Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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A PROCESS FOR TREATING TOBACCO
The present invention relates to a process for
treating tobacco. More particularly, it relates to a
process for expanding tobacco to increase its filling
capacity.
Tobacco leaves, after harvesting, are
subjected to curing processes. As a result of water
loss suffered during the curing process, the leaves
undergo variable shrinkage. It is conventional
practice in the tobacco industry to treat cured
tobacco intended for cigar or cigarette manufacture to
shrinkage by increasing its filling
th
e
recover
capacity. It is generally considered that by treating
the tobacco in this way the cellular structure of the
cured tobacco leaf is expanded to a state similar to
that found in the leaf prior to curing.
A number of processes exist for increasing the
filling capacity of tobacco. These are widely used
within the industry to achieve product recovery after
curing. The present invention is based on the
discovery that filler expansion levels similar to and
sometimes better than those achieved by conventionally
used expansion processes and hence recovery can be
achieved by the use of isopentane as the expansion
medium in the vapour phase in a carefully controlled
process.
Accordingly, the invention provides a process
for treating tobacco comprising a series of steps:
(1) subjecting in a chamber the tobacco to a reduced
pressure of not greater than 70 mbar (7 kPa);
(2) impregnating the cell structure of the tobacco
with isopentane vapour at temperatures in the
f 70C to 90C and maintaining the tobacco
range o
in contact with isopentane vapour at a pressure
of at least 4 bar (400 kPa) for up to 30 minutes
to cause impregnation of the tobacco structure;
(3) removing excess isopentane vapour from the
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impregnated tobacco by evacuating the chamber,
the pressure change being effected
adiabatically;
(4) contacting the impregnated tobacco with steam
to expand the tobacco: and
(5) subjecting the expanded tobacco to vacuum re-
ordering.
The tobacco which is treated according to the
process of the invention will typically be in the form
of pieces of cured tobacco leaf obtained by threshing,
flailing or slicing whole cured leaves. The tobacco
may alternatively be in the form of strips cut from
whole leaf or may be shredded leaf. The tobacco to be
treated will be arranged in baskets in the processing
chamber.
The cured tobacco is, according to the present
invention, subjected to a reduced pressure of not
greater than 70 mbar (7 kPa). By this treatment, air
20 in the processing chamber and air retained in pockets
between tobacco leaf pieces or within the cell
structure which would otherwise interfere with the
subsequent impregnation of the cellular structure by
the isopentane vapour is removed. The use of reduced
pressures above 70 mbar do not sufficiently remove
occluded air in the tobacco and, as a result, the
subsequent impregnation of the tobacco cellular
structure by isopentane vapour is impaired.
Preferably, the pressure in the chamber is reduced
30 below 70 mbar ( 7 kPa ) as far as it is possible to do
so and this is, of course, dictated by the performance
of the evacuation and recovery system used. We have
found that pressures in the range of from 40 - 70 mbar
(4 - 7 kPa) are consistently achievable in this
35 process and give good results.
Isopentane vapour is then pumped into the
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processing chamber. It is important in the invention
that no liquid isopentane is allowed to enter the
process chamber. Therefore, liquid isopentane stored
outside the process chamber must be completely
vaporised before it enters the process chamber and
comes into contact with the tobacco. Since isopentane
is a highly volatile and flammable solvent,
engineering design of the process and recovery system
must be carefully undertaken. The temperature of the
isopentane vapour entering the chamber will be in the
range of from 70C to 90C. Isopentane vapour having
a temperature greater than 90C should not be used in
the invention since it impairs the subsequent steam
expansion treatment and does not enable sufficient
expansion of the tobacco to be achieved. Furthermore,
if the heat exchanger is set to produce isopentane
vapour at a temperature less than 70C there is a risk
that liquid isopentane might pass through and enter
the process chamber. Isopentane vapour at such a
temperature might, on entering the chamber, be cooled
by the contents of the chamber to the extent that it
condenses. The effect of allowing liquid isopentane
into the process chamber is to disrupt the process.
Firstly, any liquid isopentane present in the chamber
will take energy out of the system as it evaporates.
Secondly, the energy requirements of the excess
isopentane recovery procedures will be increased.
The amount of isopentane impregnating the
cells in the tobacco leaf is controlled by the
pressure of isopentane vapour created in the process
chamber. The isopentane vapour is injected into the
chamber until an internal pressure of at least 4000
mbar (400 kPa), preferably in the range of from 4000
-
4500 mbar (400 - 450 kPa), is achieved. When this
pressure value is reached, the chamber is sealed after
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which the internal pressure will continue to rise
(typically to about 5000 mbar (500 kPa)) as the
temperature of the isopentane vapour continues to .
rise. The tobacco is maintained in contact with
isopentane vapour at a pressure of at least 4000 mbar
(400 kPa) for up to 30 minutes to allow complete
penetration of the tobacco leaf cells by the
isopentane to occur. We have found that optimum
expansion of the tobacco is achieved by maintaining
the high pressure for about 30 minutes. During the
impregnation phase, it is assumed that isopentane
appearing within the cell structure is squeezed under
pressure into the liquid phase.
