The coffee we drink is made from the roasted seeds of the berries produced by the coffee tree, which must therefore be separated from the rest of the fruit. In the world of speciality coffee, processing refers to all the steps that take place from the moment the fruit is picked from the tree until the bean is ready and prepared for shipment. This process is called processing.
To understand the processing process, we first need to know the morphology of the coffee fruit.
The ripe coffee fruit, known as the coffee cherry, consists of the pulp, formed by the exocarp (epidermis) and part of the mesocarp; the colour of the epidermis varies from green to yellow and red. Enveloped by the epidermis is the mucilage or mesocarp, consisting of a thick layer of spongy tissue rich in sugars and pectins, which surrounds the two beans facing each other on their flat side. In Arabica, the pulp represents between 39% and 49% of the weight of the ripe cherry. The beans or almonds are covered by a double membrane: the parchment and the silver film.
The coffee processing process consists of a series of operations to transform coffee cherries into high-quality parchment coffee, which, due to its stability in a wide range of environmental conditions, is the state in which this product is marketed domestically in Colombia.
The coffee processing is mostly carried out at facilities on their farms, which they call beneficiaderos, where they basically receive, pulp, remove the mucilage, wash, sort and dry the coffee. Manual del cafetero colombiano (Colombian Coffee Grower’s Manual), Volume III. FNC-Cenicafé 2013.
Once the coffee cherries are harvested, they are transported to the processing plant. The quality of the coffee in the cup is closely related to the type of raw material processed at the plant, which is usually highly variable, as it includes:
- Fruits in all stages of ripeness in varying proportions.
- Defective fruits from plants with disease or nutritional deficiencies.
- Fruit attacked by insects, such as the fruit fly, as well as heavy or light impurities.
Similarly, the quality of the raw material depends on the time of harvest, as at the beginning and end of the harvest, when ripe fruits are scarcer, undesirable fruits are more common. Poor-quality fruits from the field cannot be converted into good-quality beans during the processing stage.
Proper homogeneity of the raw material in the processing would be achieved through a strict harvesting control process. The collection of fully ripe coffee cherries is essential for the quality of any coffee, regardless of the processing method. Even if only 15% of the cherries are unripe, a sour taste will appear in the cup of coffee.
The optimal sugar content in ripe cherries for harvesting ranges from 15% to 21%. Without a refractometer, it must be measured by the colour and uniformity of the cherry on the branch. Terms such as “bull’s blood”, “red wine” and “burgundy” (in the case of red varietals) are used to help farmers recognise the perfect level of ripeness. On farms with high standards dedicated to specialty coffee, pickers are financially rewarded for selecting only ripe cherries.
As it is impossible to harvest only ripe cherries to achieve the best quality raw material, a classification is carried out before pulping. This is achieved through density classification in water, which separates most of the unripe or dried fruits and light impurities such as leaves, wood chips, stones or sand.
Every variation in the process affects the final flavour profile of the bean. Coffee processing varies greatly from one farm to another and from one region to another. It changes depending on the amount of time the cherry is stored, the method used to pulping the cherry, or the cleanliness of the equipment. The type and length of fermentation, water quality, and the speed and temperature of the drying process also have an influence. These are the main factors that can affect the flavour of a coffee within the same processing category.
There are various techniques for processing coffee. To understand these variations in general terms, it is essential to categorise and understand the basic coffee processing methods. These are divided into natural, semi-washed and washed.
Today, in this blog by Cafés El Magnífico, we are going to explain these coffee processes in detail. We will talk about natural or unwashed, washed and semi-washed coffee. Let’s get started.
Unwashed Process (Natural)
The natural process is the original way in which coffee began to be processed. The cherries are dried with the beans inside, like drying a grape into a raisin. The beans are dried with all their layers intact, including the cherry and the mucilage.
The cherry is harvested once ripe and taken to dry in patios or on African beds (raised platforms) for approximately 21 days. The cherry and mucilage are composed of sugars and alcohols, which play an important role in the sweetness, acidity and final flavour profile of the coffee. The seed (coffee bean) is in a closed environment, which encourages natural fermentation (which sometimes rots if not cared for) and helps to create the final flavour profile.
The coffee beans are left to rest inside the dried cherries before being peeled (husked) and prepared for shipment. At this stage, the cherry has the texture of the fruit’s skin. The result is a heavy, dense body with exotic flavours of wild berries and ripe tropical fruit that have become synonymous with naturally processed coffees. However, the cup profiles of natural coffees can be inconsistent, so rigorous analysis at the tasting table and in the laboratory is an important part of the selection process.
‘Pasa’ coffee refers to another technique for producing coffee through the natural process. In this method, the farmer allows the coffee cherry to ripen and dry on the branch, rather than picking and then drying the cherry on raised beds or patios.
The vast majority of Brazilian coffees use the natural processing method. Natural coffees tend to have a heavier mouthfeel, higher sugar levels than other processes, and exotic and intense flavour profiles. High-quality Ethiopian natural coffees are extraordinary.
Why does the natural process contain higher levels of sugar?
