Tobacco is a tall perennial herbaceous flowering plant that belongs to the solanaceae or nightshade family. It is the world's most widely cultivated non-food crop and is chosen by farmers from more than 120 countries because of its performance under widely varying climatic (merely requiring a frost free period of 100-130 days) and soil conditions (see Why Grow Tobacco?) to meet the demands of many different markets.
The tobacco plant grows from one to three metres in height and produces 10 to 20 leaves from its central stalk. More than 90% of the world's tobacco grows between 40º north and 40º south, although it can be grown up to 60º north.
An indigenous crop of the Americas, tobacco is cultivated for its leaves. However, for commercial growing the flowers are cut off as to encourage the leaves to grow further down the stem. Differences in soil and climate produce leaves that have specific characteristics and require different methods of fertilization, insect and disease management, harvesting and curing. All tobacco varieties belong to the Nicotiana genus, although the main source of commercial tobacco is Nicotiana Tabacum. Nicotiana Rustica is also grown, albeit to a far lesser extent, and used in Oriental tobaccos.
Growers have developed a wide range of morphologically different types, from the small-leaved aromatic tobaccos to the large, broad-leaved cigar tobaccos. Yet, each type of tobacco is generally defined by the curing method applied to it.
Curing is the final step in the production of tobacco. Thereafter, the leaves are sold to be transformed into the final tobacco product, e.g. cigarettes, cigars, chewing tobacco and snuff.
Through curing, the moisture content in the tobacco leaf is reduced from 80% to about 20%, thus ensuring the tobacco's preservability. Further, the different methods of curing also enhance the leaf's natural aroma. As different tobacco products require leaves with different characteristics, the distinctive flavour of each type of tobacco is what determines its suitability for use in different tobacco products.
In curing barns leaves will be dehydrated over a period of time. After the curing process is completed and the leaf has dried out sufficiently, fresh air is released into the curing barn, slightly moistening the leaves as to allow them to be transported for sale without crumbling.
There are four curing methods used for curing tobacco grown for commercial purposes: Flue-curing, fire-curing, air-curing and sun-curing.
- The most common curing process is known as flue-curing. Used mainly in the manufacture of cigarettes, the most common type of flue-cured tobacco is Virginia . This tobacco is also known as 'bright tobacco' because the heat-drying process gives the leaves a bright, golden colour. Originally from the south-eastern U.S. state of the same name, it is today the most grown tobacco variety in the world.
- Flue-cured tobacco is dried in a closed building with furnace driven heat directed from flues or pipes that extend from a furnace into the barn. The temperature of the furnace is gradually raised until the leaves and stems are completely dried. Flue-curing takes about a week and fixes the natural sugar of the leaf, which has a high sugar and a medium-to-high nicotine content.
- Today, many farmers find that bulk curing flue-cured tobacco is far more cost-effective. Racks of tobacco are placed in bulk barns where heat and ventilation are controlled while air is forced through the leaves.
- Flue-cured varieties require warm weather, humidity, light rainfall and a sandy, loam soil for their four-month growing season.
- Some tobacco leaves are air-cured following their harvest. Air-cured tobacco is traditionally cured hanging in structures with a roof, but with open sides to allow air to freely circulate. As with flue-curing, the aim of air-curing is the timely removal of moisture from tobacco leaves. This process takes four to eight weeks: If cured too fast, the leaf will become patchy, if cured too slowly, the leaf will rot away.
- Commonly, air-cured tobacco is subdivided into dark air-cured and light air-cured tobacco. Burley is the second most popular tobacco in the world, belonging to the light air-cured variety. Burley, also known as White Burley tobacco, is primarily used to make cigarettes and aromatic blends, whereas dark air-cured tobaccos are mainly used in the production of chewing tobacco and snuff.
- Burley is a slightly smaller plant than the flue-cured Virginia type, but with similarly broad leaves. Once picked, its leaves are dried naturally – or ‘air-cured' – without the use of extra heat. This gives the leaves a light brown to mahogany appearance and very low sugar content. Burley tobaccos are somewhat cigar-like in taste and appearance, lending themselves to the production of flavoured, blended cigarettes commonly referred to as "American". Burley tobacco can be grown in limestone soils and requires only light fertiliser.
- Although curing methods may vary, all fire-cured tobaccos are subjected to wood smoke to dry the leaves. It is the type of wood used to smoke the tobacco leaves and the amount of smoke exposure that gives fire-cured tobacco leaves their distinctive flavours.
- Fire-cured tobacco, generally darker in colour, is used mostly for pipe tobacco mixtures, snuff, and chewing tobacco and has a low sugar but high nicotine content. Fire curing uses an enclosed barn similar to that used for flue-curing. Small fires are built on the floor, and the leaves cure in a smoke-laden atmosphere. Whereas flue-curing takes about a week, fire curing, using far lower temperatures, may take from a few days up to 4 weeks.
- Fire-cured tobacco is dried with low-burning wood fires on the floors of closed curing barns. The leaves have low sugar content but high nicotine content. Fire-cured tobacco is a robust variety of tobacco used as a condimental for pipe blends, cigarettes, chewing tobacco, snuff and strong-tasting cigars.
- A comparatively small amount of tobacco is sun-cured. Leaves are exposed to the sun to remove most of their moisture before being air-cured to complete the process. Of all sun-cured tobaccos, the best known are the so-called Oriental tobaccos of Turkey , Greece , in the area where before used to be yoguslavia, and Balkans.
- A more labour-intensive product to harvest, Oriental tobacco is characterised by high aroma from small leaves, being low in both sugar and nicotine.
- The leaves are mostly sun-cured. Usually, the larger the leaf, the milder the aroma. Hence Oriental tobacco is regarded as expensive to harvest by many tobacco manufactures. Oriental tobaccos are often grown in poorer soils in southern Europe and the Middle East.
- Whereas after other curing processes tobacco is exposed to air to standardise the moisture content of the tobacco or 'redry', Oriental tobaccos are stored in bales and allowed to ferment. After storage, moisture is added to this type of tobacco. Pure – Turkish cigarettes contain 100% unblended Oriental tobacco – or blended, Oriental tobacco is mostly used in cigarettes, cigars, pipe, snuff or chewing tobacco.