1. Manufacturing of Black Tea:
The salient feature of black tea manufacturing involves following operations,viz. Plucking and handling of tea shoots ,Withering, Processing, Fermentation, Drying/Firing, Sorting and packaging.
1.1. Plucking and handling:
1.1.1. Plucking:
A tea shoot consist of two leaves and a bud. The making of high quality tea depends very largely on the fineness of the plucked leaf. Hence the plucking standard has important influence on the quality of tea. Tea leaves may be harvested, fine plucking i.e. two terminal leaves with a bud, while coarse plucking may include 3 or more leaves below the apical bud. Therefore, following plucking standard needs to be maintained in the field:
- Maintain the minimum standard for 2+bud tipping i.e. two soft apical leaves and one closed bud. If the bud is beginning to open the shoot immediately enters the 3+bud category, and the lower of the two leaves is then discarded.
- Maintain the minimum standard for secondary shoots from mature plucking tables i.e. two fully open leaves and a closed bud or partly open bud.
- Maintain the minimum standard of banjhi which is not more than two soft leaves and a dormant bud; hard leaves are rejected.
1.1.2. Leaf handling:
Careful handling of green leaves from the field to the factory is the pr-requisite to obtain good tea, following precautions may be undertaken:
Ø Weighment should be done frequently in cool shady places in the field.
Ø Plucking basket in preference to Patti Gamcha should be used to evade high temperature from the plucked leaves.
Ø Compressing the leaves in baskets and overloading the trailors should be avoided.
Ø Worker/jugalis should not be allowd to stand, sit or lie onto the loaded green leaves in the trailor.
Ø Unloading the leaves in the factory should be carefully done by hand on the clean floor.
1.2. Withering:
Withering means to lose freshness. It was believed that the purpose of withering of tea leaves was only to reduce the moisture content in order to make it sufficiently limp for succeeding leaf distortion operation. Now it is well known that many biochemical and physical changes occur during the withering period. Loss of moisture from the fresh leaves cause it to become limp and flaccid, and increased the permeability of cell-membrane which may facilitate the fermentation process. The majority of biochemical changes is completed in 6-10 hours. When tea is plucked, the metabolic activity is deranged rapidly but many processes including respiration to continue to function. Main biochemical changes which have been substantiated during withering are:
(1) Increase of polyphenoloxidase activity,
(2) Increase in Caffeine and permeability of cell- membrane,
(3) Breakdown of chlorophyll and proteins to amino acids and
(4) Changes in caroteniods and level of organic acids.
1.2.1. Withering system:
This operation may be carried out naturally or artificial means. Of various withering systems followed by tea producing countries, Chung or Rack withering and Trough withering are most common in Bangladesh tea.( Faruk, 1989)
1.2.2. Processing:
The next stage of the manufacture is the leaf distortion/maceration of the withered leaf, i.e. processing. The withered leaf is sifted through Green Leaf Sifter to removed extraneous material before it is processed. The process of leaf distortion is aimed at bringing contact of the chemical compounds, polyphenols with copper based enzyme, polyphenoloxidase in the leaf cell. Several other reactions are also initiated during rolling, e.g. the breakdown of chlorophyll by chlorophyllase the sequence of reactions leading to the formation of compounds responsible for flavour and colour of the formation of the liquors and other non enzymic reactions. Thus the types of processing adopted are very important in tea manufacturing.
The are various types of tea processing in vogue in tea growing countries, viz. orthodox, Rotor vane, C.T.C, L.T.P. etc. in Bangladesh.
Table-4: The recommended moisture content in the withered leaf is shown as follows:
| Type of Manufacture | Required Physical Wither (%) | Moisture (%) in withered leaf |
| Orthodox | 64 | 65 |
| Roll-CTC | 70 | 68 |
| Rotor vane-CTC | 75 | 70 |
| LTP | 80 | 72 |
1.3. Fermentation:
Fermentation of tea leaf is the process of oxidation of various chemical constituents of tea leaf through a series of chemical reactions. No micro-organisms are involved in the so-called fermentation but the term is probably too firmly established to change it despite its inaccuracy.
1.3.1. Requirements for Optimum Fermentation:
The spread of dhool affects the rate of fermentation. If the dhool is spread too thick, the oxygen supply will be restricted and the dhool will be overheated resulting the retardation of fermentation process. On the other hand, the thinly spread dhool tends to be cool and dry resulting a slow down fermentation. Optimum thickness of leaf spread should be for CTC 1.25 cm. (i.e. about 8-9 kg of dhool per sq.m) while 2.50 cm. (i.e. 5-6 kg. of dhool per sq.m). for Orthodox manufacture. The room temperature should be maintained between 260C and 290C and the humidity in fermenting room should be adjusted by hygrometric difference of 1.70C maximum. The room should be well-ventilated and humid: Room air should be changed at least 10 times an hour either using fan or proper ventilation as dry air leads to drying the leaf surface and reducing the rate of theaflavin formation.
1.3.2. Fermentation Methods:
Following methods are being practiced in Bangladesh tea factories;
- Floor Fermentation
- Rack Fermentation
- Gumla Fermentation
- Trough Fermentation
