Methods of processing green coffee
Fermentation as the basis of processing
Fermentation is at the heart of any coffee processing. This is a natural process in which microorganisms, primarily yeast and bacteria, process sugars and other organic compounds contained in the coffee berry. In this case, by-products are formed, some of which can be stored in the grain and affect the formation of the taste profile.
Active fermentation occurs in the early stages of processing, while the grain retains high humidity. As the drying process progresses, the conditions for microorganisms gradually change and their activity decreases. This usually happens when the grain moisture approaches a level of about 20%, after which the fermentation processes noticeably slow down.
Further drying is aimed at stabilizing the grain. Humidity is reduced to standard values, at which metabolic processes practically stop, and green coffee becomes suitable for storage and transportation.
Differences in processing methods
In order to understand the differences between the processing methods, it is important to imagine the structure of the coffee berry and which layers are preserved during the drying stage. There are six main layers in the coffee berry:
The skin (exocarp) is the outer protective layer. In ripe berries, it can be red, yellow or orange, depending on the variety.
The pulp (mesocarp, or pulp) is a juicy sweet tissue rich in sugars and moisture.
Gluten (muselage) is a gel—like sticky layer of pectins and sugars.
The parchment shell (patchment) is a solid protective layer that preserves the shape of the grain and regulates moisture loss.
Silver skin (silverskin) is a thin film adjacent to the surface of the grain.
The grain is the seed of the coffee tree, which, after roasting, is used to make a drink.
The structure of the coffee berry
During processing, the outer layers of the berry are subjected to changes — peel, pulp, gluten and parchment shell. The differences between the processing methods are determined by the stage at which these layers are removed and in what form the grain enters drying. From this point of view, there are four basic approaches to coffee processing:
Berry drying — the grain is dried inside the whole coffee berry, with all the layers. This method is called the natural or dry method.
Gluten drying — the peel and part of the pulp are removed, and the grain is dried with gluten. This approach has several variations and can be called honey, pulp natural, semi-washed or semi-dry method.
Parchment drying — the peel, pulp and gluten are removed before drying, and the grain is dried in a parchment shell. This method is called the washed method.
Drying without pigment — the peel, pulp and gluten are removed, and the parchment shell is removed at an intermediate stage at high humidity. Further drying of the grain takes place without a protective layer. This method of processing is called wet-hull.
Historically, the choice of processing method was determined by climate and available infrastructure. In recent years, manufacturers are increasingly moving away from traditional approaches and experimenting with processing, changing the parameters of fermentation and drying.
Natural processing
Natural, or dry, processing involves drying the grain inside the whole coffee berry, without removing the outer layers. This is one of the earliest and technologically simple ways to process coffee.
After harvesting, ripe berries are cleaned of impurities, usually sorted by density in water and laid out in a thin layer for drying on patios, African beds or other drying surfaces. During processing, the coffee pulp turns brown, and sugars are caramelized or fermented by natural microorganisms. After reaching the target humidity, the dried berries are sent to halling, where all the outer layers are mechanically removed.
Other names of the method: dry, unwashed, natural, dry, fruit dried, sun dried, unwashed
Natural processing is traditionally used in countries where the climate is dry and there is no access to a lot of water. The classic examples are Yemen, Ethiopia and Brazil.
Historically, natural processing has been associated with mass and inexpensive coffee, because its main advantage is its low cost. This method does not require fermentation tanks, water and electricity — there is enough sunlight. Now the natural method of processing is again widely used. The specialty coffee industry focuses on taste, and this method can give a very bright taste and high marks in capping, if carried out qualitatively.
The method has its own risks — for example, it is very dependent on environmental conditions. If rains start and humidity rises, drying slows down, berries begin to mold, and defects appear in the taste of coffee. In such conditions, the natural method requires the installation of expensive mechanical dryers.
Naturally processed coffee usually has a full-bodied body and is characterized by high sweetness. This is due to the fact that the grain comes into contact with the pulp for a long time and absorbs the products of its fermentation.
Washed treatment
Washed, or wet, processing involves removing the skin and pulp before the drying stage and using fermentation to break down gluten. This is a technologically complex but popular way of processing coffee. It uses water to quickly separate the pulp and control the fermentation of coffee berries.
The harvested berries are sorted, most often in water, then depulpation is carried out — the outer skin and part of the pulp are mechanically separated. To do this, the berries are passed through a special press, or depulpator, which crushes and peels off the soft shell. As a result, grains covered with the remains of slippery pulp and full-bodied gluten come out of the machine. After that, the grain is fermented — in or without water — until the gluten breaks down, usually within 12-36 hours. Next, the grain is washed and dried in a parchment shell.
Other names of the method: fully washed, washed, fully washed, wet treatment
Washed processing is traditional for countries with a humid climate and a developed processing infrastructure. Classic examples are Colombia, Kenya, Guatemala, Rwanda and Burundi. Historically, washed processing has become widespread as a way to dry coffee faster and more stable in humid conditions. However, it requires significant resources: water, fermentation tanks, equipment.
The key difficulty of the washed method is the need for precise control of fermentation and sanitary conditions. Over-fermentation, contaminated water or insufficient cleaning of equipment can lead to the appearance of extraneous flavors and batch instability.
