Tobacco

Ripening is indicated by a change in colour of the leaf from a dark to a lighter shade of green, and by the appearance sometimes also of yellow spots. A ripe leaf easily cracks or shows a crease when folded between the fingers. The leaves on a plant decrease in age from below upwards, hence all are not ripe at one time. In high quality tobacco the leaves are "primed," or picked singly, as they ripen. The usual course is to cut the whole plants off close to the ground when the middle leaves are about ripe, and allow them to wilt before removal to the drying sheds. Here the plants are supported on laths and the primed leaves on str;ngs or wires until ready for curing.

Improvement by Selection.

Plants of the same variety grown under similar conditions reveal differences in such impor tant characters as the number, size and shape of the leaves, tend ency to form suckers, time of maturing, and resistance to disease. Variation in burning properties, elasticity of leaf, texture, taste, etc., are also observed. The differences are attributed to two fac tors: (I) variation in type due to crossing, change of soil and cli mate; (2) variations in type due to inherent tendency, local con ditions and maturity of seed.

Careful selection is necessary in the choice of plants grown from imported seeds for seed purposes, and only small crops should be grown until the required type has been perpetuated. The tobacco flower,is fortunately self-fertile, and hybridization can be avoided by enclosing the selected flowers in paper bags. The pollen also will retain its vitality for several weeks, if kept perfectly dry, and thus can be sent long distances without injury.

Further treatment of the tobacco is usually conducted in three stages, known as "curing," "fermentation" and "ageing": on the success of these operations depend the production and fixing of the right colour, and the development of an agreeable aroma in the leaf.

Curing.

Sun-curing is employed largely in Eastern countries. but is no longer practised in the so-called sun-cured district of Virginia.

Air-curing is performed in barns provided with a free circula tion of air. Cigar leaf and White Burley are usually cured thus, the process lasting about six weeks. In both sun- and air-curing the occurrence of damp weather may necessitate the use of fires.

In fire-curing, when the tobacco has acquired a rich yellow colour, slow fires are lighted on the floor of the barn to raise the temperature slowly to 15o° F and there maintain it for four or five days : re-firing is required at intervals as the leaves again be come soft.

The bright yellow leaf used for cut tobacco is cured by flue-heat in order quickly to secure and fix the required shade of colour. The heat is steadily raised from 9o° F to 16o° and even to 18o° in the final stages. The whole op eration lasts from three to five days. In the modified process known as the "Kentucky cure," a temperature of not more than oo° F is used, and the process requires from four to six weeks. Exposure to a moist atmosphere is in either case necessary to render the leaf sufficiently pliable for stripping and sorting. The tobacco is then made up into bunches or "hands" of from six to twelve leaves by twisting another leaf round the lower end.

Fermentation.

Under favourable conditions, the enzymes naturally occurring in tobacco leaf act on the organic matters present, and the considerable alteration in their chemical consti tution. thus caused, exercises a mellowing effect on the tobacco.

Changes occur in the nicotine and other nitrogenous constituents, and the starch and sugar bodies disappear, while the colour and aroma of the leaf also benefit by the operation when successfully conducted. Fermentation readily occurs when the tobacco is stacked into heaps, but precautions require to be taken to prevent the temperature rising beyond about 130° F, and the heaps are therefore frequently re-made and re-arranged during the opera tion which lasts about a month.

Flue-cured tobacco is not fer mented.

After grading, the tobacco is pressed tightly into bales or hogs heads, and stored in warehouses, kept at a moderate and fairly uniform temperature, where it may remain often for several years to mature and complete the "ageing" process, before being manufactured. Further fermen tation often spontaneously occurs during this stage. In addition to bales and hogsheads packers make extensive use of boxes or cases, especially for cigar leaf.

Manufacture.

Tobacco is manufactured in various forms for smoking and chewing pur poses, including cut smoking mix tures, cake or plug, and roll or spun tobacco. In the preparation of various smoking mixtures, the choice of leaf sufficiently mellowed by age, and the selection of suitable brands of leaf to secure the best results are all impor tant considerations. The tobacco needs damping to render it workable, and this operation is usually conducted on the large scale by passing the leaf through rotating cylinders into which steam is injected.