Online Thermal Analysis of Batch Roasted Coffee Beans

Abstract

We constructed and instrumented a fluidised-bed coffee roaster. This work has been carried out as part of a search for the “ideal point”, which is the point in time when an expert roaster would terminate the roast in order to yield beans that produce the optimal brew. We roasted Costa Rican Arabica beans whilst controlling the roasting temperature to follow a linear ramp. We measured and recorded the input, output, and coffee bean surface temperatures. We introduce the idea of “bean load”, an uncalibrated measure of the heat load presented by the material being roasted. The bean load under constantly-ramping bean surface temperature shows the roast is increasingly endothermic. Toward the end of the roast the endothermic phenomena decrease, or are assisted by exothermic activity. The bean load also has a repeatable dip around first crack. Due to limitations with the roaster we were not able to make reliable measurements at and beyond second crack. We observed no waypoints or events that might be used to pinpoint the “ideal point” to end the roast.