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(11) Patent Number: KE 429

(21)    Application Number: KE!P/2008/000720

(22)    Filing Date: 17/08/2006

(30) Priority data: 06250152.3 12/01/2006 EP and 1130/MUM/2005 19/09/2005 IN

(86)    PCT data PCT!EP06/008164 17/08/2006 W0/2007/039018 12/04/2007
73) Owner: UNILEVER PLC of , Unilever House, Blackfriars, London Greater London EC4P 4BQ, United Kingdom

(72) Inventor: BAGARIA, Hitesh, Ghanshyam ( , 417 Reed Street, Apt 11 a, Tuscaloosa, Alabama 35401 U.S.A.); GRIFFITHS, Allen ( , Unilever R & D Colworth, Sharnbrook, Bedford Bedfordshire MK44 lLQ United Kingdom); NAIK, Vijay, Mukund ( , Hindustan Lever Ltd, Research Centre, 64 Main Road, Whitefield P.o., Balndia); PElLOW, Alan, David ( , Unilever R & D Colworth, Sharnbrook, Bedford Bedfordshire MK44 lLQ United Kingdom); SHARP, David, George ( , Unilever R & D Colworth, Sharnbrook, Bedford Bedfordshire MK44 1LQ United Kingdom); BALAKRISHNAN, Padma ( , No. 201, Rr Layout, Vijinapura, Dooravaninagar Post, Bangalore 560 016 India); COOPER, Michael, Alan ( , Unilever R & D Colworth, Sharnbrook, Bedford Bedfordshire MK44 lLQ United Kingdom) and SINGH, Gurmeet ( , Hindustan Lever Ltd, Research Centre, 64 Main Road, Whitefield P.o., Bangalolndia)

(7 4) Agent/address for correspondence:
Kaplan & Stratton Advocates,, P.O. Box40111-00100, Nairobi

(54)    Title: IMPROVED PROCESS FOR TEA MANUFACTURE

(57)    Abstract: The present invention provides a prtocess for manufacturing a leaf tea product. The process comprises the steps of providing fresh tea leaf, and drying the frsh tea leafto form the leaf tea product. The aroma is recovered whilist at! east partially drying the fresh leaf in a low-convection dryer.
 
IMPROVED  PROCESS  FOR  TEA MANOFAC'l'tlRE

Technical  Field of  the  Invention

The  invention  relates  to  a  process  for  the  manufacture  of  leaf

5    tea products. The invention is particularly directed towards a process for recovery of tea aroma during the manufacture of tea without compromising the quality of the tea thereby produced.

Background of  the Invention

10    The manufacture of leaf tea products usually involves at least one drying step.

Green tea is generally prepared by heat treating (e.g. by steaming or pan-frying) freshly picked leaves to arrest enzyme

15    action and then subjecting the leaves to a series of drying and rolling steps .

Black tea is generally prepared by subjecting freshly picked tea leaves to a series of processing conditions including withering

20    and macerating the fresh tea leaves, followed by fennentation which mainly contributes to the characteristic colour, flavour and aroma of black tea. The tea is dried at high temperature after fermentation to arrest the enzyme action and to bring down the moisture to a low level.

25

Tea aroma is one of the most important factors for determining tea quality. The aroma profile of the final tea product is detennined, to a large extent, by the processing conditions employed during manufacture. In particular, some aroma compounds

30    are generated during heat-treatment steps, such as a drying step. Thus, when seeking to improve the aroma profile of heavily-

processed    tea   products    (such   as   "instant"   tea   powders   and concentrates)    it  has  been  known   to  add  aromas   recovered   from
 
"made tea" (i.e. tea already having undergone a drying step). One such process is described in WO 2003/101215 (Goodricke, 2003), which discloses a method for the production of hot water soluble instant tea, comprising the steps of: (a) forming an extract by

5    treating black tea leaves with hard warm water at a temperature in the range of 60 to 105°C, (b) stripping the extract of its aroma volatiles by passing the tea extract through a flash evaporator under partial vacuum, wherein the residence period is

about  30  seconds  to  360  seconds,   (c)   separating  at  least  about

10    12% by wt. as insoluble tea solids from the extract by subjecting the extract to repeated clarification and polishing to obtain a clarified concentrate, (d) separating 6-10% soluble tea solids from the clarified concentrate, (e) adjusting the pH of the concentrate to neutral by adding an edible acid, (f) adding the

15    aroma volatiles obtained in step (b) to the concentrate, and (g) obtaining a substantially moisture free tea powder capable of being reconstituted in hot water to produce instant tea, substantially free of cloudiness and haze.

