Coffee processing methods and their influence on taste

2016 version of the SCA Flavor Wheel

The 1995 version

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

In early 2025, the first study on a Canephora Flavor Wheel was also published.

The collection of descriptive words is diverse. The Flavor Wheel first groups aroma categories, before differentiating from these broad groups. While fruity and nutty notes are positively connoted, notes like petrol or medicine can disrupt enjoyment.

The aroma wheel provides us with a selection of aromas that can be tasted in coffee more or less frequently, 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 / Post-Harvest Process - Clarification of Terms and Influence on Coffee Flavor

If we imagine coffee as a puzzle, we notice countless small pieces that are needed for everything to fit together harmoniously. This applies to a perfectly brewed espresso as well as 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 they are picked - because red is not always the same as red.

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

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

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

Bacteria and yeasts can now react and activate their metabolism, the fruit comes into contact with oxygen, and the opening attracts insects with its sweet aromas, which in turn carry bacteria and yeasts. Every stage the coffee cherry is in now potentially influences the quality and thus the final taste of the coffee.

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

What matters now for all the positive characteristics inherent in the coffee cherry to result in good taste will be clarified in the following sections.

Step 1: from tree to further processing

The following points should be considered when separating the cherries from the stem

clean storage location

• where to put the picked cherries? Usually, workers pick the cherries and place them in a cloth, a tied-up plastic bag, or a basket-like container.
• once full, they put the cherries into a larger plastic bag. These bags quickly become a melting pot of insects, bacteria, sugars, and yeasts, which can initiate an unwanted fermentation.
• the longer coffee cherries remain in the bags, the greater the risk that unwanted or off-flavors will develop in the first step after picking.
• the bags must either be replaced or always thoroughly washed.

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

not too much weight, not too large bags

• anyone who has ever been to a grape harvest may have seen that particularly valuable grapes are transported in only one layer in small, multi-layered containers. This reduces the weight pressing on the grapes, and they are not already crushed.
• coffee cherries are much harder than grapes, but it can happen that the lowest cherries in the transport bag are already crushed.
• these cherries should be sorted out before further processing for the highest quality requirements.

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 recognized literature to pulp 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 aroma.
• in fact, the intermediate storage time of the cherries before the next processing step is decisive, depending on what is sought.

• coffees that are mechanically demucilaged or pulped before water treatment are often processed very quickly (on the same day)

• especially in Colombia, we know that producers treat coffee cherries with ozone to eliminate yeasts and bacteria on the surface. In further processing steps, they then work with the microorganisms found within the cherry, or add starter cultures.

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

• in Nicaragua, for example, we opt for a 16-hour rest period for the cherries before further processing. In contrast to the control sample, which is processed immediately, we observe slightly more sweetness and acidity in the roasted coffee.
  

• we had this scientifically supervised by ZHaW: you can find the work further down.

Step 2: the agony of choice - to pulp or not to pulp?

Whether the coffee underwent a reposa or whether the cherries are processed shortly after picking has no impact on the subsequent steps. The decision now is what happens to the coffee cherries: is the pulp pressed out, or does it remain intact?

The picked and sorted quality plays a major role here. If mostly half-ripe cherries were picked, direct drying of the coffee cherries (so-called Natural) is hardly aimed for. The cherries bring too little sugar to provide new aromatics in an intense fermentation. If the cherries are very ripe and uniformly sorted, all further processing steps are suitable.

With all further steps, an aroma can now be added to the coffee that would not have been present before.

Through targeted fermentation, aroma precursors are formed, 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 (so-called mesocarp) removed? This decision not only defines the further procedure but also the intention of which aroma should be emphasized.

1. Removing all the pulp: mechanical demucilagination

• here, so-called demucilaginators or eco-pulpers are used
• large machines that not only expose the seed but also remove all the mucilage through friction and high-pressure water jets.
• thus, no fermentation occurs.
• the coffee beans emerge from the process as wet parchment after a few minutes and then go into drying as quickly as possible.

*especially at the Peak of the Harvest, i.e., when most coffee cherries are delivered for processing in a short time, demucilaginators are the most reliable and efficient tool to process the cherries.

