1. PROBLEMS DURING CURING
Some common problems which occur during the curing of tobacco are:
Putting too much tobacco in a barn. This increases the humidity in the barn as more moisture is released from the larger amount of tobacco. This can be made worse by having poor ventilation or poor heating equipment. The extra humidity may cause barn rot.
Prolongs the humidity in the barn and leads to barn rot.
Allows air to get in through the leaks and causes the early drying out of the leaf giving a large amount of green tobacco.
Poor Heating Equipment
Prolongs the curing period and consequently the leaves cannot be dried out at the correct time.
This means that the leaves going into the barn are not at the same stage of ripeness and this fact makes an even cure impossible.
Any cure that is completed in less than 6 days is usually caused by over‐ripe tobacco being put into the barn.
These are caused by poor ventilation and poor heating equipment. They are also caused by over packing the barn, reaping the leaves when they are green and unripe and reaping poor quality leaves. Slow cures lead to a large amount of discoloured tobacco leaves.
2. ALTERNATIVE CURING METHODS
The conventional tobacco barn relies on a furnace, burning wood or coal, and feeding heat into ducts on the floor of the barn. Ventilation is provided by vents in the roof of the barn. In the conventional barn there are variations in temperature and humidity from the bottom of the barn to the top, and curing rates vary between the bottom tiers of leaves and the top tiers. Barns can be modified by fitting fans which will force air up through the barn giving a much more even distribution of both heat and humidity. The number of leaves in the barn remains the same but curing time is reduced the drying time reduced and the fuel consumption is cut down. This can give an extra 700kg of cured tobacco per barn in a season. A further modification is the fitting of a Redmile Plate in place of conventional firebars (See Lecture 7) and a fan to give a forced air system. This results in better cures and a considerable saving in fuel. Some farmers prefer a barn which is lower and longer than the normal barn with 4 ‐ 5 tiers of leaves instead of 8 ‐ 9. Due to the barn being longer, the same amount of tobacco can be packed into it for each cure and the heat and humidity distribution is much better resulting in a better cure.
Other systems are:
THE CHONGOLOLO SYSTEM
6 conventional barns in a line are fed hot air from a furnace and fan system situated at one end supplying all the barns.
Tobacco travels through the tunnel in one direction and hot air is pumped through the tunnel in the opposite direction. Air entering the tunnel is at 70° C which dries out the
tobacco at the end of the cure. By the time the air has passed along the tunnel the temperature is down to 32⁰ C which is the starting temperature for the tobacco being fed into the tunnel. The air flow and the speed at which the tobacco travels through the tunnel must be balanced so that temperatures and humidity are ideal for each stage of the cure.
These are smaller than conventional barns. They give a fast turn around, a uniform cure, reduced labour requirements, fewer breakages of the leaves and fuel savings.
Air curing applies to Burley Tobacco. The barns have no heating system and rely on natural ventilation. The tobacco is harvested and hung in tiers inside the barn and left to cure naturally. The ventilation being regulated by large flaps on the side of the barn (see figure 3 in Lecture 7). Curing is a slow process taking several weeks and during this time the tobacco is not moved; therefore the barn capacity has to match the size of the crop. Consequently there must be enough barn space to take the whole of the crop. Once the crop has been cured it is removed from the barn, graded and baled for sale.