20    Recovery of aroma from made tea is also disclosed in US 4,880,656 (SKW Troatberg Aktiengesellschaft) and GB 1 333 362 . (HAG

Aktiengesellschaft) .

The  present  inventors  have  determined  that  the  aroma  lost  during

25    conventional drying of tea is almost twice the amount retained on the tea. Thus, we have recognised that the aroma lost during drying can be recovered without compromising the final tea quality. Furthermore, we have recognised that the aroma so-
 

produced can be used to enhance the aroma of a tea product even 3 0 though the aroma is recovered from fresh tea rather than made

tea.
 US patent 5,182,926 (Nestec S.A., 1993), discloses a process for the collection and recovery of aroma frost from gases evolved during the processing of a beverage such as coffee, tea or cocoa. The aroma gases may be those evolved at any one of several points

5    in the processing of coffee, e.g. roasting of green coffee, grinding of roasted whole beans and those evolved during infusion. However, US 5,182,926 does not disclose the recovery of aroma from fresh tea leaves.


10    US patent 3,477,854 (Affico S.A., 1969) discloses a process for the production of tea extracts (i.e . instant tea) from fresh leaf. The fresh leaf may be comminuted and at least part of the aromatics stripped before extraction. However, US 3,477,854 does not disclose a process for the manufacture of a leaf tea product.

15

UK patent GB 1 097 661 (Marshall's Tea Machinery Company Ltd) discloses condensing at least part of the vapour given off during the firing of fermenting tea leaf in a tea dryer, separating at least part of the essential oils in the condensate from the

20    remainder of the condens~te, and introducing at least part of the separated essential oils into tea which has already been fired in the same, or another, tea dryer. However, GB 1 097 661 does not disclose drying tea in a low-convection dryer.

25    Japanese patent application JP 2002/330698 (Kojima Makoto) discloses leading exhaust gas discharged from a firing dryer

through a heat exchanger to collect an aqueous solution containing flavour components . The couponents can be added to green tea beverages. Again, however, JP 2002/330698 does not
30    disclose  drying  tea  in a  low-convection  dryer.


It is thus an object of the invention to provide for an economical process for the recovery of tea aroma compounds during
 
tea manufacture while ensuring that the leaf tea produced has all the qualities of traditional made tea.

Furthermore,    we  have  found  that  use  of  fresh  tea  leaf  as  the

5    source of aroma, combined with low-convection drying produces a unique aroma.

Summary  of  the  Invention

Thus,  in  a  first  aspect,  the  present  invention  provides  a  process

10    for manufacturing a leaf tea product, the process comprising the steps of:

(a)    providing  fresh  tea  leaf;

(b)    recovering  aroma  from  the  fresh  tea  leaf;  and

(c)    drying  the  fresh  tea  leaf  to  form  the  leaf  tea  product,

15    wherein the aroma is recovered in step (b) whilst at least partially drying the fresh leaf in a low-convection dryer.

The  present  invention  allows  recovery  of  aroma  that  is  currently

lost  during  drying.  The  aroma  so  recovered  may  be  added  back  to

20    the leaf tea product to enhance or modify its flavour/aroma. Alternatively, the aroma may be used for the manufacture of instant and/or ready to drink tea products.

The use  of  fresh  tea  rather  than made  tea  provides  a  unique  aroma

25    profile, as the fresh tea has not been subjected to the firing required for producing made tea in which aroma is both lost and chemically altered.


