Note: Descriptions are shown in the official language in which they were submitted.
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Process for mild decaffeination of raw coffee
Description
The invention relates to a process for mild
decaffeination of raw coffee and to equipment for carry-
ing out this process.
In processes currently used for decaffeinating
raw coffee, raw coffee beans are contacted with an aqueous
solution, the swelling of the beans takin~ place and the
caffeine being dissolved out of the beans. Such a pro-
cess with diverse aqueous extraction solutions is des-
cribed in European Patent 0,008,398. In the simplest
case, the swelling and extraction fluid is water. From
the extract separated off, caffeine is adsorbed on pre-
treated activated carbon. The decaffeinated extract is
concentrated, recombined with dried beans and absorbed
by the latter. The beans are then dried again to the
desired water content.
As the process fluid for the extraction of green
coffee, a caffeine-free coffee extract solution can also
be used, in which the concentrations of coffee constitu-
ents are so high that nothing except caffeine is dissol-
ved out of the coffee beans, as a result of the concen-
trations in the solution being in equilibrium with the
concentrations in the coffee bean (equilibrium solution).
This equilibrium is preserved even if the pretreated
activated carbon adsorbs virtually only caffeine from the
solution. It then remains only to dry the beans thus
treated. Pretreated activated carbon is likewise used
for preparing this caffeine-free extract solution.
In the decaffeination process according to Swiss
Patent Specification 211,646, water is likewise used as
the extraction fluid. The raw coffee beans are heated
with water in the presence of the adsorbent, the adsorb-
ent being enclosed in a vessel which is permeable forfluid. After the decaffeination is completed, the
coffee beans are dried in vacuo by evaporation of the
water.
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Decaffeination processes of the type described
have the disadvantage that the treated raw coffee beans,
after they have been dried to the original moisture con-
tent, show a dark discolouration, frequently coupled with
S a ~oss of aroma.
In order to overcome these disadvantageous
changes, vario-us approaches have been fol~owed in the
past:
According to Swiss Patent Specification 211,646,
a reducing agent is added to the aqueous extract before
the concentration step.
In British Patent Specification Z,076,626, it is
proposed that the activated carbon which is used as the
adsorbent and which has a basic reaction due to therma~
activation, should be neutralized before use.
In the process according to European Patent
0,040,712, a neutralized activated carbon is likewise used
for the adsorption of caffeine from aqueous solution, for
the same reasons.
A pretreatment of the activated carbon with acid
for exerting a positive influence on the colour of the
decaffeinated coffee is also known from European Patent
0,008,398.
However, it has been found that the methods lis-
ted give only unsatisfactory results.
The present invention is based on the object of
providing a process for mild decaffeination of raw coffee
wherein the raw coffee beans do not undergo any disadvan-
tageous change with respect to colour and aroma. A
further object of the invention is to be regar~ed as the
provision of equipment for carrying out this decaffeina-
tion process.
These objects are achieved in a surprisingly
simple manner by the characterizing features of Claims 1
and 5.
The advantages achieved by the invention are to be
seen essentially in the fact that the raw coffee beans do
not suffer any disadvantageous changes in their appearance
and aroma as a result of the decaffeination process.
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When the decaffeination process is carried out
with exclusion of oxygen or in an inert gas atmosphere,
the result surprisingly is that the original appearance
and aroma of the raw coffee beans are substantially
S preserved.
Experiments were carried out which represented
the influence of individual processing steps and of
the duration of treatment on the colour value of the
treated beans. It was found here that even swelling of
the raw coffee beans with water and subsequent mild dry-
ing at 60C cause a discolouration. The duration of
the treatment, which in general is 6 to 12 hours, had by
far the greatest influence on the colour of the raw
coffee beans. By contrast, the influence of the acid-
wash of the activated carbon was negligible (EuropeanPatent 0,040,712). Based on these results and on the
fact that decaffeination in an inert gas atmosphere gives
more favourable results, the discolouration arising in
known processes and also the loss of aroma is ascribed to
oxidation of coffee constituents, for example chloro-
genic acid and other phenolic compounds. The chemical
changes in the constituents can here take place both in
the beans themselves and in the extract solution, which
contains caffeine and other coffee constituents and, in
particular, is subjected to the adsorption step, and if
appropriate, also concentrating steps.
Rare gases, nitrogen and carbon dioxide can be
used as the inert gases. Preferably, carbon dioxide is
used, since - in contrast to nitrogen - it is heavier
than air. This property has a process engineering advan-
tages.
Details of the process according to the invention
are explained in more detail below by way of example:
Example 1:
About 110 9 of Colombian raw coffee were placed
into a conical glass flask. The bottom of the glass
flask was connected via a hose pump to a glass column
which contained about 21 9 of activated carbon (already
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moist). There was in turn an air-tight hose connection
from the bottom of the activated carbon column to the toP
of the conical glass flask.
