Part 5: The Art of Drying Coffee Cherries: A Guide from Cherry to Bean

Welcome back to part 2 of our deep dive into natural process coffee! In the previous article, we discussed history, taste, and the prospects of sustainability and innovation. We covered the what and why. Now, we will answer the how. Taking on this topic means we're going to roll up our sleeves and get to work. When people say "natural," one might think the process is more passive, and we let nature do the work itself. But the exact opposite is true. Producing high-quality natural process coffee is an extremely labor-intensive and precise exercise that requires knowledge, patience, and constant vigilance. Join us as we follow the coffee cherry step by step on its long journey from branch to sorted bean.

 

From Cherry to Bean: A Journey Through the Natural Processing Method

 

The natural process method, despite its apparent simplicity, is a meticulous process that demands accuracy and patience at every stage. The quality of the final product depends on how each step is executed.

 

Step 1: The Art of Selection – Cleaning and Sorting Coffee Cherries Before Drying

 

Everything starts with harvesting. To achieve the best quality natural process coffee, selective harvesting is crucial. This involves hand-picking only fully ripe coffee cherries. Ripe cherries have the highest sugar content, which is essential for the sweetness and complexity that characterize good natural process coffee. Unripe cherries, on the other hand, can result in "quakers" – beans that do not brown properly during roasting and yield an undesirable, papery taste.

After harvesting, an initial cleaning follows, where leaves, twigs, dirt, and other foreign materials are removed manually or using simple screens. Then comes the critical sorting by ripeness and defects. This can be done by manual sorting, where workers visually inspect the cherries and remove unripe, overripe, or visibly damaged cherries.

Another widespread and effective method is float sorting (floating). The coffee cherries are placed in large tanks of water. The ripe, dense, high-quality cherries will sink to the bottom, while unripe, overripe, insect-damaged, or otherwise defective cherries – which have lower density – will float to the surface and can be easily removed. This is an elegant, low-tech method that utilizes a basic physical principle – density – to achieve a significant quality improvement before the time-consuming drying process begins. Ripe cherries have higher sugar content and thus higher specific gravity, while unripe or defective cherries often contain air pockets or have less fruit pulp, causing them to float.

Thorough sorting at this early stage is absolutely crucial. It reduces the risk of undesirable flavors developing and spreading during the long drying period, ensuring a cleaner and more homogeneous end product. The choice to invest time and resources in this meticulous sorting, even in a "natural" process, signals a producer's dedication to specialty coffee quality. Since natural process coffee inherently carries a higher risk of defects, and unripe or damaged cherries are more susceptible to unwanted fermentation or mold growth during drying, this preparatory work is a critical investment in the final cup quality.

 

Step 2: The Secrets and Challenges of Drying

 

Once the coffee cherries are cleaned and sorted, the perhaps most critical phase for natural process coffee begins: the drying itself. The goal is to reduce the moisture content of the coffee cherries from around 60% down to a stable level of approximately 10-12.5%. This is crucial to prevent mold growth and ensure that the beans can be stored and transported without losing quality.

Drying Surfaces and Methods:

The coffee cherries are spread over large surfaces to dry in the sun. Common methods include:

• Raised drying beds (often called "African beds"): This is the preferred method for specialty coffee. The cherries lie on elevated beds made of mesh (nylon or metal) or traditional materials like bamboo mats, stretched over a frame. The great advantage is that air can circulate freely around each individual cherry, providing a more even and often slower drying, and reducing the risk of mold and unwanted fermentation.
  
  

• Patios: Large, flat areas of concrete or brick where the coffee is spread out. These are common on larger farms. Frequent raking is important to prevent the cherries from sticking to the surface and drying unevenly.
  
  

• Tree drying ("Pasas"): In certain very dry and hot climates, such as parts of Brazil, coffee cherries can begin to dry on the branch itself and become like raisins. This is less labor-intensive but carries a higher risk of uneven drying and the development of off-flavors.

Optimal conditions and careful management:

Successful drying depends on several factors:

• Sunshine and warmth: The sun's energy is the driving force that removes moisture from the cherries.

• Low humidity: Dry surroundings are critical. High humidity dramatically increases the risk of mold and rot, and thus the method is best suited for dry climates.

