CA1329595C - Method for decaffeinating coffee materials including a reverse osmosis permeate recycle - Google Patents

Abstract

METHOD FOR DECAFFEINATING COFFEE MATERIALS INCLUDING A REVERSE OSMOSIS PERMEATE RECYCLE ABSTRACT An improved method for extracting caffeine from a coffee material, preferably raw coffee solids, with an extractant comprising supercritical carbon dioxide. Caffeine is continuously absorbed from the extractant with an aqueous wash solution in an absorber. This wash solution is continuously treated by reverse osmosis to form a caffeine-containing retentate stream and a permeate stream containing dissolved solids but substantially no caffeine. The permeate stream is recycled and used as wash water in the absorber or is used to prehydrate solid coffee materials, or both. The permeate stream comprises acidic dissolved solids.

Description

Case 3661 1 3~9595 MET~OD FOR DECAFFEINATING COFFEE r~TERIALS
IN~LIJDI~3~ ~ REVERSE QS~S~R~ECY~LE

Various coffee decaffeination methods are known in 7 the art. Coffee beans are irst hydrated with water and then caffeine is e~tracted with liquid orga~ic solvent 9 such as benzene, ethyl acetate, isopropanol, chloroform, dichloroeythylene or trichloroethylene.
11 Various other methods are known which do not require the use of liquid organic solvents. In one such method 13 supercritical carbon dioxide is used to e~tract caffeine from hydrated coffee. The coffee material so e~tracted 15 may be in the form of premoistened raw coffee solids, either whole beans or particulate, or les~ preferably in 17 the form of a liquid estract. T~pically, caffeine is removed f rom the carbon dio~ide so that the carbon 19 dioxide can be recycled to the e~traction process. U.S.
Patent No. 4,260,639 to Zosel discloses a carbon dio2ide 21 e~traction process in which active carbon is used to remove ~h~ ca~feine ~rom the carbon dlo~ide. U.S. Patent 23 No. 4,411,g23 to Hubert~ et al discloæes a carbon dio~ids e~traction process in which ion e~change 25 materials are used to remove caffeine from the carbon dioside. ~

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. ~ ;:, 1 32~595 1 Supercritical ca~bon diosias ~i~traction proc~sses which usa wa~er to absorb caffaine from carbon dioside 3 are also known in th~ art. Some o~: thes~ processe3 include removing caffsine from ca~}'~in~ loadea water and 5 reusing ~his wat~r i~ the absorption proc~3~, U.S.
Patent No. 3,806,6}9 to Zos~l disclose~ a proc~ s in 7 which caff~ine is s~parated fro~ a ~a~h wat~r by air or nitroq~n stripF~ng. ~ator i~ ~t~ipp~d ~rom caf~ine 9 loaded wash water and is then co~den~ed and reu~ed for caffeine a~sorption. U.S. Pat3nt ~o. 4,348,422 ~olZosel 11 di~close~ a pro~ in which ca~fein~ is ~eparatad from a wash wat0r by di3tillation and tho d~tilled wat~r i~
13 th~n r~u3ed for caff~in~ absorption. Each of U.S. Patent No. 4,341,804 and 4,246,291 to Pra~ad, et al. disclose a 15 proca~ in wh~ch evaporatioQ, raver~ o~mo~i3 o~
crystallization i~ u~ed to ~eparat~ caffain~ from a wash 17 water. A membran~ p~rm~at~ can b~ reus~d ~or eaffeine absor~tion.

21 ~9~ r~aL~aY:_LIZ~ ~13 Th~ ~ro~o~ tion r~lat~ to a~ ro~ m~thod 23 fo~ ~stsacting ca~f~ino esO~ a co~ conta$~ing ma~rial with sup~c~itical ca;ho~ dlo$id~. ~or~ ~a~icularly, 25 th~ ntio~ in~olv~ 2stracting ca~ o from ~ cofe~

