To enhance the precision of Discrete Element Method (DEM) simulation parameters for the grading of mechanically harvested fresh tea leaves, this study systematically measured the intrinsic physical and basic contact parameters of the Yinghong No. 9 cultivar. Addressing the distinction between primary and secondary contact interfaces during roller screening, the extreme boundary validation method was first employed to determine simplified fixed values for the contact parameters of the secondary component. Based on the measured physical angle of repose of 36.3°, Plackett–Burman screening, steepest ascent, and Box–Behnken tests were conducted sequentially to construct and optimize a second-order regression model relating significant parameters to the angle of repose. The results indicated that the static friction coefficient between tea leaves (0.723), the rolling friction coefficient between tea leaves (0.031), and the static friction coefficient between tea leaves and the PVC roller (0.547) were the key parameters affecting the angle of repose. Verification tests demonstrated that the simulated static angle of repose was 36.9° against the measured 36.3°, yielding a relative error of 1.65%. The simulated dynamic angle of repose in the rotating drum was 39.8° compared to the physical 38.3°, representing a relative error of 3.92%, and the errors in screening efficiency on the grading bench were all less than 5%. These results indicate that the calibrated parameters accurately characterize the material properties of mechanically harvested tea leaves, providing a reliable theoretical foundation for the structural optimization of grading equipment.

Cicada black tea is made from Empoasca onukii-infested tea leaves. The biochemical differences between Cicada black tea and regular black tea, and the dynamic changes in volatile components during processing, remain unclear. This study focused on the withering and fermentation stages, which most significantly affect the quality of black tea, to systematically investigate cicada black tea aroma formation. Ninety volatile compounds were identified, among which 12 key volatiles significantly contributed to the aroma characteristics. During withering, floral and fruity aromas were enhanced. Fermentation primarily intensified honey-like and sweet notes, which were mainly regulated by carotenoid-derived volatiles with low odor thresholds, such as β-Damascenone. Withering to a moisture content of 55% (17 h) and fermenting for 5 h comprised the optimal processing parameters to achieve the best aroma attributes. These insights into the mechanism of Cicada black tea aroma formation will lead to improved processing techniques to enhance its unique flavor.