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(11) Patent Number: KE 174
(45) Date of grant: 08/04/2004
(51) Int.Cl.7: A 23F 3/08, 3/10
(21) Application Number: 2001/000200
(22) Filing Date: 11/04/2001
(30) Priority data: 0010315.0 27/04/2000GB
(87)PCT details: WO01/82713 08/11/2001
(73) Owner(s): Unilever PLC, UNILIVER HOUSE, BLACKFRIARS, LONDON EC4A 1BQ, UK, United Kingdom
(72) Inventor(s): PARRY, Andrew, David; BLAIR, Ruth, Louisa; MAYAKA, Robert, Ong’Ondi and STABLER, Peter, Joseph
(74) Agent/address for correspondence: Kaplan & Stratton Advocates, P.O BOX 40111-00100, Nairobi
(54) Title: BLACK TEA MANUFACTURE
A process for manufacturing black leaf tea that looks and feels like orthodox processed tea but has the liquor characteristics of a fuller fermented CTC processed tea. The process involves withering a first supply of freshly plucked tea leaves, macerating the withered leaves, allowing the macerated withered leaves to ferment to produce macerated dhool, withering a second supply of freshly plucked tea leaves, mixing the macerated dhool obtained from the first supply of leaves with the withered leaves obtained from the second supply of leaves, rolling the mixture, allowing the rolled mixture to ferment, and drying the fermented mixture to yield black leaf tea.
BLACK TEA MANUFACTURE
The present invention relates to tea processing, or more specifically, a process for manufacturing a black leaf tea that resembles orthodox processed tea but possesses infusion characteristics more akin to CTC processed tea.
Background and prior art
Leaf tea may be prepared as green leaf tea or black leaf tea. Generally, to prepare black leaf tea fresh green leaves of the plant Camellia sinensis are withered (subjected to mild drying), comminuted, fermented (in which process enzymes in the tea leaf use atmospheric oxygen to oxidise various substrates to produce brown-coloured products) and then fired (to dry the tea leaves). Green leaf tea is not exposed to the fermentation process.
Partial fermentation may be used to produce intermediate-type teas known as "oolong" tea.
Conventional wisdom dictates that in black tea manufacture tea must be macerated in some way to liberate the fermentative enzymes and their substrates within the leaves. One can macerate tea in many ways but broadly speaking there are two main mechanized methods for doing this.
The first, called "orthodox manufacture", involves rolling pre-weighed batches of withered tea leaves prior to fermenting, firing and drying steps. So called "orthodox tea" is typically characterized by leaf particles that are aesthetically pleasing to many (resemble dried leaves rather than "granules" of CTC tea see below) but produce lighter liquors due to less extensive
In response to those needs, the applicant has developed methods for manufacturing black leaf teas that resemble orthodox processed tea but infuse like CTC processed tea.
Our international patent application WO 99/40799 discloses one method for manufacturing fast infusing whole or large leaf teas that involves subjecting whole tea leaves to a heat shock at a temperature and for a duration that is sufficient to initiate fermentation, and enabling the tea to ferment for a time and at temperature that is sufficient to achieve desired liquor properties.
Our international patent application WO 00/10401 discloses another method for manufacturing fast infusing whole or large leaf teas.
In that method whole leaf tea is impregnated tea leaves with liquid carbon dioxide within a pressure vessel, depressurizing the vessel at a rate that is sufficient to freeze the liquid carbon dioxide, applying sufficient heat to cause the frozen carbon dioxide to sublime and consequently initiate fermentation within the leaves, allowing the tea to ferment for a time that is sufficient to achieve desired liquor properties, and drying the fermented product to yield the whole leaf tea.
The present inventors have developed a third method for manufacturing black leaf teas that resemble orthodox processed tea but infuse like CTC processed tea. This method provides at least a useful alternative to those methods, and has the advantage of potentially utilizing existing tea manufacturing equipment (but in a novel fashion; although novel equipment can also be utilized to roll and/or mix the two dhool streams) invention (in place of dhool) a lower quality (less coloured liquor) product results compared to when dhool is used.
The mixture of the macerated dhool obtained from said first supply of leaves and the withered leaves obtained from said second supply of leaves is preferably rolled using a rotorvane machine.
"Tea" for the purposes of the present invention means leaf material from Camellia sinensis or Camellia assamica. It also includes rooibos tea obtained from Aspalathus linearis however that is a poor source of endogenous fermenting enzymes. "Tea" is also intended to include the product of blending two or more of any of these teas.
"Leaf tea" means tea that contains one or more tea origins in an un-infused form.
"Black leaf tea" means substantially fermented leaf tea.
For the avoidance of doubt the word 'comprises' is intended to mean including but not necessarily "consisting of" or "composed of". In other words the listed steps or options need not be exhaustive are converted to a complex mixture of yellow and orange to dark-brown substances and a large number of aromatic volatile compounds are also produced.
