PROCESS FOR MANUFACTURING TEA PRODUCTS

TECHNICAL FIELD OF THE INVENTION
The present invention relates to a process for manufacturing a
tea product. More particularly the present invention relates to
tea products obtained by combining fermented tea juice with
unfermented tea material.
BACKGROUND TO THE INVENTION
Beverages based on the tea plant (Camellia sinensis) have been
popular throughout the world for many hundreds of years .
Traditionally such beverages are produced by infusing leaf tea in
hot water.
Most of the tea consumed in the Western World is so-called black
tea which is obtained by harvesting leaves of the plant Camellia
sinensis and withering, rolling, enzymatically oxidizing
(fermenting) , firing and sorting them. However the leaves can be
processed without the fermentation step to produce what is known
as green tea. Such tea is widely consumed in parts of the
People's Republic of China, Japan, North Africa and the Middle
East. In another variation oolong tea is prepared by partial
fermentation .
Tea leaves contain a large number of enzymes, biochemical
intermediates and structural elements normally associated with
plant growth and photosynthesis together with substances that are
responsible for the characteristics of tea itself. These include
flavanols, flavanol glycosides, polyphenolic acids, caffeine,
amino acids, mono- and polysaccharides, proteins, cellulose,
lipids, chlorophylls and volatiles.
Flavanols or more specifically flavan-3-ols tend to constitute up
to 30% of the dry weight of freshly picked tea leaves and are
known as catechins . Green tea retains most of the catechins, but
their content in black tea is greatly reduced due to both
chemical and enzymatic oxidations taking place during
fermentation to give theaflavins and thearubigins .
Catechins have been claimed to possess a variety of biological
activities including anti-tumour activity and effects on
modulating bodyshape and/or body fat.
As well as affecting tea colour, theaflavins have been recognised
as providing the "brightness" and "briskness" quality attributes
of black tea. In fact, theaflavin content is known to correlate
with the quality of black tea. Moreover, theaflavins have been
shown to have several positive health benefits. The purported
benefits include lowering blood lipid levels (e.g. cholesterol),
anti-inflammation effects and anti-tumour effects.
Tea contains many other phenols. These include gallic acid,
flavanols such as quercetin, kaemferol, myricetin, and their
glycosides; and depsides such as chlorogenic acid and paracoumarylquinic
acid. Some of these are believed to participate in
the chemical reactions that occur during fermentation.
Green tea contains many more catechins than black tea. However
despite the burgeoning health consciousness amongst many
consumers green tea is usually dismissed in Western countries as
being too pale and unpleasant to taste. Furthermore it is
typically slow to infuse and therefore not suitable for the
Western desire for convenience for the sake of quality. Further
still, some of the health benefits afforded by the theaflavins of
black tea may not be provided by the catechins of green tea. In
order to overcome some of these drawbacks, efforts have been made
to provide tea products having the advantageous properties of
both black and green tea.
WO 98/23164 (Unilever) discloses a leaf tea comprising a blend of
a first substantially fermented tea and a second substantially
unfermented tea, characterised in that the blend contains
catechins and phenols in a ratio of between 0.15 to 0.4. This
document also teaches that the ratio of gallated to non-gallated
catechins is related to bitterness and thus tea clones having a
low ratio of gallated to non-gallated catechins are preferred.
WO 2009/059927 discloses that the amount of caffeine in tea juice
expressed from dhool decreases with the degree of fermentation.
Furthermore fermented tea juice typically has a lower proportion
of gallated theaflavins compared with conventional tea extracts
and the proportion of gallated theaflavins in the juice also
varies with the degree of fermentation before expression. Thus we
have recognised that fermented tea juice can be added to
unfermented tea material to increase the black tea character
thereof whilst not imparting excessive bitterness from gallated
theaflavins and/or without bringing large amounts of caffeine.
In addition, we have now found that by combining fermented juice
with unfermented dhool before deactivating the enzymes in the
unfermented dhool, tea products with exceptional infusion
performance can be created.
TESTS AND DEFINITIONS
Tea
"Tea" for the purposes of the present invention means material
from Camellia sinensis var. sinensis and/or Camellia sinensis
var. assamica . Especially preferred is material from var.
assamica as this has a higher level of tea actives than var.
sinensis .