The apparatus was then flooded with C02 and the
air was thus displaced from the system. About 300 9 of
e~uilibrium extract were then added and circulated by
means of a pump. Circulation was terminated after 6
hours and the raw coffee, now decaffeinated, was dried to
its original moisture content within 2 hours in a flui-
dized-bed drier at 60C.
The resulting decaffeinated raw coffee beans
largely correspond to their original state with respect
to colour and aroma.
When the process described in example 1 is car-
ried out without flooding with carbon dioxide, decaffein-
ated raw coffee beans are obtained which show a substan-
tially darker colouration as compared with those obtained
in the process according to example 1.
The equipment for carrying out the process accor-
ding to the invention consists of mutually communicatingcontainers which can be sealed gas-tight and, in addition
to the inlet and outlet lines for extract solutions and
the loose material, have-connections for passing inert gas
in or through.
Figure 1 shows a diagrammatic illustration of
equipment for carrying out the process steps a) to c):
In a conical container 1, raw coffee beans Z are
dumped on a screen-like inserted plate 3. The lower part
of the container 1, which is formed by side walls, the
bottom and the screen-like inserted plate 3, serves as a
receiving chamber 4 for extract solution. At its bottom,
the container 1 communicates with a pump S, the pressure
connection of which leads via a line 6 to a spray head 7
which is located in the upper part of the cylindrical con-
tainer 8. The container 8 has a screen-like inserted
plate 9, which carries layers of activated carbon 10 as an
adsorbent. In the lower region of the container 8, between
the screen-like inserted plate and the bottom, there is a
receiving chamber 11 for decaffeinated extract solution.
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A line leads from the bottom of this container 8 to the
spray head 12 in the upper part of the container 1.
Inlet valves for introducing inert gas are fitted in the
upper region of each of the containers 1 and 8.
S Before the equipment is put into operation,
flooding with carbon dioxide is carried out and the air
is thus displaced. When the equipment described is in
operation, caffeine-free coffee extract solution is, for
example, passed through the spray head 12 onto the raw
coffee beans; the extract solution flows through the
layer of coffee beans. As a result, the beans swell due
to water absorption and caffeine is dissolved out of the
beans by the aqueous solution. The caffeine-containing
extract passes through the screen-like inserted plate 3
and into the receiving chamber 4, from where it is pumped
via line 6 into the cylindrical container 8. The extract
rains through the spray head 7 onto the previously mois-
tened activated carbon 10. On passing through the acti-
vated carbon, caffeine is adsorbed out of the extract.
2û The resulting caffeine-free extract runs through the
screen plate 9 and passes into the receiving chamber 11.
From the latter, it is transported through line 15 to the
spray head 12 for further extraction of the raw coffee
beans. The extract solution is circulated by means of a
pump until the desired degree of decaffeination has been
reached.
The use of a conical container has proved to be
particularly advantageous for the first process step.
Raw coffee beans as delivered usually have a water con-
tent of 7 to 15 %. When contacted with an aqueous solu-
tion, they absorb water, the volume of the beans being
approximately doubled. In order to avoid blockage of the
column apparatus, which is normally used for treating the
raw coffee beans, it is advantageous to use a container
of conical shape at least in the first process step.
This container is preferably constructed as a
sector-shaped cell of a rotary extractor. Preferably,
the conical container in the first process step can be a
sector-shaped cell of a rotary extractor, which has a
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multiplicity of similar cells and a stationary slotted
bottom. In such a container, two cell walls are at a
mutual angle and form a container space which conically
widens in the horizontal direction. A rotary extractor
comprises several cells which are formed by cell walls
extending radially from a common axis above a stationary
slotted bottom. In a rotary extractor, the individual
cells are rotated with their contents over a stationary
slotted bottom which is interrupted by a sector-shaped
section, so that the cell contents can drop through down-
wards in this section and can be taken away.
The first treatment stage, in which the raw cof-
fee is preswollen, is followed by the actual extraction
stage which continues over several extraction cells.
Each cell is here associated with a separate receiving
chamber. The rotary extractor constructed in this way
preferably operates as a continuous percolation apparatus
by the crossflow/counterflow process. The extract con-
centration thus rises in the individual extraction stages
(viewed in the direction opposite to that of coffee trans-
port), the preswelling stage at the same time represent-
ing a first extraction stage with maximum extract concen-
tration and the extraction fluid being taken from this
first stage to the adsorber. Preferably, the adsorber is
likewise constructed~as a rotary extractor, which not
only contains the adsorption stages but in which also the
adsorbent is preloaded before the adsorption stages and
washed after the adsorption stages. This construction
makes it particularly easy to synchronize the extraction
equipment with the adsorption equipment.
The preswelling of raw coffee beans can also be
carried out in cylindrical containers. However, the
loose material must then be kept in motion by special
measures during the swelling step. During this motion of
the beans, however, fine particles are detached from the
surface of the beans (silvery pellicle) which are taken
along by the fluid and cause blockage in the downstream
activated carbon adsorber.