As soon as this time period has elapsed all
excess isopentane vapour is removed from the chamber
by reducing the pressure in the chamber as quickly as
possible preferably to about atmospheric pressure.
The change in pressure is, thus, adiabatic. By
ensuring an adiabatic change in pressure, disruption
and breakage of the cellular structure which would be
catastrophic is avoided. We have found that this
pressure reduction can be achieved in less than 15 -
20 minutes, typically about 15 minutes.
Immediately following the evacuation of the
chamber, the temperature of the impregnated tobacco is
caused to increase rapidly by contacting the tobacco
with steam. As a consequence of the rise in
temperature, the isopentane liquid bound inside the
tobacco leaf cells undergoes a volume increase and is
released causing the cellular structure of the tobacco
to expand. Electron microscopy reveals that the cell
walls have swollen as a result of this treatment. In
addition, the surface of the leaf appears to roughen.
Typically, the steam is introduced into the chamber to
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raise the pressure therein to a value in the range of
from 1000 mbar (100kPa) to 1400 mbar (140kPa) and
preferably from 1000 to 1200 mbar (100 to 120 kPa).
Care should be taken with the addition of the steam
' so
t to create turbulence inside the chamber which
as no
would have a detrimental effect on the tobacco
expansion. Preferably the expansion stage is
considered to be complete when the steam exhausted
from the chamber by the evacuation and recovery system
has risen to a temperature of 90 to 95C especially
about 94C. At this point the introduction of steam
is discontinued. The time period from the start of
the steam introduction to the achievement of this
exhaust temperature should preferably not be greater
than 4 minutes and if possible not greater than 2
minutes.
Immediately following completion of the
expansion stage, the expanded tobacco is subjected to
evaporative re-ordering to achieve the final desired
expansion and moisture content. Typically, the final
moisture content of the tobacco will be as close as
possible to the level prior to the process. Re-
ordering may, in general, be achieved by evacuation
of
the process chamber, following completion of the
expansion stage, to a pressure in the range of 180 -
220 mbar ( 18 - 22 kPa ) . Thereafter, the pressure
is
returned isothermally back to atmospheric and the
expanded tobacco removed from the process chamber.
The thus-treated tobacco may then, if
required, be blended in the usual way and then
conveyed to a cigar or cigarette production site as
required.
In order to measure the filling value of a
cured, threshed cigar tobacco product as described in
the following examples, a filling value apparatus is
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used which is essentially composed of a cylinder 64mm
in diameter into which a piston 63mm in diameter
slides. The piston has a graduated seal on the side.
Pressure is applied to the piston and volume in
millilitres of a given weight of tobacco. 14.18g is -
determined. Experiments have shown that this
apparatus will accurately determine the filling value
of a given amount of threshed cigar tobacco with good
reproducibility. The pressure on the tobacco applied
by the piston in all examples was 12.8 kPa applied for
10 minutes at which time the filling value reading was
taken. The moisture content of the tobacco affects
the filling values determined by this method,
therefore comparative filling values were obtained at
similar moisture contents.
Example 1
150 kg of a cured, threshed cigar tobacco containing
14 to 14.5 moisture and having a filling value of
5.08 cc/g when determined by the procedure previously
indicated was arranged in baskets and treated
according to the process of the invention. The
tobacco was subjected to a reduced pressure of 64mbar
(6.4 kPa) and isopentane vapour in the range 70°C to
90°C was then pumped into the process chamber raising
its pressure to 4300 mbar ( 430 kPa) . The tobacco was
maintained in contact with the isopentane for 30
minutes, at the end of which time the pressure had
risen to 4964 mbar. All excess isopentane vapour was ,
removed from the chamber by adiabatically reducing the
pressure to 1100 mbar (110 kPa) over a period of about
6 minutes. Following this evacuation steam was
injected into the process chamber until the steam
exhausted from the chamber by the evacuation and
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recovery system had risen to 104°C. Evaporative re-
ordering by further evacuation of the chamber to a
pressure of 200 mbar (20 kPa) was finally followed by
return to atmospheric pressure and removal of the
expanded tobacco from the process chamber. The final
filling value of the tobacco was 8.14 cc/g and
moisture content 14~ to 14.5$.
The procedure of Example 1 was repeated on further
cycles of tobacco and the results noted in Table 1.
Process parameters for Examples 2, 3 and 4 were the
same as Example 1 unless stated. The pressure values
employed within the process chamber during the full
period of the treatment in accordance with Examples 1
to 4 are shown in graphical form in Figures 1 to 4
respectively.
TABLE 1
Example 2 Example 3 Example 4
Filling values (cclg)
Before 5.04 4 _74 4.67_ .
After 8.23 8.60 8.33
Chamber pressure at 4975 4811 4974
end of impregnarion
hase mbar
Steam temperature ~ . I03 ~ 104 104
exiting chamber at
end of expansion t
phase (C)
c
