Coffee brewing methods and their impact on taste

2016 version of the SCA Flavor Wheel

The 1995 version

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

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

The collection of descriptive words is diverse. The Flavor Wheel first groups aroma categories before differentiating further from these larger groups. While fruity and nutty notes are positively connotated, notes like petrol or medicinal can diminish 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 / post-harvest process - terminology and influence on coffee flavor

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

Before sowing a coffee variety, it's 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's already ripe.

There are large 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. As soon as the cherry is separated from the stem, a small wound opens in what's called the exocarp.

Bacteria and yeasts can now react and activate 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 now in potentially has an influence on quality and thus also the final taste of the coffee.

The post-harvest process doesn't begin with drying the cherry, pulping, or fermentation, but rather the moment the cherry is separated from the stem.

What matters now to ensure that all the positive properties inherent in the coffee cherry result in good flavor is what we'll clarify in the following sections.

Step 1: from 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, employees pick the cherries and put them in a cloth, a plastic bag tied around their waist, or a baskets made of straw or similar.
• when this is 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 trigger unwanted fermentation
• the longer coffee cherries sit in the bags, the greater the risk that unwanted or off-flavors form already in the first step after picking
• the bags must either be replaced or always thoroughly washed

Plastic bags with pulped and washed coffee sit on a tarp and not directly on the ground.

not too much weight, not too large bags

• if you've ever been present at a wine harvest, you may have seen that particularly valuable grapes are transported in only a single layer in small, multi-tiered containers. This reduces the weight pressing on the grapes and prevents them from being crushed
• coffee cherries are significantly harder than grapes, but it can happen that the cherries at the bottom of 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 critical
• strategies and opinions vary widely here
• it is still recommended in globally valid literature to pulp coffee cherries as quickly as possible to avoid "risking" fermentation - which makes clear that for many, fermentation is unwanted and a source of danger rather than an opportunity for more aroma
• in fact, the retention time of the cherries before the next processing step is decisive, depending on what is desired

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

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

• in much of Central America, there is the tradition of reposa, a storage of coffee cherries for several hours before further processing
  

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

• we had this scientifically accompanied by the ZHaW: you'll find the work further below

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

Whether the coffee had a reposa or whether the cherries were processed shortly after picking has no influence on the following steps. Now it's time to decide what happens to the coffee cherries: is the flesh pressed off, or does it remain intact?

The picked and sorted quality plays a major role. If mostly under-ripe cherries were picked, there's hardly any intention for direct drying of the coffee cherries (so-called natural). The cherries don't bring enough sugar with them, which could provide new aromas in intense fermentation. If the cherries are very ripe and uniformly sorted, all further processing steps are possible.

With all further steps, aroma can now be added to the coffee that wasn't there before.

Through targeted fermentation, aroma precursors develop, which are then converted into aromas during roasting.

A fundamental decision: remove 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 aromatics should be promoted.

1. Remove all the fruit flesh: mechanical demucilagination

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

*especially at peak of harvest, when most coffee cherries arrive for processing in a short time, the 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 aren't 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 delicate, clean acidity. The texture depends on the ripeness of the cherries, as does the type of aroma. However, since this is often about volume coffees, less uniform cherries end up in processing, which limits the aromatic complexity of the coffee.

Many possibilities with the demucilaginators

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

2. Partially remove the fruit flesh: pulping

• here either a despulpadora is used, a pulping machine operated manually or mechanically - often with gasoline
• cherries fall into a funnel and are pressed by a rotating drum against a front plate, where the flesh is separated from the seed
• depending on cherry size and flesh thickness, adjustments to the front plates must be made so the beans are pressed from the cherries without damage
• the majority of the slime (mucilage) remains stuck to the seed

Despulpadoras are not designed to remove all the flesh and thus the slime, which is why the process of fermenting as a biological process (= loosening the slime) and washing developed - more on that later.

3. Leave the cherry intact - the pulp stays on - 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 laid out in a dry location until the seed inside has a remaining moisture of about 12%
• in the increasingly sophisticated methods developed, technical and biological aids are used to create ever more aromas that weren't present before
• natural processing produces both the best and worst coffees I've 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 completely different level of precision in how it's done 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 pulped and washed.

