DE4400096A1 - Decaffeination of black tea - Google Patents

Abstract

Decaffeination of moistened black tea is carried out by the extn. with moist CO2 at 50-80 deg C and 150-400 bar to produce a CO2 extract loaded with caffeine and other tea substances. The extract is then washed with water in a column to selectively remove the caffeine.

Description

Because of health concerns against the physiological effect of caffeine already exists long a need for decaffeinated coffee or tea. While decaffeinated coffee one has a steady market share, the demand for decaffeinated black tea is still rising clearly.

The decaffeination is carried out in such a way that ent in the coffee beans or tea leaves caffeine dissolved by moistening with water and then by a Lö washed out. Such a solvent was z. For example, methylene chloride. Because of health concerns will be out of the group of organic solvents today only Ethyl acetate used. However, the solvents described suffer from the disadvantage, too to be less selective and the essential black tea essential flavor and To extract flavors.

A major improvement is the use of compressed gases as a solvent achieved. Especially carbon dioxide is preferred because of its higher selectivity for caffeine Properties. Also no health-threatening residues are to be expected.

The selectivity of the carbon dioxide appeared to the applicants of the first patent, which the Decaffeination of black tea with carbon dioxide is still not exhausting to be happy. In this document (DE-PS 21 27 642), a method is presented, in which dry, super-critical with respect to pressure and temperature gas, preferably carbon dioxide, the tea flavorings are removed. Then it is moistened meanwhile Tea with likewise supercritical carbon dioxide deprived of the caffeine. Finally, the ge dried tea re-impregnated the flavor removed in the first step by adding supercritical pressure charges the gas stream with the previously deposited flavor and this released by segregation or liquefaction of the gas in the tea. As a special feature is emphasized that the taste and coloring ingredients of the tea, so z. B. Gerb substances, flavins and rubies, are not co-extracted, d. H. remain in decaffeinated tea.

For three of the five steps of the process (flavor deprivation, moistening, decaffeination, Drying, flavor impregnation), namely for the first, third and fifth step expensive high-pressure vessels needed; In addition, the tea must in between in other containers  to be brought. As tastings showed, however, the achieved quality advantage justifies not the comparatively high effort.

Proposals for more cost-effective, one-step processes that are devoid of flavor extraction and reimpression can be found in the patent literature:

From DE-PS 26 37 197 is a selective separation of the caffeine from the loaded Lö known. For this purpose, the laden with caffeine and other impurities überkriti liberated from the caffeine and accompanying substances by a reduction in pressure; rather, the charged carbon dioxide flows over an acidic ion exchanger, where the caffeine is selectively adsorbed. A further improvement occurs when liquid carbon dioxide as Lö is used (DE-PS 34 13 869). Great emphasis is placed on economy put two more procedures, where again with supercritical carbon dioxide at special condition tions of pressure and temperature is extracted. The cleaning of the loaded solvent takes place by adsorption of the co-transported ingredients to activated carbon (DE-PS 33 39 181 and DE-PS 34 15 844).

That these cost-effective procedures were still not perfect, show developments in which the decaffeinated tea again flavored are (DE-PS 36 40 333, DE-PS 36 40 967 and DE-OS 38 38 952).

It has now been found that a high quality, decaffeinated black tea in one one-step process can be obtained when the separation of the caffeine from the load NEN carbon dioxide by washing with water in a countercurrent column. The height Quality of tea is not only detectable by the sensory, but is directly affected by the high Purity of the separated caffeine clearly. In contrast to the pressure reduction obtained dark green, strongly to Teearoma smelling caffeine solution is the after the The message obtained solution almost clear and has a caramel-like odor.

The washing out of caffeine from the loaded carbon dioxide is already associated with the decaffeination of coffee has been proposed:

In the basic patent AT-PS 290 962 (DE-PS 20 05 293) is a method for Entcoffeinie green coffee described in which a layer of green coffee and a layer of active coal moist carbon dioxide is passed. As an improvement, according to DE-PS 22 21 560 the Caffeine-laden carbon dioxide is passed through water where the caffeine is released. by  When the solution is saturated, it is replaced with fresh water. Out of the solution Caffeine separated and can be further processed.

According to DE-PS 29 05 078 with carbon dioxide, an aqueous coffee solution in a column decaffeinated in countercurrent. The loaded carbon dioxide is then in another Column with water, also in countercurrent, freed from caffeine and then into the extraction co lonne returned. The withdrawn from the column caffeine solution is in a known manner concentrated, z. B. evaporated.

