CA1318174C - Process and apparatus for the production of decaffeinated tea - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
By the extraction with CO2 at 60 to 150 bar and 20 to 70°C, an aroma-enriched fraction is taken from the moistened black tea, said fraction being added again to already decaffeinated and dried tea. Decaffeination starts after the aroma fraction has been obtained by pumping carbon dioxide at a pressure of between 150 to 500 bar and a temperature of between 10 to 100°C through a bulk of moistened tea. The solvent charged with caffeine is passed over an adsorber or purified by reduction of density.

Description

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This invention relates to a process and a system for the production of an aromatic decaffeinated tea.
The increasing reservations against caffeine, which used to be called "theine", causes a rising demand for black tea or green tea with a reduced caffeine content. The demand for decaffeinated tea would be expected to rise substantially if the difference in taste between the treated teas and the untreated teas is hardly noticeable. The problem of the production of a high quality decaffeinated tea is a serious one, because the tea to be treated is a finished product ready for use. Further treatment should at least not deteriorate the quality.
In the past, the caffeine content was reduced by adding a solvent to previously moistened tea leaves. Subsequently, the tea was dried and either as much solvent as possible was removed, or the tea was subjected to a further aqueous extraction for the production of instant tea.
The use of methylene chloride ~dichloromethane) as solvent has never been satisfactory, because a major portion of aroma and flavour was removed together with the caffeine. According to EU~
PS 0 050 482 of 1984, reduction of the loss of aroma has been attempted by saturating the methylene chloride with the tea constituents (except caffeine) before extraction.
Owing both to potential danyers to health and legislative measures against the use of methylene chloride for the decaffeination of tea, ethyl acetate is now used as a substitute (cf. Food Chemical News, July 16, 1984, page 25A). But this solvent, too, not only fails to meet a sufficient number of the .~ "'`' ~,,_ :iL 6~ ~ $~ ~ r~ i ~ 2 expectations made for it, to be used for the production of a high quality product, but furthermore, the plants for the production of ethyl acetate must be explosion-proof.
From DE-PS 21 27 6~2 of 1975, a process is known according to which the caffeine was removed from fermented black tea by a physiologically-acceptable solvent; it was said that flavour and aroma were left completely unimpaired. For this purpose, in a first step, the aroma substances were removed by means of a dry, supercritical (with respect to pressure and temperature) gas, preferably carbon dioxide. In a second step, the caffei.ne was likewise removed from the moistened tea by supercritical, water-saturated carbon dioxide. Finally, the dried tea was re-impregnatèd with the aroma removed in the first step by charging the gas stream at a supercritical pressure with the aroma separated previously, which was liberated from the tea by demixing or li~uifying the gas. As a prominent feature, it was stressed that those constituents of the tea which were responsible for flavour and colour, e.g., tanning agents, falvines and rubigenes, were not extracted, i.e., they remained in the decaffeinated tea.
For three out of the five steps of the above-described process (extraction of the aroma, moistening, decaffeinating, drying, re-impregnation of aroma) viz. the first, third and fifth step, expensive, high pressure vessels were required;
furthermore, the tea had to be transferred to other vessels during the process. Regrettably, the ultimately desired aim was not achieved as comparative tests of taste and flavour demonstrate.

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Further, the rather minor improvement in quality achieved by the re-impregnation of the aroma did not appear to justify the high cost; therefore, a further improvement, DE-PS 26 37 197 of 1983 disclosed a selective separation of the caffei~e from the charged solvent. To achieve this end, the supercritical CO2 charged with caffeine and other accompanying substances was separated from the caffeine and the accompanying substances not by a reduction of pressure but, rather, by passing the charged CO2 over an acidic ion exchanger which selectively absorbed the caffeine. A further improvement was achieved when the extraction became selective for caffeine by the use of liquid CO2 as solvent (DE-OS 34 13 869 of 1985).
Providing an economical process was the main object of two further processes, according to which the extraction was again effected with supercritical CO2 and the adsorption of the caffeine was effected by the less selective activated carbon (DE-OS 33 39 181 of 1985 and DB-OS 34 15 844 of 1985).
The problem of impairing the aroma may be avoided by decaffeinating green tea before it is fermented into black tea (DE-OS 34 14 767 of 1985), or by decaffeinating tea which, though fermented, has not yet been dried (EU-A- 0 167 399 of January, 1986). Both methods are similar to the decaffeination of coffee, where green beans are treated and flavour and aroma develop only by the following process of roastin~. However, it is only in the countries of origin that these possibilities would be realized advantageously.

