LeBrew·2025년 9월 19일

Moisture Content：A Key Factor in Green Coffee Processing

Abstract

In the coffee supply chain, Moisture Content is one of the most fundamental yet crucial physical parameters. It not only determines whether green coffee beans can smoothly enter the next stage of processing, but also directly impacts flavor development and quality stability. From harvest to final export, every processing stage imposes strict requirements on moisture levels.

This article will explore three key dimensions: the role of moisture content in coffee processing, the critical moisture thresholds at different processing stages, and why moisture content is a mandatory standard for green coffee exports—helping you understand why “water” is one of the most important hidden variables in coffee beans.

The Role of Moisture Content in Coffee Processing

Freshly harvested coffee cherries usually have a very high moisture content. If de-pulping or hulling is carried out directly at this stage, it can easily damage the processing machinery or cause slippage that prevents proper operation. Therefore, controlling the moisture content of fresh cherries and green beans is extremely important.

Moisture content is not only a “threshold value” in processing steps, but it also profoundly affects subsequent roasting performance. Green beans with high moisture content require more time for water evaporation during roasting, which slows down heat transfer and often delays the onset of the first crack, resulting in a dragged-out roasting curve. Conversely, beans with excessively low moisture heat up too quickly, leading to the “baked outside, raw inside” phenomenon and uneven roasting. Only within a stable moisture content range can roasters achieve consistent and controllable curves, ensuring balance and stability in flavor.

From a flavor development perspective, moisture content is equally a critical variable. A high-moisture environment provides favorable conditions for microbial activity, allowing yeasts and bacteria to generate abundant flavor precursors during fermentation. However, excessive moisture can also foster mold growth, posing quality risks. Controlled drying to an appropriate moisture level not only aids in the accumulation of flavor compounds but also reduces the likelihood of mold. Once the moisture content is lowered to a safe range, microbial activity largely ceases, and the coffee beans enter a stable state suitable for long-term storage and international transport.

Thus, from harvest to de-pulping, from drying to hulling, and later to roasting and storage, moisture content remains the central parameter in coffee processing. It determines whether each processing stage can transition smoothly and influences both flavor development and quality stability. In other words, moisture content is a critical checkpoint for coffee as it moves from fresh fruit to global trade—an invisible link connecting agronomy, processing, and the market.

Key Moisture Content Points at Different Processing Stages

High Moisture State After Harvest

Freshly harvested coffee cherries typically have a moisture content as high as 45–55%. At this stage, the skin and pulp tissues are extremely soft and sticky, making them unsuitable for direct mechanical processing. Excessive moisture not only increases the difficulty of subsequent hulling but also promotes excessive microbial growth, leading to risks of souring and mold.

Pre-depulping Drying

For example, in the Natural Process, coffee must first be dried on raised beds or in drying patios to reduce the moisture content to 20–30% before depulping can take place.

Within this range, the skin becomes less tough and no longer clings tightly to the bean surface, making mechanical depulping most efficient. If the moisture content is too high, the skin remains too soft and sticky, which can easily clog the equipment. If it is too low, the skin becomes hard and brittle, which may damage the beans inside. Therefore, a moisture content of 20–30% represents the optimal balance for depulping.

Drying Before Hulling

After depulping, fermentation, and washing, coffee beans are still covered with a layer of parchment. To enter the green bean stage, hulling is required. At this point, the moisture content must be further reduced to 10–12%:

Mechanical requirement: Within this range, the parchment becomes brittle and can be easily removed.

Quality requirement: Excess moisture causes the beans to deform under pressure during hulling, while too little moisture makes them brittle and prone to cracking.

Storage requirement: A moisture content of 10–12% is considered the safe standard for global coffee trade, as it maximizes the suppression of mold and pests and extends storage life.

In other words, from depulping to hulling, controlling moisture content is the key to ensuring smooth transitions in coffee processing.

Why Moisture Content Is a Standard for Green Coffee Export

Storage and Transportation Safety

The moisture content of green coffee beans is partially related to water activity. Since bound water only accounts for a small portion, excessively high moisture content indicates a higher proportion of free water within the beans. This raises water activity, increasing the risk of mold growth.

Excessive moisture content in green coffee beans (>12.5%) increases the risk of mold, insect infestation, and even food safety hazards such as Ochratoxin A during transportation and storage. Low moisture content (<9%) makes the beans overly brittle and prone to breakage, leading to appearance defects, while also accelerating oxidation and causing flavor deterioration. The internationally recognized safe range is 10–12%, which is the key to ensuring stability during long-distance shipping and storage.

Trade and Pricing Basis

In trade contracts, moisture content is as important an indicator as density, defect rate, and grade.

High moisture content means a lower proportion of actual coffee solids, essentially “paying for water weight.” Buyers may regard this as poor quality, leading to rejection or demands for price reductions.

Therefore, moisture content is not only a technical indicator but also a component of economic value.

International Standards and Compliance

The ICO (International Coffee Organization), ISO 6669, and national standards (such as Brazil’s export standards and China’s NY/T 4241-2022) all require that the moisture content of green coffee beans be reported for export.

Non-compliant batches may be rejected or penalized, and in severe cases, may even be barred from entering the market.

For exporters, moisture content testing and reporting are key to ensuring smooth customs clearance and maintaining credibility.

Moisture content runs through the entire coffee processing chain. It is not only the critical condition for process transitions but also the safeguard for quality and flavor. Every step of reducing moisture content is aimed at achieving better quality, and every value carries profound implications for processing feasibility, flavor expression, and trade stability. Understanding and precisely controlling moisture content not only improves processing efficiency but also ensures stable and clean flavors in the final cup.