Process for the production of a soluble tea product

A process and apparatus for preparing soluble tea products capable of being reconstituted in hot or warm water to produce tea beverages substantially free of cloudiness and turbidity, wherein a dilute tea extract obtained from Soviet (Georgian) tea leaf is concentrated, diluted, clarified and reconcentrated. The processing steps according to this invention are generally applicable to the preparation of both hot and cold-water soluble tea beverages from any tea leaf.

BACKGROUND OF THE INVENTION 
The present invention relates generally to tea and, in particular, to a 
process for making from tea leaves a water soluble product, for example, 
an extract, concentrate or powder, which is capable of being reconstituted 
to a tea beverage substantially free of undesirable cloudiness and/or 
turbidity. 
The processing of leaf tea to form a water soluble extract, concentrate or 
powder which will reconstitute to a tea beverage is, in its general 
aspects, well known in the art. Thus for example, green or black 
(fermented) leaf tea is typically extracted with hot water to form a 
dilute extract containing soluble tea solids. The insoluble leaf material 
is discarded and the extract is then concentrated to form a concentrated 
extract which may be sold as is (for example, in frozen, refrigerated or 
otherwise preserved condition) or dried in an appropriate manner to form a 
shelf-stable powder. 
In the preparation of soluble tea products intended to be reconstituted in 
cold water and/or consumed cold, much attention has been directed to the 
elimination of the turbidity or cloudiness which often manifests in the 
reconstituted beverage. To this end, a wide variety of processes have been 
proposed to effect the elimination of the cold-water insoluble materials 
which cause such cloudiness. For example, it has been proposed to employ 
chemical or enzymatic agents to solubilize the insoluble components; to 
remove the cold-water insoluble materials or their precursors; or to 
extract the tea leaf in a manner such that the insoluble materials 
contributing to or resulting in cloudiness are not leached from the leaf. 
The preparation of soluble tea products for reconstitution and consumption 
in warm or hot water is not generally attended with the difficulties noted 
with respect to cloudiness and turbidity. Hence, with the exception of a 
preliminary clarification of the dilute extract resulting from the hot 
water extraction of tea leaf to remove extraneous undissolved solid 
portions of the tea or other extraneous materials, it has not been found 
necessary in commercial processing to conduct elaborate chemical and/or 
mechanical operations aimed at removing or repressing components which 
result in cloudiness. 
In view of the foregoing, our experience with the processing of both 
fermented and green Soviet (Georgian S.S.R.) tea to form hot or warm-water 
reconstitutable tea concentrates and powde was surprising in finding that 
application of standard processing operations (i.e., extraction, 
concentration and drying) to this starting tea leaf material resulted in 
reconstituted beverages which displayed considerable cloudiness and 
turbidity. Further investigations showed that the dilute extract obtained 
from extraction of the tea leaf, when clarified, itself showed no 
turbidity or cloudiness upon dilution with warm water to beverage 
strength. However, beverages prepared by reconstituting powders obtained 
by direct spray- or freeze-drying of this dilute, clarified extract 
displayed excessive cloudiness. The same result appeared in products 
prepared by reconstituting extracts obtained by concentrating the dilute, 
clarified extract, and it was noted in these tests that the solids which 
caused the undesirable cloudiness in the beverage were generated in situ 
during the concentration process. However, it proved in further testing to 
be impractical to physically remove the solids from the concentrated 
extract once they were formed. 
As a result of our studies it became apparent that a process other than 
those typically employed or proposed in removing from tea extracts 
insoluble or suspended particles and components contributing to cloudiness 
in the final beverage would have to be developed, since the actual 
insolubles were present, not after extraction of the tea leaf, but only 
after in situ formation during further processing of the extract obtained 
from the leaf. 
