Introduction to Wet-Hulled Coffee Processing Method_Characteristics of Coffee Bean Wet-Hulling Method_Is Wet-Hulled Coffee Delicious

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Today, the editor would like to introduce you to a coffee processing method that you may not have heard of often.

Wet Hulling (Giling Basah)

This is a coffee processing method exclusive to Indonesia and a few surrounding coffee-producing countries. Giling Basah is Indonesian, literally meaning "scraping off the hard shell under wet conditions." It also has another English name called Wet Hulling.

The earliest translation of this term in the Chinese coffee circle appeared in Teacher Han Huaizong's book "Specialty Coffee Studies." In my opinion, Teacher Han's translation of "Wet Hulling" is the best understanding of this processing method. Other incorrect names, such as the typical "Semi-Washed," confuse several coffee processing methods, resulting in a near-zero understanding of wet hulling among a group of coffee enthusiasts, which is regrettable.

The significance of wet hulling to the global coffee industry is no less than that of honey processing. Coffee lovers must have drunk the must-have "Mandheling," which is processed using this method. It can even be said that most of the Arabica coffee in Sumatra and Sulawesi, Indonesia, uses wet hulling. According to the 2014 International Coffee Organization (ICO) statistics, Indonesia is the world's fourth-largest coffee-producing country. A processing method that contributes so much to global coffee production is definitely worth our study and analysis.

Why Use Wet Hulling

Due to the unique tropical rainforest climate conditions in the Indonesian region, the drying conditions for coffee beans are relatively harsh. The drying rate of the washed method is too slow and may lead to processing failure. Therefore, when the parchment (shell) is dried to a certain extent, it is ground and removed, and the raw coffee beans are directly exposed to the environment for drying, which can effectively shorten the drying time. Because the parchment (shell) is still moist when removed, this unique processing method is called wet hulling. Also, due to the short fermentation and drying time, Indonesian coffee has low acidity and possesses its unique herbal flavor and character. Understanding the reason for using wet hulling, let's now look at the processing steps of wet hulling.

Processing Steps

Floating Coffee Cherries

Whether in small coffee farms or slightly larger coffee estates, all coffee in Indonesia is hand-picked. After picking, the routine is to soak them in water to see if they sink or float for rough screening: the sinking coffee cherries are kept, while the debris and green fruits floating on the water surface are screened out.

Coffee Farmers Using Machines to Remove Fruit Skin

The mature red fruits are now put into a pulping machine to remove the skin. Unlike the washed method, wet hulling uses smaller pulping machines. These machines are so small that almost every coffee farmer can afford one, so the "pulping" stage is almost entirely completed at the farm level.

Next is fermentation. In the washed method, fermentation involves putting the de-pulped coffee beans with mucilage into fermentation tanks to soak, using bacteria's ability to remove the mucilage. This process lasts about 24-48 hours, with the water quality in the soaking tank roughly equal to the bean quality. Wet hulling fermentation is slightly different: it's only 12 hours, with very little water used for fermentation, and often conducted in smaller containers, such as plastic basins or even plastic bags. After this brief fermentation, most of the mucilage adhering to the bean shell can be easily rinsed off, leaving a small amount of mucilage on the bean shell. This step is also completed at the coffee farm level.

Coffee farmers load the wet and sticky coffee with parchment into bags and transport them to weekly agricultural markets to sell to others, often buyers from processing stations. The purchasing unit calculates by volume, with locally pre-measured dedicated buckets, one bucket marked as one liter or two liters, and pays the coffee farmers at the price of XX yuan per liter of coffee beans. Buyers often determine the payment level by observing the amount of residual mucilage adhering to the bean shell. More residue means a lower price; less residue means a higher price. The following picture shows a dedicated one-liter measuring bucket "a litera can".

After collecting many beans with parchment, the processing station directly sends the undried beans with parchment (moisture content 35%-45%) into the hulling machine, scraping off the bean shell and the mucilage adhering to it together. This is the so-called "wet hulling." This step is different from all other processing methods. Whether washed, natural, or honey processed, all involve drying the beans with parchment (moisture content 11%) before "dry hulling," scraping off the bean shell.

