Recent Developments in Coffee Processing
PART 1 | Understanding Coffee Processing, Fermentation, Modulations & Most of All: Flavours !
There are countless variables that impact the characteristics a coffee bean expresses: The coffee plant’s botanical genetics are at play, as well as the terroir where it’s planted, the ripeness of the picked coffee cherry, the roasting style and quality, and, of course, the final brewing.
At Cuprima, we happen to think that post-harvest processing is one of the biggest determining factors of a coffee’s profile and characteristics. Of course, as with everything else in coffee, not only the methodologies but also the terms and results will vary from place to place -even from farm to farm between neighbours.
Coffee is processed differently throughout the world, sometimes due to tradition, or as the result of experimentation and intentional design. Producers globally explore and tweak their processing methods every day: The results can be astounding or appalling, such is the nature of experimentation.
There are several major categories of coffee processing that are generally recognised in the coffee industry. These are called by different terms depending on what country you are in or what language you are speaking, but the basic elements and steps are generally similar or at least recognizable.
Additionally, we tend to interchangeably use the terms ‘fermentation’ and ‘processing’. There is fermentation happening during processing, but not all processing is fermentation. Below, we briefly describe and explain not only the bullet points of the processing methods themselves but also touch briefly on the role that fermentation plays in each.
In this first part, we will talk about everything related to the various post-harvest processing procedures; it’s a rather specific and technical terminology, but this deep dive will make sure you are completely ‘on track’.
In a second part (coming up in a few weeks), we will then talk mostly about the challenges these new post harvesting techniques have in store for the specialty coffee industry.
1. PROCESSING | THE BASICS
In every case we start with the fresh cherry and -depending on the choices that we make in processing- we end either with dry parchment or dry cherry.
After sorting the cherries, we are dealing with a sticky wet skin mucilage that’s all stuck on the outside of that parchment so in order to get from our cherry to our dry product, these are our steps to removing the skin and mucilage.
In order to remove mucilage there are two main steps:
One step is to ferment -which brings in the power of micro-organisms (which break down carbon chains in and lattices and starches and sugars) that sort of break those into smaller pieces that are easier to dislodge from the surface of the parchment.
The other step is washing. There are kind of two parts to washing; there’s just rinsing away those carbon chain particles that are left after fermentation, and then there’s usually a little bit of turbulence added to with a paddle or or some other sort of mechanism which helps dislodge those particles from the the parchment layer and then wash away with the water.
2. THE BASIC COFFEE PROCESSES | NATURAL – WASHED – HONEY
Processing methods vary by geography, climate, logistics, and tradition, but the three main types are: washed, honey & natural. They essentially differ just by the point in the process at which the skin is removed.
NATURAL PROCESS
Natural coffees are processed with minimal intervention, meaning as little as possible is done to alter the naturally occurring fermentation inside the cherry. In fact, the natural coffee process is the oldest technique, requiring minimal water or electricity.
Natural coffees are fermented and dried whole, and fermentation takes place inside each individual bean for up to 30 days (weather permitting). No layer of the cherry is removed until packing for export.
Because of the fruit’s need for arid, warm conditions to dry outside, humidity or rain can pose major problems, such as spoilage. To encourage even drying and air flow, producers rake the fruit on raised beds, patios, or drying tables. Drying coffee is a riskier process than washing it because it requires more attention, and thus more labour, and so poses a higher risk of spoilage or over-fermentation.
Profile: Natural coffees enjoy a special fan club of coffee drinkers who appreciate the heady, wine-like aromas of blue and black fruits. Overripe blueberries or blueberry pancakes are common tasting notes.
Countries: Ethiopia, Yemen, Costa Rica, and Brazil. There’s lots of experimentation happening in the specialty coffee realm because of dried coffee’s unique flavours and minimalist methods.
HONEY PROCESS
In the honey process, the coffee cherry’s skin or pulp is removed within 24 hours of harvest. A percentage of what’s left behind — the mucilage, also called honey — remains on the seed while it dries, with the amount left behind driving the style and flavour of the final coffee. The mucilage ferments on the bean between 18 and 25 days, and poses less spoilage risk than a natural while achieving similar flavour results.
Costa Ricans have taken the honey concept to new heights, employing colour terms – yellow, red, and black – to denote the amount of mucilage remaining, which indicates how subtle or intense the flavour will be. Yellow is milder, while black is closest to a natural coffee.
Profile: Often creamy and sweet (in flavour, not sugar) with notes of caramel, burnt sugar, jam, blackberries and blueberries, and even baked and stewed notes like a boozy Barossa Shiraz from a hot vintage.
Countries: Brazil pioneered this technique called pulped natural, but Costa Ricans have elevated the category, which is trending through Central America. Specialty coffee producers also like the nuance this method can create.