- ~ 3 ~ 1 3 2 9 5 9 5 1 material with supercritical carbon dioxide and t-hen continuously absorbing caffeine from the carbon dio~ide 3 extractant ~y contact with an aqueolls wash s~lution in an absorber. Wash solution from the ahsorber and containing 5 caffeine is continuously treated by reverse osmosis to form a permeate stream containin~ ac:idic dissolved 7 non-caffeine solids and substantially no caffeine.. In a first embodiment, at least a portion of the permeate 9 solution is recy~led to the absorber and used as at least a portion of the wash solution. In a second embodiment 11 in which the coffee material comprises raw coffee solids, at least a portion of the permeate solution is used to 13 hydrate the coffee material prior to its decaffeination with a carbon dio~ide e~tractant. Such use o a permeate 15 solution containing acidic dissolved non-caffeine solids increases the decaffeination rate of the co~fae material, 17 and the use of the permeate solution for hydration of the raw coffee solids also increases the hydration rate.
19 Where the coffee material comprises raw coffee solids, portions o the permeats solution containing acidic 21 dissolved non-caffeine solids can be used both as recycle to the ~bsorber and to hydrate the coffee material.

~IEF D~$~IPTI~N ~F T~ DRAW~
The drawing is a diagrammatic flow shee~ of the process of the instant invention, includi~g an absorber 27 and a caffeins recovery system.

29 D~SCRIPTIO~ 0~ THE I~V~TIO~
Supercritical carbon dio~ide is effective to remove 31 caffeine from coffee material and is particularly effective for decaffeination of raw coffee solids, either 33 ~hole beans or particulate. While roasted coffea solids or liqui~ es~imate of roasted coffee ma~ also be ., ~ .

' .,, ~ , ~. ' ' ' ' ' '. ~i - ~ 4 ~ 1 32 ~ 5 9 5 1 decaffeinated with supercritical carbon dioxide, the process is accompanied by rather large losses of 3 desirable constituents. Accordingly, the present invention has particular applicability to decaffeination 5 of raw coffee solids, either in whole ~ean or particulate form. The process is particularly well suited to the 7 decaffeination of green coffee beans.
If the coffee material is i~ the form of raw coffee 9 solids, it is necessary that it is hydrated to a moi~ture content between 20-50% preferably about 30-45% prior to 11 decafeination. This is accomplished by means well known in the art such as steaming or soaking. For esample, 13 green coffee beans may be steamed at about 100C for approximately two hours. In the second embodiment of the 15 instant invention, an aqueous reverse osmosis permeate solution which is described below i~ used to moisten the 17 raw co~fee solids. The use of the permeate solution rather than city water increases the rata of hydration of 19 the coffee material about 5-15% and increases the rate of decaffeination about 10-20%.
21 The coffee material is decaffeinated by contact with an estraction fluid in an estractor. The estractor can 23 be of any type known in the art capablR of operating at the temparatures and pressures o the instant invention.
25 Thc estraction 1uid comprises supercritical carbon dio~ide maintained at a temperature above it~ critical 27 temperature of 30C and at a pressure abov~ its critical pressure of 72.8 atmospheres. The e2traction f luid will 29 usually contain water vapor due to cafeine r~moval using water. The estraction fluid may also contain so-called 31 enha~cers which are added to the fluid to improve its capability to e~tract caffeine. Typ;cal enhancers 33 includ~ methanol, ethanol, a~d ~thyl acetate and are added to the e2traction f }uid at proportions between . -f-~ _ 5 _ 1 3 29 5 95 1 about 0.1~ and 20%. Since the e~traction fluid is recycled to the e~tractor after processing with water for 3 removal of caffeine, it will contain a small amount of caffeine and will also contain other substances e~tracted 5 from the coffee material. As described below, caffeine is continuously removed from the estractant by contact 7 with an aqueous wash solution. The e~traction fluid will, therefore, also contain any substances picked up 9 from this wash solution including water.
The temperature used in th~ extractor will generally 11 be as high as possible which increases the e2traction rate but not so high as to cause damage to the coffee 13 material. In general, in the case of raw coffee solids, the temperature should not e~ceed about 135% C.
15 Preferably, raw cof fe~ solids are extracted at a temperature of from 85-135~, more preferably 95-125~C.
17 Aribica's or other qualit~ coffee is e~tracted preferably at 95 to 105C and Robu~ta or other poorer flavored 19 coffee at 115 to 135C.
Pressure in the e~tractor will also generally be high 21 to favor e~traction but not so high as to requira escessively high pressure equipment or operating costs.
23 Generally, pressures of about 100 to 500 atmoæpheres are suitable, preferably about 150 to 350 atmospheres and 25 most pr~fexably 225-300 atmospheres for Arabic and 275 to 325 atmosphera~ for Robusta coffee.
27 Ths coffes material may be decaffeinated eithex ba~chwise or continuously with r~ pect ~o the movement of 29 coffe~ material into and out of th~ estractor.
Continuous processes include methods by which solid 31 coffe~ material~, which occupy a ~olume corresponding to a fractiun of ~he ~o~al e~ractor volume, are periodi-~3 cally and continuously charged and discharged from ane~txactor. These processes can be called pulse :.. ` : .
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1 3295q5 processes. A suitable process of this type is disclosed in U.S.
Patent No. 4,820,537 issued April 11, 1989. In either case, a continuous stream of extraction fluid is first passed through the extractor, then washed with water in an absorber to remove caffeine, and then recycled to the extractor. The decaffeinated coffee-material may then be passed further by means known in the art such as drying and/or roasting.
Referring to the drawing, caffeine-rich extraction fluid is fed from the extractor (not shown) into absorber 2 through inlet line 1. Caffeine-lean extraction fluid exits the absorber through outlet line 3 and is returned to the extractor. The absorber may be of any configuration known in the art to effect gas/liquid contact, such as a packed or open column. A suitable open column is disclosed in Canadian Application Serial No.
606,490, filed on even date, entitled "Caffeine Recovery from Supercritical Carbon Dioxide". The absorber preferably operates at close to the same temperature and pressure as the extractor.
In the absorber, the extraction fluid is washed with an aqueous wash solution. Caffeine-rich wash solution is removed from the absorber through outlet line 4 and is flashed to a reduced pressure, preferably about atmospheric pressure, which enables dissolved gases to be separated from the solution in vessel 5 and be recovered through vent 6. Caffeine-rich wash water containing between about 0.05% and 1% caffeine by weight is then fed through line 7 to reverse osmosis unit 8 where it is separated into a retentate stream 9 and a permeate stream 10. The retentate stream 9 contains a higher content of caffeine then the wash water, for example between about 1% and 1~