The  aroma  is  recovered  by  at  least  partially  drying  the  fresh

30    leaf in a low-convection dryer. We have found that it is- possible to collect and concentrate the aroma in a simple and economical manner when tea is dried in low-convection dryers. This is
 

because    the  aroma  is  not  diluted  by  the   large  amount  of  gas required in conventional dryers. Furthermore, low-convection drying (especially when carried out under vacuum) typically involves lower temperatures than conventional dryers and so the aroma is not chemically altered by the drying process. Also, use

5    of low convection driers avoids the necessity to use expensive, hazardous and/or environmentally harmful agents such as carbon dioxide and/or the use of cryogenic processes.

In  a  particularly  preferred  embodiment,  the  process  may  be  said

10    to be a process for recovery of aroma during the manufacture of black tea comprising:

i    . drying fermented mass obtained from tea leaves wherein at least a part of the drying is done in a low- convection

dryer  wherein  the  amount  of  inlet  non~condensable gas  into

15    said low-convection dryer is less than 5 kg of said gas per kg of water evaporated; and

ii    . cooling the exhaust gases from said low-convection dryer to prepare a condensate rich in aroma.

20    According to another aspect of the invention there is provided a tea product, selected from a leaf tea product and a ready-to-drink tea, with enhanced aroma. The tea product comprises added tea aroma as recovered by the process of the invention.
 
Detailed Description of  the  iuvention

Tea

"Tea"    for  the  purposes  of  the  present  invention  means  material

5    from Camellia sinensis var. sinensis or Camellia sinensis var. assamica. It also includes rooibos tea obtained from Aspalathus linearis. "Tea" is also intended to include the product of blending two or more of any of these materials.


10    "Tea leaf" for the purposes of this invention means a tea product that contains one or more tea origins in an uninfused form.

"Fresh tea leaf" refers to tea leaf that has never been dried to a water content of less than 30% by weight, and usually has a

15    water  content  in  the  range  35  to  90%.


"Leaf tea product" refers to tea leaf 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").

2 0 The leaf tea product of this invention is a beverage precursor that is in a form suitable for directly preparing a beverage, e.g. by contacting the leaf tea product with an aqueous medium such as boiling water. The leaf tea products of this invention are preferably packaged. The leaf tea products may be packaged in

2 5 an infusion package (e.g. tea bag) and/ or an air tight envelope such as a foil bag. It is preferred that the leaf tea product is not decaffeinated.


The  leaf  tea  product  of  this  invention may  comprise  fermented  tea 30     (i.e.   black  tea),   semi-fermented  tea   (i.e.   oolong  tea)   and/or substantially  unfermented  tea   (i.e.   green  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 by 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.

5

By "ready-to-drink tea" is meant a beverage comprising tea solids. Ready-to-drink tea usually has a water content of at least 80%, optimally between 85 and 99.9% by weight. Ready-to-drink tea may be packaged in an air tight container such as a can

10    or bottle. The tea solids content of ready-to-drink tea is typically in the range of 0.001 to 5% by weight, preferably 0.01 to 3% by weight and most preferably 0.1 to 1% by weight.

Process  for  Manufacturing a  Leaf  Tea Product

15    The process for manufacturing a leaf tea product canprises the steps of:

(a)    providing  fresh  tea  leaf;

(b)    recovering  aroma  from  the  fresh  tea  leaf;  and

(c)    drying  the  fresh  tea  leaf  to  form  the  leaf  tea product.

20

Providing  fresh  tea  leaf

In its simplest form, the fresh tea leaf is provided in freshly plucked form, i.e. without any further processing. The fresh tea leaf preferably comprises leaf and stem material. Most preferably

25    the fresh tea leaf comprises actively growing buds, e.g. in the form of the first two or three leaves together with the unopened

bud    (so-called    "two-and-a-bud"    and/or    "three-and-a-bud"

material) .


