Effects of Hot‐Air Pre‐Curing Treatment on Drying Efficiency and Structural Stability of Compressed Tea

ABSTRACT

Elastic rebound and structural loosening commonly occur during the drying of spherical compressed Pu'er raw tea. To address this problem, this study proposed a forced‐convection hot‐air pre‐curing strategy to improve early structural stability and reduce deformation during subsequent high‐temperature drying. A Box–Behnken design combined with response surface methodology was used to investigate the effects of hot‐air temperature, air velocity, and treatment time on pre‐curing performance. A comprehensive evaluation index was constructed by integrating moisture reduction during pre‐curing and surface hardness variation. The adequacy of the fitted model was assessed by analysis of variance, and the model was then used for numerical optimization and experimental validation. Numerical optimization predicted a maximum comprehensive evaluation index of 0.8656 at a hot‐air temperature of 89.06°C, an air velocity of 2.42 m/s, and a treatment time of 20.16 s. Considering equipment adjustment accuracy and operational convenience, validation experiments were conducted at 90°C, 2.5 m/s, and 20 s. During subsequent drying at 75°C, tea balls dried directly without pre‐curing exhibited a volume increase of approximately 9.0%, whereas pre‐curing‐assisted drying limited the increase to approximately 6.4%. These results indicate that hot‐air pre‐curing reduced volumetric rebound and improved shape retention under the tested conditions. Overall, the proposed strategy provides a practical engineering approach to improving the structural stability of spherical compressed Pu'er raw tea during drying.