"Leaf tea" for the purposes of this invention means a tea product
that contains tea leaves and/or stem in an uninfused form, and
that has been dried to a moisture content of less than 30% by
weight, and usually has a water content in the range 1 to 10% by
weight (i.e. "made tea").
"Green tea" refers to substantially unfermented tea. "Black tea"
refers to substantially fermented tea. "Oolong tea" refers to
partially fermented tea.
"Fermentation" refers to the oxidative and hydrolytic process
that tea undergoes when certain endogenous enzymes and substrates
are brought together, e.g., by mechanical disruption of the cells
b y maceration of the leaves. During this process colourless
catechins in the leaves are converted to a complex mixture of
yellow and orange to dark-brown polyphenolic substances.
"Fresh tea leaves" refers to tea leaves and/or stem that have
never been dried to a water content of less than 30% by weight,
and usually have a water content in the range 60 to 90%.
"Dhool" refers to macerated fresh tea leaves.
Expressing Juice
As used herein the term "expressing juice" refers to squeezing
out juice from fresh tea leaves using physical force, as opposed
to extraction of tea solids with the use of a solvent. Thus the
term "expressing" encompasses such means as squeezing, pressing,
wringing, spinning and extruding. It is possible that a small
amount of solvent (e.g. water) is added to the leaves during the
expression step. However, in order to prevent significant
extraction of tea solids by the solvent, the moisture content of
the leaves during expression is that of fresh tea leaves as
defined hereinabove. In other words, during the expression step,
the moisture content of the fresh tea leaves is between 30 and
90% b y weight, more preferably between 60 and 90%. It is also
preferred that the fresh leaves are not contacted with nonaqueous
solvent (e.g. alcohols) prior to or during expression,
owing to the environmental & economic problems associated with
such solvents.
Catechins
As used herein the term "catechins" is used as a generic term for
catechin, gallocatechin, catechin gallate, gallocatechin gallate,
epicatechin, epigallocatechin, epicatechin gallate,
epigallocatechin gallate, and mixtures thereof.
Theaf lavins
As used herein the term "theaf lavins" is used as a generic term
for theaf lavin, theaf lavin-3-gallate, theaf lavin-3' -gallate,
theaf lavin-3, 3 '-digallate and mixtures thereof. The structures of
these compounds are well-known (see, for example, structures xixiv
in Chapter 17 of "Tea - Cultivation to consumption", K.C.
Willson and M.N. Clifford (Eds), 1992, Chapman & Hall, London,
pp. 555-601). The theaflavins are sometimes referred to using the
shorthand notation TF1-TF4 wherein TF1 is theaflavin, TF2 is
theaf lavin-3-gallate, TF3 is theaf lavin-3' -gallate and TF4 is
theaf lavin-3, 3 '-digallate (or simply "theaf lavin digallate") . The
term "gallated theaf lavins" is used as a generic term for TF2,
TF3, TF4 and mixtures thereof.
Determination of Catechins and Caffeine in Leaf Tea
The amounts of catechins and caffeine in leaf tea are determined
simultaneously by reverse-phase HPLC as follows.
Sample Preparation
1 . Grind the leaf tea using a Cyclotech™ 1093 sample mill (FOSS
Ltd, Warrington, Cheshire, UK) fitted with a 0.5 screen, until
a fine powder is achieved.
2 . Weigh accurately approximately 200 mg of the ground tea into
an extraction tube, and record the mass.
3 . Warm at least 20 ml of a methanol-water solution (70% v/v
methanol in distilled water) to 70°C.
4 . Add 5 m l of the hot methanol-water solution to the extraction
tube. Gently mix the methanol-water and tea material on a vortex
mixer; place in a water bath at 70°C for 5 minutes; mix again and
then place in a water bath at 70°C for a further 5 minutes.
5 . Gently mix the methanol-water and tea material on a vortex
mixer again and then allow too cool for a 10 minutes at an air
temperature of 20°C.
6 . Centrifuge the extraction tube at a relative centrifugal
force (RCF) of 2900 g for 10 minutes.
7 . The extraction tube should now contain a liquid supernatant
on top of a plug of tea material. Carefully decant supernatant
into a clean graduated test tube.