The macerated leaves should preferably be allowed to ferment for at least 30 minutes, more preferably at least 90 minutes, and ideally for 100 to 160 minutes. Leaving the leaves to ferment for longer than three hours can detrimentally effect the quality of the final product. It can also have cost implications. These times are dependent on the ambient temperatures, but are
comparable to conventional times for fermentation of CTC tea.
Fermentation is preferably conducted at ambient temperature, i.e. about 25 °C, although 18 °C or even 15 °C can be suitable. If desired, fermentation can be accelerated at slightly higher temperatures such as 30 to 40 °C. The use of an oxygen-enriched atmosphere in a fermentation vessel is also beneficial.
The mass of fermented leaf macerate is known as known as dhool. 20 It typically has a high moisture content, for example about 62 to 746.
If desired, the dhool can be treated with tannase (flavanol gallate esterase) to generate degallated catechins and gallic acid (which subsequently leads to the generation of high levels of theaflavins and non-gallated thearubigins during fermentation) or treated with tannase followed by hydrogen peroxide in a quantity that is sufficient for the endogenous peroxidases to oxidise gallic acid liberated by the tannase treatment. These treatments generate coloured species and enhance flavour. They are described in detail in our international patent application PCT/G1300/00359, the disclosure of which is incorporated herein by reference.
Alongside this, a second supply of freshly plucked tea leaves (so 35 called green leaf) is withered in a conventional manner, is also envisaged that alternative equipment (such as an extruder) could perform this task, performing the key actions of mixing and squeezing/rolling the dhool and withered leaves.
The rolled mixture is left to ferment. The present inventors have found that the mixture should be left to ferment for at least more than one hour, preferably more than two hours but again not more than 3 hours. A fermentation time of about 140 minutes is especially preferred.
Once again, the fermentation is preferably conducted at ambient temperature, i.e. about 25 °C, although 18 °C or even 15 °C can be suitable. If desired, fermentation can be accelerated at slightly higher temperatures such as 30 to 40 °C. The use of an oxygen-enriched atmosphere in a fermentation vessel is also beneficial.
The inventors, and expert tea tasters, were very surprised at the quality of the product produced by the process of the invention. One might have expected that as a significant proportion of this
dhool mixture has been fermented (the first or CTC portion) once before mixing,"over fermented" flavors would be generated during the fermentation of the mixture and therefore a dull liquor would result (as is known from long fermentations of conventional tea). However no such notes or flaws were observed in the product. An understanding of tea chemistry suggests that the antioxidants in the withered leaf (such as vitamin C and catechins) protect the already partially oxidized materials in the CTC dhool (i.e. the fresh catechins are preferentially oxidized to theaflavins and thearubigins, whilst those formed already are effectively stabilized. Example 2 illustrates the advantage of "co-rolling" CTC dhool and withered leaf, with the generation of greater than expected levels of theaflavins (one of the key components of black tea liquors).
An additional benefit from the process of the present invention is that smaller grades of tea tend to be generated. Those grades
Comparison of black tea processes
Black leaf tea was manufactured according by the process of the invention (Process A; Figure 1). Certain characteristics of infusions made from that tea were judged by a panel of experienced
tea tasters (using the ISO methods for tea tasting, where each attribute is scored on a scale of 0.6 to 9.4, with differences of 0.2 being judged as significant) against the characteristics of infusions made from black leaf teas that were manufactured by the same process without any addition of CTC fermented dhool (Process B) and the same process with tea dust added rather than CTC fermented dhool (Process C).
In Process A the first supply of leaf was withered to a moisture content of 72%, macerated by passing through three CTC machines and fermented for 140 minutes at 22 °C. This was mixed with a second supply of withered leaf (68% moisture content), in a ratio of 35% CTC dhool 65% withered leaf (dry weight basis). The mixture was passed through a 15" rotorvane, and then fermented for 140 minutes at 22 °C, before drying in a conventional fluid bed dryer.
Process B was the same as A but with no addition of CTC dhool (i.e. 100% withered leaf passed through the rotorvane).
Process C was the same as A but with 35% wetted primary grade CTC dust (i.e. good quality material that had been dried and sorted as in conventional tea manufacture) added in place of the CTC fermented dhool.
The results are given in Table 1 below. For A, B and C BP1 size material was used (i.e. broken leaf), compared to a fanning’s/dust 35 blend for the target CTC tea.
Comparison of black tea processes
Black leaf tea was manufactured according to the process of the invention (Process A), by the same process minus the addition offermented CTC dhool (Process B), and by a standard CTC method (Process C). Starting green leaf was from the same batch for all three manufacturing runs. Levels of theaflavins (TF) wereanalyzed throughout fermentation. Theaflavins are key components of black tea liquors, being generated during oxidative reactions in fermentation, contributing to both liquor appearance (colour and brightness) and taste.
In Process A the first supply of leaf was withered to a moisture content of 72%, macerated by passing through three CTC machines and fermented for 140 minutes at 22 °C. The fermented macerated leaves were mixed with a second supply of withered leaf (68% moisture content), in a ratio of 35% CTC dhool: 65% withered leaf (dry weight basis). The mixture was passed through a "rotorvane, and then fermented for 140 minutes at 22 °C, before drying in a conventional fluid bed dryer.
