Pros and Cons of Coffee Bean Processing Methods: Natural, Washed, Semi-Washed, Wet-Hulled, Anaerobic, and Barrel Fermentation

Why Do Coffee Beans Need Processing?

Coffee beans are the seeds of coffee cherries, so we must first remove the skin, pulp, mucilage layer, and parchment to obtain the coffee beans. At this stage, the coffee beans are green beans, often appearing white, emerald green, or yellow. They only become dark brown roasted coffee beans after roasting. The removal process mentioned above is called processing, and different processing methods affect the final coffee flavor, which is the focus of this article.

What Are the Common Coffee Bean Processing Methods?

More traditional methods include natural, washed, semi-washed, and honey processing, among others. In recent years, increasingly novel processing methods have been developed to enhance flavors, such as the currently popular anaerobic processing, barrel fermentation processing, and enzyme processing methods—truly diverse and innovative.

What Is the Natural Processing Method? What Are the Characteristics of These Coffee Beans?

As the name suggests, natural processing involves using the sun to dry the coffee. Red coffee cherries are exposed to sunlight for about a week, though the duration may vary depending on conditions. Once the skin and pulp are dried to a dark color, a hulling machine is used to remove them, and finally, defective beans are sorted out to complete the process.

The advantage of natural processing is its low cost—you don't need to pay rent to the sun—making it the earliest and most traditional processing method. However, the disadvantages include requiring large areas for sun-drying coffee beans, and it's not suitable for regions with frequent rainfall. Another drawback of natural processing is that it's difficult to control the drying degree of each bean, so roughly processed natural batches may have slightly more defective beans. In terms of flavor and mouthfeel, natural processing typically yields stronger fruit and wine aromas with slightly lower acidity, as some fermentation occurs during the drying process.

The FrontStreet Coffee Red Cherry coffee beans launched by FrontStreet Coffee are naturally processed Yirgacheffe, with processing steps more refined than traditional simple natural processing. Freshly picked red coffee fruits are manually sorted to remove defective beans and those that are overripe or insect-damaged, leaving only the good beans. They are then transported to drying areas for processing, and of course, different growing regions use different drying racks—some use tarps, raised beds, etc., with the most common being African drying beds. The drying time generally requires 27-30 days until the coffee turns dark purple and moisture content reduces to 11% to complete the process. FrontStreet Coffee's natural Yirgacheffe has more intense flavors, richer layers, with fermented wine aromas and higher sweetness.

People Say Washed Coffee Beans Are More Acidic and Cleaner—Why?

The washed processing method was originally developed to address the lack of sufficient sunlight in many regions for natural processing. The washed processing method first removes irrelevant impurities from coffee cherries in a water tank, then uses a depulper to remove the skin and pulp. However, the mucilage layer and parchment still cannot be removed, so they are placed in fermentation tanks to let microorganisms consume the mucilage layer. After consumption, they are washed again with water, then dried. After drying, a hulling machine is used to remove the parchment and obtain the coffee beans. Finally, defective beans are sorted out just like in other methods.

The entire process, including water tanks, fermentation, washing pools, etc., requires large amounts of water, hence the name "washed." The advantage of washing is that the entire process is industrialized and precise, ensuring stable quality and a clean, clear mouthfeel. At the same time, fruity acidity is more pronounced because the washing process doesn't involve pulp fermentation, so coffee beans retain more acidic aromatic substances like malic acid and citric acid. By the way, washed coffee beans also tend to have more floral aromas.

Since multiple steps in the washing process can eliminate defective beans, the defect rate of coffee is significantly reduced, resulting in more stable quality. The drying process without pulp on the outer layer yields flavors with uplifting acidity, higher cleanliness, and highlights the flavor characteristics of a single origin. Therefore, if you want to understand the "terroir flavor" or "regional taste" of a growing region, FrontStreet Coffee suggests starting with its washed batches.