8 . Add 5 m l of the hot methanol-water solution to the plug in
the extraction tube. Gently mix the methanol-water and tea
material on a vortex mixer; place in a water bath at 70 °C for 5
minutes; mix again and then place in a water bath at 70°C for a
further 5 minutes .
9 . Gently mix the methanol-water and tea material on a vortex
mixer again and then allow too cool for a 10 minutes at an air
temperature of 20°C.
10. Centrifuge the extraction tube at a RCF of 2900 g for 10
minutes .
11. The extraction tube should now contain a liquid supernatant
on top of a plug of tea material. Carefully decant supernatant
into the graduated test tube containing the supernatant from step
7 .
12. Make up the pooled supernatants to 10 ml with the methanolwater
solution.
13. Add 1 ml of a solution of 2.5 mg/ml EDTA and 2.5 mg/ml
ascorbic acid in distilled water to the graduated test tube.
14. Dilute 1 part of the pooled supernatant mixture with 4 parts
(by volume) of 10% acetonitrile stabiliser solution (10% v/v
acetonitrile, 0.25 mg/ml ascorbic acid and 0.25 mg/ml EDTA in
distilled water) .
15. Decant the diluted pooled supernatant mixture into
microcentrifuge tubes and centrifuge in a bench top centrifuge at
a RCF of 14000 g for 10 minutes.
HPLC Analysis conditions
Column: Luna Phenyl hexyl 5, 250 x 4.60 mm
Flow rate: 1 ml/min
Oven temperature: 30 °C
Solvents: A : 2% acetic acid in acetonitrile
B : 2% acetic acid and 0.02 mg/ml EDTA in water
Injection volume: 10 ΐ
Gradient :
Time Solvent A Solvent B Step
0 to 10 min 5 95 Isocratic
10 to 40 min 5 - 18 95 Linear gradient
40 to 50 min 18 82 Isocratic
50 to 55 min 50 50 Wash
55 to 75 min 5 95 Isocratic
Quantification: Peak area relative to a calibration curve
constructed daily. Calibration curve is constructed from caffeine
and the concentration of catechins is calculated using the
relative response factors of the individual catechins to caffeine
(from the ISO catechin method - ISO/CD 14502-2) . Individual
caffeine standards (Sigma, Poole, Dorset, UK) are used as peak
identification markers.
Determination of Catechins and Caffeine in Juice and Beverages
The amounts of catechins and caffeine in a liquid sample are
determined simultaneously by reverse-phase HPLC as follows:
Sample Preparation
1 . 9 ml of the sample are taken and 1.12 ml of acetonitrile
added, along with 1.12 ml of a solution of 2.5 mg/ml EDTA and 2.5
mg/ml ascorbic acid in distilled water.
2 . The resulting solution is then decanted into microcentrifuge
tubes and centrifuged at a RCF of 14000 g for 10 minutes.
HPLC Analysis conditions
The HPLC analysis conditions are identical to those given above
for the leaf tea.
Determination of Theaflavins in Juice and Beverages
Reversed-phase high performance liquid chromatography is used to
quantify the amount of theaflavins in a liquid sample as follows:
Sample Preparation
1 . 2 parts by weight of acetonitrile and 1 part by weight of a
stabilising solution of 25 mg/ml EDTA and 25 mg/ml ascorbic acid
in distilled water is added to 8 parts by weight of sample.
2 . The diluted sample is then decanted into microcentrifuge tubes
and centrifuged at a relative centrifugal force (RCF) of 14000 g
for 10 minutes.
HPLC Analysis conditions
Column: Hypersil C18, 3, 100 x 4.60mm
Flow rate: 1.8 ml/min
Oven temperature: 30 °C
Solvents: A : 2% acetic acid in acetonitrile
B : 2% acetic acid in water
Injection volume: 10 ΐ
Gradient: Isocratic at 20% A and 80% B .
Quantification: The catechins are eluted at the beginning of the
chromatogram in a broad unresolved peak and the theaflavins are
eluted between 5-15 min. Detection is at 274 nm. Peak area is
measured relative to a calibration curve constructed daily. The
calibration curve is constructed from a series of solutions
containing known amounts of a tea extract previously analysed
against pure theaflavin standards.
