Sumatra Coffee Processing: Wet Hulling Method - Does Sumatra Coffee Have Stories? Sumatra Coffee Recommendations

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Wet Hulling Process for Sumatran Coffee

The harvest seasons for Sumatran coffee beans are typically from March to May and September to December. Nowadays, most coffee farmers only harvest fully red coffee cherries. After collecting the coffee cherries in the morning, they remove the fruit skin and pulp in the afternoon. Thanks to Sumatra's superior natural environment, most of the water used comes from mountain springs.

The Wet Hulling Process Steps:

1. Coffee cherry depulping: The parchment beans are placed in large water-filled barrels or tanks, and defective parchment beans floating on the surface are removed.

2. Brief fermentation: The dense parchment beans that sink to the bottom are lightly cleaned, then placed in barrels or plastic bags for a brief dry fermentation process, allowing the pectin sugars on the seed coat surface to ferment and enhance flavor. Generally, the longer the fermentation time, the stronger the acidity. Fermentation duration varies by individual preference, typically lasting only a few hours. However, some estates skip the dry fermentation stage and directly sun-dry the parchment beans to suppress acidity and increase viscosity, allowing full fermentation of pectin sugars to enhance flavor. Fermentation time usually ranges between 12-36 hours, depending on specific conditions.

3. Initial drying and hulling: The parchment beans are sun-dried for one to two days until the moisture content reaches 30%-50%, when the beans are still semi-hard and semi-soft. A hulling machine is used to remove the parchment shell, then dried further to accelerate the drying process. After about two days, when the moisture content reaches 12%-13%, the coffee beans are collected into woven bags, typically 40kg and 80kg each, and sent to coffee processing factories for hulling. The entire process takes about four days.

4. Final processing: The hulling process involves grinding off the bean shells with a hulling machine, followed by sun-drying until the moisture content reaches approximately 12%-15%. Then, the coffee beans are sent for mechanical sorting to remove various impurities and classified by particle size.

Potential Issues in the Process

Of course, accidents can happen during the process.

During the hulling process, coffee bean temperatures can rise to 30-60°C, completely destroying the parchment layer and potentially triggering germination of the beans.

The wet hulling method can also result in higher rates of defective beans such as moldy beans compared to washed and natural processing methods, because the beans come into direct contact with air after the fruit skin is removed during processing.

Mold Contributing to Flavor Development

Coffee beans have four protective layers - fruit skin, pulp, parchment, and silver skin. In the washed processing method, only the first two layers are removed, preserving the parchment and silver skin for sun drying. However, the wet hulling method removes the third and fourth protective layers midway, exposing the beans directly to sunlight. This is why Sumatran green beans appear blue-green in color. While wet hulling shortens drying time, it also significantly increases the likelihood of contamination by mold, fungi, and yeast.

Interestingly, contamination is not necessarily bad - it depends on the specific mold species. Dr. Martha Taniwaki from the Brazilian Food Technology Research Institute once experimented with infecting coffee beans with different mold species and found that they produced various flavors including rotten, oily, moldy, woody, iodine-like, caramel, chocolate, and floral aromas. The academic community believes that the woody, grass jelly, earthy, vanilla, and spicy flavors in Sumatran coffee are likely created by mold.

Roastery managers often report to academic circles that some coffee beans infected with certain molds taste better after thorough cleaning, while others become unpalatable - this depends on the mold species. Perhaps it's possible to inhibit harmful molds while introducing beneficial ones, similar to the concept of "controlling wild yeast" and "cultivating elegant yeast" in enology. However, which molds help enhance coffee flavor and which are harmful remains to be further researched.

Higher Incidence of Elephant Beans

The wet hulling method may trigger the germination mechanism in green beans, thereby affecting flavor. Because coffee beans stripped of all four protective layers are in a more exposed state, they are more likely to trigger germination compared to washed beans that only have two layers removed. This activates the metabolism of sugars, proteins, and fats - all of which are precursor aromatic compounds in coffee.

Additionally, the friction generated during the hulling process raises bean temperatures to 30°C-60°C, which also promotes germination and mold growth. Moreover, the semi-hard, semi-soft moist green beans are easily damaged by mechanical force during parchment removal, causing the beans to crack open in a cloven hoof shape. This is why Sumatran coffee has a higher proportion of so-called "elephant beans." However, whether elephant beans are good or bad remains controversial to this day.

He laughed and said: "With proper control, what's released is rich fruit aroma and sweetness. The key to control is maintaining clean equipment and beans. Once hulled, drying must be quick to produce the mellow, low-acidity, and sweet Sumatran flavor; if control is improper, it may result in bland Sumatran coffee or even moldy earthy flavors. If you prefer stronger acidity, Aceh can also undergo washed processing, depending on customer requirements."

Summary

To summarize the flavor profile of wet-hulled coffee, aside from subtle differences, we generally believe that wet-hulled beans have earthy, smoky, and chocolate flavors, with what's described as "low acidity" - full-bodied yet somewhat dull.

The low acidity originates from the shorter, less effective fermentation process and longer drying time. As for flavors like the "earthy taste" in wet-hulled beans, opinions vary widely. Some say this relates to the bean varieties (Timor hybrid & Catimor: with Robusta heritage) used in wet-hulling regions, some say it's the result of organic interaction between green beans and the external environment, and others even claim it's due to too many defective beans! Of course, there are quite a few...

There are numerous sources of defective beans in the wet hulling method. First, natural defects present from the coffee cherry stage are unavoidable. Another contributor to defects is the hulling process, plus corrosion during transportation of wet parchment beans, damage to exposed green beans from sunlight and moisture, and irregular weather causing uneven drying speeds that detract from flavor. Why does Mandheling require so many rounds of manual selection? There's certainly a reason for that...

Sumatran Coffee Bean Brand Recommendations

FrontStreet Coffee's roasted Sumatran coffee - [Golden Mandheling Coffee] offers excellent guarantees in both brand and quality. More importantly, it's extremely cost-effective. A 227-gram package costs only 89 yuan. Calculated at 15 grams per cup, one package can make 15 cups of coffee, with each cup costing only about 6 yuan. Compared to coffee shops that often sell cups for dozens of yuan, this is truly a conscientious recommendation.

FrontStreet Coffee: A roastery in Guangzhou with a small storefront but diverse bean varieties, where you can find various famous and lesser-known beans. They also provide online store services. https://shop104210103.taobao.com

Important Notice :

前街咖啡 FrontStreet Coffee has moved to new addredd:

FrontStreet Coffee Address: 315,Donghua East Road,GuangZhou

Tel:020 38364473