30    The fresh tea leaf may be withered prior to step (b). The tea leaves are typically withered for about 12 to 36 hours. Withering allows certain chemical and biochemical changes to occur and also reduces the moisture content of the leaves to around 35 to 70%.
The biochemical and/or chemical changes taking place during withering may increase the yield of the volatile flavour compounds in tea.


5    The fresh tea leaf may additionally or alternatively be macerated prior to step (b). Maceration involves wounding the leaves e.g. by rolling anrl./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

10    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 fresh

tea leaves may be macerated by a maceration process using a CTC, rotorvane, ball mill or a grinder or a hammer mill or a Lawri tea

15    processor or a Legg cutting machine or rolled using tea rollers as in orthodox tea processing. Combinations of these maceration processes may also be used.


In  the  case  of  black  and  oolong  tea,  the  process  comprises  the

20    additional step of at least partially fermenting the fresh leaf. This fermentation may be performed prior to step (b) to allow the

characteristic aroma compounds of fermented tea to be recovered in step (b) . The tea may additionally or alternatively be fermented after step (b) .

25

In the case of green tea, fermentation is usually prevented by treating the fresh tea leaf (e.g. with heat) prior to step (b) in order to deactivate the endogenous fermentation enzymes. Traditionally such treatment is achieved by steaming and/or pan

30    frying  the  leaves.
 
Aroma  recovery

The  aroma  is  recovered  while  at  least  partially  drying  the  fresh

tea  leaf.

5    A low-convection dryer is used to recover the aroma. As used herein the term "low-convection dryer" refers to those types of dryers in which the amount of inlet non-condensable gas is less

than 20 kg per kg of water evaporated, preferably less than 5 kg per kg of water evaporated, more preferably less than 1.0 kg per

10 kg of water evaporated, more preferably still less than 0. 5 kg per kg of water evaporated, and most preferably between 0.001 and

0. OS kg per kg of water evaporated. The te:rm "non-condensable gas" refers to those substances with a boiling point of less than

-10°C,   more  preferably  less  than  -20°C  and  most  preferably  less

15    than -35°C at atmospheric pressure. The non-condensable gas is usually air.



The various types of dryers which are suitable for the process of the invention include but are not limited to one or more of batch

2 0 & continuous models of dryers such as vacuum dryers, rotary vacuum dryers, vacuum plate dryer, superheated steam dryers, hollow flight evaporators or jacketed screw evaporators. In most of these types of dryers, the heat is transferred by conduction from the surface of the dryers. It is preferred that the heat

25    transfer surface temperature of the low-convection dryers is in the range of 40 to 150°C, more preferably in the range of 90 to

140°C. When dried in the low-convection dryer, it is desirable that the fresh tea leaf is not heated to a temperature higher than 70°C and is preferably heated to a temperature in the range

30    of  30  to  55°C.

The drying in the low-convection dryer is preferably carried out under vacuum. The preferred ranges of vacuum are such that the
 






-  10  -

pressure is less than 0.3 atmospheres absolute, more preferably in the range of 0.01 to 0.15 atmospheres absolute, most preferably in the range o.os to 0.15 atmospheres absolute.

5 The time over which the aroma is recovered from fresh leaf tea (e.g. by drying in one or more low-convection dryers) is typically less than eight hours, more preferably less than five hours, further more preferably in the range of 5 minutes to 5 hours. The time taken for aroma recovery is dependent on the type

10    and size of dryer employed. When a batch type of dryer is used, the aroma recovery time is preferably in the range of 1 to 5 hours. When a continuous drying unit is used, sufficient aroma

could be recovered in 5 to 30 minutes of residence time of the tea in the dryer or dryers.

15

The aroma is preferably recovered as a condensate. For example, the exhaust gases from the dryer are directed to a condenser and the aroma cOttq)ounds along with the water are condensed using a condenser temperature of less than 50°C, preferably less than

20    35°C,  further more preferably  in the  range  of  -5°C  to  30°C.

