Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Process for the preparation of concentrated extracts of
coffee, tea or substitutes therefor
The present invention relates to a process for
the preparation of a concentrated extract of coffee, tea
or substitutes therefor. The concentrated extract can
subsequently be converted into powder by conventional
methods.
In the preparation of, for example, instant coffee
powders, one of the difficult stages is the concentration of
the final extract, said concentration having to
be effected with special care to avoid damage to the
aroma. In general, moreover, since the concentration is
effected by evaporation, the aromas are removed from the
extract to be concentrated and subsequently reintroduced into
the extract after concentration. However, heat treatment
is unavoidable in such a system and losses or changes of
aroma can thereby arise.
Attempts have hitherto been made to treat coffee
extracts by ultra-filtration with moderate success. In
particular, the use of membranes conventional in the art,
which have molecular weight exclusion points of the order
of 10,000 Daltons and above, has given fractions of little
interest and which are difficult to treat by physical
means such as reverse osmosis.
The present invention, which employs similar
physical processes to those mentioned above, provides a
solution of these difficulties.
Thus, according to the present invention there
is provided a process for the preparation of a concentrated
extract of coffee, tea or substitutes therefor, for example
chicory and various herbal infusions and decoctions, which
comprises the steps of
(a) subjecting an extract of coffee tea or substitutes
therefor to an ultra-filtration (hereafter referred to as
UF) treatment using a membrane having a molecular weight
exclusion point in the range 500 to 5000 Daltons, so as to
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obtain a retained fraction containing essentially soluble
solids and an aromatic permeate fraction;
(b) subjecting the ultra-filtration permeate fraction
from step (a~ to a reverse osmosis (hereafter referred to
as RO) treatment using a membrane which is capable of
retaining at least 99% of NaCl; and
(c) mixing at least part of the retained fraction
from the reverse osmosis step (b) and at least part of the
retained fraction from the uitra-filtration step (a) to give
the desired concentrated extract.
If necessary and/or desired, the starting extract
is clarified before being subjected to UF, for example by
filtration or by centrifuging.
In an advantageous embodiment of the process, the
retained fraction from the reverse osmosis and the ultra-
filtration retained fraction are mixed after the latter has
been concentrated.
In another embodiment, the retained fraction is -
diluted while UF is being effected, this operation being
zo referred to as "diafiltration" (DF).
Of course UF and DF operations can be
combined either in series or in parallel.
It could be argued that an operation using a
membrane having an exclusion point from 500 to 5000 could
equally be regarded as "ultra-filtration" or as "reverse
osmosis". In fact, the exclusion conditions are such that the
process takes place at the limits of the range common to both
operati~ns, UF and RO bo~h involving a segregation and a
fractionation at the molecular level.
We have however deliberately chosen the term "UF",
both for clarity of description and because stage (a) of
the process according to the invention involves, above all,
retaining a maximum of coffee solids, while allowing the
aromas to pass. In contrast, the purpose of stage (b) is to
collect the aromas in the retained fraction from the RO,
ideally water alone passing through the membrane.
In the process of the invention, the conditions for
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effecting U~ and R0 are those conventionally used and, for
example, with regard to temperature, the conditions to be
selected are governéd essentially by the desire to handle the
extract as gently as possible. Thus, a
temperature of from 2 to 25 C, preferably from 5 to 25
C, may be used. The pressure in the UF treatment is
generally of the order of 4 to 20, preferably 8 atmospheres,
and in the R0 treatment of 30 to 80 atm. The membranes
used may be those conventional in the art, for example
membranes of polysulphones or cellulose acetate for UF and
membranes of poly-(ether)-amides or polyamides for R0,
provided that the exclusion point of the UF membrane is
between 500 and 5000, and that the R0 membrane is capable
of retaining at least 99~ NaCl (e.g. sea-water desalination
membranes).
In order to enable as much as possible of the aromas
to pass through the membrane in stage (a), the retained
fraction can, if desired, be diluted with water during
the UF treatment. This enables the ratio of solids to
aromas in the retained fraction to be increased .
For example, the UF treatment enables ratios of
solids to aromas in the retained fraction ranging up to
3.5 to be obtained. The leakage of solids to the permeate
fraction still remains minimal; their presence in small
quantity is, moreover, advantageous as an aroma carrier
during the subsequent RO operation. Furthermore, a ratio
of concentration of aromas of the order of 30 to 40 times may be
achieved in the retained fraction from the R0 treatment,
the leakage of aromas to the permeate fraction from the
R0 treatment is generally insignificant. Advantageously ,
the UF treatment is continued until a concentration factor
of form 2 to 5, e.g. of the order of 3, is obtained, and
with the R0 concentration factors of between 5 and 10 are
aimed at.
The desired concentrated coffee extract is obtained
by combining the retained fraction from the R0 treatment,
obtained as described above, with the retained fraction
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from the UF treatment. Advantageously, the retained
fraction from UF is concentrated by a conventional method
before it is added to the retained fraction from R0.
It goes without saying that a partial recombination
may be effected by mixing only a part of the retained
fraction from R0 with the retained fraction from UF or vice
versa, and in this way, extracts which are more or less
aromatic or of variable aromatic quality may be obtained,
in comparison with extracts corresponding to those obtained
with the total recombination.
The process accordinq to the invention which
utilises UF and RO can likewise be supplemented by convent-
ional operations in coffee technology, such as evaporation
or steam distillation of aromas.
Thus, in another embodiment of the process
according to the invention a partial steam distillation of
the starting extract may be effected before UF, ~he aromas
thus collected being added to the final concentrated extract.
