Technological and Technical Development of Tobacco Drying
Technological and Technical Development of Tobacco Drying
Technological and Technical Development of Tobacco Drying
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TECHNOLOGICAL AND TECHNICAL DEVELOPMENT OF TOBACCO DRYING<br />
Benedek Kerekes 1 <strong>and</strong> Antal Lengyel 2<br />
1. Nyíregyháza College, Department <strong>of</strong> Agricultural <strong>and</strong> Food Machine Engineering,<br />
P. O. Box 166, 4401 Nyíregyháza, Hungary, E-mail: kerekesb@nyaf.hu<br />
2. Nyíregyháza College, Department <strong>of</strong> Power Machines <strong>and</strong> Motor Vehicle<br />
Engineering, P. O. Box 166, 4401 Nyíregyháza, Hungary, E-mail:<br />
lengyela@nyaf.hu<br />
Keywords: tobacco drying, energy dem<strong>and</strong>, quality control, technical development, curing technology<br />
ABSTRACT<br />
The efficiency <strong>of</strong> the tobacco curing (drying) is influenced by many factors. The most<br />
important examined ones are the followings: the harvesting practices, curing schedules,<br />
level <strong>of</strong> the technical means (type <strong>of</strong> the barns, cost <strong>of</strong> energy, auxiliary equipments),<br />
quality control.<br />
In Hungary some laboratory <strong>and</strong> practical trials were carried out for reduction <strong>of</strong> the<br />
drying costs <strong>and</strong> improvement <strong>of</strong> the quality <strong>of</strong> flue-cured tobacco. Developed drying<br />
technology <strong>and</strong> some new technical solutions (sun-collector, recuperator <strong>and</strong> thermo<br />
generator) were applied in the conventional rack-type tobacco barns. The results were<br />
mostly considerable. The harvesting procedure had also a high affection for the quality<br />
<strong>of</strong> the dried tobacco.<br />
Analyzing <strong>of</strong> the chemical components within harvesting <strong>and</strong> curing verified the<br />
importance <strong>of</strong> the research <strong>and</strong> development work.<br />
The research work summarizes the technical <strong>and</strong> technological development means in<br />
drying <strong>of</strong> flue-cured tobacco <strong>and</strong> finds relationships between the most important<br />
parameters, which can influence the final quality <strong>of</strong> the dried tobacco. Namely: how do<br />
the harvesting practices <strong>and</strong> starting conditions <strong>of</strong> the practical drying parameters<br />
influence the quality <strong>and</strong> energy-dem<strong>and</strong> <strong>of</strong> the end-produce?<br />
The evaluation method <strong>and</strong> collection <strong>of</strong> the information can provide useful basic data<br />
for the tobacco growers <strong>and</strong> processing companies.<br />
The results will contribute to preparation <strong>of</strong> a new, more precise quality assurance<br />
system, <strong>and</strong> service the development <strong>of</strong> the engineering side (new equipments).
INTRODUCTION<br />
Harvesting <strong>and</strong> curing (drying) affects the quality <strong>and</strong> even the yield <strong>of</strong> flue-cured tobacco.<br />
Favorable curing conditions bring out the best properties <strong>of</strong> the leaves, but the final quality depends more<br />
on the characteristics <strong>of</strong> the leaves at harvest than on curing. Optimum results in curing can be obtained<br />
only with uniform, well-matured crops. But good leaves from the field may be partly or completely<br />
spoiled by improper h<strong>and</strong>ling or loading practices, poor curing, or inadequate curing facilities. Quality<br />
may be reduced after the cure by casing (conditioning) the leaves to high moisture content. Such leaves<br />
"redden", <strong>and</strong> mold may develop in the storage piles (Collins-Hawks, 1993).<br />
It is unambiguous that the good <strong>and</strong> economical curing is influenced by the growing technology,<br />