Washed coffee is usually characterized by a light body, a clean flavor profile with a more pronounced acidity.
Semi-washed treatment: honey, pulp natural
Semi-washed processing combines methods in which the skin is removed before drying, and the grain dries with partially preserved pulp or gluten. Depending on the technology, the degree of layer removal may vary.
After harvesting, the berries are depulped, removing the peel and part of the pulp. With honey and pulp natural, the grain is dried with gluten residues. When the pulp is mechanically removed after depulpation, the grain additionally passes through a demucilator, which almost completely removes the pulp and gluten, after which the coffee is dried in a parchment shell.
Other names of the method: honey, pulp natural, semi-dried, semi-dried, semi-washed, semiwashed
Semi-washed methods are traditional for Brazil and Central American countries, primarily Costa Rica and El Salvador. These methods developed as a compromise between natural and washed treatments, allowing to reduce water consumption and speed up drying.
From a practical point of view, semi-washed processing requires either careful manual drying, as in the case of honey, or expensive equipment, as with mechanical removal of pulp. At the same time, both options are sensitive to the process setting.
The main risks are related to the heterogeneity of the result. With honey, the high stickiness of the grain complicates drying and increases the risk of uneven drying. When using demusilators, there is a risk of mechanical damage to the parchment shell, which can accelerate the aging of the grain.
Semi-washed coffee usually combines the density and sweetness characteristic of natural lots with the greater purity of taste inherent in washed processing.
Wet-hull
Wet-hull is a processing method in which the parchment shell is removed at an early stage, with high grain moisture. Further drying takes place without a protective layer.
After depulpation and brief fermentation, the grain is dried in a parchment shell. At a humidity of about 20-24%, the parchment is removed, and the grain is dried in this form. As a result, green coffee is formed faster than with other methods.
Other names of the method: giling-bass, wet-hull
Wet-hull is a traditional processing method in Indonesia, primarily in Sumatra. Its distribution is directly related to the climate of the region, where high humidity and frequent precipitation make prolonged drying in parchment difficult.
From a practical point of view, wet-hull allows you to speed up processing and reduce the risk of crop damage in a humid climate. However, early removal of the protective layer makes the grain more vulnerable to drying and storage conditions.
The main risks of wet-hull processing are associated with increased sensitivity of grain to moisture and mechanical damage, as well as with faster aging in case of improper storage.
wet-hull processed coffee usually has a full-bodied body, reduced acidity and a characteristic, easily recognizable profile.
Fermentation as a tool: experimental approaches to processing
Initially, any processing methods atypical for a particular region were called experimental. For example, natural processing in countries where the washed method was traditionally used, or vice versa. In this sense, the experiment was not the process itself, but a deviation from local practice.
In the modern coffee industry, experimental approaches have begun to be called approaches in which producers purposefully change fermentation parameters. From this context, the term "funky" has grown — the designation of pronounced, atypical taste and aromatic characteristics formed during processing.
Funky is rather not the name of a particular method, but a description of the result
Examples of alternative processing approaches:
Anaerobic fermentation. Fermentation of whole berries or depulpated coffee in sealed containers without access to oxygen.
Carbon dioxide maceration. A type of anaerobic fermentation in which oxygen is displaced by carbon dioxide.
Combined fermentations. Fermentation in several stages — for example, first in a whole berry, then after depulpation, or vice versa.
Fermentation with the addition of cultures. The use of certain strains of yeast or bacteria to change the course of fermentation. Examples: lactofermentation and koji.
Extended and modified fermentations. Changing the standard fermentation duration or temperature and pressure conditions.
Such approaches are not tied to specific countries or climates and are used where the manufacturer has access to equipment and the ability to work with small batches. Most often they are used for microlots, as fermentation requires strict control.
Coffee processed using funky methods is usually characterized by atypical and vivid taste characteristics. These features are formed due to the changed fermentation conditions and require an accurate and accurate description when working with the market.
The role of processing in the evaluation and positioning of green coffee
The processing method is one of the parameters by which green coffee is described and compared on the market along with the origin, variety and technical condition of the grain. He sets the general style of the party and forms expectations from the taste profile even before capping.
Capping is the main tool for checking the quality of lot processing
When evaluating green coffee, processing is not important on its own, but in combination with how accurately the technology has been implemented. The same method can give fundamentally different results depending on the control of fermentation, drying conditions and stability of the process. Mistakes at these stages are usually irreversible and are directly reflected in taste.
In pricing, the processing method is considered as part of the overall context of the batch. It can influence the differential taking into account market demand, the complexity of production and the perception of the lot by the market, but is not an independent indicator of quality or value.
Summary
The processing of green coffee is not just the removal of the outer layers of the coffee berry, but a set of technological and biochemical processes that largely determine the potential of coffee.
Natural, washed, semi-washed, wet-hull and funky processing differ in which layers of berries are preserved at the drying stage and how fermentation is organized. These differences form different profiles of coffee, but none of the methods is a guarantee of high or low quality. Any processing method can lead to both an outstanding flavor profile and defects.
For the buyer and roaster, understanding the processing makes it possible to correctly interpret the description of the batch, assess potential risks and predict the behavior of coffee during roasting and in a cup.