Curing of tobacco
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It is necessary to cure tobacco after harvesting and before it can be consumed. Tobacco curing is also known as color curing, because tobacco leaves are cured with the intention of changing their color and reducing their chlorophyll content.
Curing tobacco has always been a process necessary to prepare the leaf for consumption because, in its raw, freshly picked state, the green tobacco leaf is too wet to ignite and be smoked. In recent times, traditional curing barns in the United States are falling into disuse, as the trend toward using prefabricated metal curing boxes has become more and more prevalent. Temporary curing boxes are often found on location at tobacco farms.
Curing and subsequent aging allow for the slow oxidation and degradation of carotenoids in the tobacco leaf. This produces various compounds in the tobacco leaves that give cured tobacco its sweet hay, tea, rose oil, or fruity aromatic flavor that contributes to the "smoothness" of the consumed product. Non-aged or low quality tobacco is often artificially flavored with these otherwise naturally occurring compounds. Tobacco flavoring is a significant source of revenue for the flavor and fragrance industry.
The aging process continues for a period of months and often extends into the post-curing harvest process.
After tobacco is cured, it is moved from the curing barn into a storage area for processing. If whole plants were cut, the leaves are removed from the tobacco stalks in a process called stripping. For both cut and pulled tobacco, the leaves are then sorted into different grades. In colonial times, the tobacco was then "prized" into hogsheads for transportation. In bright tobacco regions, prizing was replaced by stacking wrapped "hands" into loose piles to be sold at auction. Today, most cured tobacco is baled before sales are made under pre-sold contracts.
Cut plants or pulled leaves are immediately transferred to tobacco barns (kiln houses), where they will be cured. Curing methods vary with the type of tobacco grown, and tobacco barn design varies accordingly.
Air-cured tobacco is hung in well-ventilated barns and allowed to dry over a period of four to eight weeks. Air-cured tobacco is low in sugar, which gives the tobacco smoke a light, sweet flavor, and a high nicotine content. Cigar and burley tobaccos are air cured.
Fire-cured tobacco is hung in large barns where fires of hardwoods are kept on continuous or intermittent low smoulder and takes between three days and ten weeks, depending on the process and the tobacco. Fire curing produces a tobacco low in sugar and high in nicotine. Pipe tobacco, chewing tobacco, and snuff are fire cured.
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. In the 1960s conversion to gas fueled systems such as the Gastobac Burner System® was common. The process will generally take about a week. This method produces tobacco that is high in sugar and has medium to high levels of nicotine. The Smith Tobacco Barn is an example of a traditional, flue-cured tobacco barn. Flue-cured tobacco requires an estimated one tree per 300 cigarettes.
Sun-cured tobacco dries uncovered in the sun. This method is used in Turkey, Greece, Bulgaria, Macedonia, Romania and Mediterranean countries to produce oriental tobacco. Sun-cured tobacco is high in sugar and low in nicotine. In India sun curing is used to produce so-called "white" snuffs, which are fine, dry, and unusually potent.
Some tobaccos (notably Cavendish and Perique) are subjected to a second stage of curing known as fermenting or sweating. Cavendish Tobacco undergoes fermentation pressed in a casing solution containing sugar and/or flavoring.
- "Harvesting, Curing, and Preparing Dark Fire‑Cured Tobacco for Market" (PDF). University of Kentucky, College of Agriculture. Retrieved February 6, 2014.
- "Low-Cost Post-Row Field Tobacco Curing Framework". University of Kentucky. Retrieved February 6, 2014.
- "Burley Tobacco Curing Advisory" (PDF). University of Kentucky, College of Agriculture. Retrieved February 6, 2014.
- "Tobacco Barn Retrofit". The University of Georgia. Retrieved February 6, 2014.
- "Gastobac Burner System®". Retrieved June 1, 2015.
- T. David Reed. "Flue-cured Tobacco Curing" (PDF). Virginia Polytechnic Institute and State University. Retrieved February 6, 2014.
- Tobacco and its environmental impact: an overview (PDF). Geneva: World Health Organization. 2017. ISBN 978-9-2415-1249-7. Retrieved November 23, 2019.
- "TOBACCO AND BETEL". University of Illinois. Retrieved February 6, 2014.
- "Tobacco Leaf Harvesting, Curing, and Fermenting". Leaf Only. Retrieved April 20, 2017.
- "Pipe Tobacco". Archived from the original on October 17, 2013. Retrieved April 20, 2017.