Performance and quality evaluation of a vertical square bidirectional airflow curing barn for homogeneous tobacco leaf curing

This study evaluated three biomass-fired curing barns: conventional unidirectional airflow (CK), standard bidirectional airflow (T1), and vertical square bidirectional airflow (T2). Results demonstrated that the T2 barn achieved the fastest heating rate and maintained temperature deviations within ±0.9 °C of the target, shortening total curing time by 25–40 h compared to CK and T1. Its bidirectional airflow improved thermal and moisture uniformity, leading to more consistent leaf yellowing, accelerated pigment degradation, stabilized enzyme activity, and synchronized carbohydrate conversion. Consequently, T2 yielded the highest proportion of superior-grade leaves, enhanced sensory quality, and improved economic efficiency. Redundancy analysis (RDA) linked heating rate and airflow uniformity positively with sugar content and sensory attributes, while chlorophyll A, carotenoids, and malondialdehyde (MDA) showed negative correlations. The T2 system offers an efficient and scalable solution for high-quality tobacco curing. These findings highlight the potential of the vertical square bidirectional airflow system for large-scale application and provide a technical basis for further optimization of airflow design and intelligent control strategies in sustainable tobacco curing.