. Huang. Science and Civilization in China Vol.6 , Biology and Biological Technologies. Part 5: Fermentations and Food Science; Cambridge University Press, 2000.

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At its core, The Koji Collection aims to be a comprehensive resource for everything related to koji—not just its role in food but also its influence across various fields of study and practice. Naturally, food has our focus, but koji, or Aspergillus oryzae, has a far wider reach, and we plan to follow its stories wherever they lead.

Our goal isn’t to present some grand, ultimate text but to share knowledge—imperfect, evolving, and always expanding. Achieving that requires years of research, patience, and curiosity. We might not ever create a "finished" product, but at least we’ll have an archive in this Substack—a place to share what we’ve uncovered along the way.

As we continue our journey in writing this collection, we remain dedicated to ensuring that every element is crafted with care and precision. While it has taken years to come to fruition, we believe that focusing on quality over speed will ultimately produce something far more meaningful. Rushing the process would only undermine the depth and richness we aim to achieve. We are committed to delivering a story that resonates deeply with our readers, knowing that the time invested will result in a work that is truly worth the wait.

We have no set timeline and will take as long as necessary to ensure the quality we envision.

That said, let’s be honest: no book is ever truly complete. If someone claims their book is the definitive final word on a subject, well... it's probably time to explore other sources. No field of study can ever be fully "finished." There’s always more to learn and discover, which means The Koji Collection will always remain open-ended. And that’s exactly how we like it.

In the meantime, we believe in sharing what we learn as we go. This Substack, along with conversations and hands-on practice, is the best way to bring others along on the journey. The Koji Collection will grow not in isolation but through the connections we build, the feedback we receive, and the experiences we share with you.

Here’s what the collection includes so far:

• The Introduction Leaflet

• The KOJI Book

• The SHOYU Book

• The MISO Book

• The SAKE Book

• A Collection of MIRIN, AMAZAKE, SHIO KOJI, and SHOCHU

• The KOJI Additional Collection

• The RECIPE Book

For home makers, we’ll have The KOJI Book: At Home. This standalone guide will provide you with the information you need to get started making koji – no technical jargon, just straightforward instructions. You’ll also find foundational recipes for koji products, like miso (for everyone who keeps asking!) to help you get started. You won’t find koji spore-making instructions here – that’s best left to the experts.

All of these are in progress, except for The SAKE Book. While Elad, our founder, has researched and even worked a bit at a sake brewery, he hasn’t yet made sake at home. And as much as we enjoy venturing into new worlds, we won’t write about something we haven’t fully experienced ourselves. So, for now, the sake book is on hold until either we find a co-writer or gain the experience necessary to write it with confidence.

We don’t expect you to read this collection in a linear fashion, nor do we want you to take everything at face value. Instead, we hope you approach it as a living document—a system of knowledge that invites questions, doubts, and deeper exploration. If you find yourself asking, “But what about this?” or “Why is that?”—great! That’s exactly the response we hope for. Cross-reference other sources, challenge ideas, and join us in the learning process.

Even once it’s published, The Koji Collection won’t be the final word on anything. It will always be a work in progress. But we’ll get as close as we can to fulfilling this dream. Whether it becomes a series of bound books or scattered posts across the web, it will be something we’re proud of.

So, while it may take some time to bring it all to fruition, we would love your support as we work toward this ambitious goal.

How to Ask a Question:
Simply post your question in the comment section of the current Q&A, and we’ll address it in the next publication.

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