To help farmers become familiar with coffee processing methods, this article introduces the wet-processing method for Arabica coffee (also known in Vietnam as cà phê chè).
I. Sorting and Preliminary Processing
Table of Contents
1. Sorting and cleaning
First, remove foreign matter such as branches, leaves, soil, stones and other debris. Separate out unripe, green or dried cherries from the fully ripe fruit ready for processing. (A small washing and grading machine with a capacity of about 1 ton of fresh cherries per hour can be used.)
2. Pulping
Use a disc-type or drum-type pulping machine (capacity 0.3–1 ton of fresh cherries per hour) to strip the outer skin without damaging or cracking the beans or the parchment layer.
3. Fermentation
Place the pulped coffee into a cement tank, basket, or plastic tub—depending on the quantity—and cover with burlap to ferment. Do not use metal containers. Fermentation breaks down the sticky mucilage around the beans, making it easier to wash off and improving drying.
Fermentation enhances the quality and unique flavor of Arabica coffee, but over-fermentation has negative effects. Ideally, maintain the bean mass at 36–40 °C (97–104 °F) and stir 2–3 times during the process. Duration depends on ambient temperature, typically 12–36 hours.
To check if fermentation is complete, scratch the bean’s parchment with a fingernail or rub a handful in your palm—if the groove between the beans feels rough and no longer slimy, it is ready.
4. Washing off mucilage
Rinse the fermented beans thoroughly with clean water. A small mucilage-removal machine can be used.
5. Drying
After washing, drain the parchment coffee and move it to a drying yard or a small mechanical dryer. Drying is a critical step—the coffee’s final quality depends heavily on it.
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Sun-drying: Spread the beans thinly on raised bamboo trays, mats, or sieves. Turn and rake frequently so they dry evenly. You may also use brick or cement yards, but never dry coffee directly on bare soil. Protect from rain or night dew.
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Mechanical drying: If using a dryer, use an indirect-heat system fueled by coal, gas, or oil. Avoid direct hot gases from the furnace, which can taint flavor. The best results are achieved with a rotary drum dryer. Follow proper drying parameters for coffee.
The coffee is ready for storage when the moisture content is no more than 13%. Without a moisture meter, bite a few beans: if they are hard to crack and do not break apart easily, they are sufficiently dry.
II. Storage
Proper storage prevents quality loss. Keep the dry parchment coffee in jute or cloth sacks, stacked off the floor to allow airflow.
Note: Many steps in household-scale wet processing can be done by hand, but pulping must be done with a machine to ensure proper removal of the fruit skin.