Cigarettes contain blends of different types of tobaccos. Three main types of tobacco are commonly used in these blends. These are:
These main tobacco types are further distinguished into subgroups depending upon where the tobacco is grown, which part of the plant it is taken from, and other characteristics that relate to the perceived quality of the tobacco, including colour, maturity, and uniformity. These sub-groupings are called tobacco “grades”.
One tobacco plant can produce several grades of leaf. The sensory, physical, chemical and visual properties of a tobacco grade are generally determined by the leaf position on the plant. For example, the leaves at the top of the plant are more exposed to the sun than the ones at the bottom and typically contain higher levels of nicotine and other alkaloids.
Leaf is bought from growers, sorted by grade and sent for threshing to separate the stem and lamina parts of the leaves. The threshing process also enables the moisture content to be controlled, which is important as the tobacco is subsequently stored for several months to mature.
The chemical content of the leaf can vary widely depending on the type of tobacco, the soil and environmental conditions where it was grown, the way it is cured and how it is matured.
Our research to develop potential reduced-exposure products (PREPs) includes looking at the factors that might lower tobacco toxicants in the blends used.
Types of tobacco
Virginia, or flue-cured tobacco, is named after the US state where it was first cultivated. It is also called ‘bright tobacco’ because it turns a yellow / orange colour during curing. It grows particularly well in subtropical regions with light rainfall, such as Georgia, Virginia and the Carolinas in the USA, Southern Brazil and Zimbabwe.
Flue-curing is a heat driven process that creates a dry manageable product, reduces the risk of mould and promotes chemical changes that improve the sensory quality. It also produces a change in leaf colour.
Virginia tobacco can contain a wide range of levels of nicotine - 1% to 3.5% - and have reasonably high levels of naturally occurring sugars - 5% to 25%.
Virginia blends contain only flue-cured Virginia tobaccos and no flavours or additives are included. Smokers in certain countries - Canada and the United Kingdom for example - have a strong preference for cigarettes of this blend style. American-blended styles of cigarettes typically also use some Virginia tobacco, but its percentage inclusion can be as low as 30%.
In the field, Burley is a slightly lighter green leaf than Virginia. It requires heavier soils and more fertiliser than Virginia. Some of the best quality Burley is grown in US states, such as Maryland and Kentucky, and in Central America, Malawi, Uganda and Indonesia.
After harvesting Burley tobaccos are air cured. Air-curing is also a process that creates a dry manageable product, reduces the risk of mould, and promotes chemical changes that improve sensory quality. In contrast to flue-curing, air-curing takes place in ambient conditions.
Burley leaf turns brown with virtually no natural sugars remaining after air-curing giving it an almost cigar-like taste. Generally a cigarette containing only Burley tobacco would produce a sensorially irritating smoke.
Typically, Burley tobacco is treated with sugars - such as molasses - or liquorice, to replace sugars lost in curing. It is combined with other tobacco types, including Virginia and Oriental, to make an American-blended cigarette which may also contain added flavours.
Oriental is the smallest and hardiest of all tobacco types, grown in the hot summer of the Balkans, Turkey and the Middle East.
These conditions and a high planting density - combined with a suitable Oriental variety - create an aromatic flavour on smoking. This is enhanced by sun-curing - a sun driven process that promotes chemical changes. An Oriental blend can contain up to 100% of sun-cured tobacco - as found in a traditional Turkish cigarette.
Cut tobacco can be expanded to reduce the mass of tobacco burnt in a cigarette. The expansion processes are similar to those used to make puffed rice snack food. The process we use is called dry-ice expanded tobacco (DIET) and involves permeating the tobacco leaf structure with liquid carbon dioxide before warming. The resulting carbon dioxide gas forces the tobacco to expand.
Many tobacco brands with low ISO tar yields will use some proportion of expanded tobacco in the overall blend.
The manufacturing process produces some tobacco dust. This dust can be collected and reconstituted as tobacco sheet. A small portion of reconstituted tobacco may be added to the tobacco blend.