During the roasting process, coffee beans lose their outer skin which we call chaff.
This mainly happens after the drying phase in roasting (in our case: after 4-5 minutes) and then throughout the whole roast session. It is important to set airflow so that chaff will leave the roast drum. This avoids burned chaff staying around your beans, which would lead to very unpleasant taste notes as well as being a risk.
Chaff leaves with the air at the top of the drum - the air passes a chaff collector before hitting the chimney. Chaff collectors, or chaff in and around the chimney, are often a risk of fire. We control this by having temperature gauges both at the top of our chaff collector and by the entrance of the chimney. If unusual temperatures occur, we can react before a fire has the chance to start.