preparation for curing <strong>and</strong> itself the curing technology. In addition to these things, we can reduce the fuel<br />
consumption with different technical methods as making use <strong>of</strong> solar energy or regaining the waste heat.<br />
Taking the Hungarian conditions into account I have been making the following research works <strong>and</strong><br />
experiments in realization <strong>of</strong> energy savings <strong>and</strong> improvement <strong>of</strong> the quality under curing flue-cured<br />
tobacco:<br />
− Influence <strong>of</strong> the preceding technology elements for the energy need <strong>of</strong> curing, <strong>and</strong> the best quality;<br />
− Influence <strong>of</strong> the curing process for the energy scales;<br />
− <strong>Development</strong> <strong>of</strong> tobacco barn constructions in decreasing <strong>of</strong> the energy consumption, <strong>and</strong> influencing<br />
<strong>of</strong> the feature <strong>of</strong> end product;<br />
− Applications <strong>of</strong> supplementary technical solutions for speeding up <strong>of</strong> the efficiency.<br />
TECHNOLOGICAL DEVELOPMENTS<br />
In Hungary You can find exclusively h<strong>and</strong>-harvested tobacco. There are a lot <strong>of</strong> troubles under<br />
h<strong>and</strong> harvesting in the tobacco estates. Due to the shortcomings <strong>of</strong> the growing technology <strong>and</strong> the<br />
weather conditions, the tobacco <strong>of</strong>ten ripens hardly or nearly at the same time.<br />
The workers <strong>of</strong>ten harvest the unmaturated leaves <strong>and</strong> they mix the different levels because do not have<br />
so much practice or are not interested in quality.<br />
The harvesting influences not only the quality <strong>of</strong> the drying but also the energy consumption, because it is<br />
necessary more energy to cure the green, unriped <strong>and</strong> mixed leaves - the experiences showed it.<br />
The ripeness <strong>of</strong> the leaves at harvest is one <strong>of</strong> the most important factors affecting the final quality. For<br />
best results, lugs should be overripe, the cutter, middle <strong>and</strong> tip leaves ripe.<br />
Quality <strong>of</strong> the cure depends on the uniformity <strong>of</strong> the harvested leaves in ripeness <strong>and</strong> position on the<br />
stalk. To attain such uniformity the plants must be uniform in size <strong>and</strong> age, <strong>and</strong> the field uniform in<br />
fertility. Agronomic practices designed to create uniform fertility, minimize replanting, <strong>and</strong> maintain<br />
uniform growths are highly important (Davis – Nielsen, 1999).<br />
It should be harvested no more than two lugs, or no more than three cutter <strong>and</strong> middle leaves per plant.<br />
They must leave four or five tips for the final priming, as a smaller number <strong>of</strong>ten ripen too slowly,<br />
particularly in cool, wet weather.<br />
It is best to avoid harvesting during wet weather, or for 2 or 3 days after a heavy rain. Under such<br />
conditions leaves may temporarily revert to a less mature stage as a result <strong>of</strong> renewed nutrient uptake by<br />
the plants. These leaves are difficult to cure, <strong>and</strong> the final quality is usually poor. The effect <strong>of</strong> wet<br />
weather is most noticeable if the soil fertility is high or moisture has been deficient.<br />
Leaves are <strong>of</strong>ten severely damaged at the time <strong>of</strong> picking. We must h<strong>and</strong>le them carefully to avoid<br />
breakage <strong>and</strong> bruising, particularly those primed early in the morning or in wet weather.<br />
For reaching successful harvesting we have suggested a new tobacco growing technology with the help <strong>of</strong><br />
the ULT, <strong>and</strong> have been following with attention to the seedbeds, transplanting, cultivating <strong>and</strong> plant<br />
protection.
