Anaerobic, carbonic maceration, co-fermented: understanding the fermentation behind 'new wave' coffees

There was a time when you chose a coffee by its origin: an Ethiopia, a Colombia, a Brazil. Then we learned to look at variety, altitude, roast. Today a new piece of information has taken over the best roasters' labels, and it sometimes changes the taste more than everything else: the fermentation process. It has become the playground of the most ambitious producers, those seeking to draw from a bean aromas no one suspected — tropical fruit, flowers, spices, sometimes notes so intense they disorient. The enthusiasm is such that the most-followed figure in specialty coffee, James Hoffmann, has made it the global event of autumn 2026: the Fermentation Project, a planet-wide tasting of one coffee fermented four ways, held on 3 October. If the subject deserves such a project, it's because it touches a simple, fascinating question: what does fermentation actually change in your cup? You don't need to be a chemist to understand it, nor to decide whether these coffees are for you. You just need to know what these words mean — and to learn to recognise them.

Let's start by dismantling a fear: fermentation is nothing dubious or artificial. It exists in absolutely every coffee in the world, whether it's advertised or not. Why? Because coffee is a fruit. The bean we roast is the pit of a small cherry, wrapped in a sweet pulp. From the moment of harvest, naturally present micro-organisms — yeasts and bacteria — feed on those sugars: that's fermentation. As they consume the pulp, they produce compounds (acids, alcohols, esters) that soak into the bean and shape part of its aromas. This process has always existed; what's new is that we've stopped merely enduring it and started steering it. Where the producer once let nature take its course, they now control the duration, the temperature, the presence or absence of oxygen, sometimes the yeasts themselves. Fermentation then becomes a genuine lever of flavour, on par with variety or altitude. It's that new control — not fermentation itself, which is as old as coffee — that defines the 'new wave' everyone is talking about.

Here's what you need to read any label. Washed removes all the pulp before drying: the fermentation is short and controlled, the cup comes out clean, precise, with frank acidity — it's the process that best lets the origin speak. Natural dries the whole cherry, bean inside: the fermentation is longer and more intense, the cup turns round, fruity, sometimes almost winey. Honey sits between the two, part of the pulp kept on during drying, for a balance between cleanliness and sweetness. So far, the classic trio. The new part comes next. Anaerobic ferments the cherries in a sealed tank, without oxygen: starved of air, the yeasts work differently and push the aromas toward the intense, the tropical, the spicy. Carbonic maceration, borrowed from wine, adds CO₂ to the tank: even more demonstrative profiles, notes of very ripe red fruit. Finally, co-fermented (sometimes 'infused') deliberately introduces selected yeasts, or even fruit or spices, to steer the flavour — and that's where caution begins, as we'll see right after. At a glance: the longer and more oxygen-free the fermentation, the further the cup drifts from the 'naked' bean toward the spectacular.

Coffee beans drying in neat rows, a key stage of coffee fermentation

This is the point almost no one explains clearly, and yet the most important one for the enthusiast. A genuine fermentation, even a very pushed one, transforms the bean from within: the aromas are born from a biological reaction on the coffee fruit itself. Nothing is 'added'; the producer creates the conditions, the micro-organisms do the rest. At the other end of the spectrum, some coffees labelled 'co-fermented' or 'infused' are put in contact with fruit (strawberry, cinnamon, lychee…) during processing — and there the line blurs. When a strawberry note comes from a controlled fermentation that revealed the bean's potential, it's high art. When it comes from a coffee literally steeped in strawberry, we're not far from a flavoured coffee that won't say its name. Neither is illegal or 'bad' in itself; but selling them at the same price and under the same vocabulary, without transparency, misleads the reader. Our stance is simple: a good fermented coffee should taste like coffee taken to its extreme — not like candy. Be wary of profiles that are too perfect, too identical from one lot to the next, or described as 'strawberry sweet'. A roaster's transparency about what was done remains the best mark of seriousness.

Theory will never replace your palate — and the good news is the experiment is easy to set up. Get two coffees with clearly contrasting processes: for instance a washed Ethiopian (clean, floral, bright acidity) and a natural or an anaerobic from the same continent (fruity, round, intense). Brew them exactly the same way — same method, same grind, same ratio, same water — so the only variable is the process. Then taste one, then the other, and back to the first. The difference leaps to the palate: where the washed is precise and crystalline, the fermented is overflowing, sometimes bewildering. Look for three things: the intensity of the fruit (discreet or explosive?), the sense of alcohol or very ripe fruit (typical of long fermentations), and the 'cleanliness' of the cup (crisp, or a little 'funky'?). There's no right answer: some love the exuberance of an anaerobic, others prefer the clarity of a washed. What matters is knowing what you feel — and, this time, putting words to it. That's exactly the exercise the Coffee-Note notebook is built to hold.

A cup of coffee and an open tasting notebook on a table, comparing two processes side by side

Five shortcuts come up again and again; let's untangle them. First, 'fermented = alcoholic': no, roasting removes the alcohol; what you perceive is an aromatic note evoking alcohol or very ripe fruit, not ethanol in your cup. Second, 'anaerobic = better': false, it's a style, not a mark of quality; a failed anaerobic is far more disappointing than a perfect washed. Third, 'it's a fad that will pass': unlikely — directed fermentation has been studied seriously for some fifteen years and is now part of producers' palette. Fourth, 'fermented = not natural': on the contrary, fermentation is the most natural process there is; what changes is the degree of control applied to it. Fifth, 'all fermented coffees taste the same': precisely not — between a delicate honey and an explosive carbonic maceration, the gap is enormous, and that's the whole point of learning to tell them apart. The only honest rule: assume nothing, taste, and form your own opinion.

Fermentation may be the best possible subject to start keeping a notebook, because it makes the differences obvious: even a beginner's palate senses the gap between a washed and an anaerobic. Get into the habit of noting, for each coffee, its process as printed on the bag — washed, natural, honey, anaerobic, carbonic maceration, co-fermented — next to the aromas you actually perceived. Very quickly, patterns emerge: maybe you discover you love Ethiopian naturals but that very fruity co-ferments tire you, or the reverse. These are your own reference points, the ones no guide can give you. Note the roaster too: those who nail fermentations become safe bets to follow. Over the weeks, your notebook stops being a collection of notes and becomes a map of your taste — the tool that turns 'I liked it, I think' into 'I know exactly what I'm looking for'. That's the whole purpose of Coffee-Note: to make every cup an occasion to learn, one sip at a time.