Technological and Technical Development of Tobacco Drying

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INTRODUCTION Harvesting and curing (drying) affects the quality and even the yield of flue-cured tobacco. Favorable curing conditions bring out the best properties of the leaves, but the final quality depends more on the characteristics of the leaves at harvest than on curing. Optimum results in curing can be obtained only with uniform, well-matured crops. But good leaves from the field may be partly or completely spoiled by improper handling or loading practices, poor curing, or inadequate curing facilities. Quality may be reduced after the cure by casing (conditioning) the leaves to high moisture content. Such leaves "redden", and mold may develop in the storage piles (Collins-Hawks, 1993). It is unambiguous that the good and economical curing is influenced by the growing technology, preparation for curing and itself the curing technology. In addition to these things, we can reduce the fuel consumption with different technical methods as making use of solar energy or regaining the waste heat. Taking the Hungarian conditions into account I have been making the following research works and experiments in realization of energy savings and improvement of the quality under curing flue-cured tobacco: − Influence of the preceding technology elements for the energy need of curing, and the best quality; − Influence of the curing process for the energy scales; − Development of tobacco barn constructions in decreasing of the energy consumption, and influencing of the feature of end product; − Applications of supplementary technical solutions for speeding up of the efficiency. TECHNOLOGICAL DEVELOPMENTS In Hungary You can find exclusively hand-harvested tobacco. There are a lot of troubles under hand harvesting in the tobacco estates. Due to the shortcomings of the growing technology and the weather conditions, the tobacco often ripens hardly or nearly at the same time. The workers often harvest the unmaturated leaves and they mix the different levels because do not have so much practice or are not interested in quality. The harvesting influences not only the quality of the drying but also the energy consumption, because it is necessary more energy to cure the green, unriped and mixed leaves - the experiences showed it. The ripeness of the leaves at harvest is one of the most important factors affecting the final quality. For best results, lugs should be overripe, the cutter, middle and tip leaves ripe. Quality of the cure depends on the uniformity of the harvested leaves in ripeness and position on the stalk. To attain such uniformity the plants must be uniform in size and age, and the field uniform in fertility. Agronomic practices designed to create uniform fertility, minimize replanting, and maintain uniform growths are highly important (Davis – Nielsen, 1999). It should be harvested no more than two lugs, or no more than three cutter and middle leaves per plant. They must leave four or five tips for the final priming, as a smaller number often ripen too slowly, particularly in cool, wet weather. It is best to avoid harvesting during wet weather, or for 2 or 3 days after a heavy rain. Under such conditions leaves may temporarily revert to a less mature stage as a result of renewed nutrient uptake by the plants. These leaves are difficult to cure, and the final quality is usually poor. The effect of wet weather is most noticeable if the soil fertility is high or moisture has been deficient. Leaves are often severely damaged at the time of picking. We must handle them carefully to avoid breakage and bruising, particularly those primed early in the morning or in wet weather. For reaching successful harvesting we have suggested a new tobacco growing technology with the help of the ULT, and have been following with attention to the seedbeds, transplanting, cultivating and plant protection.
Every year we emphasize to do topping and sucker control in an early time, because these technology elements have a large influence for the quality and ripening time. Last and this year some trials were made to evaluate the influence of the ripeness. The experience was, that the degree of maturity had a considerable influence on the yield and quality of tobacco (Kerekes, 1999). The Table 1. shows the effect of degree of maturity at harvest on yield, quality category, nicotine content, carbohydrate and income. Table 1. Influence of maturity on some features Treatment Yield t/ha Quality category (Class) Unriped 2,13 2 nd , 3 rd Riped 2,04 1 st Overriped 1,93 1 st , 2 nd Nicotine content % Carbohydrate % Income % 3,63 15,94 83 1,21 29,86 100 2,55 15,17 91 In these tests the unriped tobacco lacked about one week of being as ripe as the growers prefer for harvesting. The overriped tobacco stayed in the field about 7 days longer than usual. These data showed a reduction in yield with a delay in harvest. The quality of the cured tobacco was worse, when the tobacco differed from the ripped condition. The nicotine content considerably high, when the tobacco unriped or overriped, comparing with the optimum harvesting. The amount of the carbohydrate was half of the required rate. The income was increased from unriped to ripped, but was decreased when the tobacco became overriped. In Hungary the racks are sometimes loaded at the barns and not directly on the field. It means more working time and labour, as well as the leaves sustain a loss. The Tobacco Processing Corporation - with my cooperation - elaborated a proposal for hand-harvesting: the farmers can gather the tobacco leaves directly into the racks placed on a special vehicle, which are transported immediately to the barns. In some cases it was used bins instead of racks, but it was found, that the loading never was perfect so that the curing was not so successful. The quality of the dried leaves was poor and the curing time increased significantly. In the tobacco farms the workers strive to load full one barn during a day. But sometimes it happens, they load the racks unevenly so that it does not develop a uniform air-circulation through the racks. In loading bulk kilns, it must be pushed the racks tightly together to ensure, that the air will move through the leaves rather than between the racks. Also, it has to be closed off any space between the racks and loading doors with fiberboard or other material. Despite the technical development, the purpose was to improve the quality of the cured tobacco and decrease the energy demand by working out a modified drying technology. During application of the conventional curing process, the cure man has to strive for that the wet-bulb temperature remains at about 30-35 o C, disregarding the start and finish phases. The relative humidity in the barn is lower and decreases rapidly. The degree of air changing is determined by this rule. It means that we have to open the external air louver of the barn too often and for a longer time. This conventional technology requires much more energy for curing and disadvantageous for the chemical components of the end-product (Kerekes, 1996). The developed experimental curing features are demonstrated in the following figures. The change of temperature and relative humidity are shown in Figure 1. and 2.
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Page 5 and 6: Air demand, [kg/kg wate Heat demand
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Technological and Technical Development of Tobacco Drying

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