Process B was the same but with no addition of CTC dhool (i.e. 100% withered leaf passed through the rotorvane).
In Process C the leaves were withered to a moisture content of 72%, macerated by passing through three CTC machines and fermented for 140 minutes at 22 °C.
The results are shown in Figure 3.
Figure 3 shows levels of total theaflavins or TFs (i.e. theaflavin, theaflavin 3 monogallate, theaflavin 3'monogallate and 35 theaflavin digallate) through fermentation. Theaflavins
Samples of approximately 10 g fresh weight dhool were taken at various points through fermentation and quick frozen on dry ice before being freeze-dried. Freeze-dried material was ground to a fine powder in a pestle and mortar. Approximately 0.2 g ground material was extracted with 5 ml 70% (v/v) methanol for 10 minutes at 70 °C, cooled and centrifuged at 2,500 rpm for 10 minutes. The supernatant was decanted and the pellet re-extracted. The two supernatant fractions were then combined, made up to 10 ml with 70% methanol before the addition of 250 ppm EDTA and 250 ppm ascorbic acid to stabilize the sample.
High Performance Liquid Chromatography (HPLC) was performed on a DIONEX system with a AS3500 auto sampler and 0540 gradient pump. A photodiode array detector (DIONEX PO40) was used to record spectra of compounds eluting from the column on-line. Peak purity, identification and integration were carried out on DIONEX EZChrom software (version 2). Column and run details are given in Table 2 below:
TABLE 2: Column and run details
Time %A %B
20 min 15-25 85-75 linear gradient
10 min 15 85 wash/equilibrate
Solvent A:2% acetic acid in acetonitrile
Solvent B:2% acetic acid in de-ionized water
Flow rate: 2 ml/min
Column Temperature:30 °C
Detection: 274 nm
Injection volume:40 µl
Column details: HYPERSIL. 3um C18 100 x 4.6 mm - PHENOMENEX™
Analysis of glycoside derived volatiles
The experiments in Example 2 were repeated, and macerated leaf samples were taken for volatile (aroma) analysis (40.0 g of leaf was blended in 250 ml saturated CaC12 solution in order to arrest any enzyme activity during thawing. Lickens Nickersen extraction was then carried out into 25 ml of a 50:50 n-pentane / diethyl ether mixture. 5 ml of the cyclohexane internal standard (100 ppm) was added to the leaf/water mixture prior to extraction. Each sample was extracted in duplicate for 3 hours. The solvent extract was concentrated to a final volume of 1.0 ml of which 3gl was injected onto the gas chromatographic column). The results are shown in Figure 6.
Figure 6 shows the levels of glycoside derived volatiles in the leaf taken from the process of the invention (Process A), by the same process minus the addition of fermented CTC dhool (Process B) and from a standard CTC process (Process C). In addition the amount of volatiles expected from the combination of the RV only and CTC only is also shown (i.e. the amount expected in the current process of the invention if there were no interaction between the two leaf sources).
It can clearly be seen that the levels of glycoside-derived volatiles were higher in the process of the invention, than either RV only or CTC only, and therefore of the theoretical combination.
This suggested an interaction between the two leaf streams in the maceration / mixing process, possibly glycosidase from the small CTC particles acting on substrates in the withered leaf.
Following fermentation and drying the levels of volatiles in the product of the current process were found to be similar to those 35 in the CTC tea, and higher than the RV only. It was also found between CTC and RV leaf since, if there were no such interaction, it would be expected that increased gallic acid would only be present in the smaller CTC size grades. Interactions between CTC dhool and RV leaf may occur via a physical association of CTC particles with RV particles and/or the transfer of soluble gallic acid from CTC particles to RV dhool during the mixing (rotorvane) step.
Effect of fermentation time
The experiments in Example 2 were repeated, and in addition a second CTC trial was carried out, with a fermentation time of 280 min (equivalent to the "standard. 150 minutes of the CTC component of the RV + CTC process, and the subsequent fermentation of the leaf / CTC dhool mixture post-maceration). Sensory analysis was performed by a trained panel. The results revealed that significant changes were found between CTC tea fermented for 150 minutes and 280 minutes in terms of liquor appearance (increases in redness, darkness and opacity) and flavour (increases in non-desirable attributes such as fruity and jemmy). These increases in colour and flavour attributes were not seen in the RV + CTC tea, again suggesting that interactions between the two leaf types ("fresh. Withered leaf and CTC dhool) protect the key quality components generated in the. CTC dhool after the first 150 minute fermentation.
Nearest conventional equivalent to the FL and D grades would be from Argentina. A tea with a colour (C) score of 7.0 would typically have a quality (Q) score of 2.8 to 3.8.
Conventional teas typically have a Q score of 1.0 to 1.4 units lower than teas made according to the process of the present invention with the same C score.
7. A process according to any preceding claim wherein the mixture is passed through a rotorvane machine to roll it.