Technological and Technical Development of Tobacco Drying

TECHNOLOGICAL AND TECHNICAL DEVELOPMENT OF TOBACCO DRYING
Benedek Kerekes 1 and Antal Lengyel 2
1. Nyíregyháza College, Department of Agricultural and Food Machine Engineering,
P. O. Box 166, 4401 Nyíregyháza, Hungary, E-mail: kerekesb@nyaf.hu
2. Nyíregyháza College, Department of Power Machines and Motor Vehicle
Engineering, P. O. Box 166, 4401 Nyíregyháza, Hungary, E-mail:
lengyela@nyaf.hu
Keywords: tobacco drying, energy demand, quality control, technical development, curing technology
ABSTRACT
The efficiency of the tobacco curing (drying) is influenced by many factors. The most
important examined ones are the followings: the harvesting practices, curing schedules,
level of the technical means (type of the barns, cost of energy, auxiliary equipments),
quality control.
In Hungary some laboratory and practical trials were carried out for reduction of the
drying costs and improvement of the quality of flue-cured tobacco. Developed drying
technology and some new technical solutions (sun-collector, recuperator and thermo
generator) were applied in the conventional rack-type tobacco barns. The results were
mostly considerable. The harvesting procedure had also a high affection for the quality
of the dried tobacco.
Analyzing of the chemical components within harvesting and curing verified the
importance of the research and development work.
The research work summarizes the technical and technological development means in
drying of flue-cured tobacco and finds relationships between the most important
parameters, which can influence the final quality of the dried tobacco. Namely: how do
the harvesting practices and starting conditions of the practical drying parameters
influence the quality and energy-demand of the end-produce?
The evaluation method and collection of the information can provide useful basic data
for the tobacco growers and processing companies.
The results will contribute to preparation of a new, more precise quality assurance
system, and service the development of the engineering side (new equipments).

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.

Curing temperature,
Relative humidity, ϕ ϕ [ [%] [
80
70
60
50
40
30
20
10
0
100
0 20 40 60 80 100 120
Curing time, T [h]
Polinom .
(input dry
tem p.)
Polinom .
(output dry
tem p.)
Polinom . (w et
tem p.)
Figure 1. Temperature change of the curing air in the new technology.
90
80
70
60
50
40
30
20
10
0
0 20 40 60 80 100 120
Curing time, T [h]
Polinom .
(output rel.
hum .)
Polinom .
(input rel.
hum .)
Figure 2. Relative humidity change of the curing air in the new technology.
The exactly controlled temperature increment and reduction of the relative humidy of the drying air
results a better quality, regarding to the chemical components of the dried tobacco, and at the same time
the cost of the drying energy also more favorable, comparing with the conventional curing schedule
(Davis – Nielsen, 1999).
The cost of energy has a close relation with the air and heat consumption during drying. The variation of
the air demand is shown in Figure 3. The change of the heat requirement can be calculated from Figure 4.

Air demand,
[kg/kg wate
Heat demand,
[kJ/kg water
90
80
70
60
50
40
30
20
10
0
6000
5000
4000
3000
2000
1000
new
technology
conventional
technology
8 32 56 72 92 104 124 136
0
Curing time, T [h]
Figure 3. Variation of the air demand of curing.
new
technology
conventional
technology
8 32 56 72 92 104 124 136
Curing time, T [h]
Figure 4. Variation of the heat requirement of curing.
The main aim was to monitor the influence of different practical features on the important quality
characteristics. Fulfilling this requirement, I arranged to study altogether four curing cycles on two farms,
applying a conventional and an advanced technology at the same time.
Four samples were taken from each curing barn and transported to the local quality-testing laboratory of
the tobacco processing company, where the four most important internal components were identified
(carbohydrate, reducing, sugar, total nitrogen, nicotine). In addition they measured the moisture content.
The results of the analytical work are summarized in Table 2.

