Orthodox Tea Manufacturing Process
The steps involved in orthodox tea manufacture include withering, preconditioning, rolling (roller or rotorvanes), roll-breaking and green leaf sifting, fermentation, drying, grading & sorting and finally packing.
Normally withering is carried out by spreading the leaves thinly on banks of trays or “tats” made of tightly stretched jute Hessian or wire-netting. The tats are kept 12 to 15 centimeters apart, to allow free access of air. There are two types of withering; open withering and closed withering. The open or “chung” type of withering accommodation admits of no control of rate of withering except by thickness of spread and the length of time of the withering phase. This is “natural withering” in its simplest form. The average length of time for withering is 18 to 20 hours where “tats” are used. In modern trough withering system 16-18 hours is the duration of wither with normal ambient air. In rainy season, to remove the surface moisture, heaters are used along with fans for two hours. Modern methods greatly reduce the withering time but they can also lower the quality of the final product by reducing the time for chemical withering. In general, south Indian tea manufacture is carried out with withered leaves having a moisture content of 60-65% for orthodox type of manufacture.
When a satisfactory wither has been obtained the leaf is ready for rolling, which twists the leaf, breaks it up and expresses the juices (substrates and enzymes). The machines used vary in size and design but their principles are alike, they compress and turn the leaf over. This step facilitates mixing up of cell constituents viz., enzymes and substrate, thereby starting fermentation, while the maceration is complete in CTC, in orthodox only internal injury is imparted due to rolling. Enzymic oxidation of the catechins (polyphenols) begins at this stage.
Rotor Vane: The rolled leaves are fed into the rotor vane, which mixes the leaves thoroughly aiding in the cell maceration and extraction of the juice from the leaves.This step ensures proper coating of the leaf with the juice thereby facilitating subsequent processes viz., rolling and fermentation.
Roll breaking and green leaf sifting: These two steps are involved mainly for the orthodox type of manufacture. On discharge from the roller the leaf mass is more or less compressed into lumps. These are broken up in the sifting process by the machine which usually combines the operation of roll-breaker and sifter. The roll-breaker and green-leaf sifter in the first instance cools the leaf, secondly it aerates the mass, and thirdly by sieving out particles of small size it separates leaf into portions that will be reasonably uniform in their rate of fermentation.
Though actual fermentation starts at rolling it is continued in the next stage. The sifted leaves are spread out in thin layers on tables or perforated aluminum trays or into aluminum drums, in order to continue the oxidative process. During fermentation, the leaf changes colour and turns into a dark coppery tone. Typical aroma develops at this stage. The ideal conditions for fermentation are dhool temperature <30oC, moisture ~55%, pH 4.5 to 5.0 and relative humidity >90%. When the fermentation is judged to be sufficient (colour & nose assessment) the fermenting dhool is transferred to the drier. Googhie cum floor Drum fermentation is extensively used in south Indian tea Industry for orthodox type of tea manufacture.
Drying: Endless chain pressure driers as described in the CTC process are also commonly used in orthodox tea manufacturing. After firing, the tea is spread out to cool and then temporarily stored to wait sorting. Modern innovations on the drier are the hot-feed drier, where hot air is supplied separately to the feeder to arrest fermentation immediately as the dhool is fed, and the fluid-bed drier where the leaf moves from one end of the chamber to the other over a perforated plate in a liquid fashion.
Grading and sorting:
Grading and sorting: Grading is carried out on mechanically oscillated sieves, similar to those used in the green leaf stage and fitted with meshes of appropriate size. Finished grades are stored in air-tight bins until a sufficient quantity has been accumulated to fill a consignment. The common grades of orthodox tea are as follows.