For many processors, the ability to pulp and wash coffee was a major step toward more consistency. Processes could be better controlled, overall coffee quality increased, which also shaped 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've seen a steep increase in post-harvest processes that lie between the poles of pulped and unpulped coffees.

New markets with new taste preferences have fueled 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 experimentation is open - and if it tastes good, these coffees find a market. Yet these coffees also regularly perplex us. I expressed my thoughts 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 constantly growing number of post-harvest processes in a graphic.

We're currently working on our own graphic, which we'll then publish here. However, we'd like to share two graphics with you. One is by Tim Willems from 2019, who runs our farm in Nicaragua. The other is by Chris Kornman from Royal Coffee.

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

Chris Kornman, Royal Coffee, 2020

Tim Willems, 2014

Naming, taste preferences, and possibilities

Until now, our article has focused on mechanical processing steps, namely whether the coffee flesh is removed or not. Explaining in processing steps will always be more precise than naming the fermentation method - or who knows what koji fermentation is? Those in the know might recognize this post-harvest process. The name implies that koji fungi were used, but not how, when, at what temperature, how long, and at what intensity. Even with koji fermentation, there are countless combinations of processes.

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

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

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

On many farms nowadays, 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 stable.

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

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

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

This presents both opportunities and risks, but most importantly, it accelerates knowledge growth 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 various processing methods taste?

Through different processing methods, aromas can be added to coffee that it didn't 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 least changed by the type of fermentation. New aroma, on the other hand, develops relatively quickly from the process.

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

If this isn't present, fermentation can't produce "softness" - except, and I've tried such coffees for the first time a few years ago from La Palma y el Tucán, lactobacilli are added, which can often have a positive effect on texture. Similarly, a reposa, which we do standardly in Nicaragua, can somewhat increase the perceived texture - but only if the cherries are already well-ripe and uniform. You need good raw material to achieve good or even better fermentation results.

Excursus on coffee fermentation: from risk to opportunity

How does coffee taste when pulped in a demucilaginador (eco-pulper)?

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

Today it's becoming standard at medium and large beneficios to use demucilaginators. With this process, no fermentation occurs because the seeds are pressed and deslimed from the cherry in just a few minutes.

Ecopulper / demucilaginator 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 and uniformity become clear - high ripeness promotes soft texture, high uniformity makes a balanced cup
• since no fermentation takes place, no new aromas are added to the coffee
• so acidity is often very present, complex aromas play a minor role
• these coffees show what the foundation can offer in a region

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

What does a reposa, a pause before pulping, achieve?

When picked coffee cherries are not pulped immediately but first rest for several hours in a controlled environment, this is called reposa in much of Central America - a pause.

I first encountered this years ago in Nicaragua when I saw a full collection bin of coffee cherries late in the evening. I asked my companion if the cherries shouldn't be pulped immediately? "No," he said at the time - the reposa in a cooler environment (due to nighttime temperatures) slows down fermentation, "not much can happen."

The next morning the coffee was pulped, fermented under water, and washed. Today this process is our standard process on Finca Santa Rita in Nicaragua. We wanted to understand what exactly happens and conducted a research project with ZHaW. A sample with reposa was processed, while 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 reposa about 1 point higher, for example 83 instead of 82. Reposa coffees often show a bit more sweetness, a bit more texture, but especially a better integrated acidity. Sometimes we encounter reposa coffees that bring slight fruitiness.

How does coffee taste when pulped on a despulpadora?

Particularly on smaller farms or in smaller, centralized beneficios, coffee is separated from the flesh with despulpadoras. Since the majority of the slime sticks to the seed, the producer faces only the decision of whether to dry the coffee with the mucilage on the seed (honey) or to remove 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, varies depending on the chosen method and can potentially affect the taste.

Despulpadora on Mil Variedades, our farm in Nicaragua

Sensory notes

Pulped coffees often bring the taste of a washed-desiccated coffee that can show further facets.

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

How do honey processed coffees taste?

