It is not commonly known that large cigarette factories include a paper mill. These paper mills produce a coarse paper that is shredded and added to the natural tobacco used in producing cigarettes.

It is obvious that the thick veins (referred to as stems) in tobacco leaves would do poorly in a cigarette. That is, they would tend both to puncture the fine wrapper paper used to wrap the cigarette, as well as to produce uneven burning. Consequently, stems are not used in the cigarettes.

These tobacco stems (not to be confused with the same large stems on which the leaves grow) contain the same organic properties as the rest of the leaves. Tobacco is a high value agricultural product, so it is unreasonable to think of simply discarding the stems. Instead, they are processed into a material that can be blended with the normal cigarette tobacco.

The process used is based on extracting all of the soluble material from the stems. These flavor solids are concentrated into a syrup. At the same time, the bland fiber that remains after solubles extraction is pulped into fibers of the right size for making paper. This pulp is screened with normal paper mill machinery, and made into a wide sheet of brownish paper, using a normal paper making machine.

A key step in the process is to add the tobacco syrup back into the pulp ahead of the paper drying operation. The resulting brownish paper has the same characteristics as regular cigarette tobacco, so it is shredded to the same size and blended with the tobacco used to make cigarettes.

Screw presses are used in the process of extracting the solubles from the stems. Separating the flavors, oils and other dissolved solids requires a counter-wash system. Water is added to the dry stems in order to dissolve (diffuse) out the solubles. Then the pulpy mass is dewatered in a screw press. The press liquor goes to the syrup evaporator, while the press cake is re-hydrated. Once diffusion is achieved, the mass is pressed once again. This step is repeated from three to five times, depending on the installation.

A variety of testing has confirmed that the Vincent screw presses used in paper mills are very well suited for this application. The interrupted flight screw design used by Vincent has proven advantageous.