What Is Fermented Coffee? Passing Fad or Bold New Trend?

Ever heard of fermented coffee? Now, I know what you’re thinking: coffee’s already fermented, so why mess with a good thing?

Well, fermented coffee beans are a trend that’s here to stay. Due to high demand in the specialty coffee sector, roasters are rethinking their value-addition strategies. Fermenting coffee was one of those strategies.

I’ve tried a few fermented coffees – I especially love a good whiskey coffee– and I can tell you they rock! So, if I’ve aroused your curiosity enough, let’s get to learning all about these unique brews.

Overview: Fermentation 101

The process of fermentation is as old as civilization itself. In fact, Egyptian hieroglyphs show that their brew masters were making beer as early as 6,000 BCE. Besides, the very origin of coffee brewing began with fermentation. I’m sure you’ve heard of the legend of Kaldi, the Ethiopian goat herder who discovered coffee’s magical qualities circa 850 CE?

Anyway, back to our topic! What is fermentation? In general terms, fermentation is an anaerobic metabolic process. Beneficial microbes, such as yeast, bacteria or mold, convert complex sugars and proteins into simpler organic compounds. The process almost always results in the release of carbon dioxide and alcohol.

Ever had sauerkraut, kefir, kimchi, kombucha or sourdough bread? Then you had fermented foods. Classed as superfoods, they rank highly for probiotics, antioxidants and anti-inflammatory properties.

It was just a matter of time before coffee producers stood up and took notice. With the rise of fourth-wave coffee, specialty roasters began experimenting with new and exciting ways to add value to their beans. As a result, it wasn’t just wine that had the dibs on the fermentation process!

And so began the roller coaster ride. Roasters, especially, saw the potential of leveraging the power of good bacteria, food-grade mold or wine yeast, to enhance the flavor of a green coffee bean.

But hang on a minute, don’t all coffee beans undergo post-harvest fermentation, anyway? You’re right, they do. But not in the same way as controlled fermentation.

After a harvest, coffee farmers carry out coffee processing as value addition. Through natural fermentation processes they produce washed, semi-washed, honey or natural-processed coffee.

But this is as far as it goes for regular coffee production. After this, farmers grade, sort and pack their beans for roasting.

Fermented coffee, as you’ll soon see, takes a whole other approach.

What Is Fermented Coffee?

Otherwise known as cultured coffee, fermented coffee ain’t your regular cup of joe. Imagine single-origin coffee beans but with a whole new twist. Popularized by Australian coffee visionary Sasa Sestic in 2015, these coffee beans have taken the world by storm.

So, what does this fermentation involve? For starters, instead of heading straight into the roasting process after normal processing, these beans take a detour.

Now, it’s important to note that we’re talking about controlled fermentation here, not letting these beans sit and rot, willy-nilly. That would be downright hazardous!

During this controlled fermentation stage, natural enzymes and microorganisms work their magic. They break down complex carbs, protein and other compounds into fermentable sugars and organic acids. Other compounds include carbon dioxide and alcohol. On completion, these beans get dried and roasted just like any other coffee.

Brewing fermented coffee unlocks a whole new world of flavors, kicking things up a notch. That’s the magic of fermentation in coffee, you see – it enhances flavor profiles in a way that regular coffee processing can’t.

Fermented Coffee vs Regular Coffee

So, apart from how they go through the value chain, what’s the difference between fermented and regular coffees?

For starters, the fermentation of regular coffee occurs with washed and semi-washed coffee processing. These processes use plain water, no additions. Water helps enzymes in the bean break down complex sugars and protein.

A similar process happens with honey and natural-processed coffees. Here, coffee producers sun-dry coffee in parchment or cherry form. The sun’s heat ferments these beans and cherries via saccharification, producing simpler sugars and new, aromatic flavor compounds. Incidentally, this tiny amount of sugar is what gives coffee its sweetness and smooth mouthfeel.

In contrast, roasters leverage the power of microorganisms, with the fermented coffee process. Lactic acid bacteria (Lactobacillus) and wine yeast (Saccharomyces cerevisiae) are top choices. They may also mix coffee with fruit, pulp and juices to enhance this process.

The result is a brewed coffee with unique flavors and tasting notes. You get these funky, fruity, umami and sometimes boozy notes you just won’t find in a regular brew.

