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Green Leaf Processing

Preparation of green leaf refers to the process which is earned out between delivery of the tobacco to the firms engaged m green leaf preparation (dealers) and pressing the tobaccos into bales or hogsheads. The term green leaf as used in this context should not be taken as relating to the colour but more in the sense of being "fresh". Tobaccos delivered to dealers have not yet been treated so that they can be packed in bales or hogsheads. Their moisture contents vary considerable- the stems have not been dried sufficiently and there are still a great number of foreign substances, such as feathers, paper, beer mate, etc. mixed with the leaf. Furthermore, the delivered tobacco still includes some leaves of the wrong colour.


There are green leaf processing plants which already incorporate threshing facilities for green leaf. Here, the finished product consists of strips pressed in bales or hogsheads and stems pressed in hogsheads. The tobacco moisture content m these hogsheads and bales is then between 10 and 12%. No biological processes, which could be harmful to the tobacco, can occur in a humidity environment of this kind.


A correctly proportioned tobacco flow is formed by means of feeders and dosing weigh belts from the tobaccos which have been delivered in hogsheads. Here the level of tobacco moisture is very irregular, i.e. between 13 and 18%. At the point where tobacco is layered, it generally receives its first steam treatment On broad conveyor belts, tike loosened tobacco leaf is fed into a conditioning drum. The broad belts are ideally suited to pick out foreign particles. Steam and water are then added to the tobacco in the conditioning drums. Leveling out the fluctuating tobacco moisture content is only conditionally feasible at this point, since continuously operating moisture meters are not yet available to be incorporated.


After the initial conditioning process the tobacco passes through a system of sorting belts where foreign bodies, bad tobacco leaves, off-colour tobacco, etc. are removed manually. Since the tobacco dries off partially on the sorting belts, it is reconditioned in drums, (slightly remoistened) and heated up to between 60 and 70 C. The moisture level is then 20 to 22 %.


The threshing lines begin immediately after conditioning. Here the middle stem is separated from the lamina. The threshing lines consist of threshers, m which lamina is mechanically separated from the stems, and classifiers or separators in which the stems are detached from the strips by means of an air flow.

As it is not possible to separate all the strips from the stems after the first threshing process, the heavy particles are put through a second threshing stage plus classifier, etc. Generally speaking, a green leaf threshing plant incorporates three to four threshing stages. The through-put capacity of a processing line can reach 10 000 kg./h. Sometimes vertical threshers are used for green leaf processing (further details are given in the article on die production of cut tobacco).


The standard of a threshing line is determined according to the following quality characteristics of the threshed tobacco: the size of die strips, the quantity of stems in die strips output and the quantify of strips in the stems output.


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