• Good air circulation: Wind and air movement help to carry away moist air from the cherries and prevent the accumulation of moisture that can lead to mold formation.

The "simple" natural drying method is, in reality, a complex balancing act. The producer must harness the sun's energy while actively combating nature's decaying forces like mold and unwanted fermentation. Success depends on constant vigilance and the ability to adapt to the microclimate. Cherries contain sugar and moisture, which are ideal conditions for microbial growth. The long drying process, which can last for several weeks, exposes the cherries to varying temperatures, humidity, and the risk of rain. Without active and precise management, unwanted microorganisms will thrive and lead to defects. The farmer's role is therefore not passive, but an active management of risk and quality preservation.

Turning and Raking – An Absolute Necessity:

To ensure that each individual cherry dries evenly and to prevent the development of mold, rot, or unwanted fermentation on contact surfaces, the coffee cherries must be turned and raked frequently. This also prevents "bruising" of the fruit that can cause off-flavors. The frequency is critical; the cherries must be turned several times daily. Some sources recommend turning every 3-4 hours at the beginning of the drying period, and then at least twice daily once some of the moisture has evaporated.

The cherries are spread in thin layers, especially at the beginning (e.g., no more than 7-8 cm thick), to maximize exposure to sun and air. As the cherries dry and lose volume, the layer can be made somewhat thicker. At night, or if there is a risk of rain, the cherries are often gathered and covered with tarpaulins to protect them from moisture.

Drying Time and Moisture Measurement:

The drying time for natural process coffee varies significantly, depending on climate, drying method, and the thickness of the cherry layer. It can take anywhere from one to six weeks. In areas with ideal conditions, producers can aim for around 20 days.

Accurate moisture measurement is a critical gatekeeper for quality and economics. The goal is to dry the coffee beans to a moisture content of between 10% and 12.5%. Too high moisture content can lead to mold, the development of mycotoxins, and overall quality degradation during storage. Too low moisture content (over-drying) can make the beans brittle, causing them to break more easily during later hulling, and can also result in a flat and lifeless taste.

Traditionally, farmers have relied on experience – how the cherries feel, the sound they make when shaken – to judge dryness. For specialty coffee, where precision is key, more accurate methods are used. Handheld digital moisture meters are now common at farm level. These instruments often measure electrical resistance or capacitance in the beans. To ensure accurate measurements, it is important that the samples tested are representative of the entire batch, and that the meters are calibrated regularly. Oven drying is a more precise laboratory method that can be used to calibrate the handheld meters. The drying process can also be divided into different stages based on moisture level and the bean's physical condition, for example, from "skin drying" to "hard black" stage.

Mechanical Drying – A Modern Aid:

Although sun-drying is at the heart of the natural method, some producers use mechanical dryers (also called "guardiolas" or drum dryers) as a supplement or alternative. This is particularly relevant in areas with unstable or humid climates, to gain better control over the drying process, or to speed up drying after an initial period of sun-drying.

Coffee can still be classified as "natural" or "dry-processed" even if mechanical dryers are involved, as long as the entire coffee cherry is dried with the pulp intact. This is similar to how sun-dried tomatoes you buy in stores are usually mechanically dried. The definition of "natural" primarily focuses on the pulp not being removed before drying, and not necessarily on only solar energy being used. Quality standards, such as those from the Specialty Coffee Association (SCA), emphasize the absence of defects and the sensory quality of the coffee, rather than dictating precisely how drying must occur, as long as quality is maintained.

Mechanical drying provides the producer with better control over temperature and humidity, which can lead to a more consistent drying process and reduce the risk of mold and over-fermentation. However, if the dryer temperature is too high, it can lead to a loss of volatile aromatic compounds and result in a "baked" or flat flavor in the cup. Therefore, it is often recommended to use low temperatures (e.g., 35-45°C) in mechanical dryers to preserve the coffee's sweetness and clarity. A hybrid approach, where coffee is first sun-dried to develop complexity and then finished in a mechanical dryer for consistency, can be a good balance. The use of mechanical dryers in the "natural" process represents a pragmatic innovation to improve consistency and reduce risk, and the industry's focus seems to be more on the result (quality and absence of defects) than on dogmatic adherence to only sun-drying. This demonstrates an evolution where tradition meets technology to improve the product.