Examples of Fermented Coffee

From fruity naturals to experimental anaerobics, there’s a fermented coffee for every palate. Each process imparts unique flavor profiles to various origin coffee beans. 

Let’s look at a few of the more popular coffee fermentation processes.

Barrel Aged Coffee

Now, you may be familiar with barrel-aged whiskey, rum and wine, but barrel-aged coffee? What in the coffee world is going on? Aren’t we taking things a bit too far?

Well, yes! And that’s the whole point; these coffees are meant to up the ante.

How does it work? To begin, producers place premium green coffee beans (with the mucilage or husk still on) into retired distillery oak barrels. Over two to three weeks, something magical happens. The beans take on the barrel’s residual flavors, developing layers of depth and complexity. Afterward, producers hull the beans to remove the husks in preparation for roasting.

The type of barrel used has a significant impact on a coffee’s flavor profile. Bourbon barrels impart a rich, sweet complexity, while whiskey barrels add a peaty smokiness. On the far side of the spectrum, wine barrels infuse coffee with sweetness and fruity undertones. The same goes for rum barrel-aged brews, which are full of spicy and tropical fruit notes.

In short, each batch of fermented coffee beans captures the essence of the alcohol that went before.

But you’ve got to be super careful! Take the beans out too early, and there’ll be hardly any flavor transfer. Leave the beans in too long, and the flavor will be too intense, ruining the coffee. Roasters in the West are all about this coffee trend as they can easily source barrels from top-tier distilleries.

Needless to say, barrel-aged coffee is trendy, especially with folks who love boozy coffee. It all makes sense if you think about it – coffee and alcohol are a match made in heaven!

Fruit Fermented Coffee

Fruit-fermented coffee isn’t just a novelty. Coffee cherries are fruits, and coffee beans are the seeds of that fruit. Thus, fermenting coffee beans with fruit to enhance flavor makes a lot of sense. Many producers in Ethiopia and Colombia (and famously Australian roaster Sasa Sestic) experiment with this type of fermentation.

Popular fruit choices include grapes, passion fruit, oranges, strawberries and sugar cane juice. In some instances, producers add wine yeast to speed up the process.

The first type of fruit fermentation involves placing the beans in a sealed container with fruit pulp or juice. Then, microorganisms work their magic for 24-36 hours, fermenting natural sugars in the fruit. This “wet” process gives rise to flavor compounds that infuse the beans.

The second type of fruit fermentation is entirely “dry.” It does away with the fermentation tanks altogether. Like natural and honey processing, roasters place green coffee beans, interspersed with fruit or fruit pulp, on raised beds. They then dry these beans under the tropical sun for 2-6 weeks, turning them constantly to ensure a decent flavor transfer. 

Despite the clear benefits, fruit fermentation is tricky and requires careful management. There’s a real chance of everything going belly up!

Roasters must control the ratio of fruit to coffee carefully. Other controllable factors include fermentation time, fermentation conditions, temperature and hygiene. It would be a sad day indeed if a producer went through all this trouble to yield an expensive but bad-tasting fruit-fermented coffee!

Anaerobic Coffee

Anaerobic fermentation is a unique process that ferments coffee in an oxygen-free environment. And this process is at the forefront of the coffee fermentation trend.

To begin, roasters seal whole cherries in airtight fermentation tanks. This restricts oxygen flow. In this environment good bacteria, typically Lactobacillus, thrive. The process can take as little as three hours to several days.

As a result, these microorganisms produce unique flavor compounds and plenty of lactic acid. The lipids, proteins and organic acids present in the cherries turn into ethanol. In turn this changes the structural composition, pH and smell of the coffee mucilage.

When dried, hulled, roasted and brewed, these fermented coffee beans are sweet, with fruity, floral and winey notes. They also have a smooth mouthfeel, clean finish and lower acidity.

As anaerobic processing blurs the boundaries between wine and coffee making, it embodies the very essence of innovation in the coffee industry. Roasters in Central America, Brazil, Australia and Ethiopia favor this type of coffee fermentation.

Koji Fermented Coffee

If there’s one thing the Japanese understand, it’s fermentation! You only have to look at some of their delicacies – sake, miso, soy sauce and nato (a funky, fermented soybean) – to understand why.

