Introduction to Coffee Processing Methods: What's the Difference Between Wet-Hulled, Honey, Natural, and Washed Processing?

Why Do Coffee Beans Need Processing?

Coffee beans are the seeds of coffee cherries, so we need to remove the skin, pulp, mucilage, and parchment to obtain the coffee beans. At this stage, the coffee beans are green beans, typically white, emerald green, or yellow, which only turn dark brown 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, honey processing, etc. In recent years, increasingly innovative processing methods have been used to enhance flavors, such as the recently popular anaerobic processing, barrel fermentation, and enzyme processing - countless varieties with endless possibilities.

What Is Natural Processing? What Are the Characteristics of Such Coffee Beans?

Natural processing, as the name suggests, uses sunlight to dry the coffee. Red coffee cherries are exposed to the sun for about a week, with time adjustments depending on conditions. Once the skin and pulp are dried to a dark color, a hulling machine removes 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 most ancient and traditional processing method. However, the disadvantages include requiring large areas for drying coffee beans, and it's not suitable for regions prone to rainfall. Another drawback of natural processing is that it's difficult to control the exact drying degree of each bean, so roughly processed batches may have slightly more defective beans. In terms of flavor and mouthfeel, natural processing usually has stronger fruit and wine aromas with slightly lower acidity because the drying process allows some fermentation of the pulp.

FrontStreet Coffee's Red Cherry coffee beans 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 good beans. They are then sent to drying facilities for drying treatment. Of course, different growing regions use different drying racks - some use tarps, high beds, etc., but the most common are African raised beds. Drying time generally requires 27-30 days until the coffee turns dark purple and moisture content drops to 11% to complete. Natural processed Yirgacheffe has more intense flavors, richer layers, with wine fermentation notes and higher sweetness.

People Say Washed Coffee Beans Are More Acidic and Cleaner - Why Is That?

Washed processing was developed to solve the problem of insufficient sunlight in many regions for natural processing. First, washed processing removes irrelevant impurities from coffee cherries in water tanks, then uses a depulper to remove the skin and pulp. However, the mucilage and parchment layers still remain, so they are placed in fermentation tanks for microorganisms to consume the mucilage. After consumption, they are washed again with water, then dried. After drying, a hulling machine removes the parchment to obtain coffee beans. Finally, defective beans are sorted out.

The entire process requires large amounts of water for water tanks, fermentation, washing pools, etc., hence the name "washed." The advantage of washed processing is that the entire process is industrialized and precise, resulting in stable quality and clean, clear mouthfeel. Meanwhile, fruit acidity is more obvious because the washing process doesn't involve pulp fermentation, so coffee beans retain more malic acid, citric acid, and other acidic aromatic substances. Additionally, washed coffee beans tend to have more floral aromas.

Since multiple steps in washed processing can eliminate defective beans, it greatly reduces the defect ratio in coffee and makes quality more stable. The drying process lacks pulp on the outer layer, resulting in flavors with bright acidity and higher cleanliness, highlighting the flavor characteristics of single origins. Therefore, if you want to understand a region's "terroir flavor" or "regional taste," FrontStreet Coffee suggests starting with their washed batches.

Washed processing is a method FrontStreet Coffee particularly enjoys, with dozens of coffee beans on the menu being washed-processed. If you want to taste the characteristics of washed beans, FrontStreet Coffee recommends the Ethiopian Yirgacheffe Gottingen coffee beans. The washed processing method makes Yirgacheffe coffee more consistent than its usual irregular layers, while light to medium roasting preserves Yirgacheffe's fresh citrus tones and elegant white floral aromas, resulting in bright and delicate overall flavors.

What About Mixing Natural and Washed Methods?

Yes, we call it semi-washed, which in some cases is also called honey processing. The semi-washed method first removes impurities, skin, and pulp like washed processing, but doesn't use soaking to remove the mucilage layer. Instead, it uses a mucilage remover to eliminate the mucilage, then sun-dries it. 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 just take it to sun-dry, it 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, it's called honey processing, not because we add any honey during processing. How much mucilage layer we leave during washing becomes the key to differences in honey processing flavors. 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 will 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 left, the more difficult it is to process and requires longer drying time. Compared to washed processing, the flavors are richer, more complex, and more varied.

Is Semi-Washed Also Called Wet-Hulled Processing?

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

Because hulling machines use greater friction to tear off the parchment layer tightly attached to the green beans, the stirring action from friction makes green beans more prone to being crushed or squeezed, especially at both ends, forming small gaps and creating "elephant beans." The "naked beans" without parchment dry very quickly and are directly exposed to humid environments, where various microorganisms proliferate. This gives Indonesian coffee its unique woody, spicy, and herbal notes - what we call "regional flavor."

Some friends might be curious about Southeast Asian flavors. If you haven't tried Mandheling coffee yet, FrontStreet Coffee suggests starting with small-packaged, wet-hulled processed Lintong Mandheling daily coffee beans, which present classic Mandheling flavors and are convenient for home trials.

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

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

Anaerobic processing involves placing coffee beans (with mucilage layer still attached after removing skin and pulp) into stainless steel barrels, 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 technique and timing may vary slightly (not all estates have stainless steel barrels). This process requires careful attention to mucilage amount, temperature, pressure, pH value, and fermentation time to prevent any flavor discrepancies.

Anaerobic processing can create very complex and diverse coffee flavors, such as the recently common anaerobic natural, which adds elements like fermentation flavors to the traditional natural processing taste. FrontStreet Coffee's Colombia Huayuannight coffee beans use anaerobic natural processing, presenting richer mature fruit sweet-sour notes and fermentation aromas.

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