The  condensate  obtained  may  be  concentrated  by  any  one  of  the

known  processes.  For  example,  the  aroma  may  be  concentrated  by

reverse  osmosis,  distillation,  cryoconcentration,  freeze  drying,

25    and/or staged/partial condensation to prepare a tea aroma concentrate. It is particularly preferred to use the process of distillation for the concentration. The tea aroma is preferably

concentrated to an aroma content of at least 25 mg/1, more preferably at least 1000 mg/1, more preferably still at least

30    5000 mg/1, and most preferably to an aroma content in the range of 10,000 mg/1 to a concentrate that is purely aroma oil (e.g. 900 g/1) .
 






-  11  -


Alternatively the condensate may be adsorbed on to one or more adsorbents selected from activated charcoal, resins, zeolites, and tea (e.g. black tea). The adsorbent may be packed in a column or fluidised bed and later desorbed to release the aroma

5    components using thermal treatment, organic solvents or super critical ~. When the exhaust gases are adsorbed on to tea itself, further desorption is not necessary.


Drying

10    The process of the invention includes the step of drying the fresh tea leaf to form the leaf tea product.

In the case of black and oolong tea, the drying step will usually involve firing. The firing involves heating and drying the

15    fermented tea to destroy the fennenting enzymes and thereby arrest fermentation.



The drying step of this invention should be such as to result in "complete drying" . By "complete drying" is meant a reduction of

20    moisture content of the tea to below 30%, more preferably between 1 and 10% and optimally to a moisture content of about 5% by weight. The drying may also lead to further chemical oxidation of tea and changes in tea aroma.


25    Drying conventionally involves exposing the tea to a blast of hot, dry air in a high-convection dryer. A large part of the aroma that is generated during this process step is lost in the exhaust gases while the tea is dried at about 120°C in such high-convection dryers. Furthermore, even if the aroma was collected

30    from such a high-convection dryer, the large volumes of gas employed would result in a very dilute aroma, requiring excessive
 

concentration.    Also,    the    high   temperatures    involved   would
 






-  12  -

chemically    alter   the   aroma,   e.g.   owing   to   the   production   of

Maillard  compounds.


Thus  according  to  the  present  invention,   the  drying  step  {c)   is 5    at  least  partially achieved  during  step  (b)  by  at  least  partially drying  the  fresh  tea  leaf  in  a  low-convection  dryer.  In  fact,   it is  possible,  as  per  the  invention  to  completely  dry  the  fresh  tea leaf  whilst   recovering  aroma.   For  example,   the  fresh  tea  leaf (e.g.  in  the  form  of  a  fermented mass)  may be  completely  dried  in

10 a low-convection dryer. Alternately the fresh tea leaf could be partially dried first whilst recovering aroma (e.g. in a low-convection dryer) and then completely dried in a conventional dryer. Another possible alternative could be that the fresh tea leaf is first partially dried in a conventional dryer and then

15    completely dried in a low-convection dryer. One could also envisage more than one such possible switchovers. Without wishing to be bound by theory, it is believed that recovering aroma at

higher  moisture   contents   produces   an   aroma   with   more   of   the "green  notes"  while  recovering  aroma  at  lower  moisture  contents 2 0    produces  more  of  the  "black  tea  notes" .    Thus  depending  on  the type   of   aroma   compounds   desired   to   be   captured,    the   aroma recovery  could  be  carried  out  over  a  selected  moisture  content

range.


2 5 By "conventional dryers" is meant those dryers utilising a large amount of air flow, i.e greater than 5 kg of air per kg of water evaporated, typically greater than 20 kg of air per kg of water . evaporated. Fluid bed dryers, and tray dryers, either batch or continuous are two such types of conventional dryers. Drying in a

3 0 fluid bed dryer is usually carried out at an air inlet temperature in the range of 90-1400C, an outlet air temperature of less than 90°C and a bed temperature in the range of 45 to 90°C.
 






