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What is Giling Basah?

What is Giling Basah?

If you're a fan of Sumatra coffees, or interested in coffee in general, you've probably heard the term giling basah in reference to the coffees you're drinking. It's a polarizing style of processing coffee which produces a recognizable profile, typical to Sumatran coffees, and with just as many people who love it as don't. For the ardent fans of Sumatran coffees, no other coffee feels quite as satisfying. This is why.
The term giling basah comes from the Bahasa language of Indonesia which translates to wet grinding or wet hulling, and it's largely responsible for the cup character associated with the Sumatran coffees. The practice was developed in Indonesia and, while it's most often associated with Sumatra, it also occurs on the islands outside Indonesia with varying frequency.

Most other processing methods are variations on fruit removal, like natural or pulped natural processing; giling basah is a variation on the hulling stage, or the removal of the papery parchment layer underneath the fruit which protects the green bean inside.

Usually coffee processing involves drying the coffee inside the parchment until the green bean has reached a stable moisture content of 10-12%, making it fairly dry and resistant to molds. Coffees are typically stored this way for 30-90 days, and the papery parchment layer is removed just before export. In Sumatra and other parts of Indonesia, it is common to remove the parchment layer much sooner. Often after just 2-3 days of drying, when the moisture content is 25-35%  and the beans are still swollen with water.

The reason this method developed in Indonesia is largely due to the moist climate where these coffees grow: wet, humid and near the equator. Whereas it can take as little as 5 - 10 days to dry coffees in Central America, it can take 3 - 4 weeks to dry coffees in Sumatra. At some point in the past century someone realized that the coffees would dry faster if the parchment was removed -- and the faster the coffee is dried, the faster it can be sold; the faster it's sold, the earlier the mills & farmers can get paid. So the practice stuck.
Ultimately, giling basah is a practical decision made by the mill which results in the flavor profile we now consider common in Sumatran coffees: an accentuated, full mouthfeel, often with woody, herbal, earthy, and spicy flavors. Produced in the typical washing style, the coffees would taste radically different.


Why these flavors occur isn't fully understood, but we can guess at the cause. Without the protective layer of the parchment the green beans are directly exposed to the environment and may be affected by ambient fungus, yeasts, and bacteria. And when directly exposed to the sun, free moisture evaporates quickly, leading to inconsistent drying and a mottled appearance in the bean (which can further lead to inconsistent roasting degrees within the bean). Excessive heat from the hulling process might also cause the coffee to age rapidly, leading to the wooden, earthy flavors we often taste in Sumatran coffees.


In most washed coffees, woody &  earthen tones could make the coffee feel dry/astringent and bitter, and possibly clash with any crisp acidity, fruit citrus and flower tones noted. But in the context of ho
w Sumatran coffees are processed - wet-hulling/ giling basah - the wood and earthen character compliments and creates deep and spicy tones of cedar, sassafras, chicory, and licorice; a powerfully aromatic profile.
Here's a link to a 2010 Coffee Review article where Miguel snuck a Hawaii-grown wet-hulled/giling basah experiment into a Sumatra coffee cupping, and they couldn't distinguish it from the real Sumatra! Mysterious No More: Sumatra Coffees.
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