Vol. X — The Coffee Specimens, Unique Alchemical Processes

I have spent the previous two volumes of these coffee notes documenting what coffee is — the origins, the varieties, the biological realities that produce extraordinary cups from extraordinary plants in extraordinary places.

This final volume is about what coffee becomes when human ingenuity is applied to its transformation.

Processing — the method by which the coffee cherry is converted into the green bean that will eventually be roasted — is the least understood variable in coffee quality, and arguably the most powerful. The same variety, from the same farm, in the same harvest year, processed differently, will produce cups so distinct from one another that a blind taster might not recognize them as the same coffee.

Eight methods are documented here. Two of them are ancient. Several are recent innovations — techniques borrowed from other fermentation traditions, or invented outright by producers who asked what would happen if they tried something no one had tried before. One of them is the oldest coffee processing tradition in the world, practiced in forests that have been producing coffee since before anyone thought to cultivate it.

I find all eight worth documenting. I find all eight worth drinking.

On Washed — The Honest Cup

Before we discuss what processing can become, we must understand what it begins as.

Washed processing — also called wet processing — is the method by which the coffee cherry’s fruit is removed before drying. The cherries are pulped mechanically, the remaining mucilage is fermented off in water tanks for twelve to seventy-two hours, and the clean beans are then dried on raised beds or patios until they reach the correct moisture content.

The result is a coffee of extraordinary clarity. Without the fruit’s sugars and acids influencing the drying process, what remains in the cup is almost entirely the expression of the bean itself — its variety, its terroir, its altitude. Washed coffees from Ethiopia’s Yirgacheffe region, from Kenya’s central highlands, from Colombia’s Huila department, are among the most transparent documents of place that coffee produces. The acidity is clean and precise. The flavors are specific rather than diffuse. There is nowhere for the processing to hide, and nowhere for the terroir to hide either.

This is why I begin here. Washed processing is not the most dramatic method in this volume. It is the most honest. Everything that follows is a conversation with what washed processing reveals.

Brew as pour-over at 93°C (199°F). Medium-fine grind. Three minutes. Pay attention to the acidity — it is telling you something about where the coffee grew.

On Natural — The Original Method

Before there were tanks, before there were pulping machines, before there was any infrastructure at all, there was this: the coffee cherry, dried whole in the sun, the fruit slowly desiccating around the bean over weeks until both could be separated by hand.

Natural processing — also called dry processing — is the oldest method in the world. It is how coffee was processed in Yemen for centuries. It is how the wild coffee of Ethiopia has always been handled. It requires almost nothing except time, sunlight, and the willingness to turn the drying cherries regularly so they do not ferment unevenly.

What it produces is a coffee of extraordinary sweetness and body. The fruit’s sugars and acids migrate into the bean during drying, producing flavors that washed processing cannot achieve: blueberry, strawberry, dark chocolate, wine-like complexity, a fullness in the body that sits in the cup like something substantial. Ethiopian naturals from Sidama and Guji are among the most celebrated coffees in the world for precisely this reason.

The risk is also real. Natural processing requires careful management — too much heat, too much moisture, uneven turning — and the result is not complexity but ferment gone wrong. The line between extraordinary and ruined is thinner than it appears. The producers who walk it consistently are worth knowing by name.

Brew as pour-over or French press at 92°C (198°F). Coarse grind. Four minutes. Allow it to cool before the first sip. The sweetness reveals itself as the temperature drops.

On Anaerobic Natural — The Controlled Chaos

To understand anaerobic processing, one must first understand what it is reacting against.

Traditional processing — whether washed or natural — exposes the coffee cherry to oxygen throughout fermentation. The microorganisms that drive fermentation in an oxygen-rich environment produce certain flavor compounds and not others. The results are predictable, controllable, and consistent. This is, for most of the coffee industry, the point.

Anaerobic processing removes oxygen from the equation entirely. The coffee cherries — whole, with the fruit intact — are sealed in airtight tanks, often with CO₂ introduced to purge any remaining oxygen. Fermentation proceeds in this sealed environment, driven by different microbial populations that produce different metabolic byproducts. The pressure builds inside the tank. The temperature is monitored carefully. The duration — anywhere from twelve hours to several days — is determined by the producer’s target flavor profile.

What emerges is a coffee of extraordinary intensity. The anaerobic environment produces elevated levels of lactic acid and specific esters that translate, in the cup, into flavors of remarkable vividness: tropical fruit, fermented sweetness, wine-like complexity, occasionally notes that border on the savory depending on how far the fermentation is pushed. The body is typically full. The finish is long and assertive.