Table 2. Comparison of the component features of differently cured tobacco
Curing method Carbohydrate Reducing sugar Total nitrogen Nicotine
%
%
%
%
Conventional 14,38 9,45 2,56 2,18
Advanced 17,62 12,81 2,23 1,87
It is now clear that measurement with the advanced (new) technology resulted in more favorable levels of
some important chemical components, that is, it was produced a better quality at the end of the curing of
Virginia type (H-11) tobacco.
TECHNICAL DEVELOPMENTS
It is well known, that under curing of flue-cured tobacco, the task is not only to remove the water
from the leaf but also to help the enzyme changing in the tobacco. Most of the curing barns using in
Hungary have many drawbacks.
'The circulation of the drying air works in opposition to the natural position of the hanged up tobacco leaf.
The air bowled upwards from below moves the leaves, the laminas are compressed, so the distribution of
air circulation is uneven and the air-resistance is increased because of the deviated leaves. In this case a
higher capacity fan is required to maintain the necessary ventilation.
The intensive air-circulation of the bigger fan results a higher pressure in the curing chamber, so there is a
continuous blowing through the gaps of the barn. It means a considerable heat-loss and vapor decreasing.
The deficit of the temperature sets back the economic result and the lower relative humidity causes a
worse quality of the end product.
When the air-circulation happens upwards from below, at first the laminas are touched intensively by the
air, so they will be dried out earlier than the veins and midribs. Due to this effect, it needs much time and
energy to reach the end of curing, while the valuable parts are over dried.
'The heat insulation of the curing barns is not solved perfectly, especially at the old type "SIROKKÓ"
equipments. In the period of curing, big amount of radiated heat can escape - mainly in the night -, which
means plus cost maintaining the temperature balance .
Figure 5. Rack type tobacco drying equipment

'There is another disadvantage, that the existing curing barns can only be used in a short period of the
year, so the utilization rate is bad. Generally we can say, that the surplus expenditures is not realized in
the quality of the cured tobacco and income.
Our purpose has been to develop a new method and equipment, which eliminates the above detailed
disadvantages and results some forwarding solutions.
It has been verified experimentally, that if the tobacco leaves are hanged up in racks as usually and the
curing air is circled evenly from above to downwards, then the laminas of the leaves are bowled as a flag
in the direction of the circulation. It is such a surplus effect, which assures a lower resistance and uniform
air-ventilation in the curing chamber. In this case the energy demand of the ventilation is less, than the
same volume curing air circulated upwards from below.
It can be guaranteed a constant intensity air movement in the whole cross-section of the barn by the
evaporating air, forced in the direction of the gravitation. It is a condition of the uniform and
homogeneous drying(Figure 5.).
The heated air is circulated from above to downwards, touches the upper part of the high water content
midrib at first, so the too early drying out of the lamina can be avoid. It was a surplus recognition,
because this solution can assure favorable heat-effect for the whole leaves. On the other hand, the
protected leaf lamina has a smaller heat-load and it has a chance to maintain an optimum respiration
process, during the yellowing and color fixing.
The uniform air-distribution and the homogeneous curing render a precise temperature and relative
humidity monitoring and control in the barn.
It is also a condition of reaching the best color and chemical components for the end of the schedule
(Kerekes – Lengyel, 1998).
It can also be reached the same similarity, when the tobacco is humidified, after finishing the process. We
can avoid the uneven moistening, which causes spots on the surface of the leaf.
Another new recognition, that an overshadowing screen can solve the recovering of the radiated heat-loss.
It means, that the heat - which radiated out from the wall of the barn - is gathered by a special screen, so
the air-space between the chamber and the screen is used as recuperator, which pre - heats the exterior air,
drawing in for curing.
Moreover, we recognized, that if we established a light - permeable cover over the heat - screen, we
would produce such a heat-trap, which could utilize the energy of the sun. This simple sun - collector
would pre-heat the entered curing air.
Finally, it was a new idea, that when the curing barn was out of the basic function, the transparent cover
could be moved back on rails, so the system could work as a greenhouse, running by the thermo generator
of the barn. This multi-purpose utilization guaranteed a more economical work.
In our region most of the curing barn can reconstruct for drying of fruits or vegetables.
In the Figure 6. you can study the setting up of the multi-purpose curing barn.
In Hungary many smaller tobacco curing barn were developed in the past ten years, according to the
requirements of the tobacco growers and the processing enterprises.
When starting production of the Virginia type tobacco, the cooperatives used mainly the big capacity
"SIROKKÓ"-type barns. Most of these equipments were working continuously after the privatization, but
they consumed too much energy and they were not able to produce a high quality dried tobacco.
'They must be renewed and reconstructed in the near future.
We have made an extended experimental and practical examination, regarding to the stated new
development (Kerekes – Lengyel – Sikolya, 1997).

