Coffee processing methods and their influence on flavor

2016 version of the SCA Flavor Wheel

The 1995 version

Since 2022, the AESAN Coffee Institute has had a modified variant that focuses on aromas used especially in Asian countries.

Additionally, the first study on a Canephora Flavor Wheel was published in early 2025.

The collection of descriptive words is diverse. The Flavor Wheel first groups aroma families before moving from the broad categories to more differentiation. While fruity and nutty notes are positively connoted, notes like petrol or medicinal can interfere with enjoyment.

The aroma wheel gives us a selection of aromas that can be tasted more or less frequently in coffee, regardless of whether they are positive or negative. But where do these aromas actually come from? And how do they get into the coffee?

This article consists of two parts.

Coffee processing / the post-harvest process - terminology clarification and impact on coffee flavor

If we imagine coffee like a puzzle, we notice countless small particles that are needed to make everything fit together perfectly. This applies both to a perfectly brewed espresso and to green coffee.

Before sowing a coffee variety, it is important to consider whether the soil has the nutrients it needs. Likewise, whether the chosen variety gets the amount of sun or shade it needs for balanced growth. And when coffee cherries are on the tree, the producer decides exactly when to pick them—because red is not always the same red.

Like a traffic light, the color of the coffee cherry shows whether it is ripe.

There are significant differences in the shade of red, which can affect the taste of the coffee.

From the moment a cherry is picked, we speak of the post-harvest process or processing. Once the cherry is separated from the stem, a small wound opens in what is called the exocarp.

Bacteria and yeasts can now react and activate the metabolism, the fruit comes into contact with oxygen, and the opening attracts insects with its sweet aromas, which in turn carry bacteria and yeasts. Each stage the coffee cherry is in has a potential impact on the quality and thus the final taste of the coffee.

The post-harvest process does not begin with the drying of the cherry, depulping, or fermentation, but precisely when the cherry is separated from the stem.

What matters now so that all the positive properties laid out in the coffee cherry result in good flavor is clarified in the following sections.

Step 1: from the tree to further processing

The following points should be considered when cherries are separated from the stem

clean storage location

• where to put the picked cherries? Usually, workers pick the cherries and put them in a cloth, a plastic bag tied around them, or a container made of bast or similar.
• once this is full, they put the cherries in a larger plastic bag. These bags quickly become a melting pot of insects, bacteria, sugars, and yeasts, which can trigger unwanted fermentation
• the longer coffee cherries stay in the bags, the greater the risk that unwanted or off-flavors will already form in the first step after picking
• the bags must either be replaced or always washed thoroughly

Plastic bags with depulped and washed coffee are placed on a tarp and not directly on the ground.

not too much weight, not too large bags

• if you've ever been at a wine harvest, you may have seen that particularly valuable grapes are only transported in a single layer in small, multi-level containers. This reduces the weight pressing on the grapes and prevents them from being pressed prematurely
• coffee cherries are significantly harder than wine grapes, but it can happen that the bottom cherries in the transport bag are already crushed
• for the highest quality standards, these cherries should be sorted out before further processing

time until the next step

• The time until the next processing step is crucial
• strategies and opinions vary widely here
• it is still recommended in globally valid literature to depulp coffee cherries as quickly as possible to avoid "risking" fermentation—which makes it clear that for many, fermentation is unwanted and a source of danger rather than an opportunity for more complexity
• in fact, the time of interim storage of the cherries before the next processing step is decisive, depending on what is being sought

• often coffees that are mechanically demucilaged or depulped before being treated with water are processed very quickly (the same day)

• in particular, we know from Colombia that producers treat coffee cherries with ozone and thus eliminate yeasts and bacteria on the surface. They then work in further processing steps with the microorganisms inside the cherry, or add starter cultures

• in large parts of Central America, the tradition of reposa exists, a storage of coffee cherries for several hours before they are further processed
  

• in Nicaragua, for example, we rely on a 16-hour pause of the cherries before further processing. In contrast to the control sample, which is processed immediately, we find somewhat more sweetness and acidity in the roasted coffee
  

• we had this scientifically monitored by ZHaW: you can find the work below

Step 2: the dilemma—depulp or not depulp?

Whether the coffee had a reposa or whether the cherries were further processed shortly after picking has no impact on the following steps. Now it must be decided what happens to the coffee cherries: is the fruit pulp pressed off, or does it remain intact?

