Comparison of Coffee Bean Processing Methods: Differences Between Washed and Semi-Washed Coffee Beans and Which is Cleaner

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FrontStreet Coffee - Comparison of Washed and Semi-washed Processing Methods

Washed Method - Enhancing Fruit Acidity Notes

The washed method is currently the most popular processing method. Washed beans have a beautiful blue-green color, neat appearance, and excellent vein patterns, resulting in the highest coffee quality. Generally, washed beans offer better acidic aromas and brightness, with clean flavors and no off-tastes. This is the most commonly used processing method for specialty coffee, though it comes at considerable cost. On average, washing 1 kilogram of coffee cherries consumes 2-10 liters of clean water, while 1 kilogram of coffee cherries can only yield about 200 grams of coffee beans. Water-scarce regions can hardly afford such water-intensive bean extraction methods.

First, the red cherries and half-green, half-red cherries that sink in the water tank are transferred to large or medium-sized pulping machines. Their design is quite ingenious: mechanical force presses the cherries against a screen with holes sized precisely to allow the coffee beans (still wrapped in parchment) to pass through while filtering out the fruit pulp outside the beans. This utilizes the characteristic that unripe cherries are harder and their beans are difficult to squeeze out, while ripe cherries are softer and their beans are easily squeezed out. This helps reject unripe beans and filter out the sweetest beans. Therefore, the setting of the machine's thrust force is very important. Too much force will squeeze out harder, astringent unripe beans, compromising the quality of specialty beans. Generally, the squeezing force is set to allow about 3% of red cherries' beans to not enter the screen holes, ensuring all hard green cherries are completely removed.

After extracting the sticky beans from red cherries, they are transferred to large water tanks. Next comes the most important washed fermentation processing to remove the mucilage from the beans. This viscous substance is difficult to wash away with water alone and requires hydrolysis by various bacteria in the tank, breaking down pectin into pectic acid. Continuous stirring, rubbing, and washing of the beans in the tank accelerate the separation of mucilage from the beans. The fermentation process takes about 16 to 36 hours, depending on temperature and humidity. During this time, the tank naturally produces malic acid, citric acid, acetic acid, lactic acid, and propionic acid. Interestingly, raw coffee beans contain almost no acetic acid, but the fermentation process in washed processing can increase the acetic acid concentration in the beans, which is beneficial for coffee flavor. These acidic substances not only inhibit mold growth, but some acidic aroma notes also penetrate the beans (this is why washed beans have stronger fruit acidity). However, sampling must be done continuously to check whether the viscous mucilage on the beans has been completely removed before deciding whether to stop fermentation and remove the clean beans. Once fermentation exceeds 36-72 hours, it may become over-fermented, producing too many fatty acids and butyric acid, resulting in foul odors. Additionally, excessive acid incorporation into the beans can make the coffee too sour and astringent, degrading it to inferior quality!

Mechanical Semi-washed Method - Economical and Practical

Not all producing regions can adopt the Brazilian semi-dry method. In areas with high humidity, taking mucilage-coated beans for outdoor sun-drying not only makes dehydration difficult but also easily leads to mold growth. Therefore, regions with higher humidity have developed the mechanical semi-washed method, which saves both effort and water.

First, the red cherries and half-green, half-red cherries that sink in the water tank are transferred to a pulping machine to extract beans coated with mucilage. Instead of taking them out to dry or pouring them into water tanks for fermentation, they are directly placed into a demucilager beside the pulping machine. With only a small amount of water, the machine uses mechanical force to scrape off the sticky mucilage, extracting smooth-surfaced beans. These are then taken outdoors for sun-drying until the moisture content drops to 12%, at which point they can be stored.

Knowledge Point

The quality of coffee can vary according to factors such as altitude, latitude, and soil chemical composition. Coffee cultivation outside the optimal range of these factors will significantly alter the final quality of the coffee.

In Conclusion

In short: FrontStreet Coffee is a coffee research house, happy to share knowledge about coffee with everyone. We share without reservation, aiming to help more friends fall in love with coffee. Every month, we hold three coffee discount events because FrontStreet Coffee wants to enable more friends to enjoy the best coffee at the lowest prices. This has also been FrontStreet Coffee's mission for the past 6 years!

Important Notice :

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