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, a neat appearance, and excellent vein patterns, and they yield the highest coffee quality. Generally, washed beans offer better acidic aromas and brightness, with clean flavors and no off-tastes. It 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 cherries yields only about 200 grams of coffee beans. Water-scarce regions can hardly afford such a water-intensive method.

First, the red cherries, along with the half-green, half-red ones, 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 let the coffee beans (still wrapped in parchment) pass through while filtering out the fruit pulp outside the beans. This takes advantage of the fact that unripe cherries are harder and their beans are difficult to squeeze out, while ripe cherries are softer and their beans come out easily. It helps reject unripe beans and filter out the sweetest ones. The setting of the machine's thrust force is therefore very important: too much force will squeeze out the harder, astringent unripe beans and compromise the specialty beans' quality. In general, the squeezing force is set so that about 3% of red cherries' beans do not pass through the screen holes, ensuring that all hard green cherries are completely removed.

After the sticky beans are extracted from the red cherries, they are transferred to large water tanks. Next comes the most important washed fermentation, which removes the mucilage from the beans. This viscous substance is hard to wash away with water alone and needs hydrolysis by various bacteria in the tank, which break pectin down into pectic acid. Continuous stirring, rubbing, and washing of the beans in the tank speeds up the separation of mucilage from the beans. Fermentation 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 in washed processing can raise the acetic acid concentration in the beans, which benefits coffee flavor. These acidic substances not only inhibit mold growth but also let some acidic aroma notes penetrate the beans - which is why washed beans have stronger fruit acidity. That said, samples must be checked continuously to see whether the viscous mucilage has been completely removed before deciding whether to stop fermentation and take out the clean beans. Once fermentation exceeds 36-72 hours it may become over-fermented, producing too many fatty acids and butyric acid and creating foul odors. On top of that, excessive acid uptake into the beans can make the coffee too sour and astringent, degrading it to inferior quality.

Mechanical Semi-washed Method - Economical and Practical

Not every producing region can adopt the Brazilian semi-dry method. In areas with high humidity, taking mucilage-coated beans out for sun-drying makes dehydration difficult and easily leads to mold. Regions with higher humidity therefore developed the mechanical semi-washed method, which saves both effort and water.

First, the red cherries, along with the half-green, half-red ones, that sink in the water tank are transferred to a pulping machine to extract the beans coated with mucilage. Instead of taking them out to dry or pouring them into water tanks to ferment, the beans go directly 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 and turn out smooth-surfaced beans. These are then taken outdoors to sun-dry until moisture 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. Cultivating coffee outside the optimal range of these factors will significantly change the final quality of the cup.

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 more people to enjoy the best coffee at the lowest prices. This has also been FrontStreet Coffee's mission for the past 6 years!

FrontStreet Coffee Recommendation

If the clean, bright character of washed coffee described above is what you enjoy, FrontStreet's Yirgacheffe Gudingding Cooperative is a strong place to start. Many people know Yirgacheffe without realizing that, because local farmers produce small volumes, they send their cherries to a cooperative for centralized processing, and Gudingding Cooperative is an accomplished team from Gudingding village. Its coffee is remarkably refined and clean, which is how it earned its reputation. The washed process lets Gudingding express jasmine florals and bright citrus acidity to the fullest, and after a light-to-medium roast the coffee also releases green tea and honey notes. It works well as pour-over, cold brew, and espresso.

For a showcase of how far washed processing can go, try FrontStreet's Kenya Cherry Tomato. Kenya is especially skilled at the double washed method, and this coffee repeats the washing steps - flotation, soaking the beans, washing off the residual mucilage, soaking again, then drying and hulling for storage. All that repeated rinsing and soaking brings the juice character out to the extreme, giving a cup rich in cherry tomato, smoked plum, snow pear, black plum, and brown sugar aromas, sweet-sour and juicy. It is a favorite among coffee lovers who prize complexity.