Coffees pulped on a despulpadora are - as described above - fermented to remove the slime. The slime, or mucilage, is often called miel in Spanish, meaning honey. In back-translation to English, miel becomes honey, and so we talk about the honey process when we mean pulped coffee that is dried with the mucilage layer.

The amount of the slime layer, the length of drying, the thickness of the stacked layers, and the prevailing temperature all matter. Less honey on the seed promotes faster seed drying to about 12% remaining moisture, more honey requires longer drying.

A honey-processed coffee dries in Ocotal, Nicaragua

This is especially done in Costa Rica with various remaining amounts of honeys. 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 on the parchment and the color of the honey becomes reddish, in so-called black honey even dark brown. The variety of drying time in combination with the amount of honey on the parchment is endless.

A black honey, Ocotal, Nicaragua

Sensory notes

• white honeys often remind of washed and/or under-water fermented pulped coffees. They show a balanced coffee, often with pronounced acidity
• yellow honeys often bring a bit more perceived texture and slightly fruity nuances to the cup
• red honeys already show noticeably fruitier notes gained through fermentation on the seed. Often the acidity recedes with this type
• black honey coffees are often accompanied by dark fruity to chocolatey, or even lavish fruity notes
• generally more intensive honey processes can add a new layer of complexity to the coffee, often a pronounced texture
  

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

How do naturals taste?

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

"Back then" it was said that naturals had more sweetness and less acidity. Today, it's said that basically nothing 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 (vinegar) acidity than their washed counterpart.

Many nutty-chocolatey coffees from Brazil are naturals, but not fruity (bubble far left in the diagram). The white arrows don't mean that all coffees dried with fermentation develop sensorily this way. Certain coffees are naturally fruity and can become even fruitier through targeted fermentation. Other coffees, such as those from Brazil, tend to be nutty-chocolatey. These coffees may not 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 produced through drying in the cherry.

Over the last few years, we've conducted numerous fermentation experiments on our farm in Nicaragua. Many experiments failed or were laborious and showed no significant sensory gain.

There are now no limits to creativity in 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 wouldn't otherwise be present. We often use terminology we wouldn't use for more classically processed coffees. It's a matter of opening yourself to something new. Often the learned vocabulary isn't enough to do these coffees justice. It's somewhat like when we taste natural wine, where we also use different vocabulary.

We've 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 down to a maximum of 16 degrees with air conditioning. Coffee is usually first put into barrels and then brought into the cold room, where fermentation starts or continues slowed.

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

The cooler temperatures slow fermentation, so cold room fermentations can sometimes last 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 that coffee and roasted it a year later. The coffee was suddenly balanced, no longer sharp and very sweet.

How do coffees taste when microbacteria are added?

By adding microbacteria during the fermentation process, which takes place in a controlled environment (e.g., 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 microbacteria are still intact. For this, they must be kept cool. This process therefore not only requires great precision but also a high hygiene standard and a well-equipped laboratory. These are criteria that very few coffee farms can meet.

A 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 non-fermented coffees.

How do coffees taste when 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've written about the process and its background here.

Lucia Solis and Oleneska Cespedes are two engineers who make the subject precise and clearly accessible. With Lucia Solis, I was involved in a project 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 fermenting coffee cherries about ten years ago. In Nicaragua, too, we've worked with different strains like Intenso or Cima.

Intenso makes the coffee somewhat more intense, here fruitier. Cima lifts the texture and length of the coffee a bit. The yeast can't work miracles, but it can enhance what's already there.

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

Here too, it depends on the quality of the raw material, in this case the coffee cherries. Ripe cherries naturally bring a high degree of sugar, yeasts, and bacteria, the starting situation is good, and an added yeast can intensify or speed up metabolism.

Precision is required here: water temperature for mixing the yeast, the amount, and the retention time in a tank massively affect success or failure.

Covert action with Lucia Solis and coffee yeast, 2018

How do coffees fermented with koji fungi taste?

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

The great advantage of koji is that fungal enzymes convert starches into easily available sugars, which then form new compounds with existing bacteria and yeasts in fermentation.

Christopher's blog article about it 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 assortment.

But here too: every inoculated fungal 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.