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

Many possibilities with Demucilaginators

Due to their high efficiency and low water consumption, demucilaginators are now used worldwide. Newer generations of these devices allow for precise adjustment of the amount of mucilage that should adhere to the coffee seed. Especially in Costa Rica, producers refined this technique in the 2000s and invented various types of Honeys.

2. Partially removing the pulp: pulping

• this involves working with a despulpadora, a pulping machine operated manually or mechanically - often with gasoline.
• cherries fall into a hopper and are squeezed by a rotating drum against a front plate, where the 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.
• the majority of the mucilage remains on the seed.

Despulpadoras are not designed to remove all the pulp and thus the mucilage, which is why the process of fermentation as a biological process (i.e., detaching the mucilage) and washing has developed – more on this later.

3. Leaving the cherry intact - the pulp remains - Natural

• the oldest method of 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 in a dry place until the seed inside has a residual moisture content of approx. 12%
• in the now highly sophisticated methods, technical and biological aids are used to create ever more aromas that were not present before
• Natural processing produces the best and worst coffees I have ever tasted

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

Until the turn of the millennium, the burning question in post-harvest processing was: washed or not washed - Naturals were the way coffees were dried for decades, but we're talking about a different level of precision than what is practiced today. With increasing efficiency in processing and new market demands, there was a steep rise in wet mills or beneficios in the 1970s, which were collection points where coffee cherries were pulped and washed.

The ability to pulp and wash coffee was a big step for many processors towards more consistency. The processes could be better controlled, the general coffee quality increased as a result, which ultimately also helped shape a mass taste.

With the advent of specialty coffee, the search for ever new flavor notes, the research into microorganisms in the cherry, and the holistic understanding of fermentation as a tool for creating new aromas, the motivation and experimentation of producers increased.

Since the 2000s, we have seen a steep rise in post-harvest processes that lie between the poles of pulped and unpulped coffees.

New markets with new taste preferences have spurred creativity in post-harvest processes, as have 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 complex aromas be created with simple means?

We regularly receive coffees that have been processed with new technologies, sequences, or bacteria. The field for experiments is open - and if it tastes good, these coffees find a market. However, these coffees also keep irritating. I commented on this a few years ago here.

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 graphic.

We are currently working on creating our own graphic, which we will also 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 one 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 respective post-harvest process.

Chris Kornman, Royal Coffee, 2020

Tim Willems, 2014

Naming, Taste Preferences, and Possibilities

So far, the focus of our article has been on the mechanical processing steps, i.e., whether the coffee pulp is removed or not. Explaining processing steps will always be more precise than simply naming the fermentation method – or who knows what a Koji Fermentation is? To those in the know, this post-harvest process might sound familiar. The name implies that Koji fungi were used, but not how, when, at what temperature, for how long, or with what intensity. Even with a Koji fermentation, there are countless combinations of processes.

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

The choice of method for processing coffee after picking depends on various factors. And just as there is no "best coffee," there is also no "best" processing method for coffee. Post-harvest processes are always dependent on

• volume of cherries to be processed
  
• space conditions
• access to know-how
• access to tools
• access to capital
• targeted market - mass market or niche market
• etc.

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

The more capital-intensive option involves working with steel tanks, as is done in wine production. The basic effects are the same, but steel tanks can handle even more pressure, analogous to maceration carbonique for Beaujolais wine.

This process first established itself among a small circle of coffee producers and is still found in many places today. Those who carry out this process in a cooler environment prolong fermentation, thereby creating a new flavor profile. For this purpose, specially air-conditioned rooms are created where the coffee is fermented.

It seems that today, every new idea for a modified fermentation protocol is met with great curiosity, applied, then refined and further developed. However, this is done by a very limited circle of coffee producers who bring the know-how, technical infrastructure, and a potential buyer network.

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

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

Through various processing methods, aromas that were not previously present can be added to a coffee. Depending on the post-harvest process chosen, other attributes such as aromas, flavor notes, acidity, and texture can be influenced.

