Here's a snippet from Wikipedia regarding the curing of
tobacco. Flue cured is just one of the ways
tobacco is prepared for consumption.
Flue
Flue-cured
tobacco was originally strung onto tobacco sticks, which were hung from tier-poles in curing barns (Aus: kilns, also traditionally called oasts). These barns have flues which run from externally fed fire boxes, heat-curing the tobacco without exposing it to smoke, slowly raising the temperature over the course of the curing. The process will generally take about a week. This method produces cigarette tobacco that is high in sugar and has medium to high levels of nicotine. The Smith Tobacco Barn is an example of traditional, flue-cured tobacco barn.
Here's a link to the page if you would like to read about the other methods of curing.
Curing of tobacco - Wikipedia, the free encyclopedia