Every year we emphasize to do topping <strong>and</strong> sucker control in an early time, because these technology<br />
elements have a large influence for the quality <strong>and</strong> ripening time.<br />
Last <strong>and</strong> this year some trials were made to evaluate the influence <strong>of</strong> the ripeness. The experience was,<br />
that the degree <strong>of</strong> maturity had a considerable influence on the yield <strong>and</strong> quality <strong>of</strong> tobacco (Kerekes,<br />
1999).<br />
The Table 1. shows the effect <strong>of</strong> degree <strong>of</strong> maturity at harvest on yield, quality category, nicotine content,<br />
carbohydrate <strong>and</strong> income.<br />
Table 1. Influence <strong>of</strong> maturity on some features<br />
Treatment Yield<br />
t/ha<br />
Quality<br />
category<br />
(Class)<br />
Unriped 2,13 2 nd , 3 rd<br />
Riped 2,04 1 st<br />
Overriped 1,93 1 st , 2 nd<br />
Nicotine<br />
content<br />
%<br />
Carbohydrate<br />
%<br />
Income<br />
%<br />
3,63 15,94 83<br />
1,21 29,86 100<br />
2,55 15,17 91<br />
In these tests the unriped tobacco lacked about one week <strong>of</strong> being as ripe as the growers prefer for<br />
harvesting. The overriped tobacco stayed in the field about 7 days longer than usual.<br />
These data showed a reduction in yield with a delay in harvest. The quality <strong>of</strong> the cured tobacco was<br />
worse, when the tobacco differed from the ripped condition. The nicotine content considerably high,<br />
when the tobacco unriped or overriped, comparing with the optimum harvesting. The amount <strong>of</strong> the<br />
carbohydrate was half <strong>of</strong> the required rate.<br />
The income was increased from unriped to ripped, but was decreased when the tobacco became<br />
overriped.<br />
In Hungary the racks are sometimes loaded at the barns <strong>and</strong> not directly on the field. It means more<br />
working time <strong>and</strong> labour, as well as the leaves sustain a loss.<br />
The <strong>Tobacco</strong> Processing Corporation - with my cooperation - elaborated a proposal for h<strong>and</strong>-harvesting:<br />
the farmers can gather the tobacco leaves directly into the racks placed on a special vehicle, which are<br />
transported immediately to the barns.<br />
In some cases it was used bins instead <strong>of</strong> racks, but it was found, that the loading never was perfect so<br />
that the curing was not so successful. The quality <strong>of</strong> the dried leaves was poor <strong>and</strong> the curing time<br />
increased significantly.<br />
In the tobacco farms the workers strive to load full one barn during a day. But sometimes it happens, they<br />
load the racks unevenly so that it does not develop a uniform air-circulation through the racks.<br />
In loading bulk kilns, it must be pushed the racks tightly together to ensure, that the air will move through<br />
the leaves rather than between the racks. Also, it has to be closed <strong>of</strong>f any space between the racks <strong>and</strong><br />
loading doors with fiberboard or other material.<br />
Despite the technical development, the purpose was to improve the quality <strong>of</strong> the cured tobacco <strong>and</strong><br />
decrease the energy dem<strong>and</strong> by working out a modified drying technology.<br />
During application <strong>of</strong> the conventional curing process, the cure man has to strive for that the wet-bulb<br />
temperature remains at about 30-35 o C, disregarding the start <strong>and</strong> finish phases. The relative humidity in<br />
the barn is lower <strong>and</strong> decreases rapidly.<br />
The degree <strong>of</strong> air changing is determined by this rule. It means that we have to open the external air<br />
louver <strong>of</strong> the barn too <strong>of</strong>ten <strong>and</strong> for a longer time. This conventional technology requires much more<br />
energy for curing <strong>and</strong> disadvantageous for the chemical components <strong>of</strong> the end-product (Kerekes, 1996).<br />
The developed experimental curing features are demonstrated in the following figures. The change <strong>of</strong><br />
temperature <strong>and</strong> relative humidity are shown in Figure 1. <strong>and</strong> 2.
Curing temperature,<br />
Relative humidity, ϕ ϕ [ [%] [<br />
80<br />
70<br />
60<br />
50<br />
40<br />
30<br />
20<br />
10<br />
0<br />
100<br />
0 20 40 60 80 100 120<br />
Curing time, T [h]<br />
Polinom .<br />
(input dry<br />
tem p.)<br />
Polinom .<br />
(output dry<br />
tem p.)<br />
Polinom . (w et<br />
tem p.)<br />
Figure 1. Temperature change <strong>of</strong> the curing air in the new technology.<br />
90<br />
80<br />
70<br />
60<br />
50<br />
40<br />
30<br />
20<br />
10<br />
0<br />
0 20 40 60 80 100 120<br />
Curing time, T [h]<br />
Polinom .<br />
(output rel.<br />
hum .)<br />
Polinom .<br />
(input rel.<br />
hum .)<br />
Figure 2. Relative humidity change <strong>of</strong> the curing air in the new technology.<br />
The exactly controlled temperature increment <strong>and</strong> reduction <strong>of</strong> the relative humidy <strong>of</strong> the drying air<br />
results a better quality, regarding to the chemical components <strong>of</strong> the dried tobacco, <strong>and</strong> at the same time<br />
the cost <strong>of</strong> the drying energy also more favorable, comparing with the conventional curing schedule<br />
(Davis – Nielsen, 1999).<br />
The cost <strong>of</strong> energy has a close relation with the air <strong>and</strong> heat consumption during drying. The variation <strong>of</strong><br />
the air dem<strong>and</strong> is shown in Figure 3. The change <strong>of</strong> the heat requirement can be calculated from Figure 4.
