Moisture Content and Flavor Rules

The International Coffee Organization sets the moisture content standard for green coffee trading at 8 to 12.5% (Resolutions 407 and 420). Coffee experts have debated the optimal moisture content, but it is generally agreed that green beans should have a moisture level of 10–12% ±1%. Levels below 9% or above 13% are considered substandard.

Too High or Too Low Moisture Content

　　 Insufficient drying poses a risk of mold damage.

Over-drying can result in insufficient aroma.

Proper moisture content helps coffee achieve balanced acidity and excellent aroma, which can improve cupping scores. Many roasters prefer a value of 12%, while the International Trade Centre recommends a target of 11% for coffee producers. Any green beans below 10% may lead to a decline in coffee quality, while higher moisture content may increase the risk of mold growth.

The moisture content of green beans is not directly related to coffee quality. A green bean with 10% moisture is not necessarily better or worse than one with 12%. However, if green beans are stored for too long, they gradually lose their vitality, eventually developing a stale odor, which is related to the decrease in moisture content.

The beginning of the roasting process involves accumulating enough heat and pressure in the roaster to remove moisture from the beans at the start. Due to the lack of a better term, this stage is often referred to as "dehydration." No significant chemical reactions occur during this phase; instead, as moisture is expelled, pressure inside the drum begins to increase, creating the conditions needed for roasting coffee.

If roasting green beans with higher moisture content, the dehydration phase requires more thermal energy. Therefore, options include:

1) Preheat at a higher temperature, but avoid scorching the outer layer of the beans.

2) Use a higher temperature during the dehydration phase.

3) Extend the duration of the dehydration phase.