Determination of Theaflavins in Leaf Tea
Reversed-phase high performance liquid chromatography is used to
quantify the amount of theaflavins in a solid sample as follows:
Sample Preparation
1 . Grind the tea leaf to a fine powder using a pestle and
mortar or hammer mill.
2 . Place 70% (w/v) aqueous methanol in a 70 °C water bath and
allow enough time to reach temperature.
3 . Weigh accurately 1 part by weight of sample into extraction
tube .
4 . Add 25 parts by weight of the hot aqueous methanol to the
tube, gently mix on a vortex mixer and then place the tube in the
water bath at 70 °C for 10 minutes.
5 . Remove tube from water bath and allow too cool for a few
minutes .
6 . Centrifuge tube at 2 ,500 rpm for 10 minutes using a Galaxy
16HD micro centrifuge.
7 . Carefully decant supernatant into a clean graduated test
tube .
8 . Repeat steps 4 to 6 to re-extract the residue in the
extraction tube. Combine the two supernatants and make up to 50
parts by weight by adding cold 70% aqueous methanol.
9 . Add 5 parts by weight of a stabilising solution of 25 mg/ml
EDTA and 25 mg/ml ascorbic acid in distilled water.
10. Decant into eppendorf tubes and centrifuge in the micro
centrifuge at 14,500 rpm for 10 minutes and decant supernatant
into HPLC vials.
HPLC Analysis conditions
The HPLC analysis conditions are identical to those given above
for juice and beverages.
Determination of Total Polyphenols
The total polyphenol content of a sample is determined using the
Folin-Ciocalteu method as detailed in the International Standard
published by the International Organization for Standardization
as ISO 14502-1:2005 (E) .
SUMMARY OF THE INVENTION
In a first aspect, the present invention provides a process
comprising the step of:
a ) expressing juice from a first supply of fresh tea
leaves thereby to produce first leaf residue and first tea juice;
b ) subjecting the first supply of fresh tea leaves and/or
the first tea juice to a fermentation step thereby to at least
partially ferment the first tea juice; and
c ) combining the at least partially fermented first tea
juice with substantially unfermented tea material comprising
active endogenous enzymes, thereby to form a mixture; and
d ) subjecting the mixture to an enzyme deactivation step
thereby to prevent fermentation of the substantially unfermented
tea material in the mixture.
In a second aspect, the present invention provides a leaf tea
product obtained and/or obtainable by the process. Such a product
will have black tea character, a significant proportion of
catechins in the polyphenols and display excellent infusion
performance .
DETAILED DESCRIPTION
Expression of Juice
Step (a) of the process of the invention comprises expressing
juice from a first supply of fresh tea leaves thereby to produce
tea juice, which for convenience is referred to as first tea
juice. The expression step also produces leaf residue which is
separated from the tea juice, e.g. by filtering and/or
centrifugation and which for convenience is referred to as first
leaf residue.
As used herein the terms "first" and "second" when applied to
supplies of tea leaves and/ or tea juice are merely labels for
conveniently distinguishing between different materials used in
the process. For example, where reference is made to a second
supply of tea leaves this merely means that the subject tea
leaves are not the same ones as from which juice was expressed
(i.e. they are not the "first supply").
If the amount of juice expressed is too low then it becomes
difficult to separate the juice from the leaf residue and/or
leads to an inefficient process. Thus it is preferred that the
amount of expressed juice is at least 10 ml per kg of the fresh
tea leaves, more preferably at least 25 ml, more preferably still
at least 5 0 m l and most preferably from 75 to 600 ml. When
referring to the volume of juice expressed per unit mass of tea
leaves it should be noted that the mass of the tea leaves is
expressed on an "as is" basis and not a dry weight basis. Thus
the mass includes any moisture in the leaves.
The expression step can be achieved in any convenient way so long
as it allows for separation of the tea juice from the leaf
residue and results in the required quantity of juice. The
machinery used to express the juice may, for example, include a
hydraulic press, a pneumatic press, a screw press, a belt press,
an extruder or a combination thereof.
The juice may be obtained from the fresh leaves in a single
pressing or in multiple pressings of the fresh leaves. Preferably
the juice is obtained from a single pressing as this allows for a
simple and rapid process.