Air dem<strong>and</strong>,<br />
[kg/kg wate<br />
Heat dem<strong>and</strong>,<br />
[kJ/kg water<br />
90<br />
80<br />
70<br />
60<br />
50<br />
40<br />
30<br />
20<br />
10<br />
0<br />
6000<br />
5000<br />
4000<br />
3000<br />
2000<br />
1000<br />
new<br />
technology<br />
conventional<br />
technology<br />
8 32 56 72 92 104 124 136<br />
0<br />
Curing time, T [h]<br />
Figure 3. Variation <strong>of</strong> the air dem<strong>and</strong> <strong>of</strong> curing.<br />
new<br />
technology<br />
conventional<br />
technology<br />
8 32 56 72 92 104 124 136<br />
Curing time, T [h]<br />
Figure 4. Variation <strong>of</strong> the heat requirement <strong>of</strong> curing.<br />
The main aim was to monitor the influence <strong>of</strong> different practical features on the important quality<br />
characteristics. Fulfilling this requirement, I arranged to study altogether four curing cycles on two farms,<br />
applying a conventional <strong>and</strong> an advanced technology at the same time.<br />
Four samples were taken from each curing barn <strong>and</strong> transported to the local quality-testing laboratory <strong>of</strong><br />
the tobacco processing company, where the four most important internal components were identified<br />
(carbohydrate, reducing, sugar, total nitrogen, nicotine). In addition they measured the moisture content.<br />
The results <strong>of</strong> the analytical work are summarized in Table 2.
Table 2. Comparison <strong>of</strong> the component features <strong>of</strong> differently cured tobacco<br />
Curing method Carbohydrate Reducing sugar Total nitrogen Nicotine<br />
%<br />
%<br />
%<br />
%<br />
Conventional 14,38 9,45 2,56 2,18<br />
Advanced 17,62 12,81 2,23 1,87<br />
It is now clear that measurement with the advanced (new) technology resulted in more favorable levels <strong>of</strong><br />
some important chemical components, that is, it was produced a better quality at the end <strong>of</strong> the curing <strong>of</strong><br />
Virginia type (H-11) tobacco.<br />
TECHNICAL DEVELOPMENTS<br />
It is well known, that under curing <strong>of</strong> flue-cured tobacco, the task is not only to remove the water<br />
from the leaf but also to help the enzyme changing in the tobacco. Most <strong>of</strong> the curing barns using in<br />
Hungary have many drawbacks.<br />
'The circulation <strong>of</strong> the drying air works in opposition to the natural position <strong>of</strong> the hanged up tobacco leaf.<br />
The air bowled upwards from below moves the leaves, the laminas are compressed, so the distribution <strong>of</strong><br />
air circulation is uneven <strong>and</strong> the air-resistance is increased because <strong>of</strong> the deviated leaves. In this case a<br />
higher capacity fan is required to maintain the necessary ventilation.<br />
The intensive air-circulation <strong>of</strong> the bigger fan results a higher pressure in the curing chamber, so there is a<br />
continuous blowing through the gaps <strong>of</strong> the barn. It means a considerable heat-loss <strong>and</strong> vapor decreasing.<br />
The deficit <strong>of</strong> the temperature sets back the economic result <strong>and</strong> the lower relative humidity causes a<br />
worse quality <strong>of</strong> the end product.<br />
When the air-circulation happens upwards from below, at first the laminas are touched intensively by the<br />
air, so they will be dried out earlier than the veins <strong>and</strong> midribs. Due to this effect, it needs much time <strong>and</strong><br />
energy to reach the end <strong>of</strong> curing, while the valuable parts are over dried.<br />
'The heat insulation <strong>of</strong> the curing barns is not solved perfectly, especially at the old type "SIROKKÓ"<br />
equipments. In the period <strong>of</strong> curing, big amount <strong>of</strong> radiated heat can escape - mainly in the night -, which<br />
means plus cost maintaining the temperature balance .<br />
Figure 5. Rack type tobacco drying equipment
'There is another disadvantage, that the existing curing barns can only be used in a short period <strong>of</strong> the<br />
year, so the utilization rate is bad. Generally we can say, that the surplus expenditures is not realized in<br />
the quality <strong>of</strong> the cured tobacco <strong>and</strong> income.<br />
