Coffee Bean Sun-Drying Processing Method Steps and Visual Guide - Differences in Flavor Characteristics Between Sun-Dried and Washed Coffee Beans

When drinking coffee, you'll often notice labels mentioning processing methods like natural, washed, or honey processing. While natural and washed processing are relatively easy to understand, terms like honey processing and wet-hulling can be completely baffling. That's why FrontStreet Coffee wants to discuss today the differences between natural and washed processing methods and how they affect the flavor of coffee beans.

The Coffee Cherry Structure

Actually, the coffee beans we drink don't grow as individual beans - they start as round fruits.

From outside to inside, they can be roughly divided into: skin, pulp, mucilage layer, parchment (also called parchment layer), silver skin, and the innermost coffee bean seed. Through various processing methods, these outer layers of skin, pulp, and mucilage are removed to obtain the innermost coffee bean seed, which becomes the coffee we drink after roasting.

Common Coffee Processing Methods

Next, let's look at how coffee beans are extracted! Common coffee processing methods are mainly divided into three types: natural, washed, and intermediate methods like honey processing, wet-hulling, semi-washed, and semi-natural processing. Today, let's first explore what natural and washed processing methods specifically entail!

Natural Processing Method

This is a relatively ancient processing method. Natural processing is a low-cost and relatively simple processing method. Natural processing reduces the moisture content of coffee through extensive drying.

Natural Processing Steps

The harvested coffee cherries are poured into large water tanks. Ripe, full cherries will sink to the bottom; underdeveloped or overripe cherries will float to the surface and need to be removed. However, in some water-scarce areas, coffee cherries are screened through mesh nets.

After screening the coffee cherries, the entire cherries with skin, pulp, and mucilage are spread directly on cement floors or drying beds for natural drying until the moisture content reaches about 12%, taking about two to four weeks depending on the climate of the origin. After completing the drying process, the dried hard skin, pulp, and parchment layer are removed using a hulling machine, and we get our desired green coffee beans.

Although natural processing is lower in cost and the process is relatively simple, it has some disadvantages. Because it must be placed in sunlight-exposed areas, the requirements for climate and environment are quite strict. It's generally concentrated in tropical countries with distinct wet and dry seasons. Due to many uncontrollable factors like weather and environment, improper handling can easily lead to defective beans, insect-damaged beans, rotting, and mold problems, resulting in more flavor impurities.

Moreover, the moisture content of coffee cherries themselves is still quite high. Leaving coffee cherries in one place for more than twenty days will naturally cause fermentation reactions. If fermentation is excessive, rotting can easily occur. If coffee cherries are piled too thickly in one area without ventilation, the rotting becomes even more severe. Therefore, significant labor is needed to frequently turn the coffee cherry piles to ensure ventilation. Additionally, natural processing involves minimal screening elements - only a rough screening after harvesting, and then they go straight to coffee sacks. The defect rate of natural processing is higher than that of washed processing.

Although coffee beans processed by natural methods may have a higher defect rate, excellent naturally processed coffee beans have higher sweetness, fuller body, and more complex aromas.

By the way, natural processing is also divided into traditional natural and refined natural processing.

Traditional Natural

The natural processing process is quite labor-intensive. Hand-harvested high-sugar cherries are first placed on African raised beds for about 10 days of sun drying, then moved to greenhouses covered with plastic sheets to create more direct heat energy for continued drying, or the harvested coffee cherries are directly placed in their own courtyards for sun drying until the moisture content reaches 11.5%.

The slow drying process allows green beans to develop more natural sweetness from within, but it also requires more careful attention and precise calculation of turning frequency. When the bright red cherries finally turn black and emit aromas of fruit cake, caramel, or even sherry wine, the process is complete.

Refined Natural

In recent years, as the coffee market pursues more extreme coffee flavors, many experienced and capable professionals have begun to control the details of natural processing to produce higher-quality coffee beans and showcase the possibilities of coffee flavor.

For example, using instruments like refractometers to determine the harvesting timing of coffee cherries. Cherries with consistent maturity taste cleaner, while higher-sugar red cherries also increase the sweetness of coffee;

Using specially designed raised drying tables allows berries to have more air convection, resulting in more even drying effects.

Washed Processing Steps

If you pay attention to coffee processing methods, you'll notice that many specialty coffees actually use washed processing. The washed method was invented by the Dutch in the 18th century and is suitable for rainy regions. Although the process is quite complicated, it is currently the most common green bean processing method.

The harvested cherries are placed in water tanks and soaked for about 24 hours. At this time, ripe cherries will sink, while unripe and overripe cherries will float and can be removed.

A machine is used to remove the skin and pulp, leaving only coffee beans wrapped in parchment. At this point, the beans still have a layer of mucilage on the outside, and the washing process is designed to clean this mucilage.