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- 3a -All the methods described so far cannot combine the three requirements (use of a harmless solvent for extraction, little impairment of taste and flavour, and dispensability of high pressure steps, i.e., low costs). In fact, such a combination of features is the object of a main aspect of the present invention.
According to a main aspect of the present invention, dealkaloidation, suitably decaffeination, is effected gently after removal of the aroma fraction in a manner known per se;
however, the tea is previously rnoistened before the aroma -satisfactory tea in a small number o~ different steps whlch, as far as taste and flavor are concerned, surprisingly surpasses all other tea samples produced according -to di~ferent methods.
In the accompanylng drawings:
Figure 1 ls a ~chema~lc dlagram lllustratlng the process steps oE the present lnventlon.
Figure 2 ls a scllamatlc diagram showing a semi-contlnuous flow ~rrangement for carrying out tl~e process 10 of the present lnventlon.
Flgure 3a S]lOWS the arrangement of Flgure 2 ln the flrs~ cycle mode wherelil aroma ls extracted from fresh tea ln a ~lrst proces~ tank and the tea from which the aroma has already been extracted ls decaf~elnated in a second 15 process tank. Ullused flow llnes are indicated ln phantom.
Figure 3b shows the ~econd cycle whereln aroma-free tea from the first cycle is dec~ffeinated ln the ~lrst process tank and fresh tea ls dearomatlzed in the second proce~s tank. Simllarly, unused flow llnes are 6hown in 20 E~l~alltom .
Figure 4 is a schematlc dlagram o~ showing the drylng and rearomatlzing steps.
Figures 5a ~nd 5b show ~wo arrang~nts for different modes oE
re-establishing the pressure oE the carbon dioxide after pressure 25 r~luction in the ara~ separation step.
Figure 6 shows an arrang~nt for an alternatel~e of carrying out the decaEfeination by means oE a washing step.

Figure 2 shows an arrange~ent for a semicontinuous operation of the process of the present invention. This arrangement comprises two interchangeable and interconnected circult systems. The primary circult 35 comprises an input pump 12 connected to high pressure line 14, joined at the other end thereof to liquified qas pump 18 which in turn i5 connected to first process tank4 2~ via high pressure line 22 containing valve 26. ~0 ~L 3 ~

First process tank 28 is connected to pressure regulator 36 via high pressure line 34 containing valve 32. Aroma separator tank 42 i~ connected to pressure regulator 36 via high pressure line 38 and to input pump 12 via high pressure line 48 which contains 5 valve 46, it is also provided with a discharge valve 44.

The second circuit comprises input pump 52 connected to ca~feine absorber 56 which in turn is 10 conne,cted to the second process tank 66 via high pressure line 58 which containssequentially circulating pump 62 and valve 64. The circuit is completed by high pressure line 68 containing valve 72 connecting the second process tank 66 to high pressure 15 line 54.

The interconnection between the circuits is provided by high pressure line 82 containing valve 84 which connects tank 28 to high pressure line 68 and high 20 pressure line 86 containing valve 88 which connects tank 28 to high pressure line 58.

Similarly, high pressure line 92 containing valve 94 connects second process tank 66 to high 25 pressure line 22 and similarly high pressure line 96 containing valve 98 connects tank 66 to high pressure line 34.

The process of the present invention is suitably 30 carried out in two alternating cycles illustrated in Figures 3a and 3b respectively.

