Why Indonesian Coffee Beans Use Wet Hulling_Process Steps of Coffee Bean Wet Hulling

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Understanding Wet Hulling: The Unique Coffee Processing Method

Many friends are curious about "wet hulling" and want to know the difference between wet hulled coffee beans and traditional washed and natural processing methods. Although we've discussed the specific processing methods before, today we'll systematically explain the complete story of wet hulling.

The Sumatra Coffee Challenge

Sumatra coffee captivates with its enchanting cedar and herbal notes, along with unique spice flavors. But do you know the real growing environment behind this one-of-a-kind coffee on the world coffee map? Sumatra Island sits on the equator, with most of the island covered by tropical rainforest. The annual humidity ranges from 70% to 90%, with yearly rainfall reaching 2000mm. Although the volcanic ash soil allows coffee trees to grow vigorously, this humid climate makes coffee cherries extremely susceptible to mold and decay.

Due to the high year-round humidity, using normal washed processing methods would require double the drying time compared to standard processing. If coffee beans are not dried promptly in a short period, they can easily over-ferment or develop mold. Every change affects the coffee's flavor. Therefore, how to process coffee cherries and preserve coffee beans has become the biggest challenge for Sumatra's coffee production.

The Wisdom of Wet Hulling

Let's first examine how Sumatrans intelligently produce wet hulled coffee beans.

Step 1: Initial Processing

First, remove the outer pulp of the coffee cherry, keeping the parchment and mucilage intact. Place them in concrete tanks or plastic barrels for overnight fermentation. This helps decompose the mucilage, making it easier to remove.

Step 2: Washing and Initial Drying

Next, wash the coffee cherries. The mucilage will be removed during this washing process, leaving us with coffee beans that still have their parchment. Dry them in the sun for 2-3 days until their moisture content drops to 20-24%, allowing the coffee beans to reach the hardness needed for parchment removal.

Step 3: Wet Hulling

At 20-24% moisture content, the coffee beans themselves are soft and still contain considerable moisture, while the parchment is semi-dry. However, Sumatra's humid climate no longer allows for further drying. At this point, we need to use machines to separate the parchment from the coffee beans. In this condition, removing semi-dry parchment often cannot be done completely, leaving some residue. With additional hulling attempts, coffee beans may become damaged, forming Sumatra's distinctive "elephant foot" beans. This is why the Mandheling green coffee beans you purchase often have some instability.

Step 4: Final Drying

Continue drying these unevenly hulled coffee beans until the moisture content drops to 12-13%. During the day, these coffee beans enjoy sunlight, while at night they are stored in burlap bags, continuing to ferment under the influence of moisture. Once drying is complete, these coffee beans can be taken away by buyers.

The Essence of Wet Hulling

The above steps represent the complete wet hulling process. Compared to other processing methods, wet hulling is a race against time, with the ultimate goal of minimizing drying time in high-humidity air conditions.

Of course, there's another crucial key that cannot be overlooked: hand sorting. Good Mandheling coffee often undergoes three rounds of manual bean sorting. Under such a processing method that battles against air humidity, Sumatra coffee beans are uneven in quality. This is where the diligent Sumatran people come in, allowing us to drink high-quality Mandheling coffee. Think about your own bean sorting during roasting, while they face an entire season's harvest, all to bring you a cup of high-quality Mandheling coffee.

The Necessity of Speed

We can see that wet hulling allows for rapid processing of coffee cherries, and the reason for pursuing this speed is that Sumatra's high humidity and heavy rainfall leave coffee farmers with no other choice.

The following image compares precipitation and rainy days between the Sumatra region and the Yirgacheffe region in 2016.

Looking at the vertical axis units, we can clearly see Sumatra's extremely high rainfall, which far exceeds that of Yirgacheffe. Therefore, under such harsh conditions, coffee bean processing becomes a race against time, against decay and bacterial infection. Although wet hulled coffee beans may not appear as refined as other coffees, believe me, when it travels across oceans to reach you, it definitely brings its own sincerity and high quality.

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