The mucilage has strong adhesion and is not easy to remove. It must be placed in tanks for about 18-36 hours to ferment and decompose the mucilage. There are two fermentation methods: wet fermentation and dry fermentation. As the names suggest, the former adds water while the latter doesn't. During the fermentation process, the seeds and internal pulp undergo special changes, which is the step that most affects coffee flavor in the washed method. Some farms add hot water or enzymes to speed up fermentation, which negatively affects coffee bean quality and is not welcomed by specialty coffee enthusiasts.

Farms using the washed method must build washing tanks and be able to introduce continuous fresh water. During processing, the fermented beans are placed in the tanks and moved back and forth, using the friction of the beans and the power of flowing water to wash the coffee beans until they are smooth and clean.

After washing, the coffee beans are still wrapped in parchment with a moisture content of 50%. They must be dried to reduce the moisture content to 12%, otherwise they will continue to ferment, mold, and rot. The better processing method is sun drying, although it takes 1-3 weeks, the flavor is excellent and quite popular. Additionally, some places use machine drying, which significantly reduces processing time but results in inferior flavor compared to sun-dried coffee.

The dried beans can then be stored in warehouses or sent to factories for hulling to remove the parchment and silver skin.

The washed method removes impurities (stones or garbage, etc.) and defective beans through each step, so the green beans appear more uniform in appearance and are generally considered high-quality coffee. The trading price is also higher than coffee beans processed by natural drying methods. Washing not only preserves the original flavor of coffee but also enhances its brightness (acidity) and special fruit aromas.

However, the biggest disadvantage of washed coffee is that coffee beans can easily pick up fermentation odors during the fermentation process. If beans have fermentation odors, it's mostly due to lack of management and maintenance of the fermentation tanks. Although soaking coffee beans with mucilage on their parchment in fermentation tanks overnight can remove the mucilage. If the microorganisms in the fermentation tanks change, it can cause coffee beans to pick up fermentation odors.

Moreover, the equipment cost for coffee washing is relatively high, and the washing steps are quite labor-intensive, thus increasing production costs.

Comparing Natural and Washed Processing

Both natural and washed processing methods are quite common today! However, the difference is that natural processing involves drying first before removing the fruit skin, while washed processing removes the fruit skin first before drying. These two processing methods have significant differences. How can we distinguish whether a coffee bean has been processed using natural or washed methods?

Natural vs. Washed Coffee Bean Comparison

Here we use FrontStreet Coffee's Natural Yirgacheffe Red Cherry and Washed Yirgacheffe Gedeb for comparison.

Green bean information is as follows:

Natural Beans: FrontStreet Coffee Natural Red Cherry

Region: Ethiopia, Yirgacheffe

Estate: Atlant Estate

Altitude: 1700-2200m

Variety: Local indigenous varieties

Processing Method: Natural processing

Washed Beans: FrontStreet Coffee Yirgacheffe Gedeb

Region: Ethiopia, Yirgacheffe

Estate: Gedeb Cooperative

Altitude: 2000-2100m

Variety: Local indigenous varieties

Processing Method: Washed processing

In their green bean state, natural beans appear yellowish-green with more silver skin; while washed beans are bluish-green with less silver skin.

However, in their roasted state, natural beans don't have much silver skin, while washed processed coffee beans actually have more silver skin.

This is because washed beans are soaked in water for long periods during processing, causing the silver skin to separate from the coffee beans. When the parchment is finally removed, the outer silver skin is peeled off along with it, leaving very little residual silver skin on the surface of washed green beans. Natural beans are the opposite - the fruit skin and pulp remain attached to the outside of the beans, and the silver skin adheres tightly to the coffee beans. When the parchment is removed, it doesn't easily fall off, so many outer silver skins remain attached to the surface of natural green beans.

Although green beans show that washed beans have less silver skin while natural beans have more, during the roasting process, the silver skin at the center line of coffee beans is the hardest to remove. Natural beans, because their outer silver skin is connected in one piece, more easily detach along with the silver skin at the center line, so after roasting, natural roasted beans shed their silver skin very cleanly.

Washed beans are the opposite - because there's almost no outer silver skin connection, the silver skin in the center line crack cannot easily detach and instead remains after roasting. This is why, from the perspective of roasted beans, washed beans have more silver skin while natural beans have less.

Flavor Comparison

Natural beans (Natural Red Cherry), because they retain the entire fruit skin and pulp for natural drying, the pulp fermentation can bring charming wine-like and fermented aromas to the coffee beans, and the sweetness is also quite obvious.

Washed beans (Yirgacheffe Gedeb) are better at preserving the coffee's own flavor, with brighter acidity and cleaner flavors.

For more specialty coffee beans, please add FrontStreet Coffee on private WeChat: kaixinguoguo0925

Important Notice :

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Tel:020 38364473