In order to minimise degradation of the valuable tea compounds,
it is preferred that the expression step is performed at ambient
temperature. For example, the leaf temperature may be from 5 to
40°C, more preferably 10 to 30°C.
The time and pressure used in the expression step can be varied
to yield the required amount of juice. Typically, however, the
pressures applied to express the juice will range from 0.5 MPa
(73 psi) to 10 MPa (1450 psi) . The time over which the pressure
is applied will typically range from 1 s to 1 hour, more
preferably from 10 s to 20 minutes and most preferably from 30 s
to 5 minutes.
Prior to expression, the first supply of fresh tea leaves may
undergo a pre-treatment including, for example, a unit process
selected from maceration, withering or a combination thereof.
The first tea juice for use in the present invention is
preferably relatively low in gallated polyphenols. This is
apparent from the weight ratio of theaflavin (TF1) to theaflavin
digallate (TF4) . Preferably TF1/TF4 in the first tea juice is at
least 2.0, more preferably at least 3.0, more preferably still at
least 3.2 and most preferably from 3.5 to 5.0. Additionally or
alternatively the amount of TF1 in the total theaflavins in the
first tea juice is preferably at least 40% by weight, more
preferably at least 42% by weight and most preferably from 45 to
60% by total weight of the theaflavins in the first tea juice.
Maceration prior to expression may help in decreasing the time
and/or pressure required to express the desired quantity of
juice. Surprisingly, however, we have found that excessive damage
to the fresh tea leaves prior to expression can result in a
lowering of the weight ratio of non-gallated to gallated
polyphenols in the expressed juice. Therefore in one embodiment
the fresh leaves are not subjected to a maceration and/or freezethaw
process prior to or during the expression step.
Fermentation
Step (b) of the process comprises subjecting the first supply of
fresh tea leaves and/or the first tea juice to a fermentation
step thereby to at least partially ferment the first tea juice.
In one embodiment the first tea juice is fermented after
expression, for example by contacting the juice with an oxidizing
agent. The endogenous tea enzymes include both oxidases and
peroxidases and so the oxidizing agent is preferably oxygen,
peroxide or a combination thereof. The oxidizing agent may
suitably be oxygen gas or an oxygen-containing gas such as air.
Additionally or alternatively the oxidizing agent may be a
peroxide such as hydrogen peroxide. This embodiment is
particularly preferred if the first leaf residue is to be further
processed after expression to yield a substantially unfermented
tea product, i.e. if the first leaf residue is to be processed to
make a green tea product.
In a preferred embodiment the first supply of fresh tea leaves
are subjected to the fermentation step and the juice is expressed
from the fermented dhool. This embodiment is particularly
preferred if the first leaf residue is to be further processed
after expression to yield a fermented tea product, i.e. if the
first leaf residue is to be processed to make an oolong or black
tea product. A pre-requisite for fermentation of tea leaves is
maceration to produce dhool. Therefore it is preferred that step
(b) comprises macerating the first supply of fresh tea leaves
thereby to produce dhool .
Maceration involves wounding the leaves e.g. by rolling and/or
crushing the leaves i.e. to break down the plant tissue
structure. In black tea manufacture this has the effect of
liberating fermentable substrates and fermenting enzymes from
within the plant cells and tissue. The maceration is preferably
achieved by passing the fresh tea leaves through a cutting
machine. Thus for the purpose of the invention the first supply
of fresh tea leaves may be macerated by a maceration process
using, for example, a CTC machine, rotorvane, ball mill, grinder,
hammer mill, Lawri tea processor, Legg cutting machine, or tea
rollers as in orthodox tea processing. Combinations of these
maceration processes may also be used.
The degree of fermentation is conveniently judged b y the
proportion of oxidised catechins . In particular, one can measure
a quantity, Co, which is the amount of catechins in the fresh tea
leaves prior to maceration in percent by dry weight of the fresh
leaves. One can then measure a second quantity, CF, which is the
amount of catechins in the dhool after a given fermentation time,
tF, in percent by dry weight of the dhool. One can then use these
values to calculate the degree of fermentation, R , as the content
of catechins in the dhool at tF as a percentage of the content of
catechins in the fresh tea leaves prior to maceration on a dry
weight basis. In other words, the degree of fermentation can be
calculated as follows:
R(%) = 100CF/Co,
such that for negligible fermentation R = 100% and for complete
fermentation R = 0%.
