Studies on the Drying Shrinkage of Tobacco Leaves (2)
Changes in the Void of the Tissue
1970 Volume 32 Issue 2 Pages 150-155
Details
1970 Volume 32 Issue 2 Pages 150-155
Changes in the void space within a tobacco leaf during curing were studied.
1. The effect of various drying parameters on the void of the tissue was considered from the viewpoint of the volume balance.
The following equation was obtained.
εd=1-a (1-εg) /k
where:
εd: void of the dried leaf
a: coefficient of real volumetric shrinkage
k: coefficent of apparent volumetric shrinkage
εg: void of harvested leaves
Among these parameters, k was considered to be the most changeable one
2. The void of the tissue was examined with both harvested and ordinarily flue-cured leaves. In the case of harvested leaves, the void was calculated from the known data on the volume percentage of the intercellular space and an assumed specific gravity of tobacco leaves. The calculated values were found to be 0.25 to 0.4 and they were greater in the lower leaves than in the upper ones. The void of the cured leaves was obtained by the measurement of their apparent and real densities. The values were found to be within the range of 0.23-0.6, and also comparably greater in the lower leaves.
By comparing harvested leaves with cured ones, it was revealed that the void of the lower leaves considerably increased during curing although that of the upper ones did not show any change.
3. Based on the above results, three methods of curing to improve the void of the leaf were examined. They were; 1) drying the leaf under tension load, 2) changing the rate of drying, and 3) freeze-drying of the leaf at the end of the yellowing stage of curing.
In the method 1), the void of leaves was increased by 4% by applying the tension load equivalent to twice the shrinkage strength. Changing the rate of drying, however, did not give any appreciable effect on the void of the dried leaves. In the method 3), about 20% or less moisture was initially removed from the leaves during the yellowing stage and then leaves were subjected to freeze-drying. This procedure increased the void of the leaves by 11%.
