Tob. Sci., 1965, 9-17, p. 80-84, ISSN.0082-4523

The influence of leaf maturity and other factors on the drying rate of bright-leaf tobacco

Harvesting and Farm Processing Research Branch, USDA, Agricultural Engineering Department, University of Kentucky, Lexington, Kentucky; and Agricultural Engineering Department, North Carolina State College, Raleigh, North Carolina USA

The investigation was concerned with the measurement of drying rates of flue-cured tobacco at different levels of leaf maturity and under a drying condition equivalent to that employed in the early phase of the curing process. Leaves were selected at three arbitrary levels of maturity. The drying rates of immature, mature and overmature leaves were measured and compared. Semi-log plots of drying curves indicated that mature leaves dried more rapidly than did immature leaves, especially during the first eight hours. The more mature leaves exhibited drying curves which were curvilinear, whereas the drying curves for the immature samples were straight lines when plotted on semi-log paper. This was consistent with the hypothesis that more mature leaves dry at a greater rate. The immature leaves, in general, followed an exponential law of drying more closely than did mature leaves. Leaf drying rates consistently increased with increasing stalk position. The differences in drying rates between the first and third primings were the same order of magnitude as differences in drying rates between immature and overmature leaves within a priming. The yellowing period greatly affected the drying rates of the tobacco leaves. For example, the immature leaves showed a decrease in drying rate with increased yellowing, while the drying rates of overmature leaves were increased by a longer yel1owing time. A better understanding of the many factors that may affect leaf drying is necessary in developing better curing methods. Therefore, these findings concerning the influence of leaf maturity and other factors on drying rates can be applied in future research and development in tobacco curing.