Green coffee beans are having a typical moisture level of 10 – 13% when they arrive at the port. The first point of moisture measurement often takes place before the beans are stored in the warehouse. The measurement could be done in a lab, at-line or even inline to make sure that the green coffee beans can be stored for some time.
During the roasting of the coffee beans a high temperature of ~ 230 °C will be applied. The well known Maillard reaction will take place and therefore the coffee develops its typical aroma. At the same time the moisture is significantly reduced. In order to stop the roasting process at the desired level often the so-called quenching water will be applied. To assure that the legal limit of 5% moisture will not be exceeded, the roasted coffee is measured right after the cooling stage using a process measuring system.