1. TYPES OF TOBACCO
Tobacco is divided broadly into two main types, according to the method used for changing and preserving the leaves of the crop:
Air‐cured, which entails simply hanging the leaves and stalks up in a shed and allowing themto dry out naturally; and
Flue‐cured, which process is undertaken in specially built barns using heat and steam.
The three types of air‐cured tobacco are Burley, Oriental and Cigar Filler. These types are comparatively easy to cure and require a simple barn, which is used to hang the whole crop, which is then left to dry out naturally. These types of tobacco are dark in colour and are used for the manufacture of cigars and pipe tobacco, and have a completely different flavour and smell from that of flue‐cured tobacco. Air‐cured tobaccos are particularly suited to smallholdings and peasant farms, as the crop is relatively simple to grow and cure and does not require a large capital outlay for multiple barns and expensive equipment.
The system of flue curing tobacco was invented by a young slave on Slade Farm in North Carolina, USA, in 1839, and became known as the Slade Method. From this system, the modern method of flue‐curing was developed, and is in use to this day. Leaf which is cured by this method is called flue‐ cured, bright tobacco, Southern Bright or Virginia tobacco. This type of tobacco is used in cigarettes.
Flue ‐curing is a much quicker process than air curing, and the flue‐cure aims at achieving the following results:
To ensure that the maximum amount of carbohydrate in the leaf, mainly in the form of starch, is broken down to sugars, with the minimum loss of carbohydrate as carbon dioxide. In the normal process of plant respiration, carbohydrates are broken down to water and carbon dioxide, with the release of heat or energy. This process has to be prevented during curing. Due to this, flue‐cured tobaccos have the highest sugar content of all tobaccos and lose the least amount of dry matter during curing. The technique of curing aims at keeping the leaf alive until almost all of the starch has been broken down to sugar, but before much sugar has been further broken down to carbon dioxide;
To achieve a bright leaf colour, in the lemon‐mahogany range, without the leaf curing to the darker brown colour, which occurs with air curing and;
To remove most of the moisture present in the leaf at harvesting and dry out the leaf.
- CHARACTERISTICS OF FLUE-CURED TOBACCO
Aroma or smell
The lower leaves of the plant have a poor aroma and flavour, being rather earthy and giving a bitter flavour to the smoke. The upper leaves have the best aroma and flavour. Aroma and flavour can be affected by the variety of tobacco grown, as the heavier bodied varieties have a higher aroma than the thin bodied varieties.
Combustibility or burning quality
Where the leaf is dense, and full cell expansion has not taken place, or when the leaf is high
in chlorine, the rate of burning is slow. The lower leaves of the plant burn better than the upper leaves. Many manufacturers blend and mix the tobacco in their cigarettes to obtain the ideal burning rate.
This is the ability of the tobacco to push the paper tube outwards when made into a cigarette. A high filling value allows the production of a firm cigarette through which smoke can be easily drawn into the smoker’s mouth.
Tobacco leaves may break up into pieces during the manufacture of cigarettes and this means that a lot of tobacco is wasted.
Other Physical Characteristics
The size and shape of the leaves, the colour of the leaf and its elasticity and feel.
A great deal of the smoking quality of tobacco depends on the chemical substances present in the leaves, and on the changes in these chemicals which take place both during the growing and the curing of the leaves. The amounts of the various chemicals will depend on the following:
The variety of the tobacco grown.
The position of the leaf on the stalk, e.g. at the bottom or at the top of the plant. The maturity of the leaf, whether it is harvested early or late in the season.
The soil in which the tobacco is grown. Most tobacco is grown on granite sandveld soils, but some is grown on red soils, which are sandy clay loams.
The climatic conditions during the growing season, that is, the amount of rain and sunshine received by the plant.
The cultivation practices used by the farmer. i.e: How the farmer grows the tobacco crop and how it is cured.
The smoking qualities of tobacco are influenced by the amount of chemicals present in the leaf, and the rate in which they are present in relation to other chemicals. The types or groups of chemicals are:
Total nitrogen, which includes both protein nitrogen and non‐protein nitrogen, the nitrogenwhich is part of the protein of the leaf and the nitrogen which is present in other, non‐ protein substances. High levels of nitrogen give a strong tasting smoke, and the amount of nitrogen in the leaves will depend on how much nitrogen has been given to the crop and when it was applied, as well as the timing of the top‐dressing;
Sugars, can vary between 12% and 25% of the total dry matter of the leaf. A very high sugarlevel gives the leaf a smooth texture or feel and a dense leaf structure, together with poor burning and a poor aroma. Sugars are produced by the breakdown of starch during curing and;
Nicotine is manufactured in the roots of the plant from sugars and nitrogen. When thegrowing plant is topped (the flowers are removed), most of the nicotine moves from the roots to the leaves and the stalks. The amount of nicotine in a cigarette varies from 1,5% to 3,5%.
The amount of nicotine in a tobacco leaf is affected mainly by the climate and cultivation practices during the growth of the crop. The greater the root growth, the larger the root system of the plant, which results in more nicotine being produced. A dry spell during the growth of the plant and topping and suckering (removing the flowering head and the side‐shoots), both increase the root growth. Drought during the growth of the crop means that the roots have to increase and spread out in order to seek any water available deeper in the soil. The higher the yield of the plant, the lower the moisture in the leaves, and conversely, if the plant is cut back hard when topped and suckered, this reduces the area of leaf and increases the moisture content. Tobacco which is over‐ ripe and over‐coloured has higher nicotine and lower sugar content.
Another factor which affects the nicotine content of the leaves is the variety grown. The mammoth varieties tend to be low in nicotine. The higher the availability of nitrogen, the higher the nicotine, and of course any damage to the roots of the plant through eelworm attacks or wet conditions will lower the nicotine content of the leaves.
To summarise, the factors which affect the nicotine content of tobacco are as follows:
|Factors which increase nicotine||Factors which reduce nicotine|
|1.||Good root growth||1.||Poor root growth|
|3.||Topping and suckering||3.||Variety|
|4.||Nitrogen availability||4.||High leaf area (yield)|
|5.||Over‐ripening||5.||Poor nitrogen availability|
Another important measure of leaf quality is the ratio between nitrogen and nicotine in the leaf. A high ratio gives a light‐bodied leaf, and a low ratio gives a heavy‐bodied leaf. A very low ratio gives a pale coloured leaf of poor texture and aroma.