Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
The presen~ invention is concerned with a process
for the production of decaffeinated tea.
Various methods are already known for decaffein-
ating tea. Whereas in the case of decaffeinaking
S coffee, raw beans can be used as starting material, in
the case of decaffeinating tea it is necessary to start
from a fermented product which, with regard to the
aroma, i5 very critical and, in the case of the removal
of the caffein, is, as a rule, very considerably
impaired.
Thus, various processes are known for decaffein-
ating with the use of organic sclvents, all of which
have, however, the disadvantage that considerable parts
of the aroma are also removed and a complete removal of
the solvent from the tea is difficult.
Federal Republic of Germany Patent Specification
No. 21 27 642 describes a process for decaffeinating
tea in which, in a first process step, the aroma
materials are removed from the dried tea with dry,
supercriti~al carbon dioxide, subsequently, in a second
step, the caffein is selectively extracted with moist
supercritical carbon dioxide and, after again drying
the tea, the aroma separated in the first extraction
step is reimpregnated~ The extraction is thereby to
be carried out at 40 to 60 C. in order not to impair
the aroma and only after removal of the aroma is a
hi~her temperature used. The caffein extraction is
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to be carried out at 200 to 250 bar. Separation of
the caffein from the carbon dioxide then takes place
by lowering the temperature and the pressure below
the critical region.
An important disadvantage of this process is
the fact that the aroma must first be e~tracted under
conditions which are a~ mild as possible before the
caffein can be extracted in a separate step under
somewhat more severe conditions. A further dis-
advantage of this process is the necessity of the
two-stage rnethod of operation. Finally, the separ-
ation of the caffein by decompression and lowering
of the temperature is also laborious ~ince subsequently
considerable energy must be expended in order again to
bring the carbon dioxide into the supercritical range.
According to Federal Republic of Germany Patent
Specification No. 26 37 197, an attempt has been made
to overcome this latter disadvantage by removing the
caffein from the carbon dioxide in the supercritical
range by means of ion exchangers. Ho~ever, the known
two-step extraction of the tea is retained unchanged,
the conditions used being 40 C. and 200 bar.
It is an object of the present invention to
provide a substantially simpler one-step process for
the production of decaffeinated tea which selectively
only extracts the caffein without co-extracting the
aroma materials and also does not require any change
between supercritical an~ undercritical temperature
and pressurè conditions when using carbon dioxide as
the extraction agent.
Thus, according to the present invention, there
is provided a process for the production of decaffein-
ated tea by extraction with carbon dioxide, which is
supercritical with regard to pressure and temperature,
in the presence of water, wherein a tea which has been
adjusted to a water content of 15 to 5~/O by weight is
first extracted in one step with moist carbon dioxide
at a pressure of from 260 to 350 bar and at a temper-
ature of from 50 to 70C., preferably of from 60 to
70C., the caffein is then removed from the caffein-
containing carbon dioxide with active charcoal in the
given pressure range and the so obtained caffein-free
carbon dioxide is recycled over the decaffeinated tea
and the latter is removed and dried.
The present invention is based upon the surpris-
ing recognition that, under the above-given pressure
and temperature conditions, in the case of the mainten-
ance of a definite moisture content in the tea, it is
possible selectively to extract practically only the
caffein and thus the separate extraction of the aroma
materials and the reimpregnation of the decaffeinated
tea therewith is superfluous. It is thereby surpris-
ing that, in spite of the high temperature employed,
practically no substantial change of the sensitive
,
aroma materials is brought about and the tea sub-
stantially retains its natural flavour and its
natural aroma. There~ore, on the ~asis of this
selective extraction, it is also possible, instead
of ion exchangers, to use cheap active charcoal for
the removal of the extracted caffein from the carbon
dioxide although, in Federal Republic of Germany
Patent Specification No. 26 37 197, the use of active
charcoal is advised against because of its insufficient
selectivity.
For the process according to the present
invention, as a rule, dry tea is used which has
previously been adjusted to the given moisture content
of from 15 to 500/O by weight by the addition of water.
The adjustment of the moisture content can be achieved
quite simply by the addition of the particularly
necessary amount of water to the dry tea in an approp-
riate mixing device and mixing for the uniform
distribution of the moisture. The tea is preferably
ad]usted to a content of 25 to 40% by weight of water,
the best results being obtained with 28 to 35/~ by
weight of water.
~s mentioned above, the carbon dioxide is used
under supercritical conditions in a moist state. ~s
25 mentioned, the pressure must be from 260 to 350 bar
and preferably from 260 to 300 bar, it being espec-
ially preferred to use a pressure of from 270 ~o
.