It is not subtle. It is not trying to be.

Brew as pour-over at 93°C (199°F). Medium grind. Three minutes. Be prepared for the aroma to fill the room before you have finished pouring. This is not a coffee for quiet mornings. It announces itself.

On Carbonic Maceration — Borrowed from the Vine

If anaerobic processing is coffee’s own innovation, carbonic maceration is borrowed — directly and deliberately — from the world of wine.

Carbonic maceration is a winemaking technique developed in the Beaujolais region of France, used to produce wines of unusual freshness and fruit-forward character. The grapes are placed whole into sealed tanks filled with carbon dioxide; fermentation begins inside the intact grape berry itself, driven by intracellular enzymes rather than external yeast. The result is a wine of distinctive character — low tannin, high fruit, a brightness that Beaujolais drinkers know well.

Coffee producers, observing the results that anaerobic processing was producing and looking for ways to further refine the technique, began experimenting with carbonic maceration in the 2010s. The coffee cherries are placed whole into tanks saturated with CO₂, and fermentation proceeds intracellularly — inside the cherry itself — before the fruit is removed and the beans are dried.

The flavor profile that results is, in my experience, more refined than standard anaerobic natural. The fruit notes are present but more precise — less overwhelming, more specific. There is a wine-like quality that is not accidental: the technique was designed to produce it. The acidity is bright and structured. The sweetness is clean.

It is a coffee that rewards the drinker who comes to it with some knowledge of what was done to produce it. Understanding the process does not change the flavor, but it changes the experience of the flavor — the recognition of intention in the cup.

Brew as pour-over or Aeropress at 91°C (196°F). Medium grind. Three to four minutes. It is also exceptional as a cold brew concentrate — the carbonic maceration character translates beautifully to cold extraction.

On Co-Ferments — The Deliberate Conversation

Co-fermentation is the newest entry in this catalogue, and the one that has generated the most argument in the specialty coffee world — which is, I have found, usually a reliable indicator that something interesting is happening.

Co-fermentation involves introducing a secondary ingredient into the fermentation environment alongside the coffee cherry: fruit, spice, botanical, or any number of other materials that contribute their own microbial populations and flavor compounds to the process. The coffee ferments in conversation with something else, and the result is a cup that carries the signature of both.

Common co-ferments include cinnamon, citrus peel, cacao, and various tropical fruits. Less common — and more controversial — are experiments with wine grapes, honey, and even spirits. The range of what is possible is, in theory, limited only by the imagination of the producer and the tolerance of the drinker.

My position on co-fermentation is this: when the secondary ingredient enhances the coffee’s own character — when it opens a door that the coffee was already standing near — the result can be extraordinary. When it overwhelms the coffee entirely, replacing its voice with something louder and more insistent, the result is a flavored coffee wearing the clothes of a process coffee. The distinction matters.

The finest co-ferments I have encountered have been those where, knowing what was added, I could taste the conversation rather than the monologue. The coffee was still present. The co-ferment was a collaborator, not a replacement.

Brew as pour-over at 92°C (198°F). Approach it with curiosity rather than expectation. Ask the producer what was added and why. The answer will tell you whether the conversation was worth having.

On Yeast Inoculation — The Named Collaborator

Wild fermentation — the kind that drives washed, natural, and anaerobic processing — relies on whatever microorganisms happen to be present in the environment: on the cherry’s skin, in the water, in the air of the processing facility. The results are complex and often extraordinary, but they are also variable. The same process, in the same facility, in two different years, will produce different results because the microbial populations shift with the season, the weather, and a hundred other factors that no producer can fully control.

Yeast inoculation is the attempt to bring that variability under deliberate control.

Specific yeast strains — selected for the flavor compounds they produce during fermentation — are introduced to the coffee at the beginning of processing, in concentrations sufficient to dominate the fermentation environment. The producer is no longer relying on whatever arrives uninvited. They are choosing their collaborator by name.

The strains used range from commercial wine and beer yeasts to proprietary strains developed specifically for coffee fermentation. Each produces a different profile: some emphasize fruit esters, some produce lactic acid, some contribute floral compounds that the coffee’s own chemistry would not generate unaided.

The philosophical objection is predictable and not without merit: if you are introducing a specific yeast to produce a specific flavor, are you expressing the coffee or manufacturing a product? I have thought about this question at some length and arrived at an answer that satisfies me, if not everyone: the coffee is still the canvas. The yeast is the brush. What matters is whether the painter knows what they are doing.

