This study was concerned with evaluating the effects of several practical parameters on moisture sorption rate of cured tobacco in bulk curing systems, Nicotiana tabacum L. cv Coker 258 was used. Tests were conducted utilizing tobacco from bottom, middle, and top stalk positions. Four curing units permitted comparative- evaluation of four humidification systems including free-surface vaporization and spray injection methods. Conditioning procedures involved cool-down from 170° F stem drying to either 120° F or 95° F, at which point moisture was added, or moisture addition during and following cool-down from 170° F to 120° F. Periodic measurements were made of tobacco weight for bottom and top tier positions. Average moisture sorption rate R, expressed in percent moisture (dry basis) per hour, was highly influenced by all factors studied. Humidification systems produced marked differences with an average R of 1.01%/hr. for the free-surface systems and 11.87%/hr. for the high (100 psi) spray injection system. Improved atomization with high pressure spray nozzles was found to be a key factor for a highly effective spray humidification system. Average R values appeared to be inversely related to stalk position with 6.72, 5.17, and 4.03%/hr. for bottom, middle, and top positions, respectively. A distinct acceleration of moisture sorption rates was noted in higher temperature conditioning treatments. R increased from 4.60%/hr. for the 95° F treatment to 6.22%/hr. for high temperature conditioning beginning at 170° F. Tier position effect was as expected, with bottom tier having ·an average R of 5.74%/hr. and top tier an R of 4.87%/hr. Experimental results of this study imply the complex nature of the moisture sorption phenomena, which include factors of physical and chemical properties of tobacco leaves; environmental parameters of air velocity, air temperature and humidity; and system parameters such as special location of tobacco, apparent density of bulked tobacco, and humidification system. Humidification system becomes a very significant factor especially for spray injection where water transport and uptake may involve both liquid and vapor flows. In this case liquid flow as fine particles or mist may be an important consideration.

(Full article published with kind permission from "Tobacco International")