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Understanding Washed and Natural Coffee Processing Methods

"Washed" and "Natural" represent the two most traditional and widely applied processing methods in coffee. Processing refers to the procedure of removing all substances from harvested coffee cherries except for the coffee beans themselves, while simultaneously drying them to a specified degree. During this process, coffee beans develop distinct flavor profiles due to different processing flows and varying fermentation levels. Because their "personalities" are so distinctive, as FrontStreet Coffee often shares, experienced coffee enthusiasts can typically identify a bean's processing method with just one taste.

Beyond taste differences, coffee beans processed through different methods also exhibit distinctive appearance characteristics. By observing whether the central crevice of coffee beans contains white silver skin, we can generally determine which processing method was applied. In a batch of coffee beans, those with more silver skin along the center line are likely washed processed beans, while those with fewer white lines are probably natural processed beans. This is a point that FrontStreet Coffee has shared in previous bean identification articles.

Why Silver Skin Serves as an Observation Point

The reason silver skin can serve as an observation point is quite simple - it's directly related to the coffee bean processing workflow. The structure of a coffee cherry from outer to inner layers consists of: skin, pulp, pectin, parchment, silver skin, and coffee bean. As mentioned at the beginning, processing methods involve removing all substances except the coffee bean, but different methods use different sequences and approaches for removal, which results in certain appearance differences in the final beans.

Differences in Processing Workflows

The natural processing workflow is quite simple - we only need to spread the harvested cherries in a location where they can receive direct sunlight. Once the cherries have dried to a certain degree, machines are used to remove the skin, pulp, and parchment layer, completing the green bean processing! The washed processing workflow is slightly more complex: conventional washed processing first requires floating selection to filter out unripe cherries and defective beans, then removes the skin and pulp from good cherries; after removal, the beans with pectin and parchment layers are soaked for fermentation; after fermentation ends, these beans are transferred to another clean water tank, where residual pectin on the surface is removed through manual stirring; when this step is complete, the coffee beans only have parchment and silver skin remaining, at which point we send them to sun-dry until they reach the specified moisture content, then remove the outer shell to extract the processed green coffee beans!

From the above, we can understand that the biggest difference between washed and natural processes lies in whether the beans are depulped before drying and whether water is used for soaking. It is precisely these two differences that cause qualitative changes in the appearance and flavor of coffee beans. Natural processed beans, because more substances participate in fermentation during processing (including high-sugar substances like pulp and pectin), and have longer sun exposure (deeper fermentation), will develop a color leaning toward golden yellow after processing is complete; washed beans, due to prolonged soaking in water and shorter drying time, will present a gentle emerald green color for the entire green bean. This represents a characteristic that can distinguish natural and washed beans at the green bean level.

The Role of Silver Skin in Roasting

Once we obtain the green beans, we can proceed with roasting! During the roasting process, beans will exhibit a second difference point due to different processing methods - that is, the "silver skin." In fact, from the green bean diagram above, we can already see different characteristics of silver skin under different processing methods. The first difference is the integrity of the silver skin: the silver skin of natural processed beans is relatively more complete; not to mention completely preserved, but at least there are connections between the silver skin; the silver skin of washed coffee beans is different - scattered here and there, with fewer connections and a very fragmented appearance!

The second characteristic is the color of the silver skin, especially the silver skin in the center line area. Natural processing not only allows coffee beans to receive sugar infiltration and full fermentation, but also gives the silver skin the same "treatment." Therefore, compared to the center line silver skin of washed beans, its color will be deeper. During roasting, beans continuously expand as roasting progresses. However, silver skin cannot continuously expand like green beans! Therefore, they will separate during the roasting process due to being pushed apart by the continuously "growing" volume of the beans. When roasting is complete, we'll find that washed beans mostly have white silver skin attached, while natural beans have little silver skin in their center lines - this is the difference caused by the integrity of silver skin preservation during processing.

Even if some silver skin in the crevices of natural beans hasn't fallen off, they will undergo more caramelization reactions during roasting because they received the same "treatment" as the beans during processing, resulting in a darker color after roasting, which from a distance appears as if there's no silver skin. Therefore, whether there's obvious white silver skin in the crevices of beans becomes the best identification characteristic for natural and washed processed roasted coffee beans. (It should be noted that what we're discussing here is "most beans" rather than "all," as nothing is absolute.) The final factor that can distinguish between them is flavor! Natural beans, due to more substances participating in fermentation and longer fermentation time, will have more prominent fermented flavors (such as wine-like aromas, fermented fruits). Additionally, they will make the coffee's flavor expression and layering richer; washed beans, due to relatively less fermentation, where the process mainly uses produced acidic substances to decompose pectin, don't have such obvious fermented flavors. Also because of insufficient fermentation, the coffee tastes cleaner and flavors are more prominent.

Conclusion

What we refer to as natural beans being sweeter and washed beans being more acidic is also influenced by these factors to some extent. But more importantly, it's the different degrees of roasting that cause variations in the proportion of acidic substances in coffee beans. Therefore, natural and washed processed coffees are relatively easy to identify. Because they all have distinctly characteristic features in terms of green beans, roasted beans, and coffee. But as always, nothing is absolute - these reference points only apply to most coffee beans, not all~

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