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.
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.
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.