The hulling in wet hulling also has its specifics. The picture above shows the dedicated hulling machine for Indonesian wet hulling. In terms of size alone, it is three times larger than the hulling machine for washed processing. More important than size is the nature of the grinding core. The following picture shows wet hulling raw beans that have just been de-hulled, with high moisture content.

From the cross-section image of undried, high-moisture-content beans with parchment in wet hulling (as shown below), we can see that the bean shell of wet hulling is still soft, while the bean shell of the washed method has become brittle and dry after exposure to the scorching sun. During the drying process of the washed method, the internal raw beans lose water and their volume decreases relatively. There is a obvious gap layer between the raw beans and the bean shell, while the beans with parchment that undergo the same wet hulling process do not have such an obvious gap layer inside, and the beans are very swollen. The two points described above make the step of removing the bean shell in wet hulling increasingly difficult, and the defective broken beans caused by intense friction in wet hulling are also quite numerous.

At this time, the exposed raw beans with still high moisture content are spread out on cement floors covered with straw mats or plastic sheets for drying. Although there are no perishable organic materials like mucilage on the bean surface, coffee workers still need to pay attention to frequently turning the beans. After all, with such high humidity, coupled with the directly exposed raw beans being very fragile, they can rot if left covered.

Without the "sealing" of the bean shell, theoretically, the drying of wet hulling is faster. This is not the case. People in the coffee industry describe the drying process in Sumatra as a "nightmare." Sumatra, Indonesia, is truly one of the few coffee-producing regions with very humid climates. According to a coffee person who has visited Indonesian producing areas, "the maximum drying time within a day can be 4 hours, taken out in the morning, and brought back when it rains heavily in the afternoon." Some coffee processing workshops with a little money build greenhouses! Drying in the shed might be more cost-effective than taking them out and bringing them back in.

The humid weather also brings great trouble to coffee picking. In producing countries with clear and stable weather distribution, such as Central America, coffee pickers can pick all coffee fruits by going to the fields an average of 3 times. As for Sumatra, which doesn't know what weather distribution is, coffee pickers need to go to the fields countless times without stopping throughout the entire 6-month period when coffee fruits mature. Because coffee trees flower and bear fruit according to the weather!

Under such harsh environmental conditions, the drying of raw beans takes about half a month, with the specific number of days depending on luck. Without the bean shell, coupled with the freshly de-hulled raw beans being moist and warm, and Indonesians not using raised beds for drying, the raw beans can be affected by many external enzymes and microorganisms, especially those on the ground. Perhaps it is due to these factors during the drying stage that Sumatran coffee generally carries a "earthy" flavor. The drying of exposed raw beans gives wet hulling raw beans a common characteristic: a forest green color.

Flavor of Wet Hulling Coffee Beans

Understanding the entire processing process, I dare to discuss its flavor issues with you all. We generally believe that wet hulling beans have earthy, smoky, and chocolate flavors, with acidity described as "low," appearing rather dull. The low acidity comes from the shorter, less effective fermentation process and longer drying time. As for flavors like "earthy" in wet hulling beans, opinions vary. Some say it's related to the bean varieties chosen in wet hulling-related producing areas (Timor hybrid & Catimor: with Robusta lineage), some say it's the result of organic interaction between raw beans and the external environment (Peter Giuliano), and some even say it's because there are too many defective beans!

First, natural defects from the coffee fruit stage are inevitable, another contributor to defects is the hulling part, as well as corrosion during the transportation of wet beans with parchment, damage to exposed raw beans from sunlight and moisture, and additionally, the irregular drying speed brought by irregular weather also detracts from the flavor.

Although Indonesian wet hulling coffee beans have a high defect rate, we should also have confidence in them. In recent years, the Indonesian Specialty Coffee Association (SCAI) has been established, strengthening quality supervision throughout the coffee production chain. Some producing areas and estates have even introduced partial washing mechanisms, and some regions have begun to follow the path of high-quality, high-supervision characteristic wet hulling. Regardless, I still maintain an optimistic attitude towards the coffee development in Sumatra, Indonesia. I don't hope such a large and important producing country continues to carry an unclear baggage. I believe it still has much room for improvement.

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