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~ 7 ~ l 329 5 ~ 5 1 15%. Caffeine can be recovered from this stream which is removed through outlet line 9 by any means known in the 3 art such as drying and then refining to produce a marketable product. The permeate stream contains 5 substantially no caffeine, preferably not more than about 0.10% by weight. It is a novel aspe~ct of the instant 7 invention that the permeate stream also comprises dissolved acidic substances which, when recycle~ bac~ to 9 the absorber 2 through line 10, produce the une~pected advantages of increasing the decaffeination rate of th~
11 coffee material by about 10-20% and improving the flavor of the decaffeinated product. The esact composition of 13 these non-caffeine dissolved substances or the mechanism by which they achieve the une~pected advantages described 15 above is not known. At least a portion of tha dissolved substances are acidic in nature. It is also known that 17 the non-caffeine dissolved substances comprise organic acids. The pH of the permeate recyc}e stream is l9 preferably less than 6, more preferably from about 3 to 5. The process can be monitored by measuring the pH or 21 the amount of dissolved substances in the permeate stream. The process can be controlled bas~d on these 23 measurements by adjusting the flow rate through the membran~ per unit membrane surface area ~th~ flu~ or the 25 membrane type can be changed. By these means, the pH can be maintained at close to a constant value. Where city 27 water is used, the ~nature~ pH of the permeate recycle stream should first be d~termined using deionized wat~r 29 to en~urQ that a desired degree of acidity i5 achieved solely because of the dissolved acidic cofee substances.
31 The reverse osmosis unit 8 can be o~ any configur-ation known in the art compri~ing module~ arranged in 33 series, in ~ar~llel or in combinations thereof. It may be opera~ed with or without recycle o~ the reten~ate but .~ . . . . .

