The bag says anaerobic. Or honey processed. Or 72-hour co-fermented. Maybe all three.
If you've been buying specialty coffee for a while, you've noticed these terms cropping up more and more — on bags, on menus, in tasting notes. And if you've wondered what any of it actually means for the coffee in your cup, you're not alone.
Experimental processing is the biggest shift happening in specialty coffee right now. Here's what's going on, why producers are doing it, and what it means when you're choosing what to buy.
What is coffee processing?
Before we get into the experimental stuff, it helps to understand what processing actually is.
After coffee cherries are harvested, the fruit surrounding the bean needs to be removed before the bean can be dried, exported and roasted. How a producer handles this stage — how long it takes, how much fruit remains on the bean, under what conditions — is what we call processing. It has an enormous influence on how the final coffee tastes.
The three traditional methods are:
Washed — the fruit is removed before drying. Clean, clear, the terroir of the bean comes through directly.
Natural — the whole cherry is dried with the fruit intact. Produces sweeter, fruitier, sometimes wilder cups.
Honey — somewhere in between. Some of the fruit's sticky mucilage is left on the bean during drying. The amount left — white, yellow, red, black honey — determines how much sweetness and body makes it through.
These methods have been used for generations. What's changed in the last decade or so is that producers have started deliberately intervening in the fermentation that happens during processing — controlling it, extending it, engineering it — to create entirely new flavour outcomes.
What is anaerobic processing?
Fermentation happens in all coffee processing. It's a natural part of breaking down the fruit. Traditionally it's been open-air and fairly brief — a byproduct of the process rather than a tool.
Anaerobic processing changes that. The coffee cherries or pulped beans are sealed into airtight tanks, removing oxygen from the environment. Without oxygen, fermentation follows a different biochemical pathway. Different microbial activity, different compounds produced, different flavours in the cup.
The result tends to be more intense: deeper fruit character, more sweetness, occasionally wine-like or tropical notes depending on how it's done. The process also significantly changes the chemical composition of the bean — which affects how it extracts and is worth knowing when you brew it (more on that later).
What makes it genuinely interesting is the level of control it gives producers. Duration, temperature, the presence of naturally occurring yeasts — all of these can be adjusted to target specific flavour outcomes. A 48-hour ferment and a 120-hour ferment from the same farm will taste meaningfully different.
What about anaerobic honey?
Honey process and anaerobic fermentation are two separate things — but producers increasingly combine them. An anaerobic honey means the coffee went through an oxygen-restricted fermentation stage while still retaining some of its mucilage during drying. Two separate decisions, deliberately layered — like the Catuai from Fazenda JS in Brazil used in the recent batch of Manhattan Coffee Roasters' Brooklyn blend.
What's happening in 2026
The conversation has moved beyond anaerobic as a novelty. A few things define where things stand right now:
Co-fermentation means adding an external ingredient — fruit, cacao pulp, hops, spices — into the fermentation tank alongside the coffee. The microorganisms present break down both the coffee mucilage and the added ingredient simultaneously, and the resulting flavour compounds end up in the bean. Think of it as flavour modification: you're introducing something new into the environment and letting fermentation do what it does.
Inoculated fermentation is different in kind. Instead of adding an ingredient, you're adding a specific, isolated microorganism — usually a particular strain of yeast — to take control of the fermentation itself. Rather than letting whatever naturally occurs in the environment run the process, you're directing it toward a targeted outcome. Think of it as flavour enhancement through precision: the same coffee, fermented more intentionally.
The simplest way to hold the distinction: co-fermentation adds something to ferment alongside the coffee; inoculation adds something to control how the coffee ferments.
Both are divisive in the specialty world — co-fermentation is broadly seen as flavour modification, inoculated fermentation as flavour enhancement — and neither is universally accepted by traditionalists who feel these methods distance the cup from its terroir.
In practice, these methods are rarely used in isolation. Producers increasingly combine and layer techniques, which is why bag labels can look bewildering. A Yeast Assisted Semi-Anaerobic Natural is telling you that specific yeasts were introduced, that fermentation was partially oxygen-restricted, and that the drying method was natural — three distinct decisions stacked on top of each other. An Advanced Fermentation Natural or Multi-Stage Washed is similarly describing a process with multiple deliberate interventions at different points. Far from being marketing noise, this kind of specificity is exactly what you want to see. It means the producer understands and can account for every stage — and is willing to tell you about it.
Processing transparency is becoming an expectation rather than a bonus. As experimental methods have proliferated, buyers and consumers have started asking more specific questions about what was actually done to a coffee after harvest. Fermentation time, tank temperature, processing date — this level of detail is becoming more common from roasters who work closely with their producers, and it matters. These variables genuinely affect what you taste, and a roaster who can't tell you anything beyond "anaerobic natural" probably doesn't know much more than that themselves.
The terms you'll actually see on a bag
The vocabulary has outrun the definitions. Most of what follows is a variation on the same two levers — how much oxygen, and how long — but the words are worth knowing, because a producer who prints one has told you something specific.