SUMMARY OF THE INVENTION 
According to a particular embodiment of the present invention, a process 
has been developed which solves the problems encountered in making soluble 
tea products from Georgian tea leaf. The process results in products 
which, when reconstituted in hot or warm water, form tea beverages 
substantially free of undesired cloudiness and turbidity. The process 
developed comprises the following steps: 
(a) contacting Georgian S.S.R. tea leaf with an extraction liquid to 
extract soluble solids from the leaf and form a dilute extract thereof; 
(b) concentrating the dilute extract to form a concentrated extract 
containing at least about 18% soluble solids by weight; 
(c) diluting the concentrated extract by addition of liquid thereto to form 
an extract containing no more than about 10% soluble solids by weight; and 
(d) clarifying the extract formed by dilution to remove insoluble 
components therefrom. 
Although the dilute clarified extract formed in the final step of the above 
process is itself useful for preparing standardstrength tea beverages 
therefrom, the clarified extract is typically concentrated and dried to 
form a substantially water-free, shelf-stable powder. Beverages prepared 
by reconstituting the powder in warm or hot water display highly 
acceptable clarity and freedom from excessive cloudiness and turbidity. 
The products are greatly improved over the unacceptable turbid, muddy 
beverages which result from processing this tea in a conventional manner. 
With reference to this particular embodiment of the invention, the Georgian 
tea leaf is extracted with a suitable extraction liquid, for example, 
water or a dilute tea extract, typically at a temperature of from about 
90.degree. C. to about 100.degree. C. in a suitable apparatus to form a 
dilute extract generally containing from about 1.5% to about 8.0% soluble 
solids by weight. The leaf is typically in comminuted form to maximize 
extraction. In the case of black or green leaf, the prior processing and 
sorting (by size) which is typically performed in tea growing areas will 
provide a suitable degree of sub-division without the need for further 
comminution for practice of the present invention. 
The dilute extract obtained may be subjected to clarification, for example, 
by filtration or centrifugation, to remove any extraneous solid materials 
from the leaf which might be present. However, as will be apparent from 
the discussion which follows, the process of the present invention, 
involving dilution and clarification performed in subsequent phases of the 
process, albeit for a different reason, makes it possible to eliminate 
this preliminary clarification. 
The dilute extract, be it clarified or that obtained directly from the 
extraction process, is then concentrated by removal of water therefrom in 
any appropriate manner, for example, in a multiple-effect evaporator, 
thin-film evaporator, falling film evaporator and the like. 
Our studies on the preparation of extracts from this Soviet tea indicated 
that the insoluble components which result in cloudiness and turbidity in 
the final, reconstituted beverages form during the concentration process 
by an, as yet, unknown mechanism. The first visible appearance of such 
components appear at a soluble solids concentration of about 12% by 
weight, with additional formation of such components increasing with 
increasing concentration. Hence, in order for the subsequent steps of 
dilution and clarification to be effective in removing a sufficient 
quantity of these insoluble components to insure an acceptable final 
beverage from the standpoint of clarity, the concentration must be 
conducted to a point where the requisite amount of these components are 
formed or generated. As a practical consideration, although concentration 
of the extract to any degree above about 12% soluble solids by weight will 
generate some insolubles and, therefore, permit their removal in 
subsequent processing, with a corresponding improvement in the clarity of 
the final beverage, concentration up to at least about 18%, and preferably 
from about 20% to 25%, soluble solids by weight permits formation, and 
subsequent removal, of the amount of insoluble components which will 
insure a commercially acceptable beverage substantially free of cloudiness 
and turbidity. 
Concentration of the dilute extract above this minimum level of 18-25% 
soluble solids by weight will generally result in a corresponding increase 
in the insolubles generated and concomitant improvement in the beverage 
made from an extract from which these components are removed. As can 
readily be appreciated, however, a practical upper limit exists where the 
degree of improvement in beverage clarity per increment of increased 
concentration becomes so slight as not to warrant the expense or 
difficulties attendant additional water removal and the transport of 
extracts of increased viscosity. Although this practical upper limit is 
somewhat arbitrary, depending as it does upon economics and subjective 
criteria of final beverage clarity, a suitable guideline has been found to 
be from about 30% to about 50% soluble solids by weight. 
