Note: Descriptions are shown in the official language in which they were submitted.
~ ~ 7731 6
DESCRIPTION
DECAFFEINATION PROCESS
TECHNICAL FIELD
The present invention relates to decaffeination,
05 and more particularly to an improved process for
decaffeinating green coffee beans with carbon dioxide
in either the liquid or the supercritical state.
The prior art has long sought a process to
effectively and non-destructively remove caffeine
from coffee beans. Recently, a method for
decaffeinating green coffee beans with moist super-
critical carbon dioxide has been developed to
achieve near quantitative extraction of caffeine
while providing a high quality final product.
Similarly, a good quality decaffeinated coffee can
be produced by extraction with liquid carbon dioxide.
Unfortunately, these procedures are guite costly and
the rates of extraction are commercially impractical
when using dry green beans. And, while moistening
the beans prior to extraction improves processing
efficiency, the process remains very costly.
Therefore, it would be desirable to improve the
rates of extraction with carbon dioxide to lower
processing costs while still obtaining the advantages
of using liquid or supercritical carbon dioxide to
extract caffeine from green coffee.
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BACKGROUND ART
Current commercial decaffeinatian of coffee is
effected by the removal of caffeine from whole,
green coffee beans. The beans are first moistened
05 and then extracted with a solvent which is relatively
specific for caffeine. The solvents employed
commercially are either a chlorinated hydrocarbon
solvent, such as discussed in U.S. 3,671,263 to
Patel et al. or a caffeine-deficient water solution
of green coffee solubles, such as disclosed in
U.S. 2,309,092 to Berry et al.
In the decaffeination process of U.S. 2,309,092
which is commonly referred to as the water extraction
system, a caffeine-laden water extract, resulting
lS from contact between caffeine-containing green
coffee and the caffeine-deficient water solution, is
directly extracted with a solvent in order to remove
caffeine. Typically, these solvents are the same
chlorinated hydrocarbons which are employed in the
direct solvent extraction processes, exemplified by
the aforementioned U.S. 3,671,263.
Recently, the coffee industry has developed a
number of procedures for decaffeinating green coffee
without the use of chlorinated hydrocarbons; however,
mo~t of the~e are more expensive than desired based
on current competitive conditions. Among the more
promising of these procedures are those which involve
contacting the green coffee beans with carbon dioxide
in either the liquid or the supercritical state.
For example, in U.S. 3,879,569 to Vitzthum et al.,
there is disclo~ed a process wherein liquid carbon
dioxide is contacted with green coffee beans to
extract the caffeine with good selectivity. In
another recent patent, U.S. 3,806,619 to Zosel,
there is disclosed a decaffeination method wherein
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near quantitative extraction of caffeine from green
coffee beans is achieved through the use of
supercritical carbon dioxide. According to this
patent, green coffee beans are contacted with carbon
05 dioxide in the supercritical state to extract caffeine.
To further improve processing efficiency, with both
liquid and supercritical carbon dioxide, the green
beans are pre-moistened and the carbon dioxide is
saturated with water.
It would be desirable to further improve the
decaffeination of both dry and pre-moistened green
coffee beans with both liquid and supercritical
carbon dioxide.
DISCLOSURE OF INVENTION
The present invention now enables decaffeination
of green coffee beans, whether wet or dry, by an
improved process of the type comprising contacting
the beans with a caffeine extractant comprising
liquid or supercritical carbon dioxide, maintaining
the contact for a period of time sufficient to
extract at least a portion of the caffeine present
in the green coffee beans, and separating the caffeine
extractant from the green beans, wherein the improvement
comprises dissolving dimethyl sulfoxide in the
carbon dioxide.
~ he present invention takes advantage of the
discovery that dimethyl sulfoxide, an aprotic solvent
with strong caffeine extraction properties from
either wet or dry coffee beans, can improve the rate
of extraction of carbon dioxide in either the liquid
or supercritical state while retaining good caffeine
specificity and high quality end-products. The
increases in efficiency achieved through the use of
dimethyl sulfoxide to facilitate the extraction of
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caffeine with carbon dioxide is surprising both in
the degree of the increase and the quality of the
final product achieved.