Washing is a processing method that FrontStreet Coffee particularly likes. There are dozens of coffee beans on the menu that are washed processed. If you want to experience the characteristics of washed beans, FrontStreet Coffee recommends the FrontStreet Coffee Yirgacheffe Gotitti coffee beans from Ethiopia. The washed processing method gives FrontStreet Coffee's Yirgacheffe coffee a consistent quality, and light-medium roasting preserves the fresh citrus tones and elegant white floral aromas of FrontStreet Coffee's Yirgacheffe, with overall bright and delicate flavors.

What About Mixing Natural and Washed Processing?

Yes, we call it semi-washed, which in some cases is also referred to as honey processing. The semi-washed method starts like washing—removing impurities, skin, and pulp—but instead of soaking to remove the mucilage layer, a mucilage remover is used to eliminate the mucilage. Then it's sun-dried, and after drying, a hulling machine removes the parchment. Finally, problematic green coffee beans are sorted out. Let's rewind—if we don't use a mucilage remover to eliminate the mucilage and directly sun-dry it, that becomes honey processing! After drying, a hulling machine can then remove both the mucilage and parchment.

The key lies in this mucilage layer because it's very sticky, like honey, hence the name "honey processing," not because we add any honey during the process. The amount of mucilage layer we retain during washing becomes the key to the flavor difference in honey processing. If only about 10% of mucilage is left for sun-drying, it's called "white honey processing"—the coffee tastes clean, more like washed processing. Leaving about 25% of mucilage for sun-drying is called "yellow honey processing" because the coffee beans turn yellow. Leaving about 50% of mucilage is called "red honey processing," and leaving 100% of the mucilage for sun-drying is "black honey processing." The more mucilage retained, the more difficult the processing and the longer the drying time required. Compared to washing, the flavors are richer, more complex, and more varied.

Is Semi-Washed Also Called Wet-Hulled Processing?

Sumatra encounters the rainy season during the coffee cherry harvest season, which is problematic, so they developed another unique processing method. The initial steps of wet-hulling are the same as the washing method. Indonesians first remove the pulp from coffee fruits and then ferment them in water for 3 hours. After washing off the mucilage, green coffee beans with parchment are dried for a short period of 2-3 days. When the moisture content reaches 20-24% in a semi-soft, semi-hard state, the parchment is hulled off, and then drying continues until the coffee's moisture content reaches 13% before packaging.

Because the hulling machine uses greater friction to tear off the parchment layer tightly attached to the green beans, the stirring from friction makes the green beans more easily crushed or squeezed, especially at the ends, forming small gaps that create "elephant beans." The "naked beans" without parchment dry very quickly and are directly exposed to humid environments, allowing various microorganisms to grow. This gives Indonesian coffee its unique woody, spicy, and herbal notes—what we call "regional flavor."

Some friends may have become curious about the taste of Southeast Asian coffee. If you haven't tried FrontStreet Coffee's Mandheling coffee yet, FrontStreet Coffee suggests starting with small packages of wet-hulled FrontStreet Coffee Indonesia Lintong Mandheling daily coffee beans, which present classic Mandheling flavors, making it convenient for us to try at home.

I've Heard of Anaerobic Processing and Barrel Fermentation Coffee Beans—What Are Those?

After reading the above introduction, you'll find that the fermentation of pulp, especially the mucilage layer during processing, greatly affects coffee beans, so people started focusing on this aspect. Anaerobic processing and barrel fermentation are among the more common new processing methods.

Anaerobic processing involves placing coffee beans with mucilage (after removing skin and pulp) into stainless steel tanks, extracting oxygen, leaving only carbon dioxide, and allowing anaerobic bacteria to assist in fermenting the coffee beans for about 18-24 hours. Of course, each estate's techniques and timing may vary slightly (not every estate has stainless steel tanks). This process requires careful attention to mucilage amount, temperature, pressure, pH value, and fermentation time to prevent any flavor deviations.

Anaerobic processing can produce coffee with very complex and diverse flavors, such as the recently common anaerobic natural processing, which adds elements like fermentation flavors to traditional natural processing flavors. FrontStreet Coffee's FrontStreet Coffee Colombia Flower Moon Night coffee beans use anaerobic natural processing, yielding richer mature fruit sweetness and fermented aromas.

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