The concentrated extract is then diluted with liquid to form an extract 
having a reduced concentration of soluble solids. Absent practice of this 
dilution step, removal of the insoluble components generated and present 
in the concentrated extract has not been practical. The dilution does not 
result in any significant degree of resolubilization of the formed 
insoluble components. Rather, the dilution serves, in a manner not fully 
understood, but believed to be related to viscosity and density, to 
convert the extract to an appropriate form or state from which the 
insolubles can be removed. To this end, it has been found necessary to 
dilute the concentrated extract down to a soluble solids concentration of 
at least about 10% by weight. Further dilution, for example, down to the 
range of from about 3% to about 6% soluble solids by weight in fact serves 
to further facilitate the removal of the undesired solids. Again, however, 
practical considerations dictate that the degree of this benefit at some 
point becomes overshadowed by the disadvantages resulting from the 
increased amount of liquid utilized in dilution, i.e., increased loads and 
processing times in the subsequent clarification step to remove insoluble 
solids and increased liquid removal requirements in the subsequent drying 
or concentration after solids removal. Our studies have indicated that 
dilution down to a range of concentrations of from about 5% to about 8% 
soluble solids by weight is preferable. 
The thus diluted extract is then subjected to a clarification procedure 
designed to remove substantially all of the insoluble components generated 
during concentration. The nature of these insoluble components has, in our 
experience, generally required the use of efficient solid-liquid 
separation apparatus such as a centrifuge. However, other forms of 
clarification, such as the use of filtration with filter aids, afford a 
useful degree of insolubles removal. 
The extract which has been clarified is typically processed, by 
concentration and drying, to a soluble tea powder according to known 
methods, although both the diluted clarified extract and more highly 
concentrated extracts formed therefrom are per se useful in preparing tea 
beverages, upon reconstitution in warm or hot water, substantially free of 
undesired cloudiness. 
In processing the diluted, clarified extract to form a stable powder, the 
extract is generally concentrated (although drying from the dilute extract 
is possible) in order to decrease the water removal loads on the less 
energy-efficient drying equipment. The extract is thus typically 
concentrated to a soluble solids concentration of from about 35% to about 
60% by weight and further processed to a substantially dry, shelf-stable 
powder by, for example, spray-drying or vacuum belt drying. 
The foregoing process may be augmented in a known manner by the removal and 
subsequent re-addition of desirable volatile flavor and aroma components 
which might otherwise be lost during one or more of the processing steps. 
Although specifically developed in response to problems associated with 
Georgian S.S.R. tea, the generalized processing sequence of the present 
invention is applicable to the preparation of reconstitutable tea products 
derived from any tea source. In particular, the process of the present 
invention may be practiced in the preparation of hot or warm water 
reconstitutable tea products wherever problems or difficulties arise in 
the in-process generation of insoluble components which result in 
cloudiness or turbidity in the final beverage. Such difficulties may arise 
either by reason of inherent properties and characteristics found 
throughout an entire strain or source of tea leaf or by reason of such 
properties appearing in isolated instances in normally non-troublesome 
leaf owing to atypical growth, climate, handling or processing conditions. 
In such instances, the conditions for practicing the present invention set 
forth above regarding minimums, maximums and optimums of concentration, 
dilution, etc. may, of course, vary somewhat from one leaf to another. 