A similar proposal is made in DE-OS 26 38 383. An optimization of Verfahrensbe conditions of the washing out to the effect that the density of herauswaschenden, laden Carbon dioxide should not exceed a value of 0.75 g / ml is presented in EP-A-10 636. Caffeine sources are coffee beans and tea, but in the examples only aqueous extracts of green coffee beans (as in DE-OS 26 38 383), of roasted coffee (as in DE-PS 29 05 078) and called by tea.

The decaffeination of green coffee beans and the subsequent cleaning of the loaded Carbon dioxide by washing in a column is also treated in EP-A-331 852. Very It is precisely disclosed that carbon dioxide in addition to caffeine other ingredients of the green coffee bean This is far from a real selectivity for caffeine. In the usual Rei The carbon dioxide reduction process, such as adsorption and pressure reduction, is the subject of this content Lost materials and then missing in the aroma of the roasted coffee. Besides, he has to kept raw caffeine be laboriously cleaned.

In two publications (Abstract Handbook, 2nd International Symposium: High Pressure Chemical Engineering, Erlangen, 1990) is also known about the washing out of the loaded Koh lendioxids reported in the decaffeination of coffee:

• Brunner et al., Extraction of xanthines from plant materials with carbon dioxide, Pages 413/414
• - Lack, E .; Seidlitz, H., Findings and experience acquired in operating industrial high pressure extraction plants with supercritical CO₂, page 477.

In the industrial area, unlike coffee, where the green beans are decaffeinated and then the roasting takes place, for the decaffeination already fermented used black tea. The product, which is ready to use, already contains all flavorings Flavorings, which in their quantity and composition in the decaffeination possible  should not be changed. According to the acknowledged prior art seems in any case, for a high-quality product in solid form, a return of the aroma to be unavoidable after decaffeination.

So there are the decaffeinated products (green coffee beans - ready tea) in their Vor treatment is very different, is a simple transfer of experience in the Decaffeination of green coffee beans on decaffeination of tea leaves is not possible Lich.

The invention is the method specified in claim 1.

It has been found that the decaffeinated tea produced according to the invention meets the requirement of a quality-conscious tea drinker. By selectively washing out the Caffeine from the dissolved in carbon dioxide mixture of caffeine and flavor and taste the solvent remains saturated with the flavorings and flavors and decreases the preferably prefers caffeine from the tea flowed through. This result is not only due to Tasting immediately evident, but can also be determined by a gas chromatograph Understand the content of some flavor components.

High-pressure processes and equipment for the extraction of natural products with compressed gases as Lö Means have been described many times. The decaffeinated, moistened tea becomes di filled directly or in use containers in a high-pressure vessel. After the container with the solvent is filled and the desired pressure is reached, is preferably a Verbin made to the solvent circuit. The solvent then flows through the bed several times in succession, preferably from bottom to top, and loads with ingredients fen. Subsequently, the loaded solvent is passed into a wash column, where, preferably example in countercurrent to the solvent, a detergent, preferably pure water out becomes. The circulation of the solvent is from a centrifugal pump, preferably under - abge see frictional losses - isobaric conditions maintained. Will changes in the desired temperatures, appropriate heat exchanger must be installed in the circle who the. Preference is given to working under isothermal conditions and the loaded carbon dioxide of at the bottom towards the wash water. The column is preferably near its Operated flooding point and the washing solution is preferably concentrated in a conventional manner and cleaned the resulting caffeine.

Preferably, a plurality of extraction containers are switched into the circuit, so that also when Filling and emptying a container of the solvent circuit can not be interrupted  got to. The per se batchwise operation with respect to the solid is characterized quasikonti ously. The extraction containers can in a known manner in parallel or in succession drive. The interconnection is then such that in each case a container for emptying and Filling can be decoupled.

Particularly advantageous effect of several containers to the effect that the concentration of dissolved ingredients in the solvent remains almost the same, d. H. the wash column works sta tionary and the loading of the washing solution can be optimally adjusted. Preferably is for washing out a packed column used with wire coils of V4A wire mesh can be filled. But it is also possible that the column is filled with other inserts or even other types of columns are used. These measures constitute a mere Optimization according to the prior art. Similarly, for each column the optima values for the volume flows of solvent and washing liquid.

The following example serves to explain the invention.

example

Experiments 1 to 5 were carried out in two differently sized plants. In the smaller one Plant were each about 200 g (air dry) filled in the extraction tank, in size each about 40 kg.