Graphic

In our experience, texture is least affected by the type of fermentation. However, a new aromatic profile emerges relatively quickly from the process.

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

If this is not present, fermentation cannot induce "softness" - unless, and I first tasted such coffees a few years ago from La Palma y el Tucán, lactobacilli are added, which can often have a positive effect on the texture. Similarly, a reposa, which we do as standard in Nicaragua, can somewhat increase the perceived texture - but only if the cherries are already well ripe and uniform. Good raw material is needed to achieve a good or even better fermentation result.

Excursion into Coffee Fermentation: From Risk to Opportunity

How does a coffee that has been pulped in a demucilaginator (Eco-Pulper) taste?

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

Today, it is standard for medium and larger beneficios to use demucilaginators. During this process, no fermentation occurs because the seeds are pressed out of the cherry and demucilaged in a few minutes.

Ecopulper / Demucilaginator at Finca La Bastilla in Nicaragua, 2017

Sensory Notes

• These efficient types of washed coffees often reveal the pure character of the green coffee.
• The ripeness and uniformity are clearly visible - a high degree of ripeness promotes a soft texture, a high uniformity makes a balanced cup.
• Since no fermentation takes place, no new aromas are added to the coffee.
• Thus, acidity is often very present, while 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 break, before pulping achieve?

When picked coffee cherries are not pulped immediately but instead rest for several hours in a controlled environment, this is referred to as a reposa – a rest – in many parts of Central America.

I first encountered this years ago in Nicaragua, when I saw a full collection hopper for coffee cherries late in the evening. I asked my companion if the cherries shouldn't be pulped immediately? "No," was the reply then – the reposa in a cooler environment (due to nighttime temperatures) slows down a fermentation process, so "not much could go wrong."

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

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

Sensory Notes

We rated coffees with a reposa about 1 point higher, e.g., 83 instead of 82. Reposa coffees often show a bit more sweetness, a bit more texture, but above all, a better-integrated acidity. Sometimes we encounter reposa coffees that bring a slight fruitiness.

How does coffee taste that has been pulped on a Despulpadora?

Especially on smaller farms or in smaller, centralized Beneficios, coffee is separated from the fruit pulp using Despulpadoras. Since the majority of the mucilage remains on the seed, the producer only has to decide whether to dry the coffee with the mucilage on the seed (honey), or whether to remove the mucilage through fermentation as a biological process. This fermentation can be done in the open air, in a closed container, or underwater. The time for hydrolysis, the breakdown of the pectin that holds the mucilage together, varies depending on the chosen method and has a potential effect on the taste.

Despulpadora at Mil Variedades, our farm in Nicaragua

Sensory Notes

Pulped coffees often carry the taste of a washed-demucilaged coffee, which can reveal further facets.

• The aromas are often more intense and go beyond the basic coffee flavor.
• Acidity often gains complexity.
• Pulped coffees in parchment fermented underwater often gain a radiant, clear, and fresh acidity.
• Pulped coffees in parchment fermented without water often gain fruitier notes.
• Depending on whether the coffee is fermented in an even layer or an uneven pile, the coffees show more uniformity/non-uniformity.

How do Honey Processed Coffees taste?

Coffees pulped on a despulpadora are – as described above – fermented to dissolve the mucilage. The mucilage, or miel in Spanish, often means honey. When translated back into English, miel becomes honey, and so we speak of the honey process when we mean pulped coffee that is dried with the mucilage layer.

The proportion of the mucilage layer and the drying time, as well as the thickness of the piled layers and the prevailing temperature. Less honey on the seed favors faster drying of the seed to about 12% residual moisture, more honey requires longer drying.

A Honey-Processed coffee drying in Ocotal, Nicaragua

In Costa Rica, especially, different residual amounts of honey are used. Less honey on the parchment, e.g., 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 in parchment is dried more slowly and the color of the honey turns reddish, and even dark brown in so-called black honey. There are no limits to the variations in drying time in combination with the amount of honey on the parchment.

