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Plantation

  • Vegetative
        Propagation
  • Planting
  • Pruning
  • Fertilizers
  • Weed Control
  • Pest Management


  • Plucking and
    Leaf Handling

    Withering

    Rolling

    Fermentation

    Drying

    Sorting


    Withering

    Definitions: 

    a)  Chemical Wither: Desirable biochemical changes from plucking to initiation of processing (manufacturing), normally 14-20 hrs.

    b)  Physical wither : Moisture loss, leaf becomes flaccid.

    c)  Percent wither (% wither). The weight of 100 kg fresh leaf at the end of the withering process.

    Different % moisture contents of fresh leaf results in different % moisture contents of withered leaf, even when the "% wither" remains the same :

    Fresh leaf           Withered leaf, i. e. 100 kg fresh leaf reduced to moisture


      80kg 75kg 70kg 65kg 60kg 55kg 50kg 45kg
    82% 78% 77% 75% 73%  71% 68% 65% 61%  
    80% 76% 74% 72% 70% 68% 65% 61% 57%
    78% 73% 72% 69%  67% 64% 61% 57% 52%
    76% 71% 69% 67% 64% 61% 57% 53% 48% 
    74% 68% 66% 64% 61% 58% 54% 49% 43%

    d)  Percent wither can be calculated by measuring the recovery % of made tea against withered leaf.

    Fresh leaf moisture Recovery % of tea made against withered leaf (theoretical)

    82% 19 22 25 27 30 31 35 38 43
    78% 23 26 30 33 35 38 42 47 53
    74% 28 31 36 38 42 45 50 56 62

    Calculated

    % wither 90  80  70 65 60 55 50 45 40

    The same recovery % indicates light wither on dry leaf 

    medium average leaf  
    hard moist leaf  

    Fresh leaf moisture content determines withering (and drying) loads; 8 percentage points less moisture results in 40 - 45% increase in recovery .

    Example : At 80% wither, a reduction from 82% to 74% moisture gives an extra 10 on 22, i.e. 45%.

    Controlled Wither

    (i)  Normal requirement for :  

     
    Moisture content of
    Equivalent, % wither on
      

    Withered leaf

    Moist
    Average
    Dryish
    CTC 70% 58 73     80  
    Orthodox (plains) 66% 52 65     74  
    Orthodox (hills) 33% 26   33

        39  

         (ii)   Equipment : Heated lofts, drums, Tocklai tunnels and troughs.  

    (iii)  Method : When more moisture is there in the fresh leaf, more % wither must be given to achieve 70% moisture in withered leaf :

    Example : To achieve 70% target moisture content from fresh leaf of any moisture %  

    Fresh leaf moisture %  82 80 78 76 74
    Required % wither  58 65 70  77 83

    N.B. As specific moisture meters for the purpose are not available at present, experience has to be applied for an estimate of leaf moisture %. Rains leaf, with surface moisture, has about 82-84% moisture.  Dry leaf in a dry spell, just going limp, has 72 -74% moisture.

    Green Leaf Storage System (GLSS)

    Keeps green leaf in Fresh and undamaged condition upto 48 hours. Can be used in conjunction with the existing troughs so that the same troughs may be used upto 3 times a day. Adds to saving on power and space upto 60%.  

    Dimensions 37.27m x 2m x 3.7m
    Capacity  14000 kg
    Power required HP-6KW - 4.5  

    Spreads

    a)      In lofts - 

    Orthodox 1 kg on 2 mt2,  0.5 kg per mt2
    CTC I kg on 1.5 mt2, 0.7 kg. Per mt2

    b)    In troughs  

     

    CTC

    Orthodox

       

    Plains

    Hills

    Kg per running m of trough 1.8 m wide Kg per mt2
    38-48
    33-43
    28-38
    20-25
    17-23
    15-20 

    Withering air in troughs

    a) Air volume controlled with fan and damper (or bypass) ratio varies from 0.4 m3/kg. with fine leaf at 15 cm deep to 0.7 m3/kg with standard leaf at 20 cm deep depending on leaf quality and spread, the air volume per m2 trough surface will vary from 8 to 18 m3/min.

    b)Temparature 

    Controlled by adding hot air. Heaters should supply 1/10 of the required volume at  
    100 degrees centigrade maximum. Fan inlet temperature should not exceed 38
    degrees cent.(plains), 30 degrees cent (hills).

    c) Hygrometic difference

    The depression of wet bulb below dry bulb temperature should ideally be about 4 degrees C.

    High differences speed up moisture removal, but can give uneven wither.  They can be used for drying off surface moisture initially,

    d) Air pressure

    Normally 12 mm Water Gauge. This should not drop below 6 mm when working against the normal spread of leaf.  

    Building troughs

    a) Selecting a fan for an existing through : Kg leaf to be loaded x air ratio selected = air requirement in m3. Compare this with air delivery figure in fan manufacturers’   table, at 12 mm Water Gauge pressure : choose nearest larger standard size of axial flow fan.  

    Larger dia fans use less power per volume than smaller fans. By using pairs of smaller fans, flexibility is obtained, but this requires troughs 3-4 m wide.

    b) Making a trough for an available fan

    Fan capacity (rating), m3            =    Kg leaf capacity  
    air ratio selected

    Divide leaf by spread selected (seel.4 b above) to get running m of a 1.8 m wide standard trough, or required m2 of trough surface.  


    c)      Calculating requirements Total no. of troughs   =    

                     1% of estimated annual GL (Kg)                               
    Spread selected (kg/m2) x Planned area per trough (m2)  


    (includes additional capacity large enough for any anticipated peak day; will prevent the collapse of quality control under adverse climatic conditions.)



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