The quality of the picked and sorted cherries plays a large role. If mostly semi-ripe cherries were picked, direct drying of the coffee cherries (so-called Natural) is unlikely to be aimed for. The cherries don't bring enough sugar to create new flavors in intensive fermentation. If the cherries are very ripe and uniformly sorted, all further processing steps are possible.

With all further steps, aromaticity can now be added to the coffee that was not present before.

Targeted fermentation creates aroma precursors, which are then converted into aromas during roasting.

A fundamental decision: remove the pulp or not?

Is the coffee cherry dried as an intact cherry, or is the pulp (called mesocarp) removed? This decision not only defines the further procedure but also the intention of which aromaticity should be promoted.

1. Remove all fruit pulp: mechanical demucilagination

• here, so-called demucilaginators or eco-pulpers are used
• large machines that not only expose the seed but also remove all mucilage through friction and high-pressure water jets
• this prevents any fermentation
• the coffee beans come out as wet parchment within a few minutes and then go directly into drying

*especially at the peak of harvest, when most coffee cherries are delivered for processing in a short time, the demucilaginadores are the most reliable and efficient tool for processing the cherries

**no fermentation takes place in this processing, so no new aromas are created that are not already present in the coffee seed as so-called aroma precursors. Depending on sensory standards, these coffees often seem somewhat austere. High qualities often have a delicate, clean acidity. The texture depends on the ripeness of the cherries, as does the type of aromaticity. However, since this is often about volume coffees, less uniform cherries end up in processing, which limits the aromatic complexity of the coffee.

Many options with the demucilaginators

Due to the high efficiency and low water consumption, demucilaginators are now used worldwide. Newer generations of machines allow the amount of mucilage that should remain on the coffee seed to be adjusted precisely. Especially in Costa Rica, producers refined this technique in the 2000s and invented various types of honeys.

2. Partially remove the fruit pulp: depulping

• this is done either with a despulpadora, a manually or mechanically—often gasoline-powered—depulping machine
• cherries fall into a funnel and are pressed by a rotating drum against a front plate, where the fruit pulp is separated from the seed
• depending on the cherry size and pulp thickness, adjustments must be made to the front plates so that the beans are pressed out of the cherries without damage
• most of the slime (mucilage) remains attached to the seed

The despulpadoras are not designed to remove all the fruit pulp and thus the slime, which is why the process of fermenting as a biological process (= releasing the slime) and washing has developed—more on that later.

3. Leave the cherry intact—the pulp stays on—Natural

• the oldest method of further processing coffee after picking is drying in the coffee cherry
• the method is also known as natural processing
• in the most rudimentary version of this processing, the coffee cherry is spread out at a dry location until the seed inside has a residual moisture of about 12%
• in the highly refined methods used today, technical and biological aids are used to constantly create new aromas that were not previously present
• natural processing produces both the best and worst coffees I have ever tasted

The coffee world between the poles—all other types of processing

Until around the turn of the millennium, the burning question in the post-harvest process was: washed, or not washed—naturals were the way coffees were dried for decades, but we're talking about a different level of precision in how that's handled today. With increasing efficiency in processing and new market demands, the 1970s saw a steep rise in wet mills or beneficios, collection stations where coffee cherries were depulped and washed.

For many processors, the ability to depulp and wash coffee was a major step toward greater consistency. The processes could be better controlled, and the general coffee quality increased as a result, which also helped shape a mass taste.

With the emergence of specialty coffee, the search for ever new flavor notes, the study of microorganisms in the cherry, and a holistic understanding of fermentation as a tool for creating new aromas, the motivation and experimental enthusiasm of producers increased.

Since the 2000s, we have seen a steep increase in post-harvest processes that move between the poles of depulped and non-depulped coffees.

New markets with new taste preferences have fueled creativity in post-harvest processes just as much as pragmatic considerations:

how can more water be saved in the processes?

How can a lot of coffee be processed in a small space?

And how can one create complex aromas with simple means?

We regularly receive coffees that have been processed with new technologies, sequences, or bacteria. The field for experimentation is open—and if it tastes good, these coffees find a market. Nevertheless, these coffees also sometimes perplex us. I expressed my thoughts on this here a few years ago.

Fact-sheet on post-harvest processes

Over the years, there have been repeated efforts to break down the steadily growing number of post-harvest processes into a single graphic.

