To prevent breakage and bruising during the handling necessary in curing, it is desirable for the leaf to wilt without sunburning. Tobacco may be left in the field from a few hours to two days to wilt. Curing The three common methods of curing are by air, fire, and flue. A fourth method, sun curing, is practiced with aromatic types and to a limited extent with air-cured types. These involve physical and chemical changes in the leaf and are regulated to develop the desired properties.
Air curing is accomplished mainly by mechanical ventilation inside buildings.
Coke, charcoal, or liquid petroleum gas may be burned to provide heat when conditions warrant. Air curing, which requires from one to two months' time, is used for many tobaccos, including dark air-cured types, cigar, Maryland, and Burley. The fire-curing process resembles air curing except that open wood fires are kindled on the dirt floor of the curing barn after the tobacco has been hanging for two to six days. The smoke imparts to the tobacco a characteristic aroma of creosote. The firing process may be continuous or intermittent, extending from three weeks to as long as 10 weeks until curing is complete and the leaf has been cured to the desired finish.