In yet another em~odiment traces of aromas which may have
been retained with the solids in the retained fraction from
UF are removed by steam distillation and are reintroduced
into the final concentrated extract (or into the
concentrated retained fraction from UF, if said fraction
has undergone such a treatment).
The following Examples illustrate the process
according to the invention. In the Examples all percentages
are expressed as percentages by weight.
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Example 1
An industrial coffee extract obtained by a conventional
process is treated by ultra-filtration in a DDS* 35.9.3 module
equipped with GR* 8 P polysulphone membranes. The membranes have
a mean exclusion point of 2500 Daltons. The ultra-filtration is
effected at a pressure of 7x105 N.m ~7 bars~ at 2Q C. UF is
continued until a concentration factor of 2 is obtained. The
permeate obtained is then treated by reverse osmosis in a module
equipped with PA 300 TFC* poly-(ether~-amide membranes which are
capable of retaining at least ~9.4% of NaCl. The reverse osmosis
operation is effected at 60xlO N.m t60 bars~ at 10 C. R0 is
continued until a concentration factor of 10 is obtained. Under
these conditions it is noted that 99~ of the solids are found in
the retained fraction from ultra-filtration and it is estimated
that more than 90~ of the aromas, also, are found in the retained
fraction from reverse osmosis.
The whole of the retained fraction from reverse osmosis
and the retained fraction from ultra-filtration which are ob-
tained above are then mixed. The mixture is converted into
instant coffee powder according to conventional method.
The powder reconstituted in water gives a coffee of
excellent quality whose aroma, in particular, is judged to be
"very true".
Example 2
The procedure described in Example 1 is repeated, but the
u~tra-filtration is continuous until a concentration factor of
4 is obtained. The results obtained are very comparable, the
mixtures of the retained fractions from ultra-filtration and from
reverse osmosis have a slightly lower concentration and thus make
it necessary to evaporate a little more water to produce the
instant coffee powder.
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Example 3
The procedure described in Example l is repeated,
but, once the concentration factor of 2 is obtained in the
ultra-filtration step, the operation is continued by diluting
the ultra-filtration retained fraction (diafiltration).
For diafiltration a quantity of water equal to half the
quantity of coffee extract used in the operation is
employed. The reverce osmosis operation proceeds as
described in the foreqoing Examples.
By drying the mixture of the retained fractions
from reverse osmosis and from ultra- iltration (diafiltrat-
ion) a powder is obtained which, after reconstitution,gives a coffee of excellent quality.
The losses of aroma and of coffee solids may be
considered as negligible.
Example 4
The procedure described in Example 1 is repeated,
with the following two differences: on the one hand, the
ultra-filtration is effected at a pressure of 15xlO N.m
(15 bars) and, on the other hand, the ultra-filtration re-
tained fraction is subjected to a steam distillationoperation at 100C for one minute, the aromas thus collected
being added to the final mixture before drying.
Example 5
3 The procedure described in Example 2 is repeated,
but the retained fraction obtained at the end of the ultra-
filtration operation which has a content of dry substances
of 12.2% is concentrated thermally until a content of dry
substances of 56% is obtained. This concentrated retained
fraction is added in this form to the retained fraction
from reverse osmosis to constitute the final mixture
which, after drying, gives instant coffee powder.
Example 6
An industrial coffee extract is ultra-filtered in a
DDS module equipped with cellulose laboratory membranes
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having an exclusion point of 500 Daltons. The pressure applied is
30x105 ~.m 2 (30 bars) and the temperature is 20C. The operation
is stopped when a concentration factor of 2 is obtained.
The ultra-filtration permeate is treated by reverse osmosis
in a module equipped with PA 300 TFC poly-(ether)-amide membranes,
as indicated above. The operation is effected at a pressure of
60x105 N.m 2 (60 bars) and a temperature of 10C and is limited
to a concentration factor of 4.
The retained fractions from reverse osmosis and from ultra-
filtration are combined to give the mixture from which instantcoffee powder is prepared.
Example 7
The ultra-filtration operation described in Example 1 is
repeated, starting from an industrial coffee extract whicn has
previously been concentrated thermally to a concentration factor
of 3. Subsequently, the ultra-filtration permeate is subjected
to a reverse osmosis operation~ as described in the foregoing
Example 6.
A combination of the two retained fractions from reverse
osmosis and from ultra-filtration gives the mixture from which
instant coffee powder is obtained.
COMPARATIVE EXAMPLE
An industrial coffee extract is treated by ultra-filtration
in a module equipped with Romicon PM 5Q* membranes of the poly-
sulphonic type having an exclusion point of 50,0Q0 Daltons. The
operation is effected at 1.5x10 N.m Cl.5 bars~ at 20 C untii
a concentration factor of 4 is obtained, The distr;bution of
solids between the retained fraction and the permeated fraction is
catastrophic since at least 30% of the solids can be found in the
permeated fraction. Furthermore, the aromas are distributed
approximately equally between the retained fraction and the per-
meate fraction.
The ultra-filtration permeate is then treated by
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reverse osmosis under the conditions described in the other
Examples. The pressure is 60x105 N.m 2 (60 bars) and the
temperature is 10C and the operation is continued until a
; concentration factor of 4 is obtained.
A combination of the retained fractions from
reverse osmosis and from ultra-filtration gives a mixture
which can be converted directly into an instant coffee pow-
der, but it is noted that this powder has a reduced aro-
matic value. The considerable loss of aroma during
ultra-filtration is manifestly the reason for this.
Moreover, the loss of solids which is also considerable
makes the operation of little potential interest on an
industrial scale.
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