We are currently working on our own graphic, which we will then publish here. However, we would like to share two graphics with you. One is from Tim Willems from 2019, who manages our farm in Nicaragua. The other is from Chris Kornman of Royal Coffee.

Both graphics are very precise. While Tim focuses on the sequence, Chris names the individual work steps that do or do not take place for a given post-harvest process.

Chris Kornman, Royal Coffee, 2020

Tim Willems, 2014

Naming, taste preferences, and possibilities

So far, the focus in our article has been on the mechanical processing steps, that is, whether the coffee pulp is removed or not. Explaining in terms of processing steps will always be more precise than naming the fermentation method—or who knows what a koji fermentation is? Those in the know might be familiar with this post-harvest process. The name suggests koji molds were used, but not how, when, at what temperature, for how long, and with what intensity. Even with a koji fermentation, there are countless combinations of processes.

The more we discuss the work steps and less the pleasing names, the better we understand what exactly is meant by which coffee fermentation.

The choice of method for how a coffee is further processed after picking depends on various factors. And just as there is no best coffee, there is no best processing method for coffee. The post-harvest processes always depend on

• the volume of cherries to be processed
  
• space availability
• access to knowledge
• access to tools
• access to capital
• target market—mass market or niche market
• etc.

On many farms today, I see rain barrels that have been used since the early 2010s especially in Costa Rica for so-called anaerobic fermentations before this approach spread worldwide. These barrels are inexpensive and sturdy.

The more capital-intensive variant is to work with steel tanks, as is done in wine production. The basic effects are the same, but steel tanks allow for even more pressure to be applied, analogous to maceration carbonique in Beaujolais wine.

This process was first established in a small circle of coffee producers and is still found in many places today. Those who carry out this process in a cooler environment extend the retention period and create a new flavor profile. For this purpose, specially air-conditioned rooms are created in which the coffee ferments.

It seems that every new idea for an altered fermentation protocol is now received with great curiosity, applied, then refined and further developed. However, by a very limited circle of coffee producers who bring the knowledge, technical infrastructure, and potential buyer network.

This offers opportunities and risks, but above all it accelerates knowledge growth on the production side. The sensory diversity of these coffees can hardly be compared with a "traditionally" washed coffee.

Part 2: How do coffees from various processing methods taste?

Through the various processing methods, aromas can be added to a coffee that it did not have before. Depending on which post-harvest process is chosen, other attributes such as aromas, flavor notes, acidity, and texture can be influenced.

Graphic

From our experience, texture is the least changed by the type of fermentation. New aromaticity, on the other hand, results relatively quickly from the process.

The prerequisite for a soft and round texture is a high and uniform ripeness level.

If this is not the case, fermentation cannot create "softness"—except, and I've had such coffees for the first time a few years ago from La Palma y el Tucán, lactic acid bacteria are added, which often can have a positive influence on texture. Likewise, a reposa, which we standardly do in Nicaragua, can somewhat increase the perceived texture—but only if the cherries are already well ripened and uniform. Good raw material is needed to achieve a good or even better fermentation result.

Excursus on coffee fermentation: from risk to opportunity

How does coffee taste that has been depulped in a demucilaginador (eco-pulper)?

Coffees that are depulped and demucilaged in a water-saving demucilaginador are closest to what is called washed coffees. Before demucilaginators existed, the coffee was freed from the mucilage with the help of fermentation as a mechanical process before being washed.

Today, it is becoming standard practice at medium-sized and larger beneficios to use demucilaginators. During this process, no fermentation occurs because the seeds are pressed out of the cherry and demucilaged within a few minutes.

Ecopulper / demucilaginador on Finca La Bastilla in Nicaragua, 2017

Sensory notes

• this efficient type of washed coffee often shows the pure character of the green coffee.
• The ripeness level and uniformity become clear—a high ripeness level favors a soft texture, high uniformity makes for a balanced cup
• since no fermentation takes place, no new aromas are added to the coffee
• thus, the acidity is often very present, and complex aromas play a secondary role
• these coffees show what the foundation in a region can offer

Mucilage, miel, slime, Finca La Bastilla, Nicaragua, 2017

What does a reposa, a pause before depulping, accomplish?

If picked coffee cherries are not picked immediately but first rest for several hours in a controlled environment, it is called a reposa in large parts of Central America—a pause.

I first encountered this years ago in Nicaragua when I saw a full funnel for coffee cherries late in the evening. I asked my companion if the cherries shouldn't be depulped immediately? "No," came the reply—the reposa in a cooler environment (due to nighttime temperatures) slows down a fermentation process, "not much can happen."