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, - 8 ~ 1 329 S 9 5 1 is preferably operated with such recycle. Any reverse osmosis membrane which will affect the separation 3 descri~ed above can be used. One such-suita~le membrane ls *ZF 99 manufactured by Paterson Candy, Incorporated.
5 The average flu~ of solution through this particular membrane is typically about 30 gallons per square foot 7 per day. At least a portion of permeate stream is mixed with a make-up water stream from an inlet line 11 to form 9 a caffeine-lean wash solution stream by any suitable means such as feeding both the permeate stream and the 11 water stream into absorber feed tank 12. The make-up water stream may ~e either city water or deionized 13 water. While the pH can also be adjusted to maintain a desired value by the addition of a food grade acid or 15 base, it is essential that the permeate stream is acidic solely as a result o the non~cafeine substances 17 dissolved therein arriving from the use of the water to remove caffeine from the supercritical carbon dio~ide.
19 It is preferred that this ~natural" pH is less than 6 and more preferably less than 5. Preferably, 60-100~ of the 21 permeate stream is mi~ed with the make-up water stream.
The remainder may be used for backwashing the reverse 23 osmosis membranes or to hydrate fresh green beans, or both. The flow rate of the make-up water is selected 25 such that the process will run at a steady state. The flow rate of make-up water stream 11 may be between about 27 1% and 25% of the flow rate of the wash solution stream. In a first embodiment, the wash solution stream 29 i~ pumped through line 13 by high pressure pump 14 back to the absorber 2. In a second embodiment (not shown) at 31 least a portion of the permeate recycle stream ~ay ~e used to hydrate raw coffee solids prior to feedin~ the 33 raw coffee so}ids to the extractor as described above.
Where raw coffee solids are being processed, a first *Trade mark C ' ~ , ' : , .

1 portion of the permeate recycle stream may be directed to the absorber column and a second portion may be used to 3 hydrate the coff~e solids prior to e~traction.
The instant i~vention is illustrated in the following 5 examples. In E~ample 1, coffee mat.erial i~ decaffeinated by a process like that of the instalnt invention with the 7 a~ception that the wash water fed to th~ absorber consists of fresh city water rather than an acidic 9 reverse osmosis permeate as is use~ in the instant process. In E~ample 2, coffee material is decaffeinated 11 by the process of the instant in~ention.

A volume of green Colombian coffee bean~ is 15 moisturized to 43~9~ by contact with steam at 100C for about 2 hours in an agitated mi3er. The moisturized 17 coffee beans are added to a 4 inch ID s 30 foot high extraction vessal by a volume of about 0.2 cubic feet 19 being added to a blow case every 36 minutes, pressurizing the blow case to 248.8 bar, then dropping these beans 21 into the extraction vessel. Simultaneously, beans which have 96.9% of the caffeine removed are dropped from the 23 bottom of the e~traction vessel into a pressurized blow case~ These decaffeinated beans are dried to a target ~5 moisture content of 10.5~ in a fluid bed drier for about 20 minutes at 180F outlet air temperature.
27 Caffeine-lean supercritical carbon dio~ide at 248.8 bar at 100C is re~irculated countercurrently into the 29 bottom of the estraction vessel at a flow rate of 964 pound~ p~r hour and esits the top of the extractor at 31 a caffeine concentration of 115 part~ per million. This c~ffeine-rich supercritical carbon dioside is counter-33 currently contacted with fresh city water at 2~8.a bar at100C in a 4 inch ID s 40 foot hiqh absorber. The water , : ~ r ~ - lo ~ 1329595 1 removes 99~ of the caffeine from the carbon dio~ide which is then recirculated back to the estractor. This is 3 equivalent to a removal rate of 0.110 pounds of caffeine per hour.
Caffeine-rich water which is removed from the ab~orption vessel is flashed to atmospheris pressure to 7 remove dissolved gases and is sent to a caffeine concentration/refining system.
g The dried decaffeinated beans are then roasted to a 50 RC.

