While reading the article “Processing Arabica Coffee” by Mr. Thinh Coi and noticing farmers’ feedback, I would like to share a portion of my presentation prepared for the Sustainable Coffee Development Conference scheduled for October 15, 2010 in Dak Lak. This is intended for farmers who have the means to carry out wet processing on a small household scale.
Farmers who cannot yet meet the conditions described below—particularly those who must still harvest a high percentage of green cherries—are advised to wait for the upcoming article about dry processing.
I. Cleaning and Sorting the Coffee Cherries
Table of Contents
Cleaning and sorting are the first essential steps in wet processing. Freshly harvested cherries must be separated from twigs, leaves, stones, and other debris.
There are many cleaning methods, but observations from visits to various regions reveal that most farmers and many buyers of fresh coffee cherries still do not clean properly—wasting effort with little effect.
Traditional cleaning device (used for hundreds of years)
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Water is continuously poured into a large tub.
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A hand crank stirs the cherries so that those with higher density (good cherries) sink and flow out with the water through a side pipe.
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Light cherries (defective, insect-damaged), along with twigs and debris, float and exit through a small chute at the top.
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A hook on the left side releases stones and heavy sediment from the bottom.
Farmers can adapt the design as needed, but the principle remains: good cherries are slightly heavier than water and sink; light or damaged ones float. Water from the outlets should be collected and reused. If the chutes and pipes are too large, water is hard to recover; if too small, cherries and debris can clog them.
Small washing and sorting machine (capacity: 800–1,000 kg cherries per hour)
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Cherries mixed with twigs and dirt are fed into a vibrating screen on the left.
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The vibrating motion removes twigs and debris to a side discharge.
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Clean cherries fall into a tank, then pass onto a shaking trough.
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Good cherries sink; floaters move straight ahead.
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Stones are released through an upper outlet visible from the front.
II. Pulping Machines
The pulper’s job is to separate the fruit pulp from the beans.
Older pulping machines
These machines crushed the entire pulp into slurry and flushed it out with water, creating heavy pollution. Wastewater carrying the slurry clogged groundwater veins and wells.
Modern pulpers
Today’s machines only break the pulp loose without crushing it. They separate green cherries so only ripe ones are pulped. Removing the parchment (husk) is handled by a different machine.
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Disc-type pulpers:
Although an older design, disc pulpers have the advantage of not shredding the pulp. They lack the ability to separate green cherries and have lower capacity, but they suit small farms that harvest mostly ripe cherries.Operation: Clean cherries are fed into the top hopper. As the disc rotates, cherries are rubbed between disc and fixed surface, the bean slips out while the flattened skin sticks to the disc and drops into a rear chute. Water supply is needed for operation.
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Drum-type pulpers:
Similar function to disc machines but with higher capacity. They pulp and separate beans and skins simultaneously, though they cannot separate green cherries. This design is the ancestor of modern “crush-and-dry” pulpers.
Modern integrated pulping line
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After cleaning, cherries are lifted by a bucket elevator to the green hopper.
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Beneath it, the pulper separates beans from pulp (green cherries are diverted to a separate upper-right pipe).
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Ripe cherries proceed to a vertical-axis “robo” machine that separates husk and bean: pulp exits left, beans drop into a mucilage remover on the right.
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The mucilage remover discharges beans through a lower right pipe.
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Below is the wastewater and mucilage outlet—a major environmental concern in wet processing.
III. Drying
Drying is crucial for final quality. Even if earlier steps are done well, poor drying ruins results.
When weather is favorable, sun drying is ideal. But for large-scale wet processing, relying on sunshine is risky. A single long rain can quickly cause mold and spoil wet parchment coffee if there is no proper drying facility.
Recommended drying methods:
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Static dryer:
After mucilage removal or fermentation, wet parchment should be dried in a static dryer for 6–8 hours. Direct-fired heat (e.g., coal) can be used initially without imparting smoke odor. Start with hot air around 80 °C, then reduce to below 60 °C once coffee begins to dry. For best quality and color, rely mainly on good airflow rather than very high temperatures. -
Rotary drum dryer:
After the static stage, parchment is transferred to a rotating drum dryer where bean temperature is maintained below 50 °C—ideally around 45 °C, which research shows preserves natural color and flavor, especially for Arabica. This method uniquely avoids cracking or peeling the parchment layer.
Drying time is about 20–24 hours, depending on airflow efficiency. Never shorten drying by raising the temperature, as professional Arabica buyers can detect such mistakes.
IV. Key Takeaways
The basic principles of wet coffee processing, developed more than 150 years ago, remain unchanged. Yet in Vietnam, many farmers still use crude, makeshift equipment, making wet processing laborious and challenging for producing clean, high-quality coffee.
Our coffee is often processed faster, less cleanly, and less methodically than elsewhere, which inevitably lowers quality and price.
In the next installment, we will introduce small-scale waterless wet-processing methods and time-saving controlled dry-processing of fresh cherries—practical alternatives for household farmers.