-  13  -



Tea  Product  with Enhanced Aroma

The invention also provides for a tea product with enhanced aroma comprising added aroma as recovered in step {b) of the process of

5    the invention. Preferably the aroma is in the form of a concentrate. The tea product is a leaf tea product or a ready-to-drink tea. The leaf tea product may be black, green or oolong tea. The aroma concentrate is preferably added at less than 10% with respect to weight of leaf tea product. When the tea aroma

10    concentrate is added to ready-to-drink tea, it may be added at up to 500% by weight of tea solids present in ready to drink tea. It is preferred that the amount of added aroma in the ready to drink

tea is such as to provide at least 10 ppm TOC {i.e. 10 mg of total organic carbon per litre of beverage), more preferably the

15    amount of added aroma is in the range 50 to 2000 ppm, more preferably still in the range 75 to 750 ppm, and most preferably in the range 100 to 500 ppm.


It  is  preferred  that  the  tea product  is  not  decaffeinated.

20

Examples


Example  1

This    example   details   analysis   of   the   tea   aroma   condensate

25    produced by a  process  according  to  the  invention.

Tea leaves from Daverashola (in South India) were processed by the conventional steps of withering, maceration and fermentation and then dried from a moisture of 71. 6t to St in a rotary vacuum

30    dryer (RVD) where the ratio of amount of inlet air to amount of moisture evaporated was about 0.05 kg /kg. The aroma condensate was collected using a condensor operated at 5°C.
 






-  14  -


The aroma condensate was analysed by head space gas chromatography (HSGC) for which the procedure is given below.

HSGC  conditions:

s    The volatile organic compounds were analysed used a Perkin-Elrner'IM XL gas chromatograph (GC) and head space Turbomatrix'IM 40. The head space was maintained at 95°C for a cycle time of 50 minutes. The gas from the head space was injected into the GC equipped with a CP-Sil'lM 8 CB analytical column from Varian.

10    Helium gas at a pressure of 17 psi (1.2 bar) was used and the molecules were detected using an FID detector at 220°C.

The data indicated that the condensate contained compounds which were strang indicators of the desired aroma of tea. The

15    following  three  main  groups  of  tea  aroma  compounds  were  observed:

(1)    Fatty acid degradation products: 1-penten-3-ol, hexanal, cis-3-hexenol, trans-2-hexenal, heptanal, octanal, cis-3-pentenol;

(2)    Terpenes:  linalool,  geraniol,  nerol,  linalool  oxides;  and

(3)    Aromatics: phenylacetaldehyde, benzaldehyde, benzyl alcohol, 20 2-phenylethanol, and methyl salicylate.

Example  2

This example demonstrates the high quality of black tea produced by a process according to the invention.

25

Two   trials   were   conducted   using   a   process   according   to   the invention  (samples  1  and  2) .  Tea  leaves  were  withered,  macerated, fennented  and  then  dried  in  a  500  litre  rotary vacuum  dryer  (RVD) where  the  ratio  of  amount  of  inlet  air  to  amount  of  moisture 3 0    evaporated  was   less   than   0. OS   kg  of   air   per   kg   of   moisture evaporated.     The  RVD  was  operated  at  a   heat   transfer  surface temperature  of  l10°C,   and  under  vacuum  i.e.   a  pressure  of  0 .15 atmosphere  absolute.    The  tea  was  dried  from  an  initial  moisture
 






-  15  -

content of 70% to a moisture content of 50% after which the tea was dried in a conventional dryer (fluid bed dryer where the ratio of amount of inlet air to amount of moisture evaporated was 40 kg of air per kg of moisture evaporated) to a final

5    moisture  content  of  5 wt%.

Two trials were conducted using a conventional process (samples A and B). Tea leaves were withered, macerated, fermented and then

dried  in  a  fluid bed dryer where  the  ratio  of  amount  of  inlet  air

10    to amount of moisture evaporated was 40 kg of air per kg of moisture evaporated. The tea was dried from an initial moisture content of 70 wt% to a final moisture content of 5 wt%. The air inlet temperature was maintained at 120"C and the air outlet temperature ranged from 80 to 90"C.

15

The  hot  water  infusions  of  black  tea  produced  from  samples  1  and

2 and comparative samples A and B were evaluated by tea tasters for liquor quality (Q), liquor brightness (B), liquor colour (C) and liquor mouthfeel (M) an a scale of 1 to 10 and the average

20    reading is summarized in Table 1, with the higher value being more preferred.