We have found that fermenting the first supply of fresh leaves
for a time (tF) sufficient to reduce the content of catechins in
the dhool to less than 50% of the content of catechins in the
fresh tea leaves prior to maceration on a dry weight basis (i.e.
R < 50%) results in significant changes in the composition of the
juice expressed from the dhool . In particular, the greater the
degree of fermentation (lower R ) , the lower the proportion of
gallated theaflavins and/or caffeine is found in the expressed
juice. Preferably, tF is sufficient to reduce the amount of
catechins in the dhool to less than 40% (i.e. R < 40 ), more
preferably less than 30%, and most preferably from 25 to 0% of
the content of catechins in the first supply of fresh tea leaves
prior to maceration on a dry weight basis.
The exact time required to produce the desired degree of
fermentation will depend, amongst other things, on the
temperature of the dhool, the degree of maceration of the dhool
and the supply of oxygen to the dhool. Typically, however, tF is
at least 1 hour, more preferably at least 1.5 hours, more
preferably still at least 1.75 hours and most preferably from 2
to 24 hours.
The preferred fermentation temperature is from 10 to 40°C, more
preferably from 15 to 25°C. Too low a temperature results in a
slow rate of fermentation whilst too high a temperature may
result in deactivation of oxidative enzymes and/or generation of
unwanted reaction products.
Preferably the fermentation is sufficient to provide black tea
juice. In particular it is preferred that the fermentation is
sufficient to oxidise most of the catechins in the first supply
of fresh leaves. Thus, it is preferred that the at least
partially fermented first tea juice comprises polyphenols and the
polyphenols comprise catechins wherein the weight ratio of
catechins to total polyphenols is less than 0.40:1, more
preferably less than 0.30:1, more preferably still less than
0.20:1 and most preferably from 0.15:1 to 0.000:1.
Combining the Tea Juice with Unfermented Tea Material
Step (c) of the process of the invention comprises combining the
at least partially fermented first tea juice with substantially
unfermented tea material comprising active endogenous enzymes,
thereby to form a mixture.
Despite comprising active endogenous enzymes, such as oxidases,
peroxidises or a combination thereof, the substantially
unfermented tea material still comprises significant amounts of
catechins . Thus it is preferred that the substantially
unfermented tea material comprises polyphenols and the
polyphenols comprise catechins wherein the weight ratio of
catechins to total polyphenols is at least 0.40:1, more
preferably at least 0.50:1 and most preferably from 0.60 to
0.99:1.
In order to allow for greater process flexibility it is preferred
that the substantially unfermented tea material is derived from a
second supply of fresh tea leaves. Prior to combining with the
first tea juice, the second supply of fresh tea leaves may
undergo a pre-treatment including, for example, a unit process
selected from maceration, withering or a combination thereof. In
a particularly preferred embodiment the substantially unfermented
tea material is dhool produced by macerating the second supply of
fresh tea leaves. Additionally or alternatively the substantially
unfermented tea material is leaf residue remaining after
expressing tea juice from the second supply of fresh tea leaves.
The juice expressed from the second supply of fresh tea leaves
and the leaf residue thereby produced are conveniently referred
to as second tea juice and second leaf residue respectively. Such
an expression step allows for an extra product stream (i.e. the
second juice stream) to be produced whilst not significantly
affecting the quality of the substantially unfermented tea
material for combination with the first tea juice.
The first tea juice may be combined with the substantially
unfermented tea material in any amount. We have found however,
that particularly desirable tea products can be prepared when the
first tea juice is combined with the substantially unfermented
tea material such that the resulting mixture comprises soluble
tea solids derived from both the juice and tea material in
roughly equal amounts. Thus it is preferred that the combination
results in a mixture wherein the weight ratio of water-soluble
tea solids derived from the first tea juice to water-soluble tea
solids derived from the substantially unfermented tea material is
in the range 5:1 to 1:5, more preferably 2:1 to 1:2 and most
preferably 1.5:1 to 1:1.5.
