CA1083880A - Method for decaffeinating green coffee - Google Patents

Abstract

ABSTRACT

Green coffee beans are contacted with a caffeine-deficient water extract of green coffee. This aqueous solution extracts caffeine from the green coffee beans during the con-tact period and the caffeine-containing solution is then con-tacted with particles of a high surface area, non-ionogenic, macroreticular, water-insoluble cross-linked polymer of polymerizable ethylenically unsaturated molecules. The polymer adsorbs caffeine from the aqueous solution and there is produced a caffeine-deficient water extract of green coffee solubles which is then used to contact caffeine-containing green coffee beans.

Description

Current commercial decaffeination of coffee is effected by the removal of caffeine from whole, green coffee beans. The beans are first moistened 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. Patent No. 3,671,263 to Patel et al., or a caffeine-deficient water solution of green coffee solubles, such as disclosed in U.S. Patent No. 2,309,092 to serry et al. (See also Canadian Patent No. 432,659).
In the decaffeination process of U.S. Patent No.

2,309,092 which is commonly referred to as the water extraction system (Note: Sivetz, Coffee Processing ~echnology, Vol. 2, p. 208, AVI Publishing Co., Inc., 1963) the caffeine-laden water extract, resulting from contact between caffeine-containing green coffee and the caffeine-deficient water solution, is solvent extracted in order to remove caffeine. Typically these solvents are the same chlorinated hydrocarbons which are emplo,yed in the direct solvent extraction processes, exemplified by the aforementioned 3,671,263 patent.
As a result of the presence of organic solvents, such as chlorinated hydrocarbons, in commercial green bean decaffeina-tion processes, the decaffeinated coffee products presently being sold, either roasted and ground or soluble, contain at least trace amounts of residual solvent. This solvent residue can impart an off-flavor to coffee beverages and its presence within coffee` products is not desired.
Thus the coffee industry is desirous of finding alternative systems~for decaffeination which will avoid the use Oæ organic solvents. Removal of caffeine from concentrated ~ .

extracts of roasted coffee by means of ion-exchange resins of the cation exchange type has been proposed by Turken et al. in U.S. Patent No. 3,1~8,876. This system, which is appIicable only for producing soluble coffees, has not however proven to be commercially feasible as, in addition to caffeine, the resin removes many of the desirable coffee flavors and aromas from the roasted coffee extract. It has also been proposed, U.S.
Patent No. 3,749,584 to Kurtzman et al., to decaffeinate aqueous coffee extracts by microbiological techniques wherein caffeine i8 metabolized by a suitable organism. This process, however, does not presently appear to be suitable for scale-up to effective commercial operation.
One of the main features of any system of d~caffeina-ting coffee, such as in the decaffeination of whole graen coffee bean3, is to identify a solvent which will extract only the caffeine from the coffee and which can itself be completely removed from the coffee without deteriorating or materially changing the chemical composition of the bean. Unfortunately, no such solvent has presently been identified.
Water decaffeination systems which employ a caffeine-deficient extract of green coffee (hereinafter referred to as "lean green extract") would not be concerned with solvent residues in the decaffeinated green coffee since the solvent would contain only compounds which are naturally occurring in green coffee. However, once the "lean green extract" has con-tacted and removed caffeine from the coffee material, economics dictate that some means must be found to remove caffeine from the caffeine-containing green extract (hereinafter referred to as "rich green extract'~). In this manner, the green extract .
.. ..