Below is a table summarizing key variables for different drying methods within natural processing:

Table 1: Drying Methods for Natural Processed Coffee: Key Variables and Impact

Drying Method	Air Circulation	Temperature Control	Labor Intensity	Risk of Defects	Typical Drying Time	Quality Potential
Patio (concrete/brick)	Moderate	Low (depends on sun)	High (raking)	High	2-5 weeks	Variable, depends on precision
Raised Drying Bed	Good	Low (depends on sun)	High (turning)	Moderate to High	3-6 weeks	High, provides more even drying
On-tree ("Pasas")	Variable	None direct	Low	Very High	Variable	Lower, often uneven
Mechanical Dryer	Controlled	High	Moderate	Low to Moderate	Hours to Days	Potentially high, but risk of "baked" flavor if misused
Hybrid (Sun + Mechanical)	Good to Controlled	Moderate to High	High	Moderate	2-4 weeks	High, combines complexity with consistency

Step 3: Undressing – Hulling (milling) of the dried cherries

 

Once the coffee cherries have dried to the optimal moisture level, it's time to remove the outer, hard layer to get to the green coffee beans. This step is called hulling or milling. The purpose is to remove the now rock-hard, dried fruit pulp (known as "husk" or pericarp), the thin parchment skin (endocarp) that surrounds the bean, and often much of the silverskin.

This is usually done with specially designed machines called hullers or huskers. These machines often use friction-based mechanisms, such as rotating rollers or "cross beaters," to rub and break off the dry material around the bean. Some modern hullers are designed to handle both dried whole cherries (from natural processing) and dried parchment coffee (from washed processing). They can also be equipped with aspirators to suck away husks and dust, and oscillating screens to separate the finished beans from the waste.

Hulling natural processed coffee presents some specific challenges. The dried coffee cherries are very hard and brittle. This places high demands on the robustness of the hulling machinery and the precision of the machine's adjustment. If the pressure or friction is too great, or if the cherries are over-dried and extra brittle, there is a risk that the coffee beans themselves may break or be damaged. Broken beans are a quality-reducing defect. The process can also generate a significant amount of dust from the dry fruit pulp. Furthermore, naturally processed beans can be less uniform in size and shape, and they often have more silverskin intact compared to washed beans. This variation can affect the efficiency of the hulling machine if it is not optimally adjusted. To address some of this variation, machines have been developed that can size-grade the coffee cherries before they enter the huller.

The mechanical process of removing the hard, dried fruit layer from natural processed coffee is often more "brutal" than removing the thinner parchment skin from washed beans. This emphasizes the importance of proper equipment and careful calibration. A system described in [source not provided] involves first dehydrating the cherries and then a gentle hulling process, designed to preserve quality.

Another characteristic of natural processed beans is that they often have more silverskin remaining after hulling. This is because the bean has been in longer contact with all layers of the fruit, and the silverskin adheres more tightly or is less effectively removed during the drier hulling process. Reddish-colored silverskin is common on natural and honey processed coffees and is rarely considered a sensory problem, but it can lead to more chaff during roasting. This is not a defect, but contributes to the characteristic, slightly less uniform appearance of natural processed beans.

On a smaller scale, and traditionally, hulling could also be performed manually using a mortar and pestle, but this is extremely labor-intensive and inefficient for commercial production.

 

Step 4: The Finishing Touches – Cleaning, Sorting, and Packaging of Green Beans

 

After the dried fruit pulp and parchment skin have been removed, we are left with what we call green coffee beans. But the process is not yet complete. Now follows a series of cleaning and sorting steps that are crucial for the final quality and uniformity of the coffee batch.

Cleaning:

First, any remaining husk fragments, dust, and other foreign matter such as stones, twigs, or clumps of dirt are removed. This can be done using fans (aspiration to remove lighter particles), screens of various sizes, and so-called "destoners" – machines that use vibration and air currents to remove heavier objects like stones based on density differences.

Sorting (Grading/Sorting):

This is a critical stage, especially for specialty coffee, where the goal is to create as uniform a batch as possible. Natural processed coffee can have inherently greater variation, making this step particularly important. Sorting usually occurs according to several criteria:

• Size: The beans pass through a series of screens with holes of different diameters. This separates the beans into different size categories (e.g., screen 15, 16, 17, etc.). Uniform bean size is important because it contributes to more even roasting, as beans of different sizes will absorb heat and develop differently in the roaster.