The next morning, the coffee was depulped, fermented under water, and washed. Today, this process is our standard process on Finca Santa Rita in Nicaragua. We wanted to understand exactly what happens and conducted a research project with ZHaW. A sample with reposa was processed, and the control sample was processed without reposa.

Barbara Beck (photo above) examined and documented the development of yeasts, bacteria, and acids in this paper.

Sensory notes

We rated coffees with a reposa about 1 point higher, for example with 83 instead of 82. Reposa coffees often show somewhat more sweetness, somewhat more texture, but especially a better integrated acidity. Sometimes we encounter reposa coffees that bring slight fruitiness with them.

How does coffee taste that has been depulped on a despulpadora?

Especially on smaller farms or in smaller, centralized beneficios, coffee is separated from the fruit pulp with despulpadoras. Since most of the slime remains stuck to the seed, the producer is faced with the choice of either drying the coffee with the mucilage on the seed (honey) or removing the mucilage through fermentation as a biological process. This fermentation can be done in the open air, in a closed container, or under water. The time for hydrolysis, the breakdown of the pectin that holds the slime together, is different depending on the method chosen and can have a potential effect on flavor.

Despulpadora on Mil Variedades, our farm in Nicaragua

Sensory notes

Depulped coffees often bring the flavor of a washed-demucilaged coffee, which can show further facets.

• often the aromas are more intense and go beyond the basic coffee flavor
• the acidity often gains complexity
• depulped coffees in parchment that are fermented under water often gain a radiant, clear, and fresh acidity
• depulped coffees in parchment that ferment without water often gain fruitier notes.
• Depending on whether the coffee is fermented in even layers or in an uneven pile, the coffees show more or less consistency

How do honey-processed coffees taste?

Coffees depulped on a despulpadora are—as described above—fermented to release the slime. The slime, or mucilage, is often called miel in Spanish, meaning honey. In the back-translation to English, miel becomes honey, and so we speak of honey process when we mean depulped coffee that dries with the mucilage layer.

The proportion of the slime layer and the length of drying, as well as the thickness of the stacked layers and the prevailing temperature, all matter. Less honey on the seed favors faster drying of the seed to about 12% residual moisture, while more honey requires longer drying.

A honey-processed coffee dries in Ocotal, Nicaragua

Especially in Costa Rica, different remaining amounts of honeys are used. Less honey on the parchment, for example 25%, allows for faster drying. This type is often called white or yellow honey because the small amount of miel on the parchment turns yellowish. With 50% or more honey, the coffee dries more slowly in the parchment and the color of the honey becomes reddish; with so-called black honey, it's even dark brown. There are no limits to the variety of drying time in combination with the proportion of honey on the parchment.

A black honey, Ocotal, Nicaragua

Sensory notes

• white honeys often resemble washed and/or water-fermented, depulped coffees. They show a balanced coffee, often with pronounced acidity
• yellow honeys often bring somewhat more perceived texture and slightly fruity nuances to the cup
• red honeys already show distinctly fruitier notes gained through fermentation on the seed. Often, the acidity recedes in the background
• black honey coffees are often accompanied by dark fruity to chocolatey, or even lush fruity notes
• in general more intensive honey processes can add a new layer of complexity to the coffee, often pronounced texture
  

however, we also encounter many honeys where the clarity of aromas and acids is obscured. This often has to do with the fact that fermentation on the parchment cannot be controlled very well—unlike, for example, with intact cherries

How do naturals taste?

"Naturals," or "coffee seeds dried in the cherry," were in earlier times the opposite of "classic washed coffee." Today, it still holds true that the coffee seeds dry inside the cherry before the dried fruit pulp is rubbed off. However, especially in the last ten years, new types of fermentation and drying protocols have become established for naturals.

"Back then," it was thought that naturals had more sweetness and less acidity. Today, it's true that basically nothing holds true anymore.

We've had naturals that were as lean as washed coffees. Then we had naturals that were lush and fruity, and then we had naturals that had much more (vinegary) acidity than their washed counterparts.

Many nutty-chocolatey coffees from Brazil are naturals, but not fruity (bubble on the far left of the diagram). The white arrows don't mean that all coffees that dry ferment develop sensorially that way. Certain coffees are naturally fruity and can become even fruitier through targeted fermentation. Other coffees, such as those from Brazil, are more naturally nutty-chocolatey. These coffees may not be able to be given a tropical note if the green coffee doesn't naturally allow for it.