290 bar. The given temperature range of 50 to 70 C.
is critical. If the lower limit of 50C~ is gone
below, the amount of caffein extracted ~rop~ drastic-
ally and the process then operates substantially less
economically and requires considerably longer
extraction times. In the case of exceeding the upper
limit of 70C., undesired changes in the aroma occur.
The amount of carbon dioxide to be used depends
upon the amount of caffein to be extracted from the
tea. Since, under the given pressure and temperature
conditions, about 0.2 g. of caffein can be removed per
kg. o~ carbon dioxide, it is preferable to use about
2 to 20 kg. and more preferably about 3 to 10 kg. of
carbon dioxide per gram of caffein to be extracted
from the tea.
After the extraction, which generally lasts
from about 2 to 10 hours, the carbon dioxide loaded
with caffein is passed, while maintaining the pressure
and temperature conditions in the given range, into
contact with active charcoal, preferably in the form
of an active charcoal packing, the caffein thereby
passing into the active charcoal. Subsequently, the
decaffeinated carbon dioxide is again recycled under
the extraction pressure to the already extracted tea
and thereby again passes thereto about the same amount
of moisture w~ich was previously removed by the
extraction. The process is preferably carried out
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with the use of several extraction autoclaves which
can be connected in series or in parallel and which
can be removed individually from the process cycle.
After ending of the recycling, there is thus obtained
a moist tea with a greatly reduced caffein content
and a practically unchanged aroma material content.
~his tea is then dried, preferably at a temperature
o from 60 to 80C., and can then be used directly.
In the case of the adsorption of the caffein
on to the actlve charcoal, a temperature of from 50
; to 70C. is preferably maintained. The recycling of
the carbon dioxide to the already extrac-ted tea, with
; remoistening thereof, preferably takes place in a
temperature range of from 50 to 70C. and more
preferably of from 60 to 70C.
The caffein-containing active charcoal can be
extracted with a solvent, the caffein separated from
aroma substances by salt formation and the aroma
substances again added to the extracted tea.
~he extraction of the tea can be carried out
~ in a conventional autoclave which is filled with tea
; and through which carbon dioxide then flow~ in the
longitudinal axis. Such an extraction autoclave
preferably has a cylindrical shape and can typically
25 have a length to diameter ratio of about 3:1 to 8:1.
Such extraction autoclaves are of simple construction
and can easily be supplied with material to be
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extracted by means of a removable lid.
~ 2 have found that in the case of an extraction
autoclave constructed in this manner, an undesired
solidification of the filling material frequently
occurs. The reason for this is that, in the case of
tea, as well as also in the case of most other
natural materials, because of their particulate form,
a high degree of cohesivity is present. In addition,
process parameters, such as the degree of moisture,
the carbon dioxide volume flow~ the rate of compress-
ing and the changing velocities of the volume stream~
also bring about a tendency to solidification.
In the case of commencement of a solidification
of the loosely packed material, the loss of pressure
during the flowthrough of the packing increases,
which results in a further solidification. The
result of thi~ is a canal formation which, in turn,
brings about inhomogeneities of the degree of extract-
ion referred to the cross-section and height of the
autoclave. This can result in a considerable pro-
longation of the necessary extraction time~.
According to a preferred embodiment of the
present invention, these disadvantages can be overcome
by arranging the material to be extracted, namely tea,
i ` 25 in the form of a hollow cylinder, the extraction being
carried out concentrically by introducing unloaded
carbon dioxide from a cylindrical surface, the loaded
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carbon dioxide collecting behin~ the other cylindrical
surface and being passed from there to the active
charcoal. The introduction of the carbon dioxide
thereby takes place especially preferably from the
outer cylindrical surface. In the case of an approp-
riate shaping of the hollow cylinder, ther~ is hereby
also provided the possibility of arranging the active
charcoal in the inner space of the hollow cylinder,
especially favourable flow conditions thereby being
provided.
According to this preferred radial flow method,
the flowed-through cross-section changes continuously
on the path from one surface of the hollow cylinder
to the other surface thereof in which direction the
flowthrough must take place. In the case of the
especially preferred embodiment with flowthrough from
the outside to the inside, in comparison with the
usual axial flowthrough of a cylindrically shaped
extraction autoclave, the packed material mantle
surface impinged against is 15 to 20 times greater,
at the end upon reaching the internal hollow chamber
about five times greater, depending upon the diameter
of the inner hollow chamber. Correspondingly low
are also the empty tube as well as the canal velocities
between neighbouring particles. In the case of
unchanged average residence time within the autoclave,
the period of contact on an individually considered
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particle is considerably increased.
