What are the benefits of Indonesian Wet Hulling? Mandheling coffee beans wet hulling method ensures stable production

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The Wet Hulling Process of Sumatra

Wet hulling is a Sumatra processing method. Common methods like washed and natural processing wait until coffee beans are dehydrated and hardened, with a moisture content of 12-13%, before removing the parchment. However, due to Sumatra's humid climate, local farmers adapted to their environment and invented wet hulling. In this process, coffee beans are hulled while still moist, with moisture content as high as 30-50%, before continuing to dry. This significantly shortens the drying time.

Currently, Sumatra does not have independent processing plants that directly purchase coffee cherries. Therefore, small farmers must use their own buckets as traditional washing fermentation tanks. After fermentation processing, coffee beans are immediately put into a hulling machine (but because the beans are still soft, they get squeezed by the machine, resulting in a hoof-like shape). The pulp and parchment are removed from the beans, leaving moisture at about 30-40% or even higher. This is very different from traditional washed or natural processing, which usually begins processing when moisture content is only around 13%. If they waited until the beans were truly dry before selling to collectors, the time to realize profits would be extended (since natural drying typically requires 27-30 days). Therefore, the beans are sun-dried or machine-dried at the trader's facility to reduce moisture to 13%, followed by screening and hand-sorting. They are then divided into different grades based on defect rate and bean size, and the beans are rested for 90 days to allow them to properly "recover" and achieve consistent moisture (this is called moisture activity balance).

This entire process is handled by different people at different stages, making conditions and quality difficult to control. Additionally, the small farmers' washing fermentation doesn't actually involve true fermentation—it merely uses washing and flotation to remove very poor beans, lacking the function of traditional washing fermentation tanks. Therefore, the flavor is more earthy, yeast strains are difficult to control, and the taste is not as clean. In terms of natural processing, unlike traditional natural methods that use pulp as a fermentation base to produce fruit-flavored coffee beans, this approach lacks that foundation. Consequently, Sumatra wet-hulled coffee can only compete with "distinctive" flavors in the global specialty bean market, and the long-term outlook appears not very optimistic.

Conclusion

The wet hulling process has created the unique coffee flavor profile of Sumatra coffee. Although some new processing methods have been attempted, I personally prefer that Sumatra continue using wet hulling methods, as this can more fully ensure stable production quality.

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