~XAMP~ 2 13 Green Colombian coffee beans are moisturized to 40.2%
by contact with steam at 100C for about 2 hours in an 15 agitated miser. The moisturized cofee beans are added to a 4 inch ID s 30 foot high e~traction vessel by a 17 volume o~ 0.2 cubic feet being added to a blow case every 36 minutes, pres~urizing the blow case to 247.7 bar then 19 dropping these into the estraction vess~l. Simultan-eously, beans which have 97.3% of the caffeine removed 21 are dropped from the bottom o the e~traction vessel into a pressurized blow casa. These decaffeinated beans are 23 then dried to a target moisture content of 10.5~ moisture in a fluid bed drier for approsimately 20 minutes at 25 180F outlet air temperature.
Caffeine-lean supercritical carbon dioside at ~47.7 27 bar at 100C is recirculated countercurrently into the bottom o~ the estraction vessel at a flow rate of 29 971 pou~d~ per hour and esits the top of the e~tractor at a caffeine concentration of 136 parts per million. This 31 caffeine-rich supercritical carbon dio~ide is contacted with acidic reverse osmosis parmeate solution at 33 247.7 bar at 100C in a 4 inch ID s 40 foot high absorber. The solution removes 98.3~ of the caffeine .

1 32q 5q 5 1 from the carbon dio~ide which is recirculated back to the extractor. This is equivalent to a removal rate of 3 0.130 pounds of caffeine per hour.
Caffeine-rich solution is ~irst removed ~rom the 5 absorption vessel, then flashed to atmospheric pressure to remove dissolved gases and is then sent to a caffeine 7 concentration system. This caffeine concentration system comprises a reverse osmosis unit whi.ch concentrates the 9 caffeine in the solution from about 0.148 to about 3.8%.
The reverse osmosis membrane is *ZF99 manufactured by 11 Paterson Candy, Incorporated. The reverse osmosis permeate solution has virtually no caffeine (typically 13 about 0.002%), but contains dissolved solids, including organic acids which bring the pH to less than 5. A small 15 amount of deionized make-up water is then added to the permeate solution and the combined stream is fed back to 17 the absorber. The reverse osmosis retentate solution is sent on for recovery of caffeine.
19 The dried decaffeinated beans are roasted to 50 RC
and organoleptically compared to caffeinated beans and 21 beans decaffeinat~d by the process of E~ample 1. The beans produced by the process of Esample 2 (the instant 23 process) are judged by an espert panel to taste closer to the caffeinated control than those produced by the 25 process of Example 1.
A comparison of E~ample 1 and E~ample 2 illustrates 27 the advantage~ of the present invention. Not only does the present process produce a better tasting decaf-29 Feinated product, it also increase~ the rate Qfdecaffeination. The caffeine removal rate from the 31 e~tractant (and hence from the coffee beans~ of 0.130 pounds per hour as shown in Esample 2 represents an 33 increased rate of about 18% when compared with the 0.110 pounds pe~ hour rate shown by Esample 1. Also, the *Trade mark . .
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. r~ - 12~- 132~595 1 product of E~ample 2 shows an increased lavsl of decaffeination of 97.3~ as compared with the 96.9% level 3 shown in E~ample 1.
E~amples 3 and 4 which follow compare processes which 5 use cit~ water and permeate solution, resp~ctively, to remove caffeine from a fluid extractant comprising 7 supercritical car~on dioxide. E~amples 3 and 4 dif~er from E~amples 1 and 2 ir. that the pressure in the 9 e~tractor is substantially higher.

11 EXAMPLE ~
Green Colombian coffee beans are moisturized to 41.1%
13 by contact with steam at 100C for about 2 hours in an agitated miser. The moisturized coffee beans are added 15 to a 4 in ID ~ 30 foot high e~traction vessel by adding a volume of 0.2 cubic feet every 36 minutes to a blow¢ase, 17 pressurizing the blowcasa to sy8tem pressure and dropping these beans into the extraction vessel whil~ removing an 19 equal volume of decaffeinated coffee from the bottom into a pressurized blow case. The SiZ8 of the blowcase is 21 such as to give a 6 hour residence time of the coffee in the e~tr~ctor.
23 Caffeine lean supercritical carbon dioxide with 7.1 ppm caffeine at 296.7 ~ar and 101.2C is recirculated 25 countercurrent}y into the bottom of the estraction vessel at a flow rate of 1959 lb/hr and e~its th~ top of thP
27 estractor at a ca~feine concentration of 69.3 ppm. This caffei~e rich supercritical carbon dio~ide is 29 countsrcurrently contacted with tap water at the same pressur~ an~ emperature i~ a 4 in ID s 40 foot high 31 absorber. The water remove 89.8% o~ the caffeine from the C02 which is recirculated back to the ~tractor.
33 Beans decaffeinated with this process have 95.06% of the , , ~