The green coffee beans employed according to
05 the present invention can be any of the principal
commercial varieties. It is an advantage of the
present invention, however, that the milder and more
highly aromatic coffees such as Colombian cofee can
be decaffeinated effectively. Green coffee beans
can have any desired moisture content, but higher
rates of extraction can be achieved with higher
moisture contents. It is surprising, however, that
green coffee beans with moisture contents of less
than about 20% based on the total weight of the
beans, and even as low as from about 4% to about 9%,
the usual moisture content during shipping and
storage, can be employed with a relatively high
degree of selectivity and degree of extraction. The
moi~ture content of the beans will be determined
based upon the desired balance between the added
cost of moistening and then drying the green beans
versus the improvement in extraction rates which can
be achieved through the moistening procedures.
The extractant will comprise carbon dioxide in
either the supercritical or the liguid state and
will also contain dimethyl sulfoxide to facilitate
the removal of the caffeine from the green coffee
beans. While the extractant can consist essentially
of these two materials, there are circumstances
under which other materials such as water, dissolved
coffee solubles, and other additives may be desired.
By the term "supercritical", it i5 meant that the
carbon dioxide is above its critical temperature and
pressure. By the term "liguid", it is meant that
carbon dioxide is maintained at a temperature below
J ~ 7731fi
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its critical temperature of about 31C but is at a
pressure sufficient to cause a phase change from the
gaseous state to the liquid state with the evolution
of the latent heat associated with the phase change.
05 The improvement according to the present invention
is obtained whether the carbon dioxide is in the
liquid state or in the supercritical state. Thus,
to this extent, the specific temperatures and pressures
employed according to the present invention do not
affect the operability of the invention. It may be
desirable under certain circumstances, to increase
the temperature to a level in excess of the critical
temperature where the added costs of doing this are
justified by the increases in extractive efficiency.
There are other cases, however, where it will be
desired to maintain the carbon dioxide at a
temperature below the critical value but maintain
the pressure at levels high enough to maintain it in
the liquid state.
Within these broad ranges, it is found that
temperatures lower than about -10C or above about
150C either provide very slow rates of extraction
or adversely affect the flavor of the final decaf-
feinated coffee product. Preferably, the temper-
ature of the extractant will be maintained between
about 10C and about 100C.
Broadly, the pressure should be within the
range of about 20 to about 400 bar. As with the
temperature, it is to be understood that the working
pressure of the process depends upon the desired
proce~sing, the desired degree of extraction, the
configuration of the specific process, and the other
variables of the procedure; and a specific value
within this range will be chosen for practical
reasons.
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The dimethyl sulfoxide is dissolved in the
carbon dioxide to form what is believed to be a true
solution under the conditions of extraction. Even
minor amounts of dimethyl sulfoxide are effective
05 to facilitate the removal of caffeine from green
beans due to its high solvating capacity. This is
true regardless of whether the beans are in their
dry comm~rcial state or have been pre-moistened for
processing. Typically, the dimethyl sulfoxide will
be employed in an amount of at least 10% of the
weight required for complete saturation under
conditions of extractive contact. Preferably,
however, greater amounts of the dimethyl sulfoxide
will be employed, with levels of above 50% of the
weight required for complete saturation being preferred.
Especially preferred are extractant compositions
wherein the dimethyl sulfoxide is employed at near
its saturation level.
As disclosed in my copending Canadian
application, Serial No. 384,99~ filed on the
same date as this application and entitled "Aprotic
Solvent Decaffeination" (Case 2797), it is believed
that a complex exists in the green coffee beans
between potassium chlorogenate and caffeine. It is
further believed, without any desire to be bound to
a particular theory of operation, that the dimethyl
sulfoxide is capable of efficiently breaking up this
complex. Dimethyl sulfoxide is a colorless, hygroscopic
liquid having a boiling point of about 189C. It is
known to be an extremely powerful aprotic solvent
which readily penetrates animal skin and other
tissues Regardless of the theory of operation, it
is apparent that the dimethyl sulfoxide rapidly
penetrates the cellular structure of the green
coffee beans to facilitate the removal of the caffeine
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by the extractant which comprises carbon dioxide.
Where the green coffee beans are pre-moistened
to enhance the rate of extraction by the supercritical
or liquid carbon dioxide, the extractant will also
- 05 preferably contain water. Preferably, the extractant
will contain water in an amount sufficient to saturate
the extractant under the conditions of contact with
the green coffee beans. The water content of the
extractant will typically be selected to maintain a
pre-determined minimum water content for the green
coffee beans to be maintained throughout the processing.
