Study On Key Technology Optimization Of Flue-cured Tobacco By Bulk Curing

: Comparative trial of bulk curing barn and traditional curing barn, experiment of curing technology optimization and demonstration test of optimizated bulk curing technology of three aspects were carried out from 2008 to 2010 repectively. The results was as follows.(1) Comparative trial of bulk curing barn and traditional curing barn: During three stage of curing, air speed in gap among leaves of bulk curing barn was higher than that of conventional curing barn by 0.13 m/s, 0.14 m/s and 0.1 m/s, and was 2.18, 1.78 and 2.11 times of conventional curing barn repectively. Bulk curing could save 17 h, 11 h and 7 h at the three stage, save 34 h during the whole curing process, and saved by 30.91%, 19.30%, 15.00% and 22.37% comparing with conventional curing barn.O₂ content in two types of barns first reduced and then increased, and also had no significant difference (P>0.05) at any temperature point. CO₂ content in two types of barns first increased and then reduced. CO₂ content in bulk curing barn changed more greatly during curing and was higher than that in conventional flue-curing barn significantly (P<0.05) at the end of 42℃. O₂/CO₂ ratio in two types of barns first reduced and then increased, and they had no significant difference at any temperature point. O₃ content in two types of barns first increased and then reduced. O₃ content in bulk curing barn reached maximum later than in conventional flue-curing barn, and they were significant (P<0.05) or extremely significant (P<0.01) difference at leaf-yellowing stage and leaf-drying stage. CO₂ content, O₃ content and O₂/ CO₂ ratio in two types of barns had big difference with large amplitude of changes and they had great effects on the quality of tobacco leaf.States of tobacco leaves changed slowly in leaf-yellowing stage, rapidly in leaf-drying stage and slowly in stem-drying stage during bulk curing. They had similar changing trends in traditional flue-curing barn, but more smooth. States changing values of bulk cured tobacco leaves were extremely significantly or significantly smaller than that of corresponding treatment of traditional flue-curing barn expect vertical rolling index of upper leaves. In addition, single leaf weight, leaf density and thickness of tobacco leaves cured in bulk curing barn were bigger, whereas, percentage stem, balanced moisture content and tensile breaking strength were smaller. States of tobacco leaves changed less during bulk curing, which finally caused tight structure and some non-ideal physical properties of tobacco leaves.L values of front and back tobacco leaves in conventional curing barn had the similar change tendency with bulk curing barn during curing, but were less than that of bulk curing barn all the time. a values of front tobacco leaves in conventional curing barn and bulk curing barn had small difference, but a values of back tobacco leaves and b values of front and back tobacco leaves in conventional curing barn were a little less than that of bulk curing barn from the beginning of leaf-drying stage. On the whole, luminance of tobacco leaves in conventional curing barn was lower than that of bulk curing barn, which indicated that color of tobacco leaves in conventional curing barn were darker than that of bulk curing barn, and the later was brighter.(2) Experiment of curing technology optimization: Four key curing technologies could inprove appearance quality, chemical components harmony, aroma quality and smoking quality of tobacco leaves to some extent repectively, which were stay 12 h at the dry-bulb temperature of 42℃and 54℃, setting wet-bulb temperature at 37℃±0.5℃and 39℃±0.5℃when the the dry-bulb temperature was at 42℃and 54℃, keeping the rate of temperature increase at 1℃/2h during leaf-drying satge, keeping the fan speed at 960 r/min when the the dry-bulb temperature was from 47℃and 60℃and 720 r/min at all the rest time.(3) Demonstration test of optimizated bulk curing technology: On the basis of results above and previous research, optimized bulk curing technology was drawn up centering on the principle of leaf-yellowing at a low dry-bulb temperature and middle wet-bulb temperature, leaf-drying at a middle wet-bulb temperature and slow the rate of temperature increase, stem-drying at a high wet-bulb temperature relatively and controlling the fan speed at different curing stages. The optimized technology could improved smoking quality of lumbar tobacco leaves in Anhui Wannan, Henan Xuchang, Hunan Chenzhou and Sichuan Liangshan of four regions except Guizhou Zunyi in spite of improving its aroma volume. The optimized technology had a positive effect on the smoking quality of umbar tobacco leaves to some extent, but was not ideal to the lower and upper leaves which shoud be studied in the future.