Our purpose has been to develop a new method <strong>and</strong> equipment, which eliminates the above detailed<br />
disadvantages <strong>and</strong> results some forwarding solutions.<br />
It has been verified experimentally, that if the tobacco leaves are hanged up in racks as usually <strong>and</strong> the<br />
curing air is circled evenly from above to downwards, then the laminas <strong>of</strong> the leaves are bowled as a flag<br />
in the direction <strong>of</strong> the circulation. It is such a surplus effect, which assures a lower resistance <strong>and</strong> uniform<br />
air-ventilation in the curing chamber. In this case the energy dem<strong>and</strong> <strong>of</strong> the ventilation is less, than the<br />
same volume curing air circulated upwards from below.<br />
It can be guaranteed a constant intensity air movement in the whole cross-section <strong>of</strong> the barn by the<br />
evaporating air, forced in the direction <strong>of</strong> the gravitation. It is a condition <strong>of</strong> the uniform <strong>and</strong><br />
homogeneous drying(Figure 5.).<br />
The heated air is circulated from above to downwards, touches the upper part <strong>of</strong> the high water content<br />
midrib at first, so the too early drying out <strong>of</strong> the lamina can be avoid. It was a surplus recognition,<br />
because this solution can assure favorable heat-effect for the whole leaves. On the other h<strong>and</strong>, the<br />
protected leaf lamina has a smaller heat-load <strong>and</strong> it has a chance to maintain an optimum respiration<br />
process, during the yellowing <strong>and</strong> color fixing.<br />
The uniform air-distribution <strong>and</strong> the homogeneous curing render a precise temperature <strong>and</strong> relative<br />
humidity monitoring <strong>and</strong> control in the barn.<br />
It is also a condition <strong>of</strong> reaching the best color <strong>and</strong> chemical components for the end <strong>of</strong> the schedule<br />
(Kerekes – Lengyel, 1998).<br />
It can also be reached the same similarity, when the tobacco is humidified, after finishing the process. We<br />
can avoid the uneven moistening, which causes spots on the surface <strong>of</strong> the leaf.<br />
Another new recognition, that an overshadowing screen can solve the recovering <strong>of</strong> the radiated heat-loss.<br />
It means, that the heat - which radiated out from the wall <strong>of</strong> the barn - is gathered by a special screen, so<br />
the air-space between the chamber <strong>and</strong> the screen is used as recuperator, which pre - heats the exterior air,<br />
drawing in for curing.<br />
Moreover, we recognized, that if we established a light - permeable cover over the heat - screen, we<br />
would produce such a heat-trap, which could utilize the energy <strong>of</strong> the sun. This simple sun - collector<br />
would pre-heat the entered curing air.<br />
Finally, it was a new idea, that when the curing barn was out <strong>of</strong> the basic function, the transparent cover<br />
could be moved back on rails, so the system could work as a greenhouse, running by the thermo generator<br />
<strong>of</strong> the barn. This multi-purpose utilization guaranteed a more economical work.<br />
In our region most <strong>of</strong> the curing barn can reconstruct for drying <strong>of</strong> fruits or vegetables.<br />
In the Figure 6. you can study the setting up <strong>of</strong> the multi-purpose curing barn.<br />
In Hungary many smaller tobacco curing barn were developed in the past ten years, according to the<br />
requirements <strong>of</strong> the tobacco growers <strong>and</strong> the processing enterprises.<br />
When starting production <strong>of</strong> the Virginia type tobacco, the cooperatives used mainly the big capacity<br />
"SIROKKÓ"-type barns. Most <strong>of</strong> these equipments were working continuously after the privatization, but<br />
they consumed too much energy <strong>and</strong> they were not able to produce a high quality dried tobacco.<br />
'They must be renewed <strong>and</strong> reconstructed in the near future.<br />
We have made an extended experimental <strong>and</strong> practical examination, regarding to the stated new<br />
development (Kerekes – Lengyel – Sikolya, 1997).
