Shape formation mechanism of roasted green tea during roasting process

Abstract

Drum roasting is a critical step in roasted green tea processing, directly influencing tea quality. Due to a lack of understanding of the movement mechanism of tea leaves during the drum roasting process, improper operation techniques often occur in production, resulting in prominent problems such as collision damage and even breakage of tea leaves. This study investigated the motion law of tea during the drum roasting process, and determined the motion parameters of tea through theoretical analysis, including the sliding angle, separation angle, tea separation speed from the vane plate, falling height at maximum separation angle, tea-drum contact time, and tea impact energy on the drum wall; Based on the motion law of tea leaves in the drum, a discrete element simulation model was constructed to numerically simulate their motion in the drum. The results indicated that the tea-drum wall rolling friction coefficient, spiral guide vane plate rear inclination angle, and drum speed are the main factors affecting the movement of tea leaves. The sliding angle, separation angle, tea separation velocity from the vane plate, and tea falling height increased with drum speed. With increasing axial distance, the average velocity of tea particles initially rose and then declined, with the highest coefficient of variation in zone one. It was also shown that the average coordination number of tea exhibited a negative correlation with drum speed. The variation law of separation angle of tea leaves in the drum was analyzed by high-speed camera, and the results were basically consistent with theoretical analysis and numerical simulation, verifying the transport mechanism of tea particles in the drum.