        TABLE  1       
               
Sample    Q    B    c    M
1    4.2    5.0    5.4    4.4
               
2    4.2    5.0    5.4    4.4
               
A    4.0    4.8    4.8    4.2
               
B    4.0    5.0    5.0    4.2
               

25    The data in Table 1 indicates that tea produced by the process of the invention is of comparable quality to that produced by a conventional process. Sample 1 and sample A were analysed for volatile organic compounds using a Head-Space Gas Chromatograph
 






-  16  -


(HSGC) . The data indicated that the aroma content of the black tea produced by the process of the invention is comparable to that produced by a conventional process.

5    Example  3

This example demonstrates the use of added aroma to enhance the aroma of tea.



Tea  aroma  was  captured  in  the  RVD  during  production  of  samples  1

10    and 2 in Example 2, using a condenser operated at a cooling temperature of 20 to 30°C. About 35 kg of tea aroma was captured

from a 90 kg tea batch. In addition, the total organic carbon (TOC) of the tea aroma condensate which is an indicator of the strength of the aroma, was measured using a ~ analyser and a

15    platinum electrode was used to oxidise all the carbon compounds to carbon dioxide. The average value of TOC was found to be about 300 mg/L of tea aroma condensate.

Experiments   were   conducted   on   addition   of   the   tea   aroma 2 0    condensate  prepared  using  the  process  of  the  invention  to  black tea by  comparison  of  the  resulting product   with  control  samples.

45 panelists were given two cups of tea each. One cup contained tea infusion prepared from black tea. The second cup contained tea infusion prepared from identical black tea and to which

25    infusion, 2 ml of tea aroma condensate was added. The panelists were asked to rate the cups of tea for aroma on a 7 point scale. The scores were summarised and averaged. It was found that the

tea to which tea aroma condensate was added scored significantly higher with a score of 4.64 as against a score of 3.62 for black

3 0    tea  alone.
 





-  17  -


Example  4

This exarrq>le demonstrates the effect of various process parameters on the recovery of aroma in a process according to the invention.

5

A 90 kg batch of tea dhool with a water content of 66% by weight, after having undergone 140 minutes of fermentation was dried in a rotary vacuum dryer using a vacuum at 500 rrmHg (0.65 atm) and a surface temperature of 120°C for 91 minutes. The dhool was dried

10    to a moisture content of 45%. The condensate was collected in 5 litre batches ("cuts") and the rate of production of aroma condensate during the drying is summarised in Table 2 below.



15                TABLE    2   
                       
    Volume  of  condensate    (litres)        Drying  time  (mins)   
                       
    5            15   
                   
                       
    10            25   
                       
    15            38   
                       
        20            47   
                   
    25            60   
                   
        35            91   
                           


The total organic carbon content was measured over each of the cuts and ranged from about 680 11'9/litre to about 90 11'9/litre with
20    an  average  of  about  260 11'9/litre.

The various cuts were analysed for the presence of individual aroma compounds using HSGC, as described in Example 1 and using Solid-Phase Micro-Extraction (SPME) Head space gas

25    chromatography. The HSGC is used to measure the aroma compounds that are produced in abundant quantities while SPME-HSGC is used
 






-  18  -

to measure less abundant compounds which are nonetheless significant due to their odour potent nature.

SPME-  HSGC  Conditions:

5    In this method, volatile compounds in a sanq;>le are allowed to equilibrate with the headspace in a sealed vial and are subsequently extracted via absorption onto a polymer coated fused silica fibre. 'The analytes are thermally desorbed from the fibre through direct exposure to a heated GC injection port.

10

The    sample   was   incubated   at   65°C   for   5   minutes   before   the

headspace was sanpled for 20 minutes using the SPME fibre. This was carried out using a CombiPal'IM autosanq;>ler fitted to an Agilentm 6890 Gas Chromatograph. '!he GC was fitted with a CP-

15    wax'IM 52 CB or an equivalent BP-20 Carbowax'IM analytical col= with helium as the carrier gas. The compounds were detected using an FID detection system at 2609C.