WASHED PROCESS
Washed coffee is the most omnipresent – and potentially the most water-intensive – coffee process. Within 24 hours of harvest, cherries have their outer skin and most of the fruit flesh removed mechanically with a depulper machine. The beans then undergo fermentation in an open tank (stainless steel, cement, or even a plastic bucket) for around 18 to 36 hours, sometimes up to 72 hours, or even several days for a “wet” or underwater fermentation.
The fermentation method and amount of water used depends on resource availability and wastewater disposal options, though in essence, the process breaks down remaining mucilage so it can be removed or rinsed away with more water. This washed method is a conventional form of processing used all over the world for its ease and efficiency.
Less time required means less labour and less opportunity for things to go wrong (like spoilage). Additionally, wet processing naturally sorts out bad cherries, which weigh less than “good” cherries and float away down the water channels.
Profile: A terroir-driven cup with clean acidity and bright, articulate flavours depending on origin.
Countries: This method is used in almost every coffee-growing region, with the exception of those with scarce water resources, such as Yemen. If the product’s packaging doesn’t refer to a process, it was likely washed.
3. FERMENTATION
The microorganisms that perform fermentation are found almost everywhere, and they will begin to consume fuel as soon as they have access to it, which means that fermentation can actually begin before the coffee cherry is even picked. The more fruit material that is exposed to the environment and to the population of microorganisms (when the skin is removed from the cherry, for instance), the faster this process can happen.
Different types of bacteria and yeast populations -which will vary based on location, climate, and health of the local ecosystem- consume different compounds and convert them into fuel for their own use, (generally speaking they will continue to ferment whatever useful material is available to them until they are no longer able to survive) leaving behind useful byproducts such as ethanol and various acids. These converted compounds are incorporated into the cell structure of the seed and when heat is applied to these seeds in the roaster, these compounds are converted into the flavours we love so much in coffee: Complex flavours, fruity acids and other good -or at least interesting- things.
In a ‘natural process coffee’, the fruit material around the seed will ferment until either all of the fuel is metabolised or until the environment is too dry for them to live. In a ‘wash process coffee’, the fermentation might happen all the way through the drying process, depending on how much mucilage was left on the parchment after the washing was completed.
✔ A Nuance on Terminology
Fermentation occurs in almost every style of coffee preparation; it is an integral part of post-harvest coffee processing and plays a major role in the development of coffee flavour. And yet we often use the words ‘fermentation’ and ‘processing‘ interchangeably and wrongly: Although related, they are not identical. Fermentation is a natural event carried out by living microorganisms seeking sources of energy; processing is a purely agricultural series of mechanical and technical steps designed to prepare a plant product for export. Although fermentation can be used as part of processing, that distinction is important.
Interest in innovative post-harvest processing styles is building across the coffee supply chain. Producers and consumers are seeing benefits like unique flavour profiles that add value to coffee, help producers, processors, mills, farms, and coffees stand out from the crowd, and help diversify offerings.
One practice gaining recognition is anaerobic fermentation, meaning coffee is fermentated in a low-oxygen environment for some period of time.
1. ANAEROBIC FERMENTATION & CARBONIC MACERATION
To ferment in this way, fresh coffee is loaded into a container that is then sealed. Closing the container off to the ambient environment allows the carbon dioxide released from the fermenting fruit to build up and concentrate in the space. No oxygen (O2) is allowed to enter, and whatever oxygen was in the tank at the start is pushed out by the building carbon dioxide. This creates a low-oxygen environment and fosters the development of different microbial species than those common to oxygen-rich environments.
Microbes are the force responsible for how fruit tissue breaks down, the compounds and flavour precursors that are released during fermentation, and nearly all other fermentation outcomes. Therefore, creating an environment for fermentation that favors certain microbe species over others can result in unique flavour profiles – exactly what we see in well-cared-for anaerobically fermented coffees.
Anaerobic fermentation is a modulation to a process because it is an action taken to control or adjust (or to modulate) the process. The presence of air (aerobicis) is more complex and harder to monitor, the absence of air –anaerobic is easier to steer because you don’t have that oxygen variable.
So looking at the timelines washed, honey and natural, we can see such a modulation -in this case the anaerobic fermentation– can be added or implemented to any of these 3 basic processes – natural, honey & washed.
The moment in the process that this modulation is implemented depends on the process itself, actually on when the skin is removed in the process.
✔ A Nuance on Terminology
When we use the term ‘anaerobic‘ in coffee processing, we are only referring to one of the steps or modulations the coffee has gone through. We would be more accurate if we said something like, ‘an anaerobic fermentation step for X duration of time,’ or, ‘fermented in an anaerobic environment X period of time’.
Anaerobic fermentation comes more or less directly from the winemaking world, where grapes are fermented within enclosed containers to attenuate temperature, oxygen, and other factors which effect grapes’ fermentation.