can be reused to again remoVe caffeine from green coffee material.
Up to the present time, the only means which have been used for removing caffeine from the rich green extract has been direct contact with organic solvents (e.g., methylene chIoride and trichloroethylene) which are known to be specific for caffeine.
Unfortunately, however, these solvents cannot be completely removed from the water extract after contact, and solvent resi-dues are also found to be contained in the decaffeinated green coffee material. It would, therefore, be desirable i~ some means could be found for completely and exclusively removing caffeine from rich green extract without passing non-coffee material into the green water extract.
This invention is directed towards a method of decaffeinating green coffee wherein caffeine-containing green coffee is contacted with a caffeine-deicient water extract of green coffee which extracts caffeine from the coffee and which extract is thereafter processed to remove caffeine, the improve-ment comprising, contacting the caffeine-containing extract with particles of an essentially non-ionogenic, high surface area macroreticular water-insoluble bead or suspension polymerized cross-linked polymer of polymerizable ethylenically unsaturated molecules comprising about 2 to 100 weight percent of at least one poly(vinyl~ benzene monomer selected from the group consis-ting of divinylbenzene, trivinylbenzene, alkyl-divinylbenzenes having from 1 to 4 alkyl groups of 1 to 2 carbon atoms substituted in the benzene nucleus, and alkyltrivinylbenzenes having from 1 to 3 alkyl groups of 1 to 2 carbon atoms substituted in the benzene nucleus, which polymer has a porosity of at least 10%
and a surface area of at least 10 square meters per gram.

The present invention describes a process for removing caffeine from the "rich green extract" by means of an essentially non-ionogenic, high surface area, macroreticular, water-insoluble, cross-linked polymer of polymerizable ethylenically unsaturated molecules comprising about 2 to 100, preferably at least 50, weight percent of at least one poly(vinyl) benzene monomer selected from the group consisting of divinylbenzene, trivinyl-benzene, alkyl-divinylbenzenes having from 1 to 4 alXyl groups of 1 to 2 carbon atoms substituted in the benzene nucleus, and alkyltrivinylbenzenes having from 1 to 3 alkyl groups of 1 to 2 carbon atoms substituted in the benzene nucleus, which polymer has a porosity of at least 10%, a surface area of at least 10 square meters per gram, and which polymer is not appreciably swollen by caffeine.
The macroreticular resins employed as the adsorbents herein are not new in themselves. Known and commercially-availabIe polymers of this type are useful. Granular cross-linked polymers of the aforementioned type, prepared by suspen-sion polymerization, are fully described in U.S. Patent No. 3,53l,463 to Gustafson.
Suspension polymerization i9 conducted by polymerizing monomers which can cross-link in the presence of a phase separating or phase extending solvent or mixture of solvents that i9 miscible with the monomers but which does not dissolve the polymer. Suitable methods are disclosed in U.S. Patents Nos. 3,275,548 and 3,357,158 and in British Patents Nos. 932,125 and 93Z,126.

.
-~083880 This invention is based on the surprising discovery that the aforementioned macroreticular resins preferentially adsorb caffeine from a "rich green extract" containing an array of soluble solids of which caffeine constitutes only about 3 to 5% by weight. The surprising nature of this invention is augmented by the fact that, although some non-caffeine soluble solids are also removed from the "rich green extract" by the resins, the absence of these less preferentially adsorbed solids does not negate the suitability of the process for producing an acceptable decaffeinated coffee product.
The process of this invention is directed to a con-tinuous process for decaffeination wherein green caffeine-containing coffee i8 contacted with an aqueous extract of green coffee ~olubles deficient in caffeine.
Green aoffee, according to this invention, may be a blend of coffee varieties or a single coffee variety and may either be whole beans or some subdivided form thereof.
The preferred method of practicing this invention includes a semi-continuous water decaffeination system such as described in Berry et al. U.S. Patent No. 2,309,092. Caffeine is extracted with an aqueous extraction liquid from green coffee contained in a battery of extraction columns connected in series.
At steady-state operation, the extraction columns contain green coffee of varying degrees of extraction and the process is countercurrent in operation.
During opexation, the "lean green" extraction liquid is fed to the extraction column containing the ~ost extracted green coffee, is passed through the ccffee extracting caffeine therefrom, and then is passed out of the column into the extraction column containing the next most extracted green coffee in the battery. In this manner, the extraction liquid passes through green coffee of increasing freshness, thereby increasing in caffeine content, and is drawn-off from the extraction column containing the least extracted coffee in the battery for this cycle (une cycle being the period between suc-cessive draw-offs of extraction liquid from the fresh column).
The "rich green" extraction liquid is then processed to remove caffeine in accordance with this invention.
As taught by Berry et al., in beginning a new cycle, the most extracted green coffee in the previous cycle is dis-charged from the extraction column and is in the desired final decaffeinated form. This coffee is then further processed into roasted and ground coffee or soluble coffee according to methods well-known in the art. The "lean green" extraction liquid is then fed to the column containing the most extracted green coffee for this cycle, this coffee being the next most extracted coffee from the previous cycle, and the extraction process continues with the caffeine-laden, "rich green" extraction liquid being drawn off after contacting the freshest green coffee which is generally previously unextracted green coffee. Cycles are con-tinued in this manner such that in each succeeding cycle a given column of green coffee becomes progressively more extracted and hence more deficient in caffeine.
In Berry et al., the aqueous extraction liquid fed to the first extraction column in the battery containing the most extracted green coffee, is a water solution of green coffee solubles other than caffeine. In this manner, a continuous dynamic equilibrium is substantially maintained between the solids ~08388(~