For the experiments, a ceylonese tea (fannings) with a caffeine content of 3.36 wt .-% in the dry substance and a water content of 6.7 wt .-% used. To the Entcof The tea was humidified to about 20% by weight, but the exact moisture content was not is critical. It can vary between about 12 and 50 wt .-% (DE-OS 38 17 736). Off host For reasons of economy, the water content will be kept low. The pressure in the plants was to 250 bar and the temperature adjusted to 60 ° C. As known from DE-PS 36 40 333, The extraction pressures may be 150 to 400 bar, preferably 250 to 350 bar. The Experimental results are summarized in Table I.  

Table I

test results

Explanations:

Pressure in the extraction vessel and in the separation column | 250 bar Temperature in the extraction vessel and in the separation column 60 ° C Caffeine content of the tea used 3.36% by weight Column diameter in experiments 1 to 3 70 mm Column diameter in experiments 4 and 5 200 mm

In experiments 4 and 5 was driven close to the flood point of the column, the capacity the pump used in experiments 1 to 3 was too low to close the flood point to reach.

In experiments 1, 2 and 4 only one container of tea was switched on, while on Trials 3 and 5 several containers were connected in series. From the uniform loading of the CO₂ results in the higher concentration of caffeine in the Wash solution.

The column packing consisted of V4A wire mesh towers.

From the comparison of the results obtained in the two plants can be seen that with Increasing the size of the plant necessary for the achievement of the desired residual caffeine content moderate amount of solvent (relative solvent flow rate = amount of solvent per  amount of tea or caffeine). That should be on the one hand by the height On the other hand, a better ratio of filling amount to the inner surface of the container (problem of Randgängigkeit) lie.

The most important aim of the invention is the improvement of the flavor impression of the decaffeinated Tea. These were the tea samples by tasting and analysis of some aroma components compared. By way of example, the decaffeinated teas from Experiments 3 and 5, which were a realistic production according to the invention come closest, with the starting tea as well compared with a tea (tea "A"), in which the purification of carbon dioxide from caffeine by Adsorption on activated carbon was carried out (similar to that described in DE-PS 34 15 844). For all three decaffeinated samples were in accordance with caffeine and water content, as well as the drying conditions conditions had been kept the same.

The tea samples of experiments 3 and 5 came the initial tea for leaf and color (in particular after adding milk according to the tasting rules), as well as the flavor and taste of the The starting tea is much closer than the activated carbon decaffeinated tea "A".

In addition, gas chromatograms of the tea from Trial 5, Tea "A" and Off Gangstee added. The individual peaks could not be identified but were based on the corresponding peaks of the Ausgangsstees, so that an immediate impression of the Quantity ratios arise.

A total of 44 peaks were evaluated. The comparison between the tea from trial 5 and tea "A" shows that 29 peak areas are larger, 5 are equal and 10 are smaller. Even without knowledge of the one Individual aroma components say the result (especially together with the tasting, which reflects the taste and aroma impression), that in the test tea after Entcof quantitatively more flavor components are present than in a conventional Ver drive decaffeinated tea (tea "A"). The results are summarized in Table II.  

Table II

Comparison of flavor components

Claims (10)

1. A method for decaffeination of moistened, black tea by extraction with humid carbon dioxide as a solvent at pressures of 150 to 400 bar and temperatures of 50 to 80 ° C and then separating the caffeine from the solvent laden with it, characterized in that from the loaded with caffeine and other Teeinhaltsstoffen carbon dioxide caffeine is washed out selectively with water in a column. 2. The method according to claim 1, characterized in that the decaffeination at pressures from 250 to 350 bar. 3. The method according to claim 1, characterized in that the purified from caffeine Koh Lioxided dioxide fed back to the teaspoon and a total of several times circulated. 4. The method according to claim 1, characterized in that a plurality of containers in a row or be flowed through in parallel by the CO₂, before the caffeine is washed out. 5. The method according to claim 1, characterized in that decaffeination and caffeine-off washing at the same pressures and temperatures. 6. The method according to claim 1, characterized in that for washing a filler column is used. 7. The method according to claim 1, characterized in that loaded CO₂ and wash water be conducted in countercurrent. 8. The method according to claim 1, characterized in that the loaded CO₂ from below to is headed above. 9. The method according to claim 1, characterized in that the column near its flood point is operated. 10. The method according to claim 1, characterized in that the washing out of the caffeine concentrated washing solution and purified the resulting crude caffeine becomes.