The assessment of wet hulled coffees is challenging, to say the least. The potential range of coffee flavors, process flavors and environmentally imparted off flavors is dramatic. In general these coffees occupy a range from earthy to vegetative. Scoring relies heavily on discerning between sweeter and “cleaner” (e.g.. clean earth vs compost or roasted pepper vs raw) versions of each. Despite the frequent assertion that wet hulled coffees are low acid, we’ve found that carefully processed coffees can display significant and vibrant fruit acidity, integrated with the wilder flavors imparted by the process itself.
This process is common practice in some areas of Indonesia. This likely is a result of legacy, but the resulting cup profile is something that has become distinctly indicative of the region. Wet hulled coffees are pulped at the farm level, and without any additional formal processing; the wet beans in parchment and mucilage are usually sold to a nominated processing facility. Here, they actually remove the parchment (still covered in mucilage), and dry the coffee beans completely exposed to the elements.
“Most small-scale farmers on Sulawesi, Sumatra, Flores, and Papua use a unique process, called ‘giling basah’, which literally means ‘wet grinding’ in Bahasa Indonesia. The industry also uses the terms wet hulling, semi washed and semi dried for this method. To avoid confusion, SCAI is encouraging the term ‘giling basah’.
In this technique, the outer skin is removed from the cherries mechanically, using rustic pulping machines, called ‘luwak’. The coffee beans, still coated with mucilage, are then stored for up to a day. Following this waiting period, the mucilage is washed off and the coffee is partially dried for sale (to 30% to 35% moisture).
Processors then hull the coffee in a semi-wet state, which gives the beans a unique bluish green appearance. This process reduces acidity and increases body, resulting in the classic Indonesian cup profile.” (SCAI)