The  data  form  the  HSGC  and  SPME  HSGC  analyses  of  the  samples  from 2 o   Example   4   indicated  the   presence   of   the   following   compounds: hexanal,   trans-2-hexenal,   1-penten-3-ol,   Z-2-penten-1-ol,   hexan-

1-ol, Z-3-hexen-1-ol, linalool, acetaldehyde, 2-methyl propanal, 2-methyl butanal, 3-methyl butanal, linalool oxide (trans), phenylacetaldehyde, and methyl salicylate. These compounds all

25    contribute  significantly  to  the  unique  aroma  of  tea.
 





-    19  -

Claims


1. A process for manufacturing a leaf tea product, the process comprising the steps of:

5    (a)   providing  fresh  tea  leaf;

(b)    recovering  aroma  from  the  fresh  tea  leaf;   and

(C)    drying  the  fresh  tea  leaf  to  form  the  leaf  tea  product,

characterised in that the aroma is recovered in step (b) whilst at least partially drying the fresh leaf in a low-

10    convection  dryer.


2. A process according to claim 1 wherein the low-convection dryer is a vacuum dryer, a rotary vacuum dryer, a batch or continuous vacuum plate dryer, or a superheated steam dryer.

15

3. A process according to claim 1 or claim 2 wherein the amount of inlet non-condensable gas into said low-convection dryer is less than 5 kg of said gas per kg of water evaporated.


20 4. A process according to claim 3 wherein said non-condensable gas is air.



5. A process according to any one of the preceding claims wherein the exhaust gases from said low-convection dryer are

25    cooled  to  prepare  a  condensate  rich  in  the  aroma.


6.    A process according to any one of the preceding claims wherein the temperature of the tea in the low-convection dryer is less than 70°C.

30

7. A process according to any one of the preceding claims wherein the at least partial drying in step (b) is carried out under vacuum.
 





-    20  -



8. A process according to claim 7wherein said vacuum corresponds to a pressure of 0.01 to 0.15 atmospheres absolute.

5

9. A process according to any one of the preceding claims wherein the exhaust gases from. the low-convection dryer are cooled at a condensor temperature of -5°C to +35°C.


10 10. A process according to any one of the preceding claims wherein the aroma is recovered as a condensate.

11.    A process according to claim 10 wherein the condensate is concentrated to prepare an aroma concentrate.
15

12.    A process according to claim JJ wherein the aroma concentrate has an aroma content in the range of 5000 mg/1 to 900 g/1.


20    13. A process according to any one of the preceding claims wherein the fresh tea leaf is withered prior to step (b).

14.    A   process   according   to   any   one   of   the   preceding   claims

wherein  the  fresh  tea  leaf  is  macerated  prior  to  step  (b).

25

15.    A process according to any one of the preceding claims wherein the fresh tea leaf is treated in order to deactivate enzymes in the fresh leaf thereby to prevent fermentation.


30    16. A process according to claim 15 wherein the tea product is green tea.
 





-    21  -


17. A process according to any one of claims 1 to 14 wherein the process comprises the additional step of at least partially fermenting the fresh tea leaf.


5 18. A process according to claim 17 wherein the at least partial fermentation is performed before step (b) .

19 . A process according to claim 18 wherein, after step (b), the process comprises the additional step of further fermenting

10    the  fresh  tea  leaf.


20.    A process according to any one of claims 17 to 19 wherein the tea product is black tea.



15    21. A process according to any one of the preceding claims wherein the process comprises the additional step of combining at least part of the aroma recovered in step (b) with the leaf tea product produced by the drying step (c).


20    22. A process according to any one of the preceding claims wherein the process comprises the additional step of packaging the leaf tea product.


23.    A  process  according  to  claim  22  wherein  the  leaf  tea  product

25    is  packaged  in  an  infusion  package.

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