Coffee processing is the art of transforming freshly picked coffee cherries into what we know as green coffee beans. While processing isn’t regularly discussed it plays a determining role in a bean’s flavor profile. During processing, nearly all of the material surrounding the cherry’s seed is removed and the seed is dried until it reaches a humidity content of 11%. How the material is removed depends on the type of processing. To understand processing, it’s important to understand the anatomy of a coffee cherry. The cherry is composed as follows (for descriptions of each layer, see the bottom of this blog entry):
The method of processing used to clean a bean greatly impacts its acidity, flavor profile, and even texture. There are four primary forms of processing: dry, wet, semi-washed, and honey. All four can produce extraordinary coffee. Let’s begin!
Dry-processing, also known as natural or traditional processing, is the oldest form of processing and is believed to have originated in Ethiopia. Freshly picked coffee cherries are laid out in full sun to ferment and dry. The cherries must be turned multiple times per day to protect against rot and covered in the evening to protect against rainfall. As the cherries dry, they ferment and the bean absorbs the pulp’s brilliant fruit flavors. If the cherries are dried on concrete or brick rather than raised beds, the beans will also pick up subtle tones from their drying surface. Cherries can take several weeks to dry and must be diligently cared for throughout the process. Once dry, the husk, mucilage, and hull* are removed from the beans. At this point, the beans are ready to be sorted, bagged, and exported.
Dry-processing is a minimalistic, eco-friendly, wildly inconsistent method with the potential to produce extraordinarily nuanced beans. Beans grown in nutritious soil and meticulously cared for during processing have good body and produce vivid fruit, berry, and wine tones rarely found in wet-processed beans.
*In some cases, farmers leave the hull, also known as pergamino, on until the roaster is ready to receive the beans as the hull helps preserve the bean. Beans that arrive in this state are referred to as “in pergamino”.
Wet-processing also referred to as washed, is the most common, most consistent method of processing. During wet-processing, fresh coffee cherries are sorted by size and passed through a pulping machine that separates the husk from bean. Once pulped, the beans are submerged in a water-filled fermentation tank for at least a few hours and up to a few days, depending on the farmer’s desired taste profile. Soaking the beans has a two-fold advantage: it ferments the beans while naturally dissolving the parchment and mucilage. Once fermented, the beans are first washed to remove any remaining parchment and then they are dried — either in the sun or in large drying tumblers. Once dry, the beans are ready to be bagged and exported.
Wet-processing is a resource-heavy, potentially high-waste process that requires naturally flavorful beans. The process is also extremely consistent with the potential to produce extraordinarily pure, natural-toned coffees. Unlike dry-processed beans, wet-processed beans absorb little flavor from the pulp or external environment. Instead, these beans produce marvelous natural tones inherent to their varietal / cultivar and reflective of their growing environment.
The semi-washed process, also known as wet hulling or giling basah, is the most common processing method among small-holding / micro-lot farmers in Indonesia. During the semi-wash process, the husk and some of the mucilage is removed from the bean and left to ferment and dry for up to 48 hours. Next, the remaining mucilage and parchment are removed and the beans are laid out to dry while their moisture levels are still high. As with dry-processing, the beans, in this moist state, absorb flavors from their drying surface — be it asphalt, brick, or earth. Often semi-processed beans are dried during transport, allowing the beans to develop very earthy tones.
The semi-washed process is generally eco-friendly and when applied to very high-quality beans, can produce a stunning, textured cup of coffee with low acidity and rich, deep earth tones.
Honey-processing, also known as pulped natural or miel processing, is a more modern twist on semi-washing that grants producers greater control over a bean’s texture, acidity, and flavor profile. During honey-processing, the husk and some of the mucilage are removed from the bean. The amount of mucilage remaining determines the color and character profile of the bean. Mucilage is a sticky sweet, honey-flavored substance separating the parchment from the pulp. If 90%+ of the mucilage is left on for drying, Black honey-processed coffee is produced. If approximately 80% of the mucilage remains for processing, Red honey-processed coffee is produced; at approximately 50% mucilage, you have Yellow honey-processed coffee, and at approximately 25% you have Golden honey-processed coffee. At less than 25% mucilage, White honey-processed coffee is produced. The beans absorb the mucilage’s sweet honey flavor during drying and fermentation. The more mucilage attached to the beans, the longer the beans take to dry and the sweeter the flavor. Once the beans reach a humidity level of 11%, they are milled, sorted, bagged, and ready for export.
Honey-processing is a higher risk, complex process with the potential to create an array of deliciously smooth, sweet, complex beans. Processed properly, these beans are mildly acidic and clean with delicate honey, fruit, and floral notes.
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Coffee cherry anatomy
Outer skin: the outermost layer of the cherry.
Pulp: the cherry flesh resting directly below the outer skin.
Mucilage: a thick, sticky, sweet protective layer separating the pulp and parchment.
Parchment (also known as endocarp or hull): a think layer of skin separating the seeds from the mucilage.
Silverskin: a tough, translucent, microlayer of skin surrounding the coffee seeds. The silverskin remains on the bean throughout processing and is only removed during roasting, where it is referred to as chaff.
Seeds: What we know of as coffee beans.