As shown in Figure 3a, fresh tea whose moisture content has been raised to a predetermined level, is 35 charged to first process tank 28,~'Carbon dioxide at a predetermined pressure is pumped by input pump 12 into high pressure line 14 and circulated by liquiEied gas pump 18, through high pressure line 22 and open valve 26 3.~4~

to tank 2~ where i-t absorbs moisture and aroma. ~he C02 stream then passes vla line 34 and open valve 32 into aroma separation tanlc 42, the pressure whereof ls reduced by pressure regulator 36 whereby the content of tank 42 is split into three fractions, namely, a liquid 5 aqueous phase, a liquid carbon dioxide phase, and a gaseous carbon dioxide phase. The aqueous phase containing the aromatic components is removed through discharge valve 44 and utilized for rearomatiYa-tion Of the decaffeinated tea in a later step. 10 In one modification oE this ~x~ent the liquid carbon dioxidc is evapora~ed by heating by heating device 43 ancl is passed through a condenser45(shown in Figure 5a)and reintroduced into high pressure line 14. 15 ~lternatively, the evaporated carbon dioxide is passed to a compressorll8(shown in Fiyure 5b) which, after compression, again introduces the carbon dioxide into the cycle.
It will of course be clear to those in the art that the 20 important step in both of these recycling modes is the evaporation step, so that the recycled carbon dioxide does not carry any aroma material, hence, is enabled to absorb the maximum amount from the mixed batch of tea.
Contemporaneously with the foregoing cycle, the decaffeination is carried out in the second circuit. This second circuit operates under isobaric conditions. In the operation of this circuit during the first cycle, valves 72 and 64 are open and valves 84, 88, 94 and 98 are 30 closed. Thus, the carbon dioxide introduced into said second circuit through second input pump 52 will flow into the entire system to a predetermined pressure level.
Circulation pump 62 is then activated, whereby the carbon dioxide passes through tank 66 which con-tains 35 damp dearomati7ed tea. ~he carbon dioxide solvent is thus circulated into the caffeine absorber 56 which has previously been charged, either with activated -6- ~0 -- 7 ~
carbon or a suitable ion exchanger, for the removal of caffeine.
In an alternate mode shown in Fiyure 6, adsorber 56 may be a washing tank, where water is pressed into the carbon dioxide stream containing caffeine by a pump 57. The a~ueous wash is removed from the system via discharge valve 59. The water pressed in from reservoir 55 by pump 57 may contain a complexing agent, e.g. a solution of tanning agents, forminy a precipitate with caffeine. This mode of operation is more effective than washing out the caffeine by water alone.
When the predetermined amount of aroma has been removed from the first processing tank and similarly, a predetermined amount of caffeine has been removed from the second processing tank, the operation goes into the second cycle as shown in Figure 3b. In this cycle, after closing the appropriate valves, tank 66 is taken out of the system and is replaced with a similar tank 166, containing fresh tea moistened to the predetermined level. First processing tank 28 is left in place. Valves 26, 32, 64 and 72 are closed and valves 84, 88, 94 and 98 are opened. The effect of this r~arrangement is to place the second processing tank 166 into the aroma extraction circuit which will operate as described hereinabove. The now dearomatized tea in the first processing tank 28 is placed into the caffeine removal circuit which, again, is operated as previously described. When the predetermined degree of aroma and caffeine removal have been reached, valves 84 and 88 are closed, first processing tank 23 is disconnected 1 ~ ~3 - 8 ~
from the system and replaced with a similar tank 128, again containing fresh humidified tea.
It will be noted that tank 166 now contains dearomatized tea and original tanks 66 and 28 contain dearomatized and decaffeinated tea, which can be processed as described hereinbelow. The system is now ready to recommence the two-cycle operation as described hereinabove. It will be understood by those skilled in the art that tanks 66 and 28 can be replaced by fresh tanks as the progress of the operation proceeds.
The apparatus for the final step is illustrated in Figure 4 and comprises a hopper means 142 comprising a discharge means 143 issuing onto a continuously-heated belt 144. The belt is oriented to provide a discharge into a mixing tank 152 provided with mixing means 154 and discharge means 156.
In the operation of the final step, the moist dearomatized, decaffeinated tea 140 is discharged into hopper 142 from first and second process tanks 28, 66. The moist tea then passes through discharge means 143 to provide a layer 146 on belt 144 where it is dried hy the application of a predetermined amount of heat (Q) by rising the temperature of the tea to 40 to 80C
and is dischar~ed into mixing tank 152 wherein it is agitated while the blend of aromas 150 obtained from aroma tank 42, are added thereto.
The exact process conditions for carrying out the extraction of the aroma fraction and the removal of the caffeine will depend upon the nature of the tea to be processed. It is preferred that prior to the actual processing step, the conventionally-obtained ~ 3 ~
_ 9 dry tea be humidified to a point where the humidified tea contains between 25 to 50%, preferably 40% by weight (based upon wetted material) of water. In the aroma extraction step, the moist tea is subjected to carbon dioxide extraction at a pressure of between 60 to 150, suitably 90 to 110 bar at a temperature of between 20 to 70C, suitably between 50 to 60C. The extract range will depend on the tea utilized. The extraction conditions are chosen to dissolve the aroma but:to prevent any caffeine from being dissolved. The amount of carbon dioxide utilized in this step will of course vary, but it has been found that between 10 to 30 kg. of carbon dioxide/kg. of air-dried tea may be utilized.
While the extraction may be carried out in the lower end of this range, namely, between 10 and 15 kg. of carbon dioxide/kg. of tea, it is preferred to operate in the higher end of the range, namely, utilizing between 20 to 30 kg./kg. of tea.
In the decaffeination circuit, the carbon dioxide may ~e utilized in the pressure range of from about 150 to about 500 bar, suitably from 250 to 350 bar, at a temperature which may range between about 10 to 100C, most suitably from 60 to 70~C.
Again, the amount of carbon dioxide will vary. When purification is carried out ~tilizing activated carbon as the caffeine removal agent, it has been found useful to utilize between 250 to 500 kg., most suitably between 300 to 350 kg. of carbon dioxide/kg.
of air-dried tea treated. It will be understood by those skilled in the art that while it is preferred to remove the caffeine from .~