Figure 6. Outline of the “MKD-25” small barn (new system).
Table 3. Comparing of the most important specific drying characteristics.
Type of the curing barn
Description of character New system Old system
Curing period (hours) 120-140 130-150
Average oil-consumption
(kg/h)
1,28 1,36
Specific oil-consumption
0,54 0,82
(kg/kg dried tobacco)
Specific heat-demand for
evaporation of water (kJ/kg
water)
4200 7800
Specific electric energy
consumption (kwh/kg dried
tobacco)
0,46 0,87
Substance-rate (green/dried
tobacco)
4,7 5,5
Water-evaporation capacity
of the barn (kg/h)
12,7 6,2
Capacity of humidifying
(kg/h)
5,9 4,1
Period of humidifying (hours) 9,6 7,1
Specific heat-loss (kWh/h)
(ambient temperature:10°C)
(internal temperature: 70°C)
10 22
The technical data and the specific drying characteristics of the new system barn were compared with a
conventional system, but newly manufactured tobacco equipment.

The Table 3. represents the results of the practical curing, comparing the measured and calculated curing
features.
Comparing the data in the above-mentioned table, we can conclude, that the newly established drying
equipment produces better parameters in every view of points.
CONCLUSIONS
The presented research work tried to summarizes the technical and technological development work in
curing of flue-cured tobacco and to find relationships between the most important parameters which can
influence the final quality of the flue-cured tobacco. Namely: how do the starting conditions of the
practical drying (curing) parameters influence the quality of the end-produce?
The evaluation method and collection of the information can provide useful basic data for the tobacco
growers and processing companies.
The results will contribute to the preparation of a new, more precise quality assurance system, and service
the development of the engineering side (new equipment).
Summarizing the presented research and development work, the results and the practical experiences
represent a considerably better quality at the dried tobacco leaves and assure more than forty percent
spare of the drying energy. The Nyíregyháza College incorporates these results into the running training
programs and establishes cooperation with local tobacco farmers and the processing corporation.
LITERATURE
Borsos, J., 1994, A dohány termesztése (Production of tobacco), Akadémiai Kiadó, Budapest, pp. 186-
225.
Collins, W. K., Hawks, S. N., 1993, Principles of flue-cured tobacco production, N. C. State University,
USA, pp. 216-231.
Davis, D. L., Nielsen, M. T., 1999, Tobacco Production, Chemistry, Technology, Blackwell Science, pp.
104-142.
Kerekes, B., 1996, Technological development for improving the quality of flue-cured tobacco,
Hungarian Agricultural Engineering, Vol. 9, pp. 62-63.
Kerekes, B., Lengyel, A., Sikolya, L., 1997, Development of the tobacco curing technology and
equipment for improvement of the quality, Scientific Bulletin of the International Multidisciplinary
Conference, Baia Mare (Romania), pp. 2-7.
Kerekes, B., Lengyel, A., 1998, New method and equipment for curing of flue-cured tobacco, Hungarian
Agricultural Engineering, Vol. 11, pp. 36-38.
Kerekes, B., 1999, Technological development of harvesting and curing of tobacco, Bulletin of
“Tessedik” Agricultural Scientific Days, Deberecen, pp. 123-129.