What Are the Flavor Characteristics of Washed Process Coffee Beans? Differences Between Washed and Semi-Washed Methods

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Washed Processing Enhances Fruit Acidity

The washed processing method is currently the most prevalent processing technique. In Central and South America, with the exception of Brazil, almost all regions use the washed method. Washed beans exhibit beautiful blue-green coloration, uniform appearance, and excellent visual appeal, representing the highest coffee quality. Generally, washed beans offer superior acidic aroma and brightness, with clean flavors free from impurities, making it the most commonly used processing method for specialty beans. However, the cost is considerable. 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 water-intensive bean extraction methods.

The washed processing method represents the most technically sophisticated of all bean extraction methods, ensuring coffee quality through multiple screening procedures. First, inferior floating beans are screened out in large water tanks, then the red cherries and nearly ripe green cherries that sink to the bottom are transferred to large, medium, or small pulping machines. Their design is quite ingenious, using mechanical force to press cherries against a screen with holes sized precisely to allow the parchment (coffee beans enclosed in the parchment layer) to pass through while filtering out the pulp outside the parchment. This utilizes the characteristic that unripe cherries are harder and their parchment is difficult to extract, while ripe cherries are softer and their parchment easily enters the screen holes, thereby filtering out unripe beans and selecting parchment with optimal sweetness. Therefore, the machine's thrust setting is crucial—too much force would extract harder, astringent unripe beans, compromising specialty bean quality. Generally, thrust is set to allow 3% of red cherry parchment to fail entering the screen holes, ensuring all stiff green cherries are completely filtered out. In other words, it's better to set the thrust slightly lower, losing a small portion of red cherries, rather than letting one bad bean spoil the entire batch.

After extracting the sticky parchment from red cherries, it's transferred to large water tanks for the most crucial washed fermentation processing to remove the mucilage layer from the parchment. This transparent, viscous substance cannot be easily washed away with water and requires hydrolysis by various bacteria in the tank, breaking down pectin into pectic acid, while constantly stirring, rubbing, and rinsing the parchment in the tank to accelerate mucilage separation from the parchment. The fermentation process takes approximately 16 to 36 hours, depending on temperature and humidity, during which malic acid, citric acid, acetic acid, lactic acid, and propionic acid naturally develop in the tank. Interestingly, raw beans themselves contain almost no acetic acid, but the fermentation process in washed processing can increase the bean's acetic acid concentration, benefiting coffee flavor. These acidic substances not only inhibit mold growth but also allow some acidic aromatic compounds to penetrate the beans (this is why washed beans have heavier fruit acidity). It's essential to continuously sample and inspect whether the viscous mucilage on the parchment has been completely removed before deciding whether to stop fermentation and extract the clean parchment. Once it exceeds 36 to 72 hours, over-fermentation may occur, producing excessive fatty acids and butyric acid, creating foul odors. Additionally, excessive penetration of acidic substances into the beans can make coffee overly astringent, reducing it to inferior quality beans.

Washed processing is an ever-evolving treatment method with frequent technological innovations, making it the most relied-upon bean extraction method for specialty beans. Generally, washed beans offer the purest flavors with minimal impurities, optimal fruit aroma and fruit acidity, and excellent bean appearance, though their sweetness is inferior to natural-processed beans. Even the notorious robusta beans can achieve improved elegant flavors and value when processed using the washed method, making it the most widely adopted processing method today.

Mechanical Semi-Washed vs. Brazilian Pulped Natural

Due to insufficient water resources for washed processing but a desire to improve natural-processed bean quality, semi-washed and pulped natural methods emerged. These processing methods can be divided into Brazilian natural depulping method (Pulped Natural, also called pulped natural) and mechanical semi-washed method (Semiwash). Among these, the mechanical semi-washed method is more widely used, commonly employed in Colombia, Costa Rica, El Salvador, Vietnam, Indonesia, Laos, Myanmar, and several African countries. On average, processing 1 kilogram of coffee cherries requires only half a liter of clean water, much more economical than the washed method.

