Get to Know Indonesia’s Wet-Hulled Coffee Process

Depulping-wet-hulled

Wet-Hulled coffee, known also as semi-washed, Sumatra process, or giling basah, is a distinctive post-harvest processing technique prevalent in Indonesia. This method is particularly suited for regions with high humidity, enabling coffee to dry effectively in damp and cloudy conditions. In this article, we delve into the Wet-Hulled process as practiced in the Gayo Highlands of Aceh, Sumatra, a region renowned for its unique coffee profile.

 

Understanding the Wet-Hulled Process

The Wet-Hulled process begins similarly to other coffee processing methods, with the depulping of the coffee cherries. This initial step involves mill workers de-pulping sacks of coffee cherries, a process conducted as soon as possible to maintain the coffee’s quality.

Indonesia Coffee Cherry Processing - depulping

Indonesia Coffee Cherry Processing – depulping

 

depulped-coffee-beans

depulped-coffee-beans

The de-pulped seeds, still covered in their mucilage, are then placed in a fermentation tank overnight. This controlled fermentation is a distinctive feature at most of the Sumatra Coffee Mill, where there is oversight over each step from start to finish.

Coffee-fermentation-tank

Coffee-fermentation-tank

 

Pre-Drying: Preparing for Wet-Hulling

Before the coffee can undergo Wet-Hulling, it requires a quick pre-drying phase. The seeds are raked into thin layers and left to dry for several hours to a full day, depending on the prevailing humidity and cloud cover. This pre-drying is crucial, as it reduces the seeds’ moisture content to about 30–35%, making them ready for the Wet-Hull process.

coffee pre drying

coffee pre drying

 

Wet-Hulling: The Core of the Process

The essence of Wet-Hulling lies in removing the parchment layer from the coffee seeds before they are fully dry. This contrasts with other methods where the parchment remains on the seeds until they are ready for export. The Wet-Hulling machine, similar in operation to a depulper but calibrated differently, removes the parchment layer efficiently.

Wet Hulling Machine

Wet Hulling Machine

 

wet hulled coffee

wet hulled coffee

In regions with less humid climates, the parchment serves to protect the coffee seeds against moisture and temperature fluctuations. However, in Indonesia’s humid and cloudy environment, removing the parchment early allows for more effective drying. Despite its benefits, Wet-Hulling is somewhat traumatic for the seeds, often resulting in some being chipped, crushed, or split.

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Post-Hulling Drying and Final Preparation

Once Wet-Hulling is complete, the coffee seeds, now green coffee beans, are further dried. The seeds are spread out on tarps on concrete and raked into thin layers. This drying process exposes the seeds to sunlight, heat, and air, which are critical for drying in Indonesia’s humid climate. The unique earthy, savory, and herbaceous flavors characteristic of Indonesian coffees, particularly those from Sumatra, are largely attributed to this processing method, alongside the specific cultivars and regional climate.

coffee drying final stage

coffee drying final stage – on concrete

The final stage involves drying the coffee to a moisture content of 11–12%. The dried coffee is then bagged and stored in a warehouse until it is ready to be shipped. This meticulous process ensures that Wet-Hulled coffee retains its distinctive profile, making it a sought-after product in the global coffee market.

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