The generalized process principles of the present invention are also 
applicable to the preparation of cold-water soluble (reconstitutable) tea 
products. As noted earlier, such products present unique difficulties in 
the presence of components which are soluble in warm or hot water but not 
in cool or cold water, and numerous processes have been proposed for the 
elimination of these components. In one aspect of the present invention, a 
typical cold-water soluble tea process can be augmented by the present 
process. Thus, dilute tea extract obtained by extraction of tea leaf from 
any source is cooled (for example, to about 40.degree.-50.degree. F.) and 
treated, e.g. by centrifugation, to remove from the extract materials 
which are insoluble at such temperatures. These "cold-water insolubles" 
are then treated in an appropriate manner, for example, through addition 
of enzymes such as tannase or chemical agents such as sodium hydroxide 
and/or hydrogen peroxide, to effect solubilization thereof. After a 
subsequent separation to remove any remaining insolubles, the solubilized 
solids are then reincorporated into the dilute extract from which they 
were removed and the combined extract is then concentrated, typically to a 
solids concentration of from about 20 to 60% by weight. This concentrated 
extract, be it obtained from Georgian S.S.R. or any other source tea leaf 
often is cloudy or turbid. According to the present invention, this 
concentrated extract may, therefore, be diluted, clarified, 
re-concentrated and dried to produce a cold-water soluble tea powder of 
acceptable clarity. Alternatively, either the solubilized tea solids 
stream or the original extract remaining after removal of cold-water 
insolubles may be separately treated according to this invention should it 
be apparent that the unacceptable cloudiness is solely or primarily 
contributed from only one of these sources. 
The present process may also be utilized in conjunction with cold-water 
soluble tea processes wherein chemical or enzymatic solubilizing agents 
are added to the entire body of dilute extract. After concentration, this 
extract may then be diluted, clarified, re-concentrated and dried to form 
a cold-water soluble tea powder. 
DETAILED DESCRIPTION OF THE INVENTION 
The process of the present invention is described in further detail 
hereinafter with reference to the preparation of a hot or warm water 
reconstitutable shelf-stable powder from fermented Georgian S.S.R. tea. 
Referring to the Figure, the fermented tea leaves are extracted with a 
suitable extraction liquid in extraction operation 10. The extraction is 
designed to remove soluble tea solids from the leaves and may be conducted 
in accordance with any of the well-known procedures for accomplishing this 
purpose. An example of such an extraction process is the counter-current 
contact of tea leaves and water in a series of extraction columns, wherein 
columns containing tea leaves of increasing degrees of extraction are 
contacted counter-currently with extraction liquid. Thus, for example, the 
most extracted (spent) leaves are contacted in a column with hot water and 
the dilute extract formed thereby is then passed through the next 
succeeding column, containing, for example, fresh unextracted leaves, and 
the extract therefrom then processed further in accordance with the 
process of this invention. In the next cycle, a fresh column of 
unextracted leaves is placed on stream while the previously fresh column 
becomes the spent column for admission of hot water. Such a process may, 
of course, be conducted in a continuous, semi-continuous or batch manner 
with any number of extraction stages. 
Other suitable extraction methods may also be utilized, such as single 
stage counter-current contact of water and leaves, co- or counter-current 
extraction in a screw press, and the like. 
The temperature of the water utilized in extraction is generally between 
about 90.degree. C. and 100.degree. C. for operation at atmospheric 
pressure, and preferably in the range of from about 90.degree. C. to about 
100.degree. C. Higher temperatures may, of course, be utilized in a 
pressurized extraction system. The selection of appropriate temperatures 
is, in general, a function of the interrelated considerations of 
extraction of a suitable quantity of soluble solids from the leaf and 
avoidance of excessive temperatures at which degradation of flavor, color 
and aroma components occurs, each such consideration being affected by the 
method of extraction employed. 
The dilute extract resulting from the extraction operation will typically 
contain from about 2% to about 6-8% soluble solids by weight depending 
upon particular batches of leaf, extraction conditions and extraction 
methods. 
The dilute extract (or a portion thereof) resulting from the extraction may 
optionally be subjected to fractionation operation 12 wherein volatile 
aromatic/flavor components are removed therefrom in a suitable apparatus 
and recovered by condensation. The condensed volatile fraction may then be 
concentrated for re-addition to the extract at one or more stages of the 
ensuing process, typically to the concentrated extract just prior to 
drying. 
The extract is then optionally clarified at 14 utilizing a suitable 
centrifugation or filtration method to remove extraneous objects or solid 
materials from the tea leaves. 