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- 9a -the carbon dioxide solvent under isobaric conditions by adsorption on carbon, separation can a]so be effected by reduction of density of the solution by means of reduction of pressure and/or rise of temperature (US Patent No. 4,167,589 patented September 19, 1979 by Vitzthum et al).
While the art dlscloses a prejudice against the stability of tea aroma in water (EU-PS 00 50 482 of 1984), column 1, lines 41 - 43), it has been found that when utilized in the process of 10 aspects of the present invention, the aqueous aroma suspension is sufficiently stable to impart a fresh flavour to the dried tea when the tea is impregnated with it, in accordance with the procedures of aspects of the present invention.
While it is preferred to rearomati~e the tea by adding the 15 aqueous extract to it as described hereinabove, an alternate mode may also be employed. ~he aroma A

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containing extract may be microancapsulated in accordance with procedures well known in the art and the thus obtained microcapsules mixed wlth the decaffeinated, dearomatized, dried tea, as described hereinabove.

In a sensorial test, samples o~ tea were decaffeinated according to the above~mentloned known processes and compared to untreated tea and to tea which had been decaffeinated according to thP invention. The tea used was "range Broken". Five tea tasters judged the 10 tea in accordance with "J. Schormuller, Handbook of Food Chemistry, Volume VI, Springer-Verlag~ 1970". The judgments were rated according to a scale of grades from l to 5; the untreated tea was attributed the highest grade of l. 15 Method of DecaffeinationGrad_ None (untreated tea) According to the invention 1.5 20 According to DE-PS 21 27 642 3 According to DE-PS 26 37 197 2 According to DE-OS 34 13 869 2 According to DE-OS 34 15 844 3 Decaffeinated with dichloromethane 5 25 Decaffeinated with ethyl acetate 5 The ratings show that tea decaffeinated according to the invention was preferred to all others. It was particularly surprising to find that there was hardly any 30 difference in taste between the untreated tea and the tea which had been treated according to the invention.