A Black Honey, Ocotal, Nicaragua

Sensory Notes

• White honeys often resemble washed, and/or underwater fermented, pulped coffees. They exhibit a balanced coffee, often with pronounced acidity.
• Yellow honeys often bring a slightly more perceived texture and subtle fruity nuances to the cup.
• Red honeys already show distinctly fruitier notes, acquired through fermentation on the seed. Acidity often recedes into the background with this type.
• Black honey coffees are often accompanied by dark fruity to chocolatey, or even lush fruity notes.
• Generally, more intense Honey processes can add a new layer of complexity to the coffee, often a pronounced texture.
  

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

How do Naturals taste?

"Naturals", or "coffees dried in the cherry," were once the opposite of "classically washed coffee." Today, it remains true that the coffee seeds dry within the cherry before the dried fruit flesh is rubbed off. However, especially in the last ten years, new types of fermentation and drying protocols have been established for Naturals.

"Previously," it was thought that Naturals had more sweetness and less acidity. Today, nothing really applies 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 (acetic) 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 do not mean that all dry-fermented coffees develop sensorily in this way. Certain coffees are naturally fruity and can become even fruitier through targeted fermentation. Other coffees, such as those from Brazil, are more nutty-chocolatey. These coffees may not be able to be given a tropical note if the green coffee naturally does not allow it.

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

Over the past few years, we have conducted numerous fermentation experiments on our farm in Nicaragua. Many experiments went wrong or were complex and did not show a massive sensory gain.

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

How do strongly fermented coffees taste?

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

Aromas that we consistently discover in strongly fermented coffees are collected in the graphic.

What does a cold room do?

A cold room, or cool room, are spaces cooled down to a maximum of 16 degrees Celsius with air conditioners. Coffee is usually first placed in barrels and then brought into the cold room, where fermentation slowly starts or continues.

Cold Room in Nicaragua with nitrogen cylinders to displace oxygen in 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, for the first time, we had a sample from Nicaragua that — to put it mildly — we disliked. 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 with added microorganisms taste?

By adding microorganisms during the fermentation process, which takes place in a controlled environment (e.g., tanks), new reactions between yeasts, bacteria, and sugars can be initiated. This inoculation of the ferment, the substance to be fermented, only works if the microorganisms are still intact. For this, they must be cooled. This process therefore requires not only great precision, but also a high hygienic 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, perfumed, and fruity notes with strong intensity and an aroma spectrum not found in unfermented coffees.

How do coffees processed with yeast taste?

Since the mid-2010s, coffees to which isolated yeast strains have been added during fermentation have been offered, first uncommented and later with much commentary. I wrote about the process and its derivation here.

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

https://www.luxia.coffee/

Taste-wise, yeast fermentation – similar to wine – can be controlled with different yeasts. Lallemand were the first to launch a special yeast for the fermentation of coffee cherries almost ten years ago. In Nicaragua, we have also worked with various strains like Intenso or Cima.

Intenso, as the name suggests, makes the coffee a bit more intense, fruitier here. Cima slightly enhances the texture and length of the coffee. Yeast cannot work miracles, but it can amplify what is already there.

Coffee yeast is something like an amplifier. Good might get better, bad gets worse.

Here again, it depends on the quality of the raw material, in this case, the coffee cherries. Ripe cherries inherently bring a high degree of sugar, yeasts, and bacteria, the starting situation is good, and added yeast can enhance or accelerate the metabolism.

Precision is required here: Water temperature for mixing the yeast, the quantity, and the residence time in a tank massively influence success/failure.

Night and fog operation with Lucia Solis and coffee yeast, 2018

How do coffees fermented with Koji molds taste?

Christopher Feran worked for several years to establish a process with Koji molds, which caused a big stir in the specialty coffee 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 the mold's own enzymes process starches into readily available sugars, which then form new compounds with existing bacteria and yeasts during fermentation.

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

The coffees we've tasted so far are as fruity and sweet as the best yeast-fermented coffees. Coffee Circle recently had a koji-fermented coffee in its range.

But here, too, the rule applies: any inoculated fungi or yeast strains can only work as well as the raw material allows. The cherries must be of high quality for the process to produce desirable aromas.