The dilute extract is next subjected to a concentration operation 16 
wherein water removal is effected. Apparatus typically employed for this 
process include multiple effect evaporators, thin-film evaporators, 
falling film evaporators and the like. The degree to which the extract is 
concentrated in this particular process is, as discussed earlier typically 
between about 18% to about 50% soluble solids by weight. Within these 
degrees of concentration, varying amounts of insoluble components, 
resulting in cloudiness and turbidity in this and subsequent extracts and 
beverages, are generated. 
The concentrated extract is then diluted at 18 in an appropriate mixing 
vessel. Although dilution is generally accomplished with addition of 
water, it is also possible to utilize a dilute tea extract which, because 
of its origin or treatment, will not result in the generation of insoluble 
components upon subsequent concentration of the extract diluted therewith. 
The dilution is preferably conducted in a manner to result in an extract 
having a soluble solids concentration of from about 3% to about 10% by 
weight, as earlier discussed. 
The diluted extract is then subjected to centrifugal separation or to 
filtration at 20 at conditions effective to remove from the extract 
substantially all of the insoluble particles contained therein. The 
centrifugal separation is preferred, although filtration may be utilized 
to accomplish the desired removal. 
The thus clarified extract is then concentrated at 22 in a suitable 
apparatus such as those earlier described, in order to form an extract 
suitable for drying, for example, having from about 30% to about 60% 
soluble solids by weight. This extract is then dried at 24 in a suitable 
manner (e.g., spray-dried; vacuum belt dried) to provide a substantially 
water-free, shelfstable powder which can be reconstituted to beverage 
strength. 
The tea beverages produced in accordance with this invention are 
substantially free of cloudiness and turbidity and are of acceptable 
flavor, color and aroma. 
The present invention also provides for a sequence of unit operations for 
preparing reconstitutable products from tea which comprises extraction 
means for contacting tea leaf and an extraction liquid to provide a dilute 
tea extract; means for concentrating the extract; means for diluting the 
concentrated extract; clarifying means for removing insoluble solids from 
the diluted extract; means for concentrating the diluted, clarified 
extract; and means for drying the thus concentrated extract to form a 
shelf-stable tea powder. The particular apparatus arrangement may, of 
course, be augmented by appropriate means for forming cold-water 
reconstitutable products, such as means for removing, solubilizing and 
re-incorporating cold-water insoluble materials.

The process of the present invention is illustrated by the following 
examples. 
EXAMPLE I 
Fifty-four (54) pounds of Soviet black tea leaf (Georgian S.S.R. Blended; 
mean mesh size (calculated), 34.7 (U.S. Standard Sieve); % moisture, 7.5; 
% caffeine, 2.4; % ash, 6.3) were extracted at a rate of 18 lbs/hr in a 
six (6) stage counter-current extraction unit over the course of 3 hours 
with water at an average temperature of about 95.degree. C. at a rate of 
216 lbs/hr (water:leaf ratio, approximately 12:1) to produce 548 pounds of 
extract having a solids concentration of about 3.0% by weight (extraction 
yield, 30%). 
Volatiles were recovered from this extract by flash evaporation, and the 
volatiles concentrated by distillation. 
The extract was then concentrated by evaporation. under vacuum 
(temperature, 50.degree. C.; pressure, 90 mm Hg) in a Kontro 
"Adjust-O-Film" evaporator (Model 02) for 6 hours to obtain 52 pounds of a 
concentrated extract containing about 29% soluble solids by weight. This 
hazy, turbid concentrated extract was then diluted with water (25.degree. 
C.) to a solids content of about 3.6% by weight and the diluted extract 
centrifuged at 35.degree. C. in a Centrico centrifuge (Model No. OOH-205) 
(rate, 0.6 lbs/min.) to remove insolubles. 
The thus clarified extract was then concentrated in the Kontro evaporator 
(temperature 50.degree. C.; pressure 90 mm Hg) to a concentration of about 
39% solids by weight. Concentrated volatiles were then added 
stoichiometrically to the extract and the extract spray-dried (inlet 
temperature 200.degree. C.; outlet temperature 60.degree. C.) in a Bowen 
Engineering Laboratory SprayDrier to a powder (% moisture, 6.8). When 
reconstituted to beverage strength (0.4% solids) in hot water (95.degree. 
