Quality improvement of Orthodox
Rotorvane type of tea through
optimization of degree of wither
Dr W S Botheju
Head, Process Technology Division
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Background
 Tea – Non alcoholic healthy beverage
 Quality and price of high grown tea – determined by
Liquor Color, Strength, brightness of Infused leaf and the
blackness of made tea
 Price and quality of tea – assessed by the tasters’ evaluation
 Quality of tea also can be assessed by chemically
(estimation of TF & TR contents) except in flavor season
 Black tea processing – withering is very important unit
operation as far as quality & cost
factors are concerned
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Background
 Most upcountry and certain Uva factories – Orthodox & RV
mix type of manufacture and the trend was to produce 30 –
40% BOP.
 Now produce higher % of small grades - several RV passes
and also due to severe rolling of the RV machine – generate
more heat as well.
 Therefore factories have deviated from the recommended
degree of wither 45% to softer wither.
 Study was carried out to determine the most suitable
degree of wither for the present style of Orthodox & RV
manufacture.
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Objectives
1. To study quality characteristics of tea with respect
to appearance and liquoring properties of tea at
different degrees of wither
2. To determine the most suitable degree of wither
having the best quality character
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Materials & Methods (Miniature scale)
 Study was conducted - two
different scales
1. Miniature
2. Commercial
 5kg of green leaves with average
about 68% good leaf standard were
plucked from St. Coombs estate.
 Bulk was divided into five fractions.
Each fraction was withered using
Environment controlling chamber up
to following degrees of wither.
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Materials & Methods (Miniature scale) contd.
Withering
 Fraction
F1
F2
F3
F4
F5
D/wither (%)
36
40
43
45
47
Degree of wither = MT x 100
WL
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Materials & Methods (Miniature scale) contd.
Rolling
Hand sieve
(2.5 mm)
Dhool extraction
Firing
Fermentation
ECM chamber
Fermented dhool
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Materials & Methods (Miniature scale) contd.
Grading & Packing
Made Tea
-----------No 12
Pekoe
-----------No 16
BOP
-----------No 24
BOPF
-----------No 30
Dust 1
-----------No 40
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Materials & Methods (Miniature scale) contd.
 Graded tea samples produced at five different
degrees of wither were analyzed for chemical quality
parameters and organoleptic assessment.
 Five replicates were conducted.
 Data were statistically analyzed.
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Results – Miniature Experiment
Degree of wither (%)
Characteristics Grade
36
40
43
45
47
LSD
(p = 0.05)
Blackness of
graded tea
BOP
BOPF
Dust 1
3.66a
3.73a
3.72ab
3.92a
4.43a
4.33a
3.72a
3.67a
3.55ab
3.85a
4.02a
3.95ab
3.68a
3.73a
3.42b
ns
ns
0.1768
Liquor color
BOP
BOPF
Dust 1
3.00b
3.10a
3.10a
3.20ab
3.40a
3.20a
3.30ab
3.50a
3.50a
3.40ab
3.60a
3.30a
3.60a
3.50a
3.40a
0.1971
ns
ns
Liquor strength BOP
BOPF
Dust 1
3.30a
3.50b
3.90a
3.60a
3.80ab
4.50a
3.50a
4.10ab
4.30a
3.60a
4.20a
4.50a
3.80a
4.10ab
4.60a
ns
0.1599
ns
Note: Results were calculated based on tasters’ score data
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Results – Miniature Experiment contd.
Degree of wither (%)
Tea
Character
Grade
36
40
43
45
47
Liquor
quality
BOP
BOPF
Dust 1
4.50a
4.40a
4.60b
5.10a
5.00a
5.40a
4.80a
4.70a
4.90ab
5.10a
4.90a
5.00ab
Overall
quality
BOP
BOPF
Dust 1
18.07a
18.47b
19.05c
19.52a
20.37a
21.03a
18.98a
19.63ab
20.22ab
19.45a 19.22a
20.32a 19.87ab
20.55ab 19.85bc
4.70a
5.10a
4.80ab
LSD
(p = 0.05)
ns
ns
0.1693
ns
0.0492
0.0120
Note: Results were calculated based on tasters’ score data
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Results – Miniature Experiment contd.
TF content - Miniature exp
1.3
1.14a
1.1
0.96ab
0.99a
43
45
0.9 ab
0.9
0.67b
0.5
TF:TR ratio - Miniature exp
47
17
13
9
43
45
17.51ab
21
16.44ab
25
Degree of wither (%)
14.09b
40
21.15a
36
16.27ab
0.7
TF : TR
TF content (%)
1.5
5
36
40
47
Degree of wither (%)
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Results – Miniature Experiment contd.
Table 1: Percentages of three main grades
Degree of wither (%)
Grade
36
40
43
45
47
BOP
21
21
23
20
23
BOPF
40
42
39
39
38
Dust 1
30
25
27
25
26
 No considerable variation of grade % for five different
degrees of wither
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Conclusion – Miniature experiment
 Based on the above results it can be concluded that
tea produced at 36% and 47% degrees of wither
were in poor quality for three different grades.
 Therefore commercial scale experiment was
designed by omitting these two extreme degrees of
wither.
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Commercial experiment
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Materials & Methods
 Three withering troughs (58’ x 6’) were selected to study
the commercial scale experiment.
