Most articles about coffee processing make a subtle error. They describe washed coffee as the "clean" method and natural coffee as the "fermented" method — as if one involves microbial activity and the other doesn't. This framing is wrong, and understanding why changes how you think about everything from a bag's tasting notes to why certain coffees cost what they do.
All coffee is fermented. Every single bag. The question is never whether fermentation happened — it's where it happened, how long it ran, how much the producer controlled it, and how that shaped what ended up in your cup.
What Fermentation Is Actually Doing to Coffee
A coffee cherry is a fruit. Inside the fruit, surrounding the seed (the bean), is a layer of sticky, sugar-rich pulp called mucilage. When the cherry is picked, microorganisms — primarily yeasts and lactic acid bacteria — immediately begin breaking down that mucilage and the sugars within it. This is fermentation, and it is unavoidable. It begins the moment the cherry leaves the tree.
What fermentation produces is not just the breakdown of sugars. The microbial activity generates organic acids, alcohols, and volatile aromatic compounds — many of which are absorbed by the bean and become precursors to the flavours you taste in the cup. Lactic acid bacteria produce compounds that translate into fruity, bright, clean acidity. Yeasts produce esters that read as tropical fruit, stone fruit, and florals. Acetic acid bacteria, if present in quantity, produce the sharp, fermented funk that distinguishes a poorly processed natural from a well-managed one.
The roaster applies heat that drives off water and transforms these compounds. But the foundation — the raw material of flavour — was built during fermentation, at origin, before anyone got near a roaster. Processing is where most of the flavour work happens. Roasting is refinement. Fermentation is architecture.
The Spectrum: From Controlled to Extended
Rather than thinking about processing as three separate boxes — washed, honey, natural — it is more accurate to think of it as a spectrum of fermentation control. At one end, the producer limits fermentation aggressively: short duration, controlled conditions, mechanical assistance. At the other end, they allow fermentation to run long and slow, inside the intact fruit, with the bean absorbing everything the process produces. In the middle are various degrees of managed exposure. And beyond the traditional methods, a new generation of producers is engineering the fermentation itself with scientific precision.
Washed: Short, Controlled, High Clarity
In washed processing — also called wet processing — the skin and pulp of the cherry are mechanically removed within hours of picking, typically using a depulping machine. The bean is then fermented in water tanks for anywhere from 12 to 72 hours. This is the step that catches people out: yes, there is a fermentation stage in washed processing. The purpose is to break down the remaining mucilage so it can be washed away, leaving the bean clean before drying.
Because fermentation is short and takes place in a controlled water environment, its influence on the final cup is relatively limited. What you taste is largely what was already in the bean — the genetics of the variety, the soil, the altitude, the harvest timing. This is why washed coffees are described as transparent or terroir-driven. The process does not add much; it mostly gets out of the way.
The result in the cup is typically clean, bright acidity, clarity of flavour, and a lighter body. Florals and fruit notes come through precisely rather than amplified. TANAT's Hacienda La Papaya Typica Washed is a textbook expression of this — the bean has been grown at over 1,900 metres and processed to show exactly what that altitude produces, without the process adding anything on top. Similarly, People Possession's Doña María Rodríguez Chiroso Washed lets the Chiroso varietal's natural jasmine-forward character speak without amplification.
The trade-off is environmental: washed processing can use up to 200 litres of water per kilogram of coffee. In water-stressed growing regions, this is a real concern — one that partly drove the innovation of the honey process, and that is increasingly influencing how farms think about their processing choices.
Honey: The Calculated Middle Ground
Honey processing emerged in Costa Rica in the early 2000s, driven as much by necessity as experimentation. Following a 2008 earthquake, government water restrictions forced producers to find alternatives to the water-intensive washed process. The Chacón family at Finca Las Lajas developed machinery that allowed precise control over how much mucilage remained on the bean after depulping — giving them something between a washed and a natural without the water requirements of one or the defect risks of the other.
The name comes not from the ingredient but from the texture: the mucilage left on the drying bean is sticky and amber-coloured, like honey drying on the parchment. How much mucilage is left determines the style — yellow honey retains the least, red honey more, black honey the most — and directly determines how much fermentation influence reaches the bean during drying.
The cup profile sits between washed and natural accordingly: the clarity of a washed coffee but with more sweetness, more body, and a rounder fruit character. DAK's Bonita Geisha uses honey processing on a variety — Geisha — more commonly seen as washed, and the result is a warmer, more accessible expression of the variety than the typical Panama-style washed Geisha: the florals are present but the body is fuller and the sweetness is immediate.