The mechanical stressing of the packing is also
considerably reduced in the case o~ this embodiment.
The pressure loss depends, as is known, quadratically
upon the empty tube velocity and is directly proport-
ional to the running pat~ of the fluid. Therefore,
in the case of the radial flow method of extraction,
the running path of the carbon dioxide is only about
one tenth of the running path in the case of axial
10wthrough of the autoclave. Pressings of the pack-
ing material are, therefore, avoided.
The especially preferred embodiment of the
; extraction with radial flowing in the case of the
introduction of the extraction fluid from the oute-r
cylindrical mantle has, in addition, the advantage
that, in the hollow inner chamber of the hollow
cylinder, there can be provided the active charcoal,
In this way, pressure losses in pipes between
extraction autoclaves and separation autoclaves are
avoided and an especially advantageous mode of
operation is possible.
The invention is illustrated in particular and pref ~ ed
I e~bodiments ky reference to the accompanying drawings in which:
i Fig. 1 is a schematic illustration of a device accord~ to
the present invPntion, which is explained in more detail in
the Example; an~
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Fig. 2 is an illus~ation of an ~traction autoclave with raaial
flow~ough ~ccord~g to the prese~t invention.
A device according to the present invention f~r
carrying out the radial extraction process, such as
is illustrated, for example in Fig. 2 of the accompany-
ing drawings, comprises a cylindrical autoclave 1, an
extraction agent inlet 2, a lid 3 and an extraction
agent removal means 4 and has a cylindrical extraction
material container 5, placed in the autoclave, with
a perforated mantle 6 and a per~orated extraction
agent collecting cylinder 7, arranged in the
cylinder axis, which is in flow connection with the
extraction agent removal means 4. The perforated
extraction agent collecting cylinder 7 can have a
tubular shape. This is especially preferred when
the extraction fluid is to be collected and passed
directly from the extraction autoclave via the
extraction agent removal means 4 to a separate
separation autoclave with active charcoal filling~
However, according to a special embodiment of the
device according to the present invention, the
extraction agent collecting cylinder 7 has an active
charcoal filling, a separate separation autoclave
thereby being rendered superfluous. '~he extraction
material container 5 can have an annular-shaped lid
8 through which extends the extraction agent collection
cylinder 8.
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In the case of the device according to the
present invention, there is obtained a uniform flow
over the packing to be extracted.
~he container 5 for the material to be extracted
S can be arranged fixedly in the autoclave 1 or can be
removable therefrom. Depending thereon, the supply-
ing with the material to be extracted takes place
into the cylinarical autoclave or also after removal
of the container for the material to be extracted.
The extraction agent collection cylinder 7 is prefer-
ably constructed in such a manner that, in the case
of filling with the packing material, it can be
removed from the device ~his simplifies the empty-
ing of the packing material. Before renewed filling,
the pipe is then again inserted. However, the
collection cylinder can also be fixedly installed.
The embodiment of the process and of the device
according to the present invention with radial flow-
through of the material to be extracted can, in
principle, be used for any kind of packing materials
which are to be subjected to a high pressure extraction
with an extraction agent, such a9 carbon dioxide.
The following Example is given for the purpose
of illustrating the present invention, reference
thereby being made to the accompanying drawings~
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Exam~le.
10 kg. of a Ceylon blend type of tea containing
5.9% by weight of water and 3.3% by weight of caffein
are moistened with 3.5 litres of water in a mixing
apparatus and subsequently placed in an extraction
autoclave (E). Adsorber (A) is provided with 7 kg.
active charcoal. The extraction autoclave and the
adsorber are brought to a pressure of 200 bar with
carbon dioxide from a liquid storage vessel (V~ with
the help of a pump Pl, whereafter the pump is taken
out of the circulation. After switching on pump P2,
carbon dioxide is circulated via the extraction
autoclave and the adsorber, the temperature in the
èxtraction autoclave thereby being increased to 63C.
by heat exchanger Wl. The pressure in the extraction
autoclave is 290 bar. The adsorber is operated at a
pressure of 280 bar and at a temperature of 61 C.
After ~.5 hours, the extraction is discontinued, the
carbon dioxide in the extraction autoclave is let off
up to pressure equalisation in the carbon dioxide
storage vessel and thereafter released into the
atmosphere. The tea is removed from the extraction
autoclave and dried in a drier at 70C~ The extracted
tea thus obtained has a residual moisture content of
4.5% by weight of water and a caffein content of
0.08% by weight.
