There are different types of tobacco which are characterized by the curing of the leaves. At the end of the growing phase, in most of the cases tobacco leaves are harvested one by one or in groups of two or three in a sequence which guarantees the right level of ripening. The tobacco leaves in the field contain about 85-90% of water and to be stored and used they need drying. The loss of water is the most evident event of the curing phase, and it is coupled with complex chemical and physical changes until the commercial properties are obtained. Curing can occur by heat, by air at room temperature, with fire or in the sun. The three main steps of the curing are the yellowing of the leaves, the colour fixing and the drying. During the first two steps there are mainly changes in the chemical composition of the leaf, while the last step corresponds to the loss of water. Some tobacco types also undergo a subsequent fermentation which consists in piling the leaves in stacks which become hotter and lose also a certain amount of weight.
The European Union divides tobacco in eight groups:
- Tobacco cured by artificial heat (Virginia flue-cured): this is the tobacco type more widely grown, reckoning for about 70% of the world production. It is a broad-leaf tobacco growing mainly in sandy poor soils. The curing occurs in special barns with a furnace and forced ventilation: the heat produced by the furnace is distributed within the mass of tobacco through flues, hence the name. Since temperature is gradually raised to about 80°C, the entire curing process lasts about 6-7 days. Virginia tobacco is used in different percentages in the blends of nearly all blond American style cigarettes. Most of English type cigarettes contain instead 100% Virginia tobacco.
- Light tobacco cured by air at room temperature (Burley, Badischer Burley, Maryland): this is a broad-leaf tobacco which represents about 15% of the world production. The curing takes place by air in special simple sheds which protect tobacco from sunrays and from the wind. Within the sheds the temperature should not be lower than 16°C and relative humidity around 70%. The length of curing lasts from 20 to 40 days depending on the position of the leaves on the stalk of the plant, the level of ripening and the weather conditions. This tobacco is used mainly for the blends of American style cigarettes and for cut rag, in some cigars and chewing tobacco.
- Air cured dark tobacco (Beneventano, Havanna, Paraguay, Badischer Geudertheimer): this is a broad-leaf tobacco which represents no more than 2% of world production. It is cured in the shade for about 60 days. After the drying this tobacco is subjected to fermentation in piles of 80 to 200 kg for up to 10-11 months. This type of tobacco is used mainly for French-style dark cigarettes, cigars, pipe tobacco and snuff. (shorter than the Italian version)
- Fire-cured tobacco (Kentucky): This type of broad-leaf tobacco represents about 1% of world production. After being let dry in appropriate barns for a few days without a fire, fires are lit and covered in order to produce smoke. The temperature of the barns is progressively brought to 50°C and while drying some fermeting processes also take place. This type of tobacco is mainly used for Tuscan cigars and for roll-your-own cut rag. (shorter than the Italian version)
- Sun cured tobacco: This type of tobacco has a medium-small leaf and it is called “oriental” as it is a typical product of the former Ottoman Empire. Because the leaf is much smaller than the other types of tobacco it is difficult to speak of production in terms of volume without making the volumes of oriental seem very small compared to the broad-leaf tobaccos: in terms of surface, it covers about 4% of the world tobacco cultivation. It normally grows in marginal soils or in mountain areas where hardly anything else grows. It is mostly dried in the sun during the summer months. The drying process lasts 10-20 days according to the level of ripeness of the leaves. The European Union divides this type of tobacco in four groups, based mainly on the size of the leaves and the place of origin. The first group is properly called sun-cured tobacco, and the others are:
- Basmas tobacco with small leaves and sweet and delicate taste
- Katerini tobacco, with rather neutral taste
- Kabakoulaks tobacco, with medium-sized leaf, mainly used as filler tobacco.
In Italy the main types which are grown are
- Virginia, mainly concentrated in Veneto, the Upper Tiber Valley and Tuscany.
- Air-cured Burley type tobacco: Italy is the 6th largest world producer after Malawi, Brazil, United States, Mozambique and Argentina. This type of tobacco is mainly growin in Campania.
- Dark air cured tobacco, mainly grown in Veneto and Campania.
- Dark fire-cured tobacco, mainly grown in Campania, Umbria and Tuscany.