Temperature and humidity distributions and their influences on tobacco leaf quality in air ascending bulk curing barn

In order to clarify the distributions of temperature and humidity fields during flue-curing in curing barns and its influence on the quality of tobacco leaves, temperature and humidity sensors were uniformly placed in a curing barn to collect the ambient temperature and humidity data during the curing process. The distribution patterns of temperature and humidity in the air ascending curing barn from vertical and horizontal directions were analyzed, and the curing quality difference of tobacco leaves at different locations of the curing barn was studied. The results showed that: 1) There were significant differences in temperature and humidity in both vertical and horizontal directions, the difference was small from early yellowing stage to middle yellowing stage; it then increased from late yellowing stage to early color fixing stage and decreased from middle color fixing stage to late stem drying stage. The difference was greater in vertical direction than in horizontal direction. 2) According to the cluster analysis of the temperature and humidity time series data of the curing process, 18 locations in the barn could be divided into three categories: high temperature and low humidity area, medium temperature and medium humidity area, and low temperature and high humidity area. 3) When the quality of the fresh tobacco was the same, there was no significant difference in the total curing loss, percentage of high-grade tobacco leaves, main chemical components, and appearance evaluation score of the cured tobacco samples. 4) The contents of total sugar, reducing sugar and starch showed the trend of upper < middle < lower layers in the vertical direction, and the trend of front > middle > back parts in the horizontal direction, however the trends of reducing sugar and total sugar ratio were opposite. The leaves in the lower layer in the vertical direction had higher scores for color purity, softness, and oiliness, while the leaves in the middle part in the horizontal direction had higher scores for color purity, glossiness, softness, and oiliness. The study of temperature and humidity distribution in curing barns provides data to support for proper tobacco leaf classification and loading, as well as simulation of flue curing technology in curing barns.