Master Blender Wayne Archer dissects the distinctive characters that come from different coffee processing methods.
Making it to the top is usually considered a mark of success. But in wet (or washed) processing the opposite holds true: coffee cherries are first dunked in water to sort the wheat from the chaff—bad fruit floats; quality sinks to the bottom. “In this way, only the ripe cherries are selected for processing,” Archer says. “It means the coffee has achieved the right level of sugars and other elements which enable higher quality aroma and taste once roasted.”
Wet processing primarily suits Arabica beans and the method accounts for over half of all coffee production in the world given that it tends to give a more consistent flavour. “It’s been known since the early days of coffee growing that coffee grown at altitude and processed using the wet method results in a coffee with different quality,” Archer says.
Fermentation for up to 36 hours strips away any pulp or mucilage that remains after an initial machine pressing, leaving a rough, hard bean ready to be washed and dried to a 12 per cent water content.
Machine-assisted wet processing exposes the ripe bean without the arduous fermentation process and saves around 130 litres of water per kilo of coffee—but what machines gain in time and water, they tend to lose in distinctiveness.
“The so-called fermentation process used in the wet method has a big influence on the taste of the final product,” Archer says. “The resultant coffee develops a colour, fragrance and flavour that you cannot find in dry processed coffees. The aroma is fruitier and the appearance is fresher and greener.”
Before there were machines and fermenting barrels, there was good old-fashioned sunshine.
“This is the traditional method used in the beginning of the coffee story in Ethiopia and Yemen,” says Archer of unwashed or natural processing. “The coffee cherries after harvesting are left to dry on the ground. Today most of Coffea Robusta and Brazil Arabica are processed this way.”
It has the advantage of killing two birds with one stone, simultaneously removing the cherry fruit and drying the bean. “Coffee cherries are almost two-thirds water and need to be dried to around 11 or 12 per cent,” Archer explains.
It’s not quick, around three weeks in the sun, hence drying machines are often employed to help things along. Artificial drying is best used as a supplement, Archer believes, because the sun has a positive impact on taste. “It plays an important role in bringing depth and complexity of flavour to a coffee,” he says.
Ultimately, the classic character of dry-processed beans is a more crowd-pleasing one. “Unwashed coffees are generally less aromatic and less acid tasting compared to washed coffees of the same origin,” Archer says.
“In semi-washed or pulped natural process, the high sugar mucilage remains on the parchment skin of the coffee bean and lends itself to enhancing the natural sweetness and fruit character,” Archer says of this hybrid method.
After pulping, the mucilage stays to be dried with the bean, usually in the sun, before the parchment is hulled. Getting things right in the drying stage, however, is crucial.
“Drying is critically controlled to ensure even moisture content of the finished coffee,” Archer says. “It is vital the coffee is frequently and gently turned as uneven drying can cause major flavour faults.”
Lower acidity, a fuller body and sweeter flavours tend to characterise semi-dry processed coffee. “Care must be taken when using pulped natural coffees in blends,” Archer cautions. “The increased levels of sweetness can be difficult to manage.”