 800kg GL were loaded to each trough. For different trials
leaf standard was varied 55 – 60%.
 Each trough was withered to achieve the following
degrees of wither by intermittent checking of moisture
using MW – oven.
T1 = 40%;
T2 = 43%;
T3 = 45%
 First batch of each trough was manufactured according to
Orthodox & RV mix type of processing.
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3rd Dhool
Dhool extract
through mesh
No 7, 7, 8
2nd Dhool
1st Dhool
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Drying
Fermentation
Made Tea
-----------No 12
Pekoe
-----------No 16
BOP
-----------No 24
BOPF
Grading
-----------No 30
Dust 1
-----------No 40
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Materials & Methods (commercial scale)
 Graded tea samples were packed & coded and sent
for tasters’ evaluation.
 Graded tea samples were analyzed chemically to
determine TF & TR contents.
 Three replicates were conducted.
 Data were analyzed statistically.
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Results – Wet dhool
Table 2. Wet Dhool % for three different degrees of wither
Degree of
wither (%)
Wet dhool %
1st dhool
2nd dhool
3rd dhool
4th dhool
BB
40
9
11
23
39
18
43
12
9
31
30
18
45
22
29
26
9
14
 1st and 2nd dhool % have increased from 40% to 45% degree of wither.
 4th dhool % has decreased from 40% to 45% degree of wither.
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Results – Main grades
Table 3. Main grades & off grades % for three different degrees of wither
Graded tea %
Degree of
wither (%)
BOP
BOPF
Dust 1
Pekoe
Off grade
40
7
34
43
1
15
43
7
36
42
1
14
45
10
30
44
1
15
 No substantial variation of grade %
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Results – Prices
Table 4. Prices of main grades for three different degrees of wither
Degree of
wither (%)
Price (Rs. /kg)
BOP
BOPF
Dust 1
NSA
40
326.70
326.70
398.30
363.50
43
315.00
320.00
385.00
351.70
45
307.50
317.50
376.70
347.00
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Results – Blackness
Blackness
Dust 1
3.66b
BOPF
3.67b
3.84ab
3.66a
3.00
4.72a
4.61a
4.5a
Tasters' score
4.00
4.11ab
BOP
5.00
3.5a
6.00
2.00
1.00
0.00
40
43
45
Degree of wither (%)
Fig 1. Blackness of three grades for three different degrees of wither
 Significantly higher blackness was achieved for BOPF and Dust 1 when
the degree of wither is 40%.
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Results – Liquor color
Liquor color
3.50a
3.67a
3.50a
3.33a
2.00
2.83b
3.00
3.50a
4.00
Dust 1
3.83a
BOPF
4.00a
BOP
2.83a
Tasters' score
5.00
1.00
0.00
40
43
45
Degree of wither (%)
Fig 2. Liquor color of three main grades for three different degrees of wither
 Significantly higher liquor color was achieved for BOPF when the degree
of wither were 43 and 45%.
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3.17a
2.00
4.00a
Dust 1
4.33a
3.00
3.67b
4.00
BOPF
3.33b
BOP
3.83a
5.00
4.17a
Liquor strength
4.83a
6.00
3.50a
Tasters' score
Results – Liquor strength
1.00
0.00
40
43
45
Degree of wither (%)
Fig 3. Liquor strength of three different degrees of wither
 Significantly higher liquor strength was achieved for BOPF when the
degree of wither is 40%.
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Results – Liquor quality
Liquor quality
6.00
BOP
BOPF
Dust1
4.17a
4.17a
4.83a
4.83a
4.67a
3.67b
3.00
4.50a
4.67a
4.00
4.83a
Tasters' score
5.00
2.00
1.00
0.00
40
43
45
Degree of wither (%)
Fig 4. Liquor quality of three different degrees of wither
 Significantly higher liquor quality was achieved for BOP when the degree
of wither is 40 and 43%.
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Results – Total quality
19.17a
16.67b
14.00
18.17b
Dust1
20.72a
20.94a
BOPF
20.00ab
16.00
20.61a
18.00
19.16 a
Tasters' score
20.00
19.16a
BOP
22.00
12.00
10.00
40
43
45
Degree of wither (%)
Fig 5. Total quality of three main grades for three different degrees of wither
 Significantly higher total quality was achieved for BOPF when the degree
of wither is 40 %.
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Results – TF content and TF:TR
Table 5. Theaflavins content and TF : TR of graded tea
Degree of
wither (%)
Tea grade
BOP
TF
TF:TR
40
43
45
BOPF
TF
TF:TR
Dust 1
TF
TF:TR
1.12a
1:12a
1.10a
1:14a
1.17a
1:15a
1.06a
1:15a
1.08a
1:15a
1.08ab
1:17ab
1.02a
1:16a
1.04a
1:16a
1.00b
1:18b
 Significantly higher TF content was achieved for BOPF and Dust 1 when the
degree of wither was 40%.
 Significantly lower TF : TR was achieved for Dust 1 when the degree 40%
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Conclusions
Therefore controlling degree of wither between
40 – 43% would be more beneficial to produce
better quality orthodox + RV type of tea.
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© 2011, Tea Research Institute of Sri Lanka
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