What Are the Three Major Variables Affecting Coffee Processing: The Connection Between Coffee Fermentation and Coffee Processing Methods

In the coffee world, we're probably most familiar with coffee processing methods, such as washed processing, natural processing, and honey processing. These three traditional coffee processing methods are theories that our editors know well.

However, it's less common to discuss how these processing methods are affected by other factors. FrontStreet Coffee is now going to discuss these three major factors that influence coffee processing.

1. Cherry Quality

Good coffee cherries are the foundation of coffee quality. If the coffee cherries are of poor quality—whether picking unripe or overripe fruit—even the most meticulous processing methods will be futile. The flavor will exhibit undesirable off-notes, astringency, and even negative tastes such as grassy, cardboard, rotten fruit flavors, or pungent off-flavors. Most coffee harvesters worldwide are paid based on the "quantity" of coffee cherries they collect each day, not based on quality.

Therefore, workers won't exclusively harvest ripe cherries, making fruit harvesting—the first step in quality control—particularly important.

2. Fermentation Control

Traditional washed processing requires large amounts of water, and this processing model is known as the washed or wet processing method. The washed method requires water in the following stages:

First stage: Harvesting coffee cherries

Second stage: Removing the fruit skin and using water flow for initial grading

Third stage: Allowing the depulped fruit to enter fermentation tanks for fermentation

Fourth stage: Completing fermentation and subsequent washing stages

The primary purpose of the washed method is to use fermentation to remove the mucilage still attached to the hard shell before sun-drying or machine-drying.

The duration of fermentation varies by region, ambient temperature, and fermentation tank conditions. Short fermentation may complete in just one night, while longer fermentation can extend to 36 hours. Natural processing, Brazilian PN, or honey processing methods also require fermentation control.

Natural processing involves drying the entire fruit directly. Honey processing retains the mucilage layer, but both natural and honey processing must handle the fruit, with fermentation changes occurring during processing and drying. The sugars and moisture in coffee cherries are unstable during processing. Typical failures in traditional natural processing include pungent low-quality alcohol flavors and rotten overripe fruit flavors.

Excluding inherent quality issues in the coffee cherries themselves, many negative flavors actually result from improper "fermentation management" during the natural drying process. Honey processing can also experience improper fermentation or even spoilage due to uncontrolled environmental humidity, improper nighttime handling, or rain exposure. Managing the fermentation process well—especially understanding the relationship between fermentation degree and flavor impact—is crucial for controlling green bean quality.

3. Drying Process

There are four key aspects to managing the drying process:

"Drying duration"

"Whether drying is uniform"

"Temperature control in artificial drying methods"

"Ventilation management"

Insufficient drying leads to excessive moisture activity, while over-drying causes beans to turn pale white, resulting in significant flavor loss. Both under- and over-drying directly impact flavor, making the moisture content of the beans extremely important.

These three major processing methods have given rise to numerous processing variations. Regardless of the method used, the goal is to bring out the distinctive characteristics of that processing style. Understanding different coffee processing methods helps us better appreciate each cup of coffee and see what's called "the God in the cup."

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