Figure 6. Outline <strong>of</strong> the “MKD-25” small barn (new system).<br />
Table 3. Comparing <strong>of</strong> the most important specific drying characteristics.<br />
Type <strong>of</strong> the curing barn<br />
Description <strong>of</strong> character New system Old system<br />
Curing period (hours) 120-140 130-150<br />
Average oil-consumption<br />
(kg/h)<br />
1,28 1,36<br />
Specific oil-consumption<br />
0,54 0,82<br />
(kg/kg dried tobacco)<br />
Specific heat-dem<strong>and</strong> for<br />
evaporation <strong>of</strong> water (kJ/kg<br />
water)<br />
4200 7800<br />
Specific electric energy<br />
consumption (kwh/kg dried<br />
tobacco)<br />
0,46 0,87<br />
Substance-rate (green/dried<br />
tobacco)<br />
4,7 5,5<br />
Water-evaporation capacity<br />
<strong>of</strong> the barn (kg/h)<br />
12,7 6,2<br />
Capacity <strong>of</strong> humidifying<br />
(kg/h)<br />
5,9 4,1<br />
Period <strong>of</strong> humidifying (hours) 9,6 7,1<br />
Specific heat-loss (kWh/h)<br />
(ambient temperature:10°C)<br />
(internal temperature: 70°C)<br />
10 22<br />
The technical data <strong>and</strong> the specific drying characteristics <strong>of</strong> the new system barn were compared with a<br />
conventional system, but newly manufactured tobacco equipment.
The Table 3. represents the results <strong>of</strong> the practical curing, comparing the measured <strong>and</strong> calculated curing<br />
features.<br />
Comparing the data in the above-mentioned table, we can conclude, that the newly established drying<br />
equipment produces better parameters in every view <strong>of</strong> points.<br />
CONCLUSIONS<br />
The presented research work tried to summarizes the technical <strong>and</strong> technological development work in<br />
curing <strong>of</strong> flue-cured tobacco <strong>and</strong> to find relationships between the most important parameters which can<br />
influence the final quality <strong>of</strong> the flue-cured tobacco. Namely: how do the starting conditions <strong>of</strong> the<br />
practical drying (curing) parameters influence the quality <strong>of</strong> the end-produce?<br />
The evaluation method <strong>and</strong> collection <strong>of</strong> the information can provide useful basic data for the tobacco<br />
growers <strong>and</strong> processing companies.<br />
The results will contribute to the preparation <strong>of</strong> a new, more precise quality assurance system, <strong>and</strong> service<br />
the development <strong>of</strong> the engineering side (new equipment).<br />
Summarizing the presented research <strong>and</strong> development work, the results <strong>and</strong> the practical experiences<br />
represent a considerably better quality at the dried tobacco leaves <strong>and</strong> assure more than forty percent<br />
spare <strong>of</strong> the drying energy. The Nyíregyháza College incorporates these results into the running training<br />
programs <strong>and</strong> establishes cooperation with local tobacco farmers <strong>and</strong> the processing corporation.<br />
LITERATURE<br />
Borsos, J., 1994, A dohány termesztése (Production <strong>of</strong> tobacco), Akadémiai Kiadó, Budapest, pp. 186-<br />
225.<br />
Collins, W. K., Hawks, S. N., 1993, Principles <strong>of</strong> flue-cured tobacco production, N. C. State University,<br />
USA, pp. 216-231.<br />
Davis, D. L., Nielsen, M. T., 1999, <strong>Tobacco</strong> Production, Chemistry, Technology, Blackwell Science, pp.<br />
104-142.<br />
Kerekes, B., 1996, <strong>Technological</strong> development for improving the quality <strong>of</strong> flue-cured tobacco,<br />
Hungarian Agricultural Engineering, Vol. 9, pp. 62-63.<br />
Kerekes, B., Lengyel, A., Sikolya, L., 1997, <strong>Development</strong> <strong>of</strong> the tobacco curing technology <strong>and</strong><br />
equipment for improvement <strong>of</strong> the quality, Scientific Bulletin <strong>of</strong> the International Multidisciplinary<br />
Conference, Baia Mare (Romania), pp. 2-7.<br />
Kerekes, B., Lengyel, A., 1998, New method <strong>and</strong> equipment for curing <strong>of</strong> flue-cured tobacco, Hungarian<br />
Agricultural Engineering, Vol. 11, pp. 36-38.<br />
Kerekes, B., 1999, <strong>Technological</strong> development <strong>of</strong> harvesting <strong>and</strong> curing <strong>of</strong> tobacco, Bulletin <strong>of</strong><br />
“Tessedik” Agricultural Scientific Days, Deberecen, pp. 123-129.