C.), a tea beverage of excellent clarity was obtained. 
In control experiments, the same leaf tea spray-dried directly from the 
originally concentrated extract (and also from the original dilute 
extract) produced beverages of unacceptable haze and turbidity. 
In additional experiments, Soviet leaf tea was processed under identical 
conditions as above with the exception that the diluted extract was 
filtered, rather than centrifuged, using Johns-Manville 505 filter aid 
(extract temperature, approximately 35.degree. C.). After concentration 
and spray-drying, beverages of acceptable clarity could be prepared. 
EXAMPLE II 
Clarified extract containing chemically-solubilized tea solids, and an 
aroma concentrate, were obtained in the normal manner from a leaf tea 
blend (containing no Georgian S.S.R. tea) having a mean mesh size and 
moisture, caffeine and ash contents typical of those utilized in 
commercial instant tea manufacture. The clarified extract had a solids 
concentration of 6.0% by weight and was divided into three (3) 150 pound 
portions. 
The first extract portion was concentrated by evaporation under vacuum in a 
Kontro "Adjust-O-Film" evaporator (temperature, 57.degree. C.; pressure, 
125 mm Hg) to a soluble solids concentration of about 40% by weight. Aroma 
concentrate was then added to the concentrate and the mixture spray-dried 
in a Bowen Laboratory Spray-Drier (inlet temperature, 200.degree. C.; 
outlet temperature, 38.degree. C.) to produce a cold-water soluble instant 
tea powder (8.5% moisture). 
The second extract portion was cooled to about 5.degree. C. and clarified 
in a Sharples Super Centrifuge at a rate of about 3 lbs/min. The 
centrifugate was then concentrated by evaporation to a solids 
concentration of 46% by weight in the Kontro evaporator (temperature, 
57.degree. C.; pressure, 125 mm Hg). Concentrated aroma was added to the 
concentrated extract and the mixture spray-dried in the Bowen Laboratory 
Spray-Drier (inlet temperature, 200.degree. C.; outlet temperature, 
39.degree. C.) to produce a cold-water soluble instant tea powder (7.9% 
moisture). 
The third extract portion was evaporated under vacuum to a solids 
concentration of 49% by weight in the Kontro evaporator (temperature, 
58.degree. C.; pressure, 125 mm Hg). The concentrated extract was diluted 
down to a solids concentration of 5.5% by weight by the addition of water. 
The dilute extract was cooled to 5.degree. C. and clarified in the 
Sharples Super Centrifuge at a rate of about 3 lbs/min. The centrifugate 
was then evaporated under vacuum to a solids concentration of 43% by 
weight in the Kontro evaporator (temperature, 58.degree. C.; pressure, 125 
mm Hg). Concentrated aroma was added to the solids concentrate and the 
mixture spray-dried in the Bowen Laboratory Spray-Drier (inlet 
temperature, 200.degree. C.; outlet temperature, 46.degree. C.) to produce 
a cold-water soluble instant tea powder (7.0% moisture). 
When reconstituted with cold (5.degree. C.) water to beverage concentration 
(0.4% w/w), a hazy beverage of unacceptable clarity (as is on occasion 
obtained in commercial production) was produced by the instant tea powder 
from the first extract portion. A hazy beverage of marginal acceptance was 
obtained from the instant tea powder from the second portion, and a 
brilliantly clear beverage obtained from the instant tea powder from the 
third extract portion. When the clarity of the cold beverages was measured 
in a laboratory Hazemeter (Radiometer, Copenhagen, NV), the following 
values were obtained (lower values indicated clearer beverages): 
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INSTANT TEA HAZE VALUE 
POWDER ASBC FORMAZIN UNITS 
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First Portion 800+ 
Second Portion 
710 
Third Portion 330 
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