• Density: After size sorting, a density table (also called a gravity separator) is often used. This is an inclined, vibrating table with a controlled airflow from below. Heavier, denser beans (which are often of higher quality) move to one side, while lighter beans (which may be immature, insect-damaged, or otherwise defective) move to another.

• Color:

  • Optical Sorters: These are high-tech machines that have revolutionized the sorting process. They use cameras (often with various light spectra) and computer processing to analyze the color of each individual bean passing at high speed. Beans that deviate from the pre-set "acceptable" color (e.g., unripe green, over-fermented dark, black, or sour beans) are removed from the stream with a precise air jet. For natural processed coffee, which can have greater natural color variation and more silverskin, precise calibration of these machines is crucial to avoid discarding good beans. Artificial intelligence (AI) and machine learning are increasingly used to improve the accuracy and efficiency of optical sorters.

  • Manual Sorting (Hand-picking): Even with advanced technology, manual sorting is often the final quality control step, especially for top-grade specialty coffee. Trained workers visually inspect the beans on large tables or conveyor belts and hand-pick any remaining defective beans. This is a very time- and labor-intensive process; one person can typically hand-sort around one 60-kilo bag per day.

• Defects: The goal of all sorting is to remove beans with various types of defects. Common defects include broken or chipped beans, insect-damaged beans, moldy beans, black beans (full black), sour beans (full sour), unripe beans (quakers), and beans with husk residues. The Specialty Coffee Association (SCA) has established standards for classifying and counting defects. Natural processed coffee, if the process is not carried out with great precision, can have a higher incidence of certain types of defects related to fermentation and drying. As mentioned earlier, more silverskin is common on natural processed beans, but this is usually not considered a defect in itself, although it affects the appearance.

The sorting process for natural processed coffee is particularly challenging due to the inherent variation the method can introduce into the beans. Investments in advanced sorting technology or thorough, time-consuming manual sorting are therefore often a hallmark of producers committed to delivering high-quality natural processed specialty coffee. The SCA standards for defects were originally developed with washed arabica in mind, so some "forgiveness" or adjusted expectation may be necessary when evaluating natural processed lots, but the goal is always to minimize defects to achieve the best cup quality.

Polishing:

Sometimes, the green beans are polished to remove any remaining silver skin. This gives the beans a shinier and more uniform appearance. Polishing, however, is an optional step. The process can generate heat, which could potentially negatively affect the flavor if not performed carefully. Many specialty coffee producers, especially those working with natural processed coffee, choose not to polish the beans. They consider the silver skin a natural part of the bean that falls off as "chaff" during roasting anyway, and some believe it can offer some protection for the bean. The choice often reflects a philosophy of minimal intervention versus the market's aesthetic expectations.

Packaging:

Finally, the fully cleaned and sorted green coffee beans are packaged for storage and export. They are usually packed in woven sacks made of jute or sisal, often with an inner plastic lining (like GrainPro bags) to protect against moisture, oxygen, and loss of aroma. The standard sack size is often 60 kg or 70 kg. More exporters also offer vacuum packing in plastic, which is then packed into smaller boxes of 20-40 kg. Proper packaging is crucial to preserve the quality of the green beans until they reach the roastery.

 

Conclusion: A Craft Demanding Precision and Patience

 

As this detailed review shows, natural processed coffee is anything but a simple or passive process. Every single step, from the meticulous sorting of ripe cherries to the weeks-long, vigilant drying and the painstaking final touches, requires immense effort, knowledge, and dedication from the coffee producer.

The term "natural" refers to the pulp remaining intact on the bean, not to a lack of human intervention. On the contrary, it is the producer's constant and precise work that transforms the risk of defects into the potential for exceptional and rich flavor. It is a craft that balances on a knife-edge between harnessing nature's gifts and controlling its destructive forces.

Next time you enjoy a complex and fruity cup of natural processed coffee, we hope you spare a thought for the enormous effort that goes into it. It is the sum of countless decisions and hours of hard work under the sun that ultimately culminates in the unique experience in your cup.