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~ 13 1 32q595 caffeine removed in 6 hr which corresponds to a 0.501 hr~l decaffeination rate (assuming first order rate 3 kinetics).

Another batch of Colombian green coffee beans (from 7 the same lot as those above) is moi~sturized to 41.6% in the same agitated mi~er as above. They too arP added to 9 the e~traction vessel every 36 min. to effect a 6 hr residence time in the e~tractor.
11 Caffeine-lean supercritical carbon dio~ide with 6.7 ppm caffeine at 297.5 bar and 59.9C is recirculated 13 through the estractor at a flow rate of 1960 lb/hr and esits the top of the estractor at a caffeine concen-15 tration of 78.4 ppm. The caffeine rich ~upercriticalcarbon dio~ide is countercurrently contacted with an 17 acidic reverse osmosis permeate solution at the same pressure and temperature as in tha estractor. The 19 permeate solution removes 91.4~ of ths caffeine from the carbon diozide which is recirculatea back to the 21 e~tractor. The permeate solution i8 obtained b~ a method which is described below.
23 The caffeine-rich water which leave~ the absorber is flashed to atmospheric prsssure and i~ then ent to a 25 reverse o~mocis unit which concentrates the caffeine from 0.12~ to 4.5% The reverse osmosi~ membran~ used is ZF99.
27 The water which permeates through the membrane has 0.002%
caffeine and a pH of 3.6. A small amount of tap water 29 (about 4.5 lb) is added to bring the wat~r flow rate to 163 lb/hr. This acidic solution is recycled back as feed 31 to the water absorber.
Beans dec~ffeinated in this manner have 97.1~ of the 33 caffeine removed in 6 hrs which corre~ponds to a 0.588 hr~l decaf4eination rate (assuming first order rate 35 kinetics).

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' :` :' . ' , 1 E~ample 4 e~hibits a first order decaffeination rate constant o~ 0.588 hr~l which is 17% greater than the 3 0.501 hr~l value e~hibited by E~ample 3.
E~amples 5 and 6 which follow compare processes in 5 which filtered tap water and permeate solution, respect-ively, are used to hydrate coffee beans prior to caffeine 7 e~traction. In both e~amples, carbon is used to remove caffeine from the supercritical carbon dio~ide 9 e~tractant. The permeate solution used to hydrate the beans in E~ample 6 is derived from the process of 11 E~ample 4.

Four and one half pounds o~ green Robusta beans are 15 moisturized to 34.0~ using filtered tap water with a pH
of 6.5. The moisturized beans are added to a 3-1/2 inch 17 ID x 36 inch high vessel and 1.5 lb *Calgon CPG carbon are added to an equally sized vessel.
19 The system is pressurized to 297.8 bar (4318 psig) and 245F ~118.3C). Carbon dio~ide at a flow rate of 21 300 lb/hr is recirculated with a pump through a heat e~changer to maintain temperature from the e~traction 23 vessel to the carbon adsorption vessel for 3 hrs. The syste~ is vented to atmospheric pressure, the beans are 25 removed from the e~tractor and measured to be 86.2%
decaffeinated. Assuming first order rate kinetics, the 27 decaffeination rate is 0.66 hr~l.

zg ~E~i Four and one hal pounds of Robusta green beans from 31 the same batch as Esample 5 are moiskurized to 3S.3% with reverse osmosis solutio~ produced by the process o~
33 E~ample 4. This solution has a pH of 3.6. These beans are loaded into the same e~traction vessel as E~ample 5 35 and 1.5 lb Calgon CPG carbon is added to the absorber.

