There are Two “basic” Methods of Processing Freshly Picked Coffee Cherries.
Natural processed coffee is the more primitive process of drying the freshly harvested fruit completely in one step on open-air patios or barbecues prior to milling. This “Dry Curing” method of processing coffee cherries is still used for more than three fifths of the world’s production. This process requires a dependable dry climate after harvest.
We in the trade also refer to this simple method as dry processed coffee. The coffee cherries are spread to dry on open patios in direct sunshine and raked to turn and re-spread them several times a day for an even and quick drying. Each night they are raked into piles and covered for protection against moisture and rewetting. In two to three weeks the fruit is completely dry throughout and ready to be transported to a mill for hulling and grading.
The “Wet Process” is mechanized and dependent on a sufficient quantity of clean fresh water. First the freshly harvested ripe cherries are de-pulped by a special machine to separate the fruit skin from the two encased seeds inside. The wet and sticky seeds are then sequestered for a day or so to facilitate an enzymatic breakdown and loosening of any remnant of residual fruit sticking to the seeds. This step is also called the fermentation stage. The seeds, which are still encased in a paper-thin parchment shell, are then soaked, rinsed and sluiced to wash away the fermented dregs and dross. Hence the synonym ‘washed process.’
This Wet Processed method was a development of the Dutch, probably in Java around 1740. It served to reduce the spoilage of coffee that can be damaged by mold. It also allowed for a thoroughly dried product more suitable for the long shipment to European ports.
Washed process coffee is produced in climates where humidity is extremely high or where it is not suitable for dependable sun drying. Places that have unpredictable summer showers can rewet the dried coffee and promote damage and spoilage.
The wet process requires considerable amount of clean fresh water to carry out the multiple steps of flotation grading, transportation through the mill, wet fermentation, soaking and final rinsing during the processing.
From this point the coffee beans follow the same final steps as the “natural processed coffee” by patio drying, greenhouse drying or mechanical drying and then milling.
It is obvious to cuppers that the two processes produce distinct flavor characteristics to the coffee bean. Many roasters prefer dry processed coffees for espresso and French Roast blends because they often have heavier body and sometimes more complexity. Washed coffees usually are sweeter, brighter and cleaner in taste, which make them preferable for drip-brewed coffees.
Some countries or origins may opt for one system of processing over another. Brazil and Sumatra produce 90% Dry Processed coffees and maybe 10% washed. Yemen and Ethiopian Harrar is always natural processed coffee. There is hardly any dry processed coffee available from Central America. Colombian coffee is always washed coffees. Ethiopian Sidamos are mostly washed coffees but occasionally you can find a natural Sidamo. Ethiopian dry processed coffees are referred to as grade 4 and their washed coffees are grade 2. Often decaf coffees are made from dry processed coffees where it is available.