Coffee Bean Washed Processing Method: The Clean Coffee Journey

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FrontStreet Coffee - Introduction to Washed Coffee Processing

Wet Processing Method

In 1740, the Dutch invented the wet processing method. The process flow, simply put, is: harvesting → fresh fruit flotation → mechanical depulping → fermentation to remove mucilage → washing → drying (sun-dried or machine-dried) → hulling to obtain beans.

Specifically, the process involves: first pouring harvested fresh fruit into a washing tank, using flotation to distinguish red berries that sink to the bottom from unripe fruit based on density differences. A depulping machine removes the pulp and skin from mature coffee cherries. After depulping, coffee cherries still have residual mucilage, which is typically placed in cement fermentation tanks to soak and ferment for 1-3 days (depending on specific conditions). After hydrolysis, the mucilage no longer adheres tightly to the coffee parchment. Then, running water is used to wash away the mucilage. Finally, the parchment coffee is dried by sun-drying or machine-drying until the moisture content drops to 10%-12%, then a hulling machine removes the hard pulp and parchment. After winnowing, the seeds of the coffee fruit are obtained – coffee beans.

Coffee beans processed by washing have a clean appearance with very little residual silver skin, showing a gray-green color. Coffee beans processed by sun-drying differ from washed processing, appearing more yellowish, so washed beans have less silver skin than sun-dried beans before roasting. However, during the roasting process, as moisture is lost, silver skin falls off and is collected in the roaster's silver skin collector (you can review our article on perfect coffee roasting for more details). Compared to sun-dried coffee beans where the entire silver skin falls off together during roasting, the "inner silver skin" in the crevices of washed beans doesn't easily come off and remains in the center after roasting. Therefore, when grinding, you'll find that washed beans have more inner silver skin than sun-dried beans.

Flavor of Washed Beans

Because washed beans are dried only after all mucilage is removed, their greatest flavor characteristic is bright, clean acidity! For example, citric acid, malic acid, or stimulating acetic acid, with lower viscosity, sweetness, and wild flavors. The original market believed that washed coffee beans had better quality because fewer foreign objects were mixed into the coffee cherries after flotation, and the quality was stable and easy to control after removing all mucilage. Additionally, the refining process is time-consuming and requires expensive equipment, so the price is higher than naturally dried coffee beans, giving a premium feeling. However, the washing method requires large amounts of water and also generates large amounts of wastewater. For example, producing 1 kilogram of green beans requires 50-100 kilograms of water.

Compared to the flavor of sun-dried beans introduced earlier, washed beans have significantly fewer flavor layers. As the specialty coffee market increasingly demands richer flavors, cleanliness has gradually become not the only goal pursued by the washing method. Producing countries no longer focus solely on removing mucilage but instead strengthen the possibility of improving coffee quality during the fermentation process. For example, in recent years, some estates have developed the "double washing method." This divides one natural fermentation process into two stages. After the first fermentation removes about 80-90% of mucilage, after washing, the second fermentation continues to remove the remaining mucilage. Because the amount of mucilage in the second fermentation is small, even if the fermentation time is extended, no odor is produced. Additionally, more attention is paid to the pH of water during fermentation to control whether the fermentation process belongs to alcoholic fermentation.

Knowledge Point: Coffee beans are the fruit of the coffee tree, which belongs to the Rubiaceae family of perennial evergreen shrubs or small trees.

Summary

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