Why is Natural Processing Called Volcano Processing? How Are Coffee Beans Actually Dried in Natural Processing?

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What is Coffee Bean Processing?

The so-called "coffee bean processing method" refers to the process of converting coffee from fruit to green beans.

After harvesting, coffee beans must undergo complex processing procedures to be refined into green coffee beans. The refined coffee beans have the perishable outer and inner fruit skins and pulp removed, and the seeds are extracted. Generally, about five kilograms of coffee beans can be refined into one kilogram of green beans. The refined coffee green beans are also known as "Green Bean."

Currently, there are three common coffee refining methods: natural processing, washed processing, and the semi-washed method that combines the two.

1. Natural Processing Method

After harvesting, coffee beans are dried through natural drying methods, turning the originally bright red coffee beans into black Dry cherries. Coffee beans processed through this method will have their moisture content significantly reduced to 11-12%. The natural processing method is very simple - just spread the harvested coffee beans evenly in an open-air sun-drying area and expose them to sunlight for several days. To ensure uniform drying and avoid fermentation, the coffee beans need to be constantly turned during the drying process, similar to the "grain drying" technique used by Taiwanese farmers.

During natural processing, in addition to turning and stirring the green coffee beans, a waterproof tarp must be placed over them at night to block dew. If the coffee beans have sufficient maturity, they can undergo further refining after several days of sun-drying. If the coffee beans lack maturity, it may take a week or longer to complete the drying process.

In addition to natural sun-drying methods, large-scale machinery has also been used in recent years for coffee bean dehydration procedures.

Coffee beans dried through natural or mechanical methods undergo pulp removal procedures, where the hardened black fruit skin is removed to become green coffee beans. After extraction, the green coffee beans undergo selection and grading before being transported to market for sale.

The advantage of natural processing lies in its low cost, simple operation, and lack of need for complex equipment. Therefore, almost all coffee-producing countries previously used this method to process green beans. However, the biggest disadvantage of this processing method is its dependence on weather conditions, longer time requirements, and the tendency to mix in too many defective beans or impurities.

Currently, with the exception of a few countries, almost all other countries have switched to washed processing methods for green bean treatment. Countries that maintain natural processing include Brazil, Ethiopia, Yemen, and Bolivia. Among these, Ethiopia's Harar Mocha and Yemen Mocha are famous naturally processed coffee beans.

2. Washed Processing Method

The washed processing method originated in the mid-18th century and is currently the main method for green coffee bean processing, prevalent in Central and South American countries.

Unlike natural processing where pulp is removed after drying, the washed processing method removes the pulp at the beginning. The coffee beans with pulp removed are then stored in fermentation tanks to eliminate residual mucilage and parchment. Finally, the cleaned beans are dried. Coffee beans processed through this method have a moisture content of approximately 12-13%.

The washed processing method begins by placing all coffee beans in water tanks for selection, and throughout the subsequent process, unripe and defective beans are continuously removed early. This is the greatest advantage of the washed processing method. Therefore, green beans processed through this method have extremely high quality and better appearance than naturally processed beans, resulting in higher transaction prices.

Unfortunately, the complex procedures of the washed processing method also create difficulties in operation and management. Especially during fermentation, coffee beans can easily absorb fermentation flavors, becoming overly acidic and turning into low-quality beans. If fermentation tanks are poorly managed, microbial changes can occur, leading to reduced green bean quality.

Furthermore, washed processing is extremely water-intensive. Statistics show that to extract one kilogram of green coffee beans, 50 liters of clean water are needed for washing operations. This is nearly an impossible task in some water-scarce coffee-producing countries. The washed processing method also requires extensive machinery for various operations, which is a heavy burden for coffee farmers in certain countries.

3. Semi-Washed/Semi-Natural Processing Methods

Semi-natural processing improves upon traditional natural processing methods. First, freshly harvested coffee beans are immersed in large water tanks for selection, removing defective beans and impurities. Then machines are used to remove the pulp and outer fruit skin while preserving the parchment layer. Finally, the coffee beans still covered with parchment are sent to sun-drying areas for natural drying.

During sun-drying, the coffee beans are still turned periodically to ensure uniform dehydration of the green beans and avoid over-fermentation. Coffee beans processed through semi-natural methods are left to rest with their parchment intact for a period before export to allow flavor development. The parchment is removed just before export.

This method began to be used primarily within Brazil. Additionally, some Brazilian estates have abandoned mechanical harvesting in favor of higher-cost manual coffee picking, followed by semi-natural processing for subsequent treatment, significantly improving coffee quality. The refining method of drying coffee beans together with parchment through natural processing is generally called Pulped Natural (semi-natural).

In some regions, semi-washed processing completely removes the inner and outer fruit skins and pulp before sun-drying. This method is mainly used in more humid coffee-producing countries like Indonesia. This approach aims to prevent coffee beans with parchment from developing undesirable flavors during drying due to high humidity.

This processing method is called Semi-Washed.

Green coffee beans processed through natural methods have lower moisture content, while washed-processed green beans have higher moisture content, which also creates significant differences in appearance. Generally, washed-processed green coffee beans have a color closer to green-blue, while naturally processed coffee beans tend to be whiter. Washed-processed green beans have smoother, more glossy skins, while naturally processed coffee beans mostly retain their silver skin.

Although current green coffee bean processing methods mostly trend toward washed processing or adopt semi-washed methods according to national climate conditions, we cannot conclude that washed green coffee beans are inherently good coffee.

The reason washed processing coffee receives high evaluation lies in its uniform appearance, but good appearance doesn't necessarily mean good flavor. For example, naturally processed Mocha-series coffee beans may vary in size, but their unique wine aroma, rich fruit acidity, and chocolate-like aftertaste make them irresistibly delicious coffee.

Therefore, we can understand that green coffee bean processing methods do not alter coffee's original flavor, and there is no absolute relationship between green coffee bean quality and their processing method.

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