The Drying Phase - Coffee Roasting

If you read of Coffee Roasting Basics, you know that there are multiple stages in coffee roasting. Notably, the drying phase is the first one, here are essential facts about the drying process process.

Drying Phase

We have recently seen new research emerge changing what we previously knew about water content in roasted beans. Before roasting, green beans have a humidity of around 10%, and at the end of the roast, the coffee has around 2% humidity. The drying phase starts at 100 deg C, and contrary to popular belief, coffee dries until the end of the roast.

Temperature Of The Beans

In the drying phase, the rate of water evaporation from the coffee beans is influenced by temperature, peaking around 200°C. As the temperature rises, so does the rate of water loss, which accelerates until about 6% of the moisture has been removed. After this point, the rate of water loss begins to slow down.

Chemical Water

During the initial roasting stage, beans begin to lose their natural water content initiating chemical reactions within, producing water and carbon dioxide. This process of chemical water formation contributes to the alteration of the beans' moisture levels. Extending the duration of the roast produced more chemical water which is then evaporated.