Where the moisture content is too low, the dégree of
extraction will be reduced. Where the moisture
content is too high, the cost of removing the additional
water will become excessive. A preferred minimum
water content is above 15% by weight.
The extractant should be contacted with the
green coffee beans in sufficient quantities and
under other conditions effective to provide an
acceptable rate and degree of extraction. Preferably,
the concentration of the caffeine within the extractant
shollld be maintained at a level of below about 0.010,
and preferably below about 0.002 grams per lsilogram
of extractant to obtain an effective rate of
Z5 decaffeination. The exact concentration will,
however, depend ultimately upon economics and a
number of other variables in the process. An advantage
of the present invention is that a high selectivity
characteristic of carbon dioxide for caffeine is
retained while the very high solvating power of the
dimethyl sulfoxide improves the rate of extraction.
Even with the high degree of selectivity for the
extractant solution of the present invention, certain
coffee components such as sugars are dissolved to
varying degrees by the extractant. It is preferred
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to maintain the concentration of these soluble
materials at relatively high levels, preferably near
their points of saturation, within the extractant
solution.
05 The degree of saturation of the extractant
solution with the caffeine can be maintained at an
ef~ectively low level in a batch operation by using
a sufficiently large quantity of the extractant so
that, at the desired degree of decaffeination, the
extractant solution will be capable of disscl~ing
all of the extracted caffeine. Alternatively, and
preferably, a solid adsorbent is added to the solvent
to act as a caffeine sink, drawing the caffeine from
the solution and thereby maintaining an effective
driving force for the extraction of the caffeine
from the green coffee beans.
Where the solid adsorbent is employ~ed, it is
preferably highly selective with regard to caffeine
as opposed to the other components within the
extractant solution which, after contact with green
coffee beans comprises the various components of the
solvent and also caffeine and other dissolved coffee
solids This can be achieved by selecting a solid
adsorbent material which is initially highly selective
toward caffeine or by making it so by loading it to
it~ point of saturation with other coffee solubles.
When desired, the selectivity of the solid adsorbent
can be improved by coating it with a suitable caffeine-
selective coating, such as described in my commonly
assigned, co-pending Canadian Application, Serial No.
378,295, filed on May 26, 1981, and entitled
"Adsorption Decaffeination".
The adsorbent must be able to adsorb caffeine
and be physically stable under the conditions of
processing. Among the known caffeine adsorbents are
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g
clays, such as discussed in U.S. 2,391,981 and
u.s. 2,416,484 to Kremers; zeolites and ion exchange
resins as taught in U.S. 3,108,876 to Turken et al.;
hydrated silicates as taught in u.s. 2,375,~50 to
05 Grossman; polymeric non-ionogenic adsorption resins,
especially styrene divinylbenzene macroreticular
resins of the type disclosed by Gustafson in
U.S. 3,531,463; and activated carbon/ especially
finely-divided activated carbon derived from coconut
or coal. While any of these or the other usual
solid adsorbents known to the art for uses such as
this can be employed, the solid adsorbent will
preferably comprise a member selected from the group
consisting of activated carbon, clay, hydrated
silicates, zeolites, ion exchange resins, non-ionogenic
adsorption resins, and any combination of these.
Among these, activated carbon is preferred because
of its desirable balance between cost and effectiveness.
The solid adsorbent can be employed in sufficient
quantities to maintain an effectively low concentration
of caffeine within the extractant solution during
the period of contact between the green beans and
the extractant. The exact amount of solid adsorbent
employed will depend both upon the capacities of the
extractant material and the solid adsorbent at the
particular conditions of contact. Also, it may be
de~ired to provide a major excess of the adsorbent
to obtain the highest possible driving force for the
decaffeination.
The process can be conducted either batch-wise
or continuously. Batch operation has the advantage
of ~implicity in that all that must be done to
achieve the desired results is to admix the materials.
Continuous operation is, however, preferred because
it decreases the overall size of the equipment
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required and the processing time. Moreover, by
constantly withdrawing and renewing either the
extractant liguid or solid adsorbent by removal of
caffeine, the guantity of the extractant and the
- 05 solid adsorbent can be minimized. The greatest
driving force for the extraction can be achieved
where the flow of beans is countercurrent to the
flow of extractant. This can be done either in a
totally continuous or a stage-wise procedure in
equipment of the type known to the art. Another
advantage of continuous or semi-continuous operation
is that the solvent can be contacted with the beans
in a continuously flowing stream and then passed to
a separate bed of solid adsorbent where the solvent
15 i8 renewed by removal of the caffeine. Operation in
a configuration such as this will eliminate any need
for contact between the green coffee beans and solid
adsorbent.
Another procedure for separating and continuously
renewing the extractant liquid is to withdraw them
from contact with the beans and reduce the pressure
on the extractant solution to achieve a two-phase
mixture wherein the liquid dimethyl sulfoxide is
rich in caffeine. The gaseous carbon dioxide is
recompres6ed and recycled to the process. The
dimethyl sulfoxide is also recycled after the caffeine
is removed. This can be done by evaporation or by
contacting it with a solid adsorbent. As indicated
previously, the temperature affects both the degree
of extraction and the quality of the final product.
The temperature will affect the rate of extraction,
the selectivity of the extractant solution and the
solid adsorbents, and the relative capacity of the
extractant solution and the solid adsorbent for
holding the extracted caffeine. Accordingly, it is
~ ~ ~ 77316
not possible to identify a single temperature or
range of temperatures as universally defining optimum
conditions. It is believed, however, that the
temperatures mentioned previously should provide
05 good results under most processing schemes. The
selection of a temperature will depend upon materials
and processing equipment and conditions employed,
and may be within or outside of this range.
Total contact time, or residence time within an
extractor will depend upon the factors discussed
above as well as the desired degree of caffeine
extraction. While economics is a controlling factor,
it must be borne in mind that excessively long
contact times adversely affect coffee flavors.
Those skilled in the art will be able to balance
these factors as necessary, given the exemplary
situation set forth in the following example.
The green beans decaffeinated according to the
procedure of the present invention can be roasted in
conventional fashion to obtain a high quality
decafeinated coffee and can be blended in the
normal fashion. It is an advantage of the present
invention that, because it is not necessary to
pre-wet the beans prior to decaffeination, it is not
necessary to dry the beans prior to roasting or
extend the roast time to accommodate the excess
moisture content. This can improve the overall
eficiency of operation and can decrease the amount
of energy required for roasting the beans. The
elimination of the need to drive off the excess
moisture will also tend to improve the quality of
the final product. It is equally as much an ad~antage
of the present invention, however, that very high
extraction rates can be obtained with pre-wetted
beans while still maintaining very high guality for
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the final product.
BEST MODE FOR CARRYING OUT 1~ INVENTION
The following Example is provided to illustrate
and explain what is presently considered the best
05 mode for carrying out the invention. The data is
for illustrative purposes to guide the person of
ordinary skill in the art and is not to be taken as
limiting in any regard. Unless otherwise indicated,
all parts and percentages are by weight.
Exam~le
Four samples of green coffee beans were
decaffeinated by contacting them for up to 8 hours
in a pressurized apparatus containing 10 grams of
green cofee beans with an extractant solution
maintained at a pressure of 250 bar and a temperature
of 80C. The extractant solution was continuously
fed through the apparatus at a rate of 8,000 grams
of extractant solution per gram of green coffee
beans per hour. The four samples included both
"moist" and "dry" controls which were processed in
the same manner as "moist" and "dry" beans processed
according to the present invention wherein dimethyl
sulfoxide (DMSO) was dissolved in the extractant at
a level near its point of saturation. The following
table details the test conditions and results.
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Bean Estimated Time (Hours)
Moisture Extractant for 97.4%
SampleContent (%) Solution Caffeine Removal
Dry-
05 Control7.33 Dry Co285
Dry-Invention 7.33 Dry C02 + 55
DMS0
Moist-Control 50 C02 saturated 4.5
with H20
10 Moist-
Invention 50 C02 saturated 3.0
with H20 + DMS0
The figures in the last column show that the times
estimated as necessary to achieve 97.4% decafeination,
the figure widely commercially used at present, are
greatly improved by employing dimethyl sulfoxide
within the extractant solution. These times were
estimated from the raw data by the standard method
of extrapolating on semi-log paper to the reguired
2C degree of decaffeination.
The above description is for the purpose of
describing the invention to people having ordinary
skill in the art to enable them to practice it. It
is not meant to detail all of the obvious modifi-
cations and variations of the invention which willbecome apparent upon reading. It is intended,
however, that all such modifications and variations
be included within the scope of the invention which
is defined by the following claims.
