Processing of Tea Leaves – Steps
Four principal steps are involved in the processing of tea leaves:
- Fermenting, and
Withering removes moisture from the leaf which makes it less brittle, roll well and take a twist. It is generally done by spreading the leaves evenly on racks or shelves or in withering troughs protected from the weather. In north-east India, withering is effected by allowing natural breeze to pass over the leaves in houses having open sides. In south India, the leaves are generally withered in enclosed lofts with provision for blowing-in warm air. The leaf is withered for 16-18 hours during which period the moisture in the leaf is reduced by about 40% and the leaf acquires a kid-glove feel. Some chemical changes also occur during withering. A slight increase in caffeine and a relatively large in¬crease in some of the amino acids are the earliest chemical mani-festations. These changes and the degree of wither are partly responsible for the characteristics of the liquor and physical appear¬ance and quality of the made tea.
The withered leaf is passed on to rollers where it is twisted to cause sufficient damage to the individual cells and to initiate enzymic oxidation. Rolling is usually done for 30 minutes and the rolled mass is sifted and the finer portions of the leaf are allowed to ferment whereas the coarser portions are subjected to heavy rolling. Sometimes, a third rolling may be given. A continu¬ous process to cause more extensive cell-damage, and thoroughly expose the catechins to the enzyme polyphenol oxidase has been developed.
Three major manufacturing methods commonly used are:
a) orthodox, which employs non-cutting rollers,
b) crushing, tearing and curling (CTC), which employs rotor vanes and cutting-rollers, and
c) Laurie Tea Process (LTP), which uses hammer-mill-type cutter.
The orthodox process uses conventional crank rollers while the CTC machine consists of two engraved metal rollers operating like a mangle and gives an instantaneous nip to the