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- 15 - 13295q5 1 The system is pressurized to 296.4 bar ~429~ psig~ at a temperature of 249F (120.6C~. A flow rate of 3 305 lb/hr carbon dio~ide is recirculated through the system for 3 hours. This results in 88.7~ decaffeination 5 of the beans which calculates to a 0.73 hr~l aecaffein-ation rate.
7 A co~parison of E~ample S and E~ample 6 illustrates an advantage of the second embodiment of the instant 9 invention. The second embodiment (permeate solution used for hydration) as shown in Eæample 6 e~hibits a ~irst 11 order decaffeination rate constant of 0O73 hr~} which is 10% greater than the 0.66 hr~l vaIue exhibited ~y 13 E~ample 5.

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Claims (18)

1. A process for increasing the decaffeination rate of moistened raw coffee solids comprising:
contacting moistened raw coffee solids with a fluid extractant comprising supercritical carbon dioxide to form an extractant stream rich in caffeine;
contacting said extractant stream rich in caffeine with wash water to remove a substantial portion of the caffeine therefrom to form a caffeine-containing wash water stream and a caffeine-depleted extractant stream;
recycling the caffeine depleted extractant stream to the moistened raw caffeine solids to form said extractant stream rich in caffeine;
subjecting said caffeine-containing wash water stream to reverse osmosis to form a retentate stream and a permeate stream, said retentate stream being more concentrated in caffeine than said caffeine-containing wash water stream, and said permeate stream containing substantially no caffeine and containing dissolved acidic non-caffeine coffee solids such that the pH of said permeate stream, due solely to the presence of said acidic solids, is less than 6; and utilizing at least a portion of said permeate stream to form at least a portion of said wash water stream effective to increase the extraction rate of caffeine from the moistened raw coffee.

2. A process as in claim 1, wherein said permeate stream has a pH of less than 5.

3. A process as in claim 1, wherein said dissolved acidic solids comprise organic acids.

4. A process as in claim 2, wherein the permeate stream comprises not more than about 0.010% caffeine by weight.

5. A process as in claim 1, comprising monitoring the pH
of the permeate stream and maintaining it at an acidic value.

6. A process as in claim 1, comprising utilizing at least a portion of the permeate stream to moisten said raw coffee solids prior to extracting caffeine therefrom.

7. In a process for the decaffeination of raw coffee solids comprising hydrating the raw coffee solids with an aqueous hydrating solution to a moisture content suitable for extraction of caffeine therefrom with supercritical carbon dioxide, contacting the raw coffee solids with a fluid extractant comprising supercritical carbon dioxide to extract caffeine from the coffee material, contacting the extractant with wash water to remove at least a portion of the caffeine contained therein, separating said wash water by reverse osmosis into a permeate stream containing substantially no caffeine and a retentate stream where the retentate stream is more concentrated in caffeine than said wash water, the improvement comprising utilizing at least a portion of said permeate stream to form said aqueous hydrating solution.

8. A process according to claim 7, wherein the permeate stream contains acidic dissolved non-caffeine solids and has a pH of less than 6.

9. A process according to claim 7, wherein the permeate stream has a pH of less than 5.

10. A process according to claim 8, wherein the permeate stream comprises dissolved non-caffeine organic acids.

11. A process according to claim 8, wherein the permeate stream comprises not more than about 0.010% caffeine by weight.

12. A process according to claim 8, wherein said coffee material comprises green coffee beans.

13. A process according to claim 9, comprising monitoring the pH of the permeate stream and maintaining it at an acidic value.

14. A process according to claim 1, wherein said raw coffee solids are moistened to a moisture content of 20-50%.

15. A process according to claim 14, wherein said moistened, raw coffee solids are contacted with a continuous stream of said fluid extractant in an extractor vessel through which raw coffee solids are periodically moved.

16. A process according to claim 1, wherein said permeate stream has a pH of from 3 to 5.

17. A process according to claim 1, further comprising adjusting the flow rate of reverse osmosis or changing the reverse osmosis membrane to maintain the pH of said permeate stream at said acidic value.

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