Carbonic maceration. Whole, intact cherries are sealed in a tank and carbon dioxide is pumped in from a cylinder. CO2 is heavier than air, so it displaces the oxygen immediately rather than waiting for microbes to use it up, which is the difference between this and ordinary anaerobic fermentation. With the skins intact and external microbes largely shut out, the fruit's own cells start breaking down their sugars from the inside — intracellular fermentation — before microbial activity takes over later on. It came from Beaujolais, where the same thing is done to Gamay grapes, and it reached specialty coffee through Saša Šestić, who won the 2015 World Barista Championship on a Sudan Rume processed this way. Expect red fruit, a rounded mouthfeel and a lot of aromatics. The term is used loosely, so it's worth asking whether the cherries really stayed whole.
Dry anaerobic and submerged anaerobic. A sealed tank can be dry or filled with liquid, and the bag rarely says which. Dry means the cherries go in on their own and ferment in their own juice. Submerged means the tank is topped up with water, which changes the temperature stability and the microbial balance. The choice isn't always about flavour: in parts of Ethiopia, where clean water at a washing station can't be assumed, dry is simply the more practical route.
Anaerobic natural, anaerobic washed, anaerobic honey. Anaerobic describes the fermentation. Natural, washed and honey describe how the coffee was dried. They're separate decisions, and the combination tells you where the sealed stage sits in the sequence. An anaerobic natural ferments in whole cherry and then dries in the fruit — the heaviest, jammiest outcome. An anaerobic washed is pulped first, ferments sealed, then gets washed clean before drying, which keeps the clarity of a washed coffee while building a brighter, more layered acidity. An anaerobic honey sits between the two.
Mosto. The juice that runs off fermenting cherries, collected and used in place of water in the next tank. Because it arrives already carrying a live population of yeasts and lactic acid bacteria, it starts the fermentation faster and drives it harder than water, which only dilutes. You'll see it on Ethiopian and Latin American lots, sometimes spelled mossto, and sometimes mistranslated — the French moût has been rendered as "mustard" on more than one English product page.
Lactic. Sealing a tank suppresses the microbes that need oxygen and lets lactic acid bacteria dominate. Some producers push it further with a salt brine, which the bacteria tolerate and their competitors don't, or by inoculating a specific strain outright. The house style of a lactic ferment is a creamier body and a softer acidity — yoghurt, chocolate, butter rather than sharp fruit.
Acetic. The opposite end. More oxygen, more acetic acid, a sharper and more volatile cup. It's rarely printed as a selling point, but it's what a ferment drifts towards when air gets in.
Thermal shock. After fermentation, the beans are washed with hot water and then immediately with cold. The swing halts fermentation at a chosen moment and is credited with fixing aromatic compounds in place, which is why these coffees can be extremely intense and extremely clean at once. It's associated with Finca El Paraíso in Cauca, Colombia, and it's a producer-specific technique rather than a method that travels easily.
Double fermentation. Two separate sealed stages, usually one in whole cherry and a second after pulping, sometimes with a different microbial population each time. The more extreme version interrupts the drying to ferment again — back into a cold room at day twenty, then out onto the beds to finish.
Cold fermentation. Holding the tank at a low temperature slows everything down, which is what makes very long ferments survivable: five days at 14°C is not five days in the sun. Temperature is one of the few variables a producer can hold genuinely constant, so it's often where the control is.
River Flow. Sealed bags of cherry submerged in a river, so the ferment runs at the water's temperature rather than the air's. Moving water is far steadier through a day than a drying patio, which makes this a low-tech route to the same thing a cold room buys.
Advanced fermentation, multi-stage washed, experimental. These aren't methods. They're umbrella terms for a process with several deliberate interventions, and on their own they tell you nothing except that something was done. Treat them as an invitation to ask what.
The hour counts. 48, 72, 96, 120 — printed on the bag because the number is a decision, not a detail. Longer isn't better. Longer breaks down more of the sugars in the mucilage and produces more of the volatile compounds that read as funk, and it gets harder to control as it goes: the same cherry at 48 hours and at 96 can be a clean fruit-forward cup or a fermenty, boozy one. Two lots from the same farm and the same variety, separated only by a day of fermentation, will not taste alike.
What this means when you're buying
None of this requires a science degree to be useful. A few practical things:
More processing detail is a good sign. "72-hour anaerobic" tells you something intentional was done and the producer knows exactly what. "Experimental process" tells you almost nothing.
Anaerobic coffees tend to be more soluble than conventionally processed coffees. Anaerobic fermentation significantly changes the chemical composition of the bean, which affects how it extracts. These coffees can release compounds more readily and tip into over-extraction more easily. If something tastes off, it's worth experimenting with your variables — temperature, grind and dose are all worth adjusting, and small changes can make a meaningful difference.
Experimental processing can elevate an already-good coffee — it can't rescue a poor one, and it isn't a quality ranking. A conventionally processed coffee from an excellent producer can be every bit as compelling. Processing is a dimension of flavour choice, nothing more.
The bigger picture
What experimental processing represents, at its best, is producers treating fermentation as a craft — the same way a winemaker or brewer would. The outcome of a coffee is no longer determined only by where it's grown and what variety it is. How it was handled after harvest is now equally part of the story.
For anyone buying and brewing specialty coffee at home, that's genuinely exciting. It means more complexity, more intentionality and more reason to pay attention to what's on the bag.
Try them yourself
If you'd rather drink the theory than read it, the Experimental coffee collection is where these lots live — and there's a brewing guide if you're new to them.
ROAST EDIT Co. imports specialty coffee to the UK from roasters focused on traceability, quality and producer relationships. Our current selection includes coffees processed using a range of methods — from clean washed single origins to complex anaerobic blends.