The degree and duration of fermentation define the aromas that can be created through drying in the cherry.

Over the years, we have conducted numerous fermentation experiments on our farm in Nicaragua. Many experiments failed or were time-consuming and showed no massive sensory gain.

There are now no limits to the creativity of how coffee can be fermented. This offers many opportunities but also risks.

How do heavily fermented coffees taste?

Heavily fermented coffees add notes to the coffee that would otherwise not be present. We often use terminology that we wouldn't otherwise use for more classically processed coffees. It's about being open to something new. Often, the learned vocabulary is not sufficient to do justice to these coffees. It's somewhat like when we taste natural wine—we use a different vocabulary there too.

We have collected aromas we repeatedly discover in heavily fermented coffees in the graphic.

What does a cold room accomplish?

A cold room, or cold room, is a space that is cooled with air conditioning to a maximum of 16 degrees. Coffee is usually first placed in barrels and then brought to the cold room, where fermentation slows down or continues at a slower pace.

Cold room in Nicaragua with nitrogen bottles to displace oxygen from the barrels.

The cooler temperatures slow down fermentation, so cold room fermentations can sometimes take 40 days or even longer. This can lead to super lush notes that are very intense. Our experience is that coffees from this fermentation often take longer to become truly stable.

In 2018, we had a sample from Nicaragua for the first time that—to put it mildly—we didn't like. We kept 1kg of the coffee and roasted it a year later. The coffee was suddenly balanced, no longer sharp, and very sweet.

How do coffees taste with the addition of microorganisms?

By adding microorganisms during the fermentation process, which takes place in a controlled environment (such as tanks), new reactions between yeasts, bacteria, and sugars can be triggered. This inoculation of the ferment, the substance to be fermented, only works if the microorganisms are still intact. For this, they must be kept cool. This process therefore requires not only great precision but also a high hygiene standard and a well-equipped laboratory. These are criteria that very few coffee farms can meet.

One farm that works creatively with bacteria and yeasts is Finca el Paraíso by Diego Bermudez in Colombia. These coffees often have lush, fragrant, and fruity notes with strong intensity and an aroma spectrum not found in un-fermented coffees.

How do coffees taste that have been processed with yeast?

Since the mid-2010s, coffees have been offered, first without comment and later with much commentary, to which isolated yeast strains were added during fermentation. I have written about the process and its background here.

Lucia Solis and Oleneska Cespedes are two engineers who make the topic precise and accessible to understand. I was involved in a project in Honduras with Lucia Solis where we scaled laboratory experiments with yeast fermentation to several tons.

https://www.luxia.coffee/

In terms of taste, yeast fermentation—like wine—can be controlled with different yeasts. Lallemand were the first to launch a special yeast for coffee cherry fermentation about ten years ago. In Nicaragua too, we have worked with various strains such as Intenso or Cima.

Intenso makes the coffee somewhat more intense, here fruitier. Cima somewhat elevates the texture and length of the coffee. The yeast cannot work miracles, but it can enhance what is already there.

Coffee yeast is like an amplifier. Good becomes maybe better, bad becomes worse.

Again, it depends on the quality of the raw material, in this case the coffee cherries. Ripe cherries naturally bring a high level of sugar, yeasts and bacteria, the starting point is good, and an added yeast can enhance or accelerate the metabolism.

Precision is required here: water temperature for preparing the yeast, the amount, and retention time in a tank have a massive influence on success/failure.

Cloak-and-dagger operation with Lucia Solis and coffee yeast, 2018

How do coffees taste that have been fermented with koji molds?

Christopher Feran spent several years developing a process with koji molds, which caused major waves in the specialty world in 2021. Koji is widely used in Asia and is used to produce sake, miso, and other umami-rich products.

The great advantage of koji is that mold-specific enzymes convert starches into easily available sugars that then form new compounds with existing bacteria and yeasts during fermentation.

Christopher's blog article reads like a mixture of history, science fiction, and recipe that makes you want to taste such coffees.

The coffees we've been able to taste so far are just as fruity and sweet as the best yeast-fermented coffees are. Coffee Circle recently had a koji-fermented coffee in their range.

But here too: every inoculated mold or yeast strain can only work as well as the raw material allows. The cherries must be of high quality for the process to produce desirable aromas.