Why Do Washed Coffee Beans Taste More Acidity? Flavor Characteristics of Washed Process Coffee

Have you ever encountered this scenario in a coffee shop: A taster doesn't know the information about the coffee beans, but after taking one sip of the brewed coffee, they immediately guess the processing method, "This must be washed, right?"

This is because, typically, washed processed coffee exhibits a distinct cleanliness and clear mouthfeel. When using light to medium roast, it often carries bright and more intense fruit acidity, reminiscent of fruits we've tasted before, such as green tangerines or lemons. Therefore, when we regularly select coffee beans, if we enjoy acidic flavors, we tend to choose from the washed series.

What Causes These Flavors in Washed Coffee Beans?

Before discussing processing methods, let's first understand the structure of coffee cherries.

Processing Method = Coffee Cherry → Green Coffee Bean

If we cut through a harvested coffee cherry horizontally, we can see from outside to inside: the skin, pulp, mucilage layer, parchment, silver skin, and finally the seed (coffee bean). The so-called processing method is the process of extracting the internal seed from mature fruit.

Initially, coffee bean processing had only two methods: "wet" process and "dry" process. Among them, the dry process is also known as natural processing, where coffee cherries are dried under the sun, and finally, the seeds are obtained through crushing and hulling—simple and convenient. The wet process, also called washed process, broadly refers to what we know as the washed method.

How Are Coffee Beans Washed?

Simply put, washed coffee cherries undergo flotation washing after harvesting to remove impurities such as branches, leaves, and defective fruits. Then they are poured into a machine for pulping (with pulp and a tiny bit of mucilage remaining). At this point, the beans that have been stripped of their outer coating are still covered in mucilage, feeling slippery to the touch.

Next, these beans are poured into fermentation tanks and left to rest overnight or longer, undergoing anaerobic or aerobic fermentation. The purpose is to let microorganisms ferment and decompose the mucilage on the outer shell. After fermentation is complete, the coffee beans are washed with clean water to remove the mucilage. Finally, the clean parchment beans are dried or oven-dried until the moisture content decreases to 11% to 13%.

Because the pulp and mucilage are removed before drying, the moisture content is significantly reduced, and the drying time is greatly shortened compared to natural processing. This reduces dependence on weather and improves processing efficiency. From the producer's perspective, washed processed coffee beans show more consistent performance, and the short drying time is very suitable for producing large quantities of coffee with good quality.

Why Are Washed Coffee Beans More Acidic?

Regardless of the processing method used, green beans undergo varying degrees of fermentation—the process of using microorganisms to convert sugars and organic substances within the beans into other compounds, metabolizing to produce alcohol and carbon dioxide. Among these, aerobically fermented coffee beans have more sugars converted into gases and produce various organic acids. The wet fermentation (with water) in traditional washed processing belongs to semi-aerobic fermentation.

When discussing this wet fermentation, we must mention the Kenyan washed method, which takes it to the extreme. Coffee processed with the Kenyan washed method ferments for 24 hours each time. After fermentation, it's washed clean, then water is changed for repeated soaking, continuously cycling three times, totaling exactly 72 hours of fermentation. The coffee parchment beans, in a semi-aerobic environment, ferment to produce richer organic acids, such as citric acid and acetic acid—acids that easily stimulate the taste buds. When using a lighter roast to preserve most of the quality fruit acids, the brewed coffee exhibits stronger berry-like acidity, with a clean and full mouthfeel.

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