So, it’s no surprise that Koji fermented coffee tops this coffee niche. It’s no surprise either that its inventor, bioscientist Koichi Higuchi, chose a culture of Aspergillus oryzae – a food-grade mold the Japanese use in many foods – to make Koji coffee.

To kick start fermentation, roasters mix ripe coffee cherries with a fine powder of Japan’s national mold, Koji, and ground rice. They then allow these cherries to ferment in a controlled environment for 24-72 hours.

Next comes the drying stage in special silos. Here, they keep the temperature range between 68-93 degrees Fahrenheit (20-34 degrees Celsius). This fermentation stage takes 36-48 hours.

During this aerobic process, koji mold breaks down the complex sugars and proteins in the coffee cherries. Unique aromatic compounds (fermentable sugars, glutamates and amino acids) result. These radically transform the coffee’s flavor profile, sweetness and mouthfeel. After fermentation, roasters pulp, dry and roast the coffee beans to perfection.

Koji, or oryzae coffee, is an unusual, umami-rich brew. Those who love this coffee praise its fruity undertones, sweet taste and substantial body. Its popularity steadily grows among coffee enthusiasts intrigued by the Japanese coffee scene.

What Does Fermented Coffee Taste Like?

That’s not easy to answer, but I’ll do my best! Generally, fermented coffees have a noticeable aroma, complex body and depth of flavor. The taste is very different from regular coffee; I’d even go as far as to say they’re like “regular coffee 2.0.”

Some fermented coffees taste sweet and bright, alive with the sweetness of sugar and discernible flavors of fruit and wine. Imagine tart citrus, juicy berries and a trace of stone fruit. These profiles are typical in Koji, fruit-fermented and wine barrel-aged coffees. 

But it doesn’t stop there. Oh no! With liquor barrel-aged coffee, you might notice hints of peat and smoke, akin to roast barley or rye.

Let’s not forget about the acidity. These coffees, particularly the anaerobic-fermented ones, have a bright, yet subtle acidity. You know, the acidity that wakes your senses and keeps you returning for more? They also boast a clean finish and smooth mouthfeel.

Come to think of it, Indonesian Sumatran, Indian Malabar, and the infamous civet cat poop coffee embody this trait. These regular coffees kinda undergo double fermentation. As a result, they naturally have a lower acidity and moisture content. Only the first coffee acquires these traits in a fermentation tank, the second in a silo and the third in a civet cat’s stomach!

On the whole, I’d recommend enjoying fermented coffee as a blonde to medium roast brewed as French press, cold brew or pour-over. These brewing methods bring out their best qualities.

And don’t worry, you won’t risk a DUI after enjoying a cup of barrel-aged coffee! Any alcohol and probiotics present dissipate during roasting.

Is Fermented Coffee Healthier?

As a coffee pro, I always look at the health benefit claims of any coffee from a balanced perspective. I urge you to do the same.

Some diehards claim that fermented coffee is the healthiest coffee. They claim it enhances the presence of certain antioxidants and bioactive compounds. This coffee, they also insist, reduces nausea and is easier on the stomach. This might bring relief to Crohn’s disease and IBS sufferers. But then again, I’m no doctor, so I cannot verify these claims.

There’s no question, fermentation methods can significantly impact a brew’s nutritional and flavor profile.

But there are potential risks. These processes mostly occur in the tropics where the heat, bugs and dirt are forever present. Also, uncontrolled microbial activity and a lack of proper quality control may compromise the integrity of a brew. So it’s not a question of whether fermenting coffee is healthier, but more about how a producer executes the process.

Ultimately, like with protein, mushroom, maca or enzyme coffee, the scientific research on the health benefits of fermented coffee remains inconclusive. My advice? Do your research. And as with everything, enjoy this coffee in moderation.

Final Thoughts: Fermented Coffee Is Here to Stay

In closing, fermented coffees are true flavor game-changers for the coffee enthusiast.

They represent an exciting frontier in the ever-evolving world of specialty coffee. The abundance of complex flavor profiles and vibrant but subtle acidity delivers a sensory journey like no other. As such, they’re often among the most expensive coffees in the world.

Granted, this brew may not be for everyone. But if you want to level up your coffee routine, I urge you to give this coffee a shot. But I’m warning you, once you go fermented, you’ll never go back!

Fermented Coffee FAQ