Claims (15)

1. In a process for the production of an aromatic decaffeinated tea comprising the steps of:
a) dearomatizing the tea by treatment with carbon dioxide at a pressure of from 60 to 150 bar at a temperature of from 20° to 70°C;
b) separating the carbon dioxide from the tea, reducing the pressure of the carbon dioxide and separating therefrom an aroma containing fraction;
c) decaffeinating the tea which has been dearomatized in accordance with step (a) by treating said dearomatized tea with carbon dioxide at a pressure of from 150 to 500 bar at a temperature of from 10 to 100°C in the presence of moisture;
d) separating said moist, caffeine containing carbon dioxide from the tea and releasing the carbon dioxide from said caffeine containing extract;
e) drying the decaffeinated tea; and f) restoring the aroma by adding to said de-caffeinated and dried tea the aroma fraction isolated in step (b);
the improvement comprising raising the water content of the tea to 25 to 50% by weight of said wet tea (a), whereby the aroma fraction of step (b) is obtained as an aqueous suspension/solution, and restoring the aroma by adding said aqueous aroma fraction to the decaffeinated and dried tea at ambient pressure.

2. In a process of Claim 1, carrying out the dearomatization step at a pressure of between 90 to 110 bar.

3. In a process of Claim 1, carrying out the aromatization step at a temperature of from 50° to 70°C.

4. In a process of Claim 1, the improvement comprising raising the water content of the tea to 40%
relative to the weight of said wet tea.

5. In a process of Claim 1, restoring the aroma by spraying the aqueous aroma containing fraction onto the dried tea.

6. In a process of Claim 1, the steps of microencapsulating the aqueous aroma containing fraction and adding said micro capsules to said dry tea.

7. In a process of Claim 1, the step of releasing the carbon dioxide from the caffeine containing extract by reducing the pressure thereon.

8. In a process of Claim 1, the step of removing the carbon dioxide from the caffeine containing extract by contacting said extract with a caffeine absorbing material.

9. In a process of Claim 8, utilizing activated carbon or ion exchangers as the absorbents for caffeine.

10. In a process of Claim 1, releasing the carbon dioxide from the moist caffeine containing extract by washing the caffeine out of said extract.

11. In a process of Claim 1, releasing the carbon dioxide from the moist caffeine containing extract by adding a caffeine precipitating agent to said extract.

12. A water-containing tea aroma fraction obtained by humidifying black tea to a water content of from 25 to 50% by weight, extracting the moist tea with carbon dioxide at a pressure of from 60 to 150 bar and a temperature of from 20° to 70°C and reducing the pressure.

13. A system for carrying out a two-cycle extraction of aroma and alkaloid fractions from tea leaves with carbon dioxide under pressure, comprising:
a) a first carbon dioxide input means;
b) a liquefied gas pump means connected at its input to said first carbon dioxide input means;
c) a first process tank for wet tea leaves connected at its bottom end to the output of said liquefied gas pump and at its upper end to a pressure regulator means;
d) an aroma separation tank connected to said pressure regulator means by means permitting the flow thereinto of fluid from said first process tank;
e) discharge means in the bottom of said separation tank;
f means connecting the top of said separation tank to said liquefied gas pump means;
g) a second carbon dioxide input means;
h) a caffeine extractor tank having its upper end connected to said second carbon dioxide input means, the bottom of said extractor tank being connected to a circulating pump;
i) a second process tank for holding tea having its upper end connected to the top of said caffeine extractor tank, while its lower end being connected to said circulating pump.

14. A system of Claim 13, wherein said first and said second process tanks are disconnectable and replaceable.

15. A system of Claim 13, additionally comprising means for disconnecting said first process tank from said aroma separating tank and liquefied gas pump means, and further means for connecting it to the caffeine extractor whereby the top of said first process tank is connected to the top of said caffeine extractor and the bottom of said first process tank is connected via said circulating pump to the bottom of said caffeine extractor;
and means for disconnecting said second process tank from said caffeine extractor and circulating pump means, and further means for connecting the top of said second extractor tank to said pressure regulator and the bottom of said second process tank to said aroma separation tank via said liquefied gas pump means.