Brew as pour-over at 93°C (199°F). Medium grind. Three minutes. Compare it, if you can, to a washed coffee from the same farm. The difference will tell you everything about what the yeast was asked to do.

On Zero Fermentation — The Refusal

Every other method in this volume involves fermentation in some form — the deliberate or incidental activity of microorganisms transforming the coffee cherry and, by extension, the cup. Zero fermentation is the refusal of that activity entirely.

Also called mechanical demucilaging, zero fermentation processing removes the coffee cherry’s mucilage mechanically — by machine, under pressure, with water — without allowing any fermentation to occur. The bean goes from cherry to drying bed without the intervention of a single microorganism.

The result is a cup of extraordinary cleanliness. Without fermentation’s contribution — its acids, its esters, its complexity — what remains is the purest possible expression of the bean’s own chemistry: its variety, its terroir, its altitude, its harvest timing. Nothing added. Nothing transformed. Only what was already there.

I find zero fermentation coffees among the most demanding to evaluate, because they offer no processing signature to hide behind. A mediocre bean, processed without fermentation, is simply a mediocre bean with nowhere to hide. An exceptional bean, processed the same way, is an argument for the primacy of raw material over technique.

It is, in its way, the coffee equivalent of the White Ghost documented in Vol. I of these archives — the least processed, the most transparent, the most dependent on the quality of what it began as.

Brew as pour-over at 94°C (201°F). Medium-fine grind. Three minutes. This is a coffee for paying attention. It will not do the work for you.

On Wild Ethiopian Forest Coffee — The Undomesticated

And so I arrive at the specimen that, in some ways, is the most important in this entire volume — and the one that requires the least processing to discuss, because it has undergone almost none.

Ethiopia is the birthplace of coffee. This is not mythology or marketing — it is botanical fact. Coffea arabica originated in the forests of southwestern Ethiopia, in the regions of Kaffa, Bench, and Sheka, where it still grows wild today. The coffee trees in these forests are not cultivated. They are not planted in rows. They grow as they have grown for thousands of years, in the shade of the forest canopy, in a complex ecosystem that has been developing since before any human thought to harvest the cherries.

Wild Ethiopian forest coffee — harvested by communities who have been collecting it for generations, dried on raised beds or on the forest floor, processed with minimal intervention — is the oldest coffee in the world. It is also, in its finest expressions, among the most complex.

The flavor is unlike anything produced by cultivated varieties. The genetic diversity of wild coffee populations — thousands of distinct varieties growing in proximity, cross-pollinating freely — produces a cup of extraordinary complexity and unpredictability. No two harvests taste exactly alike. No two trees produce exactly the same cherry. The cup is a record of the forest itself: its soil, its canopy, its rainfall, its centuries of undisturbed development.

The forests that produce this coffee are under threat. Deforestation, agricultural expansion, and climate change are reducing the wild coffee habitat at a rate that alarms botanists and coffee researchers alike. The genetic diversity contained in these forests represents an irreplaceable resource for the future of coffee as a species. If the forests go, that diversity goes with them.

To drink wild Ethiopian forest coffee is to drink something that may not exist in its current form in fifty years. I noted the same of Junshan Yinzhen in Vol. III. I find the parallel instructive.

Brew as pour-over at 92°C (198°F). Coarse grind. Four minutes. Allow it to cool before the first sip — the complexity reveals itself as the temperature drops. Drink it slowly. Pay attention. This is what coffee was before we decided what coffee should be.

A Final Note on The Forbidden Catalogue

Ten volumes. Eight processing methods. Two categories. One catalogue.

I began this project with the conviction that most people who drink tea and coffee have never encountered the extraordinary versions of what they drink daily — and that this gap between the ordinary and the extraordinary is worth bridging, for anyone willing to make the crossing.

Having reached the end of what I am calling the first edition of these notes, I find that conviction unchanged. If anything, strengthened.

The specimens documented in these pages are not curiosities. They are not luxury items for the wealthy or obscurities for the obsessive. They are the full expression of what these plants are capable of when grown with care, processed with skill, and encountered with attention. They are what tea and coffee look like when no one has compromised them.

I hope you find them. I hope, when you do, you sit down with them properly.

The catalogue is never finished. It is only rested.

Until the next expedition.

— Professor Eldrin Nightshade, Field Notes, Ethiopia · Colombia · Beaujolais · Yemen
“We did not discover these plants. We were discovered by them. Everything since has been an attempt to be worthy of the introduction.”