The first tea juice may be combined with the substantially
unfermented tea material without any processing of the juice
following expression. Alternatively, for example, the first tea
juice may be subjected to a concentration and/or dilution step
prior to the combination step.
Enzyme Deactivation
Step (d) of the process comprises subjecting the mixture to an
enzyme deactivation step thereby to prevent fermentation of the
substantially unfermented tea material in the mixture.
A step common to manufacture of all teas is an enzyme
deactivation step. Any known treatment capable of enzyme
denaturation may be used to deactivate the fermentation enzymes
in the substantially unfermented tea material to prevent
fermentation thereof. A particularly convenient enzyme
deactivation treatment is a heat treatment. For example, the
mixture may be steamed and/or pan-fried.
In one embodiment, the process of the invention is used to
manufacture a leaf tea product with increased amounts of watersoluble
tea solids, thus allowing for increased speed of infusion
of the leaf tea product. A convenient way of manufacturing such a
product is by firing the mixture. Firing involves simultaneously
deactivating the fermentation enzymes and drying the mixture and
is, for example, conveniently performed in a fluid bed drier. The
mixture is preferably dried to a water content of less than 30%
by weight of the mixture, more preferably to a water content in
the range of 1 to 10% by weight.
In order that the catechins in the substantially unfermented tea
material undergo as little oxidation as possible the time between
the step (c) of forming the mixture and step (d) of deactivating
the enzymes should be kept to a minimum. In particular it is
preferred that the time between steps (c) and (d) is less than 30
minutes, more preferably less than 15 minutes and most preferably
from 0 to 10 minutes.
The Leaf Tea Product
The present invention provides a leaf tea product obtained and/or
obtainable by drying the mixture.
Owing to the combination of fermented tea solids (from the first
tea juice) and unfermented tea solids (from the substantially
unfermented tea material) in the product, the tea product will
comprise catechin levels intermediate between those of fermented
and unfermented tea products. In addition the leaf tea product
has excellent infusion performance, as determined by the amount
of tea solids released from the leaf tea to an infusion liquor of
freshly boiled water in 2 minutes infusion time and at a leaf to
water weight ratio of 1:100.
Processing the First Leaf Residue
In order to maximise the efficiency of the process it is
preferred that the first leaf residue is not discarded but is
further processed to produce a commercially viable product. In a
particularly preferred embodiment, the process comprises an
additional step (e) wherein the leaf residue is processed to
produce leaf tea.
The leaf residue may be processed to produce green leaf tea,
black leaf tea or oolong leaf tea. In the case of oolong leaf tea
and black leaf tea step (e) preferably comprises fermenting the
leaf residue.
The manufacturing processes of green leaf tea, black leaf tea and
oolong leaf tea are well known and suitable processes are
described, for example, in "Tea: Cultivation to Consumption",
K.C. Willson and M.N. Clifford (Eds), 1st Edn, 1992, Chapman &
Hall (London), Chapters 13 and 14.
EXAMPLES
The present invention will be further described with reference to
the following examples.
Example 1
Production of Fermented Juice
Fresh Kenyan tea leaves of Camellia sinensis var. assamica were
used. The leaves were withered to a moisture content in the range
71-72% and then cut and passed through a rotorvane followed by
one pass through a CTC machine with 8 teeth per inch (TPI) . The
dhool was then fermented for 2 hours.
The 2-hour fermented dhool was passed though a screw press (model
CP12 manufactured by the Vincent Corporation) . The feed rate was
approximately 2500 kg/hr using a screw speed of 12 rpm and a
pneumatically controlled back-pressure conical device set at 3
bar .
The pressing process resulted in the generation of two streams: a
fermented residual leaf stream and a fermented juice stream. The
fermented juice was collected and stored at ambient temperature
(~25°C) until required.
Production of Unfermented Leaf Residue
Another batch of fresh Kenyan tea leaves of Camellia sinensis
var. assamica was used. The leaves were withered to a moisture
content in the range 71-72% and then cut and passed through a
rotorvane followed by one pass through a CTC machine with 8 teeth
per inch (TPI) .