Brazilian Pulped Natural: Natural Depulping

Brazil traditionally used the natural processing method, with significant quality variations that made Brazilian beans synonymous with medium to low quality. However, this world's largest coffee-producing country initiated a coffee quality revolution in the 1990s to enhance quality and transform its image, vigorously promoting its globally unique pulped natural method.

Brazilian coffee plantations stretch endlessly, mostly utilizing mechanical harvesting for economic efficiency. When 75% of coffee cherries in a plantation turn red, mechanical harvesting begins, followed by the same preliminary procedures as washed processing: transfer to large water tanks to remove floating beans, screen out sinking beans, then use large pulping machines to remove pulp, extracting parchment coated with mucilage. The subsequent stage diverges from washed processing: instead of transferring sticky parchment to water tanks for fermentation, it's moved to outdoor drying patios. Due to Brazil's dry climate, the viscous mucilage on the parchment hardens in about a day. Large teams of workers then continuously turn the parchment to ensure even drying inside and out, preventing moisture absorption and odors. After about two to three days, with the help of sunlight and dry climate's natural forces, the parchment achieves a certain degree of dehydration. It's then further dried using mechanical dryers until moisture content reaches 10.5-12%, after which the parchment is stored in special containers for about tens of days for additional maturation to ensure quality stability. Before export, the parchment layer (i.e., the parchment) is removed to extract coffee beans, which are then graded and packaged.

The biggest difference between Brazilian pulped natural and ancient natural processing methods is that the parchment is extracted first, preventing uncontrolled fermentation while the parchment remains in the pulp, instead managing the parchment's drying conditions manually to minimize uncontrolled variables. This represents a significant improvement in quality control. The greatest advantage of this method is that the pectin sugars on the parchment can penetrate the beans, providing the sweetness and body of high-quality natural-processed beans while reducing the disadvantages of natural processing, such as susceptibility to mold infection and off-flavors from over-fermentation. However, pulped natural beans have lower fruit acidity than washed beans because they cannot additionally generate the unique acidic aromatic components like acetic acid found in washed beans. This is also why Brazilian beans have noticeably lower acidity. Brazil's dry climate is a prerequisite for pulped natural processing, and few producing countries possess Brazil's superior environment for pulped natural processing. If pulped natural processing were adopted in humid Guatemala, the parchment would certainly mold and be ruined.

In recent years, many small and medium-sized farms in Brazil specializing in specialty coffee have abandoned mechanical harvesting, using manual picking exclusively, harvesting only red cherries and delivering them to processing facilities within hours for pulped natural processing. Interestingly, in Brazil's "Cup of Excellence" premium bean auction competition, the top twenty winners almost exclusively use pulped natural processing. This clearly demonstrates the significant effectiveness of Brazil's natural depulping method promoted by authorities for nearly two decades. High-quality Brazilian beans feature high sweetness, low acidity, and rich nutty or kernel aromas, shaping Brazil's unique "terroir" and washing away the stigma of Brazilian beans lacking notable aromas.

Mechanical Semi-Washed: Economical and Practical

Not all producing regions can adopt the Brazilian pulped natural method. In humid producing regions, extracting parchment coated with mucilage and exposing it outdoors for sun-drying not only makes dehydration difficult but also easily encourages mold growth. Therefore, regions with higher humidity developed the mechanical semi-washed method, which saves both effort and water. Many countries have adopted this method in recent years, including high-humidity producing regions in Central and South America, as well as water-scarce regions in Asia like Indonesia, Myanmar, and Laos, or areas where washed processing techniques are underdeveloped.

First, harvested red cherries are poured into pulping machines to extract parchment coated with mucilage. Instead of sun-drying or fermentation in water tanks, the parchment is directly transferred to adjacent demucilagers. Using only small amounts of water, mechanical force removes the sticky mucilage layer, extracting smooth-surfaced parchment, which is then sun-dried outdoors until moisture content reaches 12% for storage. The semi-washed method has fewer variables affecting quality, requiring only investment in pulping machines and demucilagers to operate independently on the farm. Coffee processed using this method tastes less acidic than washed beans but more acidic than natural-processed beans; it's less sweet than pulped natural beans but cleaner than pulped natural, with flavors falling between pulped natural and washed processing.

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