The main form of sugar found in coffee is sucrose (5 to 9%), and the percentage found in the bean depends not on the processing method but on how it is grown. However, in the natural process, the beans contain higher amounts of fructose and glucose. Therefore, fructose and glucose levels do not increase during the washing process, but are already present in the drupe. However, they decrease as soon as water comes into play, i.e. during the washing process, the beans are submerged in water for a longer period of time and several studies have shown that sugars dissolve.
On the other hand, the seeds begin to germinate during the washing process. Germination consumes the simplest sugars stored in the seed (fructose and glucose). Furthermore, germination in washed coffees increases the concentration of certain amino acids, which are the most important aromatic precursors in coffee.
Semi-Wash Process (Honey, Pulped Natural y Wet Hulled)
The washing process and the semi-washing process are very similar in the first step – the cherry is removed (pulping), but that is where the similarity ends. Semi-washed coffees are dried with the mucilage remaining on the outside of the parchment.
The cherry can be pulped using a pulper or mechanical demucilaginators. Mechanical demucilaginators can be calibrated to modify the percentage of mucilage that remains attached to the beans. The mucilage, composed of natural sugars and alcohols, plays a crucial role in the development of sweetness, acidity and overall flavour profile in coffee beans.
The parchment, with its remaining mucilage layer, is taken directly to dry in the sun (skipping the fermentation tank and washing stage that occurs at this point in the washed processing method). Mechanical drying is not viable for beans processed in this way, as the mucilage sticks to the walls of the drying machine and destroys the equipment. Instead, it must be dried in sun patios or on drying beds (bateas) with the beans well distributed on flat, even surfaces. If any part of the drying surface is uneven, the producer runs the risk of allowing the mucilage to condense in one area of the bateas and create rot that will damage the quality of the coffee.
Coffees that are only fermented (in water tanks) for a very short period of time, too short to remove all the mucilage layer from the outside of the parchment, are also considered semi-washed (this is the case with many Indonesian coffees called Wet Hulled or Giling Basha, a variant of this process typical of Sumatra).
Drying is an extremely delicate process that requires constant attention. The beans must be stirred, usually with a rake, to ensure that they dry evenly and to prevent fermentation and rotting. During the drying stage, the remaining mucilage dries and sticks to the core of the bean, thus changing the final flavour profile.
The parchment has a slightly mottled, red/brown appearance similar to caramelised sugar on the outside of a candied nut. The coffee beans are stored and left to rest surrounded by the parchment layer and dried mucilage until they are ready for shipment. The parchment is only removed (by a mortar) before being exported.
Depending on the amount of mucilage that remains stuck to the parchment when the beans are dried, they are named: White honey, Yellow honey, Red honey, Black honey and Gold honey.
When properly processed, semi-washed coffees have an intense sweetness, dense body and rounded acidity.
Washing Process
Before being pulped (if the processing is rigorous), the coffee undergoes an initial separation process based on density through flotation in water channels (flotation). This is ideal, as the densest cherries (highest quality) sink and are sent through channels to the fermentation tank. The less dense ones (lower quality – usually unripe) float and are processed separately.
Coffee pulping is the first stage of wet processing in which the fruit undergoes a transformation, as the two seeds normally found inside are freed from their pulp or husk. This task is efficiently carried out by pulping machines, which apply cutting and compressive forces to the fruit so that the pulp is torn and the two beans are released, thanks also to the lubricating action of the mucilage that covers it.
The mucilage is a gelatinous film that is part of the fruit and is exposed when it is pulped. It is strongly adhered to the endocarp or parchment and is characterised by its strong water retention capacity due to its composition, which means that its moisture content can vary greatly depending on the climatic conditions prevailing during harvesting.
It is therefore necessary to remove the mucilage, as this gelatinous film creates a natural barrier to the flow of moisture to the outside of the bean during drying, resulting in a very long drying time and deterioration in both the physical and cup quality of the bean. It is also necessary to remove it because removing this layer significantly reduces the microbial load present in the bean.
Once the mucilage has been broken down by natural fermentation or the addition of enzymes, the beans are washed. The main purpose of this process is to completely remove the mucilage from the beans in order to prevent the development of defective flavours. The mucilage, composed of natural sugars and alcohols, plays a crucial role in the development of sweetness, acidity and the overall flavour profile of coffee beans. It is important in the washing process that ALL the mucilage is removed from the bean, leaving only the flavour that developed in the bean’s cellular structure before processing. In the washing process, the mucilage is removed either by fermentation or mechanically.
High-quality washed coffees are characterised by great transparency, good body, juiciness and a complex flavour profile, all highlighted by a sweet sensation balanced with refreshing acidity.
Once these operations are complete, the grain, which still has a high water content, undergoes a drying process to stabilise it at 10-12% moisture content. This is another delicate process, which we will discuss in future articles.
As you have read, processing is one of the most important transformations that human labour and knowledge bring to the taste profile of coffee. Processing is a highly delicate, sometimes artisanal process, which, with the help of science, allows experienced coffee growers to contribute their style while highlighting the quality of the bean that nature and the variety planted in their coffee plantation provide, thus obtaining a high-quality specialty coffee.
On the Cafés El Magnífico website and coffee packaging, you will always find the type of processing used by the coffee grower or cooperative, which is an essential part of coffee traceability.