Coffee bean particle motion in a spouted bed measured using Positron Emission Particle Tracking (PEPT)

Coffee roasting is a heat treatment process that transforms green coffee into a product that can subsequently be ground and brewed. Understanding roasting is critical in developing new downstream processes and formulations, as well as in optimising existing ones. Positron Emission Particle Tracking (PEPT) allows tracking of particles in process equipment and has been used here to characterise particle dynamics of coffee beans within a spouted bed roaster subject to varying air-to-bean ratios without roasting. Occupancy profiles associated with each air-to-bean ratio have been determined and two distinct regions identified: (i) a dense bean bed of high occupancy (ii) a dilute freeboard of lower occupancy. Results also revealed the effect of coffee density on particle dynamics within the roaster. Overall, this work demonstrates that PEPT can be a useful tool to generate data regarding granular flow patterns in roasters that might be used to improve existing heat and mass transfer models for roasting.