Natural: Long Fermentation, Full Fruit Influence
Natural processing — drying the whole cherry intact, with no depulping — is the oldest method. In Ethiopia, where coffee grows wild and processing infrastructure was historically limited, drying whole cherries on raised beds or flat rocks was simply what happened. The bean ferments slowly inside the drying fruit for three to six weeks, absorbing sugars and the full range of aromatic compounds produced by the extended microbial activity.
The results, when done well, are the most fruit-forward and complex cups in coffee: blueberry, tropical fruit, dark cherry, wine-like sweetness, a dense and syrupy body. When done badly — inconsistent drying, inadequate turning of the cherries, poor airflow — natural processing produces the fermented funk that gives the method its occasional bad reputation. The difference between a world-class natural and a defective one is almost entirely about the care taken during the weeks of drying.
Natural processing also uses almost no water, making it the most environmentally efficient of the traditional methods. This matters increasingly as specialty coffee contends with the water constraints facing many growing regions.
TANAT's Las Margaritas Geisha Natural and People Possession's Inmaculada Fellow Farms Geisha Natural both show what natural processing does to Geisha at high altitude in Colombia — the variety's florals sit above a denser, more tropical base than you'd find in a washed Geisha, and the finish is longer and more layered.
Anaerobic: Engineering the Fermentation
Anaerobic processing is the newest point on the spectrum, and it represents a fundamental shift in how producers think about fermentation — from something to be managed or minimised to something to be actively designed.
In anaerobic processing, depulped or whole cherries are sealed in airtight tanks with oxygen removed. Without oxygen, the aerobic bacteria that produce acetic acid cannot survive, and the fermentation environment shifts entirely to yeasts and lactic acid bacteria operating in a controlled, oxygen-free atmosphere. Temperature, pH, and duration can all be precisely monitored and adjusted. The result is a fermentation that is both more intense than a traditional washed and more reproducible than a natural — and that can be deliberately tuned to enhance specific flavour compounds.
Research has found that anaerobic fermentation can boost fruity esters and floral aldehydes by 300 to 400% compared to conventional washed processing. That is not subtle. It is why anaerobic coffees tend to taste unlike anything else: intensely tropical, sometimes candy-like or wine-forward, with a density of aromatic character that can seem almost engineered — because, increasingly, it is.
The method gained mainstream visibility in 2015, when Australian barista Saša Šestić won the World Barista Championship using anaerobically processed Colombian beans, introducing a large part of the specialty industry to flavour profiles that had not previously been achievable through conventional methods.
TANAT's Hacienda La Papaya B7 Anaerobic ferments cherries at below 24°C for up to 240 hours — ten days in a controlled tank — before a 30-day drying period. People Possession's El Vergel Anaerobic comes from the Bayter brothers in Tolima, who have built one of Colombia's most respected experimental operations around precisely this kind of controlled fermentation work.
Why Producers Choose What They Choose
Processing decisions are not purely aesthetic. They are economic and practical choices shaped by water access, labour costs, climate, drying infrastructure, and market conditions.
Natural processing requires almost no capital equipment and no water — but it requires weeks of drying time, labour-intensive cherry turning, and carries significant defect risk if the weather turns. Washed processing produces more consistent results and commands reliable prices from buyers who need traceability and cup consistency — but requires water infrastructure and generates wastewater that must be managed. Anaerobic processing can achieve a significant quality premium at auction, but the sealed tank infrastructure and technical expertise required represents an upfront investment that only makes sense at a certain scale.
For producers operating at the top of the specialty market — the farms that supply roasters like TANAT, People Possession and NOMAD — processing is increasingly a strategic decision about what the market values and what their terroir can best express. A farm at 1,900 metres with naturally complex beans might choose washed processing to let that terroir speak. A farm where the variety is less inherently distinctive might use anaerobic fermentation to build complexity that the raw material alone could not produce.
How to Use This When You're Buying
When you see a processing method listed on a coffee bag, it tells you something concrete about what to expect.
Washed: expect clarity, precision, and a direct expression of variety and origin. Brighter acidity, lighter body. The best washed coffees reward slow filter brewing and close attention.
Honey: expect sweetness and body alongside clarity. Good entry point for people who find washed coffees too delicate and natural coffees too intense.
Natural: expect fruit, sweetness, density. More forgiving as espresso, approachable as filter. High ceiling, higher variance.
Anaerobic: expect intensity, unusual aromatics, a profile unlike conventional coffees. Often the most polarising — the people who love them love them specifically.
None of these is better. They are different approaches to the same raw material, each of which expresses a different set of values about what coffee should taste like. The most useful thing you can do is taste across the spectrum and notice what you're responding to — and then use the processing method as one of the tools for finding more of it.