2015 World Barista Champion Sasa Sestic is generally credited with porting this concept from wine to coffee, after being inspired by a winemaker in his home of Canberra, Australia. At the 2015 World Barista Championship, Sestic used a rare variety of Colombian-grown coffee processed with a specific variation of anaerobic processing called carbonic maceration, in which oxygen is pushed out by O2. Carbonic maceration is historically associated with the production of the red-fruited Gamay wines of Beaujolais, and now with contemporary wines that are lighter-bodied and fruity. You can find winemakers working in this style in nearly every corner of the winemaking world, from Oregon to Chile to New Zealand back to France, Spain, and Italy.
There’s the addition of yeast and fermentation and this isn’t just one type, but really there are many different kinds of yeast being used in fermentation. And then we can add another fermentation step for a double fermentation that’s something that’s being done. We’re hearing more about temperature shocks being done as well -which is another type of modulation. And then this Koji step is also gaining popularity.
You can see there’s a lot of different types of modulations that can take place and each of them take place on a basic process so each of them is a modulation to a process and they each add their own impact to the flavour outcome of that coffee.
2. EXTENDED FERMENTATION | PROLONGED FERMENTATION
The producer deliberately prolongs the fermentation time to add more elaborate flavours to the coffee.
There are two ways to extend the fermentation: After picking the producer lets the coffee cherry sit in the collection bag, or in the reception tank, for hours, up to days, before depulping
Almost every coffee reference book tells you that fermentation risks spoiling a batch of coffee. Most scientific research on fermentation in coffee has focused on removing mucilage as quickly as possible (Lee et al., 2015). The rapid fermentation – in about 8 hours, is considered optimal, as the risks of microbial damage and the coffee bean are minimised. Furthermore, it is much cheaper and requires less detailed follow-up planning throughout the process.
This kind of fermentation offers producers a way to produce distinctive flavours and elevate their cup scores, achieving higher prices for their coffees, without requiring a big investment.
3. THERMAL FERMENTATION | THERMIC FERMENTATION | THERMAL SHOCK
We have already discussed this topic in an earlier insight, where we consulted Luis Campos from Cordillera de Fuego in Costa Rica. He is the person par excellence, and at CUPRIMA we buy some fantastic batches of coffee every year from this legendary coffee farm.
We once again want to point out that thermal fermentation is not a type of fermentation. It is an additional procedure or modulation that can be carried out at different stages of the coffee processing according to a previously tested and established protocol. In fact, some protocols include thermal fermentation as a modulation prior to pulping the cherries. Other protocols use it as a process prior to the fermentation of whole cherries or pulped beans. Others apply thermal shock during the drying phase of already fermented coffee beans.
The thermal fermentation process is similar to the anaerobic fermentation, the main difference is that in the anaerobic modulation, the coffee stays inside the tanks between 18 to 23 hours at a temperature of 18 degrees celsius; on the other hand the thermal fermentation modulation requires higher temperatures.
It all starts by selecting the cherries when they are at their ripest point, which gives them a high sugar content. The thermal modulation starts with a high temperature shock, about 70 degrees Celsius for a short period of time. The coffee is pulped and placed in full sun. Exposure to heat breaks down the natural sugars of the coffee cherries, causing them to partially caramelise. This inventive process gives the coffee an exceptionally sweet and fruity taste and a round and balanced cup.
The coffee is then mixed well and placed in a hermetically sealed tank. It is very important that the tank is completely closed, otherwise the CO2 will escape and no pressure will be created. During fermentation, for 18 to 23 hours, the temperature of the tank is controlled. After 15 hours, the PH is continuously measured to monitor fermentation.
Fermentation should be stopped when the sugars in the slime have been consumed but no alcohol is produced. During fermentation, the CO2 produced exerts high pressure on the beans and ensures that the flavours of the coffee juices are absorbed into the parchment.
Finally, the tanks are carefully opened, the coffee is drained (the gel put into the tank at this point is very liquid) and dried under the sun.
4. KOJI STEP
There are a lot of crazy and innovative modulation methods out there nowadays, but one of the most intriguing is the Koji process.
Koji is the fungus that is used to define the flavour of many of the basic ingredients of Japanese cuisine, such as soy sauce, miso, or rice vinegar.
With the Koji coffee modulation, you sprinkle koji spores on the coffee -either cherry or parchment to grow. The Koji unlocks sugars unavailable during fermentation with traditional yeast or bacteria. It produces glutamate in the coffee & breaks starches into fermentable sugar, which leads to enhanced complexity, structure, aroma, & sweetness.
In other words, is a ‘pre-ferment’ fermentation. Like with yeast, is possible to use koji at nearly any stage of processing, but it’s most common to apply koji to cherry.
As of now, the practice of koji fermentation remains prevalent only on a handful of farms in coffee-producing countries.
Stay tuned for the second part of this fascinating topic, in which we will talk about how these new post-harvest techniques affect livelihoods in the region of origin, how they determine the cup, and what challenges these new techniques have in store for the specialty coffee industry.