Immediately after exiting the CTC machine, the unfermented dhool
was passed though a screw press (model CP12 manufactured by the
Vincent Corporation) . The feed rate was again approximately 2500
kg/hr using a screw speed o f 12 rpm and a pneumatically
controlled back-pressure conical device set at 3 bar.
The pressing process resulted in the generation of two streams: a
substantially unfermented residual leaf stream and a
substantially unfermented juice stream.
Production of Leaf Tea
Immediately after pressing, the unfermented leaf residue was
mixed with of the stored fermented juice. The juice was added
back to the leaf residue in an amount of approximately 18 litres
o f juice t o 2 0 kg o f leaf residue. The mixture was then
immediately dried in a fluid bed drier to a moisture content of
less than 5% to yield a leaf tea according to the invention.
Infusion performance
2 g of the leaf tea was infused in 200 ml of freshly boiled
mineral water for 2 minutes and the resulting infusion compared
with infusions brewed under the same conditions but using
conventional Longjin green leaf tea or a Kenyan black leaf tea.
The catechin content of the infusion made from the leaf tea of
the present invention was similar to that of the Longjin green
infusion (0.22 mg/ml catechins for infusion of the inventive leaf
tea compared with 0.25 mg/ml for the Longjin infusion). However,
the colour of the infusion made from the leaf tea of the present
invention was close to that of the Kenyan black infusion (Hue of
77 for infusion of the inventive leaf tea compared with 74 for
the Kenyan black infusion) . Furthermore, the total amount of tea
solids delivered by the inventive leaf tea was much higher than
even that delivered by the Kenyan black leaf tea (3.05 mg solids
per m l of infusion for the inventive leaf tea compared with 2.40
mg/ml for the Kenyan black leaf tea) .
Thus the present invention allows for the provision of leaf teas
which have black tea character but which deliver high amounts of
tea solids to infusions made therefrom and which are capable of
making infusions with catechin contents close to those of green
tea infusions.
A process comprising the steps of:
a ) expressing juice from a first supply of fresh tea leaves
thereby to produce first leaf residue and first tea
juice;
b ) subjecting the first supply of fresh tea leaves and/or
the first tea juice to a fermentation step thereby to at
least partially ferment the first tea juice; and
c ) combining the at least partially fermented first tea
juice with substantially unfermented tea material
comprising active endogenous enzymes, thereby to form a
mixture; and
d ) subjecting the mixture to an enzyme deactivation step
thereby to prevent fermentation of the substantially
unfermented tea material in the mixture.
A process according to claim 1 wherein the enzyme
deactivation step comprises a heat treatment.
A process according to claim 2 wherein the enzyme
deactivation step comprises firing the mixture.
A process according to any one of claims 1 to 3 wherein the
substantially unfermented tea material is a second supply of
fresh tea leaves.
A process according to claim 4 wherein the substantially
unfermented tea material is second leaf residue remaining
after expressing second tea juice from the second supply of
fresh tea leaves.
6 . A process according to any one of the preceding claims
wherein the at least partially fermented first tea juice is
black tea juice.
7 . A process according to any one of the preceding claims
wherein the time between the step (c) of forming the mixture
and step (d) of enzyme deactivation is less than 30 minutes.
8 . A process according to claim 7 wherein the time between the
step (c) of forming the mixture and step (d) of enzyme
deactivation is less than 15 minutes.
9 . A process according to any one of the preceding claims
wherein the substantially unfermented tea material in step
(c) comprises polyphenols and the polyphenols comprise
catechins wherein the weight ratio of catechins to total
polyphenols is at least 0.40:1.
10. A process according to claim 9 wherein the weight ratio of
catechins to total polyphenols is at least 0.50:1.
11. A process according to any one of the preceding claims
wherein step (b) comprises subjecting the first tea juice to
the fermented step after the expression step (a) .
12. A process according to any one of claims 1 to 10 wherein
step (b) comprises subjecting the first supply of fresh tea
leaves to the fermentation step to produce fermented dhool
and occurs prior to expressing the juice from the fermented
dhool in step (a) .
13.A process according to any one of the preceding claims
wherein the process comprises the additional step of:
e ) processing the first leaf residue to produce leaf tea.
14.A leaf tea product obtainable by the process according
any one of claims 1 to 12.