(other than caffeine) in the green coffee and the solids in the extraction liquid. This equilibrium inhibits the net loss of green coffee solubles from the coffee to the surrounding water and, hence, the final decaffeinated green coffee is found to contain nearly the normal amount of solubles other than caffeine.
Of course, as the extraction liquid passes through the battery of extraction columns, it will become progressively more caffeine-laden. While many varying concentrations of these green coffee solubles in the extraction liquid may be employed, the concentrations and other operating factors are generally chosen so as to achieve, as nearly as possible, the dynamic equilibrium previously referred to.
The equilibrium between the soluble solids in the green coffee and the soluble solids in the extraction liquid works to minimize any concentration gradients of these materials and thereby hinders net mass transfer from the coffee to the surround-ing liquid. Since caffeine is not initially present in the extraction liquid, a suitable gradient is present to effect extraction of the caffeine from the green coffee into the extraction liquid. In actuality the dynamic equilibrium is more aptly described as equal rates of mass transfer. Thus while the net ideal result is to substantially prevent a reduction of the original amount of solubles other than caffeine in the green coffee, such prevention is the result of a combina-tion of preventing natural solubles loss from the green coffee coupled with replacement of solubles from the extraction liquid at a rate equal to the rate of solubles lost from the green coffee.

~8~880 In the Berry et al. patent, the extraction liquid drawn off from the extraction column containing the least extracted green coffee (i.e., rich green extract) contains caffeine and green solubles either present in the original feed liquid is stripped of caffeine by means of a solvent, and the solvent is removed from the remaining solution. The liquid present after solvent removal may then be recycled, usually with the addition of water, to the battery of extraction columns.
According to this invention, the rich green extract is decaffeinated by means of contact with a high surface area, macroreticular, non-ionogenic, cross-linked polymer, as described in the Gustafson patent.
The macroreticular polymer, which under most conditions is of 16 to 100 mesh in particle size, but for some special purposes may be as small as about 400 mesh, has a porosity of at least 10% (percent volume of pores in the resin body or bodies) and a surface area of at least 10 square meters per gram of the resin (up to 2,000 square meters per gram). Suitable cross-linked resins have solubility parameters (unit: ~ ealories/cc) of at least about 8.5 and those having such parameters up to 15 or more are satisfactory for use in our system.
The macroreticular resins employed as the caffeine adsorbents herein may be any of the known materials of this type. For example, there may be used the granular cross-linked polymers of this character prepared by suspension polymerization of polymerizable ethylenically unsaturated molecules comprising about 2 to 100, prefexabIy at least 50, ~eight percent of at least one poly(vinyl~ benzene monomer seIected from the group consisting of divinylb~enzene, trivinylbenzene, alkyldivinyl-. .

benzenes having from 1 to 4 al~yl groups of 1 to 2 carbon atomssubstituted in the benzene nucleus and alkyltrivinylbenzenes having 1 to 3 alkyl groups of 1 to 2 carbon atoms substituted in the benzene nucleus. Besides the homopolymers and copolymers of these poly(vinyl)-benzene monomers, one or more of them may be copolymerized with up to 98%, preferably less than 50~, (by weight of the total monomer mixture) of ~1) monoethylenically unsaturated monomers, or (2) polyethylenically unsaturated monomers other than the poly(vinyl)benzenes just defined, or (3) a mixture of (1) and (2).
Examples of the alkyl-substituted di- and tri- vinyl-benzene~ are the various vinyltoluenes, the divinylxylenes, divinylethylbenzene, 1,4-divinyl-2,3,5,6-tetramethylbenzene, 1,3,5-trivinyl-2,4,6-trimethylbenzene, 1,4-divinyl, 2,3,6-triethylbenzene, 1,2,4-trivinyl-3,5-diethylbenzene, 1,3,5-trivinyl-2-methylbenzene.
Examples of other polyethylenically unsaturated compounds include: divinylpyridine, divinylnaphthalenes, diallyl phthalate, ethylene glycol diacrylate, ethylene glycol dimethacrylate, divinylsulfone, polyvinyl or polyallyl ethers of glycol, of glycerol, of pentaerythritol, of monothio- or dithio-derivatives of glycols, and of resorcinol, divinyl-ketone, divinylsulfide, allyl acrylate, diallyl maleate, diallyl fumarate, diallyl succinate, diallyl carbonate, diallyl malonate, diallyl oxalate, diallyl adipate, diallyl sebacate, divinyl sebacate, diallyl tartxate, diallyl silicate, triallyl tricar-ballylate,: triallyl aconitate, triallyl citrate, triallyl phosphate, N,N' - methylenediacrylamide, N,N' - methylerledi-iO~33880 methacrylamide, N,N' - ethylenediacrylamide, trivinylnaphthalenes, and polyvinyl-anthracenes.
Examples of suitable monoethylenically unsaturated monomers that may be used in making the granular macroreticular resin of the latter type include: methyl acrylate, ethyl acrylate, propyl acrylate, i80propyl acrylate, butyl acrylate, tert-butyl acrylate, ethylhexyl acrylate, cyclohexyl acrylate, isobornyl acrylate, benzyl acrylate, phenyl acrylate, alkylphen-yl acrylate, ethoxymethyl acrylate, ethoxyethyl acrylate, ethoxypropyl acrylate, propoxymethyl acrylate, propoxyethyl acrylate, pro-poxypropyl acrylate, ethoxyphenyl acrylate, ethoxybenzyl acrylate, ethoxycyclohexyl acrylate, and the corresponding esters of methacrylic acid, ethylene, propylene, isobutylene, disobutylene, styrene, vinyltoluene, vinyl chloride, vinyl acetate, vlnylidene chloride, acrylonitrile.
Polyethylenically unsaturated monomers which ordinarily act as though they have only one such unsaturated group, such as iso-prene, butadiene, and chloroprene, may be used as part of the monoethylenically unsaturated category.
Decaffeination of the "rich green extract" may be carried out in a simple batch operation or by a continuous procedure. In a fixed-bed batch operation, the resin adsorbent may be supported in a suitable adsorption cell or vessel which in most practical operations normally takes the form of a tower or column suitably packed with the resin particles which may be of any suitable size or mesh ~uch as that which will pass through a 16-mesh screen but will largely be trapped by a lO0-mesh screen (U.~S. Standard~. The "rich green extract" is passed through the resin bed at a suitabIe rate, preferably from top to bottom so that caffeine may be adsorbed on the resin surfaces.

10t33880 When the "rich green extract" which normally has a solids content of about 30~ by weight, about 3 to 5~ of these solids being caffeine, contacts the resin, solids may be adsorbed until the adsorption capacity of the resin in the particular system is reached. At that point, additional solids are not adsorbed and, if operating with a fixed-bed adsorption system, the solids concentration and composition of the "rich green extract" entering the bed i9 the same as the effluent passing out of the bed. When this condition is obtained, or sooner if desired, the resin should be separated from the green extract such as by draining, centrifuging or the like, and then regenerated. Regeneration, or removal of adsorbed solids, will be necessary so that the resin may be reused in the system.
Adsorbed solids may be eluted from the resin by suitable li~uid mediums such as hot water, aqueous acid such as acetic acid, hydrochloric acid, carbonic acid, and sulfuric acid, or alkaline solutions, such as aqueous solutions of sodium or potassium hydroxide, or an organic solvent which is easily separable, such as methanol, ethanol, propanol, acetone, isopropanol, benzene, xylene, cyclohexane, ethyl acetate and the like.
Besides the single contact or batch extraction system just described, the green extract may be passed in succession through a plurality of fixed beds of the resin adsorbent or through a plurality of resin beds which are moved continuously or stepwise in countercurrent relation to thé flow of green , extract.
In addition to caffeine, the "rich green extract"
suffers the loss of other solids through adsorption on the resin.

~8388o Chlorogenic acid which is normally found in the "rich green extract" solids at a level of about 25 to 33% by weight is also significantly adsorbed by the resin. What appears ta be minor amounts of various other compounds present in the "rich green extract" are also adsorbed by the resin. The weight composition of the total solids adsorbed by the resin has been found to be about 20% caffeine, 40% chlorogenic acid and 40% other compounds including glucose, fructose, sucrose, inositol, quinic acid, and citric acid.
The essentially caffeine-free "lean green extract"
produced as a result of resin decaffeination is directly suitable for extracting caffeine from green coffee, such as in the semi-continuous, multi-stage countercurrent extraction process of the Berry et al. patent. The decaffeinated green bean~ resulting from cont~act w.ith the resin-decaffeinated "lean green extract"
of this invention are undoubtedly reduced in solids level by virtue of the fact that the "lean green extract" is somewhat deficient in chlorogenic acid and certain other soluble com-pounds; however, these green beans, after roasting and grinding are able to produce a coffee beverage which is not considered deficient in flavor or aroma.
This invention is further described but not limited by the following Example.
EXAMPLE
Seven liters of "rich green extract" containing 2450 gms. of solids (about 30% solids by weight) and obtainea from a commercial countercurrent, multi-stage water decaffeina-tion system as set forth in Berry et al. Patent No. 2,309,092 were stirred with 5240 gms. of a nonionogenic, high surface .

~083880 area, macroreticular, styrene-divinylbenzene copolymer, which had been prepared by suspension polymerization of a monomer fraction containing in excess of 80% by weight divinylbenzene.
This polymer was employed in the form of 20 to 50 U.S. mesh beads and is available from Rohm and Haas Co., Philadelphia, Pa.
19105 under the commercial designation Amberlite XAD-4*.
The "rich green extract," having an approximate com-positional make-up of solids as set forth in Table 1, was stirred with the resin beads for 3-1/2 hours after which 6 liters of a "lean green extract" (about 20% solids as per Table 1) was filtered off and used to decaffeinate 450 gms. of green Colombian beans using eight 400 ml., 1/2 hour passes in a Paar* Bomb apparatus at 70 to 80C. The resulting green beans, which were found to be 93% decaffeinated, were roasted, ground and brewed to produce a coffee beverage.
This beverage was compared against a control beverage, prepared from another 450 gms. sample of the Colombian beans, decaffeinated according to the above procedure by contact with "lean green extract" (about 20% solids) obtained by solvent (trichloroethylene) extracting the commercial "rich green extract" in a liquid-liquid extraction column (Rotating Disk Contactor). These decaffeinated beans (95% decaffeinated) were roasted, ground and brewed to produce the control beverage with the same procedure previously employed.
The two beverages were evaluated for quality and dif-ference by a taste panel of skilled coffee tasters. The samples were judged to be of moderate difference but of nearly identical quality, the control being slightly less preferred. There was no indication of off-flavors present in the beverage which had been obtained with the resin decaffeinated green extract.
*Trademark . ~
f~

Green Extract Solids Analysis Rich Green Lean Green Approx. Ratio Compound (weight ~)(weight %) (rich/lean) Caffeine 4 0.3 13.1 Trigonelline 0.9 - -Chlorogenic Acid 29 10 2.8 Glucose 1.5 1.5 0.98 Fructose 1.5 1.5 1.0 Sucrose 14 15.7 0.98 Inositol 0.6 0.6 0.96 B-Glucuronolactone 0.6 0.6 1.0 Quinic Acid 6.5 7.8 0.83 Citric Acid 3 3.6 0.84 Malic Acid 1.0 1.4 0.69 Soluble Protein 20 Undetermined 17 1 - Tentative identification.

2 - Containing mostly higher molecular weight substances (e.g. polysaccharides and polyphenoli.c compounds).

It may be desirable to recover at least a portion of non-caffeine solids adsorbed on the resin for add-back to the "lean green extract," or to the decaffeinated green beans;
however, as can be seen from the Example, this recovery and add-back process is not necessary for producing an acceptable coffee product and beverage.
As previously mentioned, the adsorbed solids typically consist of about 20% caffeine, 40% chlorogenic acid and 40%
other solids. Employing a 30% solids "rich green extract," it -.

has been found that, after extended contact with the resin, about 30 to 40~ by weight of the total solids are retained by the resin. About 5% of the total solids (essentially caffeine free) can be washed from the resin surface by means of cold water. A subsequent hot water (88c.) wash is able to remove another approximately 12 to 17% of the total solids, which ~olids typically contain about one-half the adsorbed chlorogenic acid and about 10% of the adsorbed caffeine.
As will be apparent to those skilled in the art, further elution of the resin will be desirable in order to remove essentially all of the adsorbed solids, thus making the resin ready for reuse. It may be desirable to remove adsorbed solids from the resin in such a way that fractions rich in caffeine and low in caffeine can be recovered. Such a process would facilitate the processing of the caffelne-rich fraction to obtain a pure caffeine by-product and the processing of the low-caffeine fraction for possible add-back to the decaffeina-tion system or the decaffeinated beans.
It will also be apparent that the process described in the invention could be employed if it were desired to reduce the chlorogenic acid content of green coffee beans. Such a procedure would be useful for production of a relatively low-acid coffee product.
It has also been found that the resins described herein are capable of removing caffeine from aqueous extracts of roasted and ground coffee. Resin contact with roasted coffee extract, however, removes significant amounts of desirable flavor and aroma compounds. Thus, decaffeination of roasted coffee extract is not within the scope of the present invention.

Claims (5)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In a method of decaffeinating green coffee wherein caffeine-containing green coffee is contacted with a caffeine-deficient water extract of green coffee which extracts caffeine from the coffee and which extract is thereafter processed to remove caffeine, the improvement comprising, contacting the caffeine-containing extract with particles of an essentially non-ionogenic, high surface area macroreticular water-insoluble bead or suspension polymerized cross-linked polymer of polymeriz-able ethylenically unsaturated molecules comprising about 2 to 100 weight percent of at least one poly(vinyl) benzene monomer selected from the group consisting of divinylbenzene, trivinyl-benzene, alkyl-divinylbenzenes having from 1 to 4 alkyl groups of 1 to 2 carbon atoms substituted in the benzene nucleus, and alkyltrivinylbenzenes having from 1 to 3 alkyl groups of 1 to 2 carbon atoms substituted in the benzene nucleus, which polymer has a porosity of at least 10% and a surface area of at least 10 square meters per gram.

2. The method of claim 1 wherein the polymer is comprised of at least 50 weight percent of at least one poly-(vinyl)-benzene.

3. The method of claim 1 wherein the polymer is com-prised of at least 50 weight percent of divinylbenzene.

4. The method of claim 3 wherein the polymer is a copolymer of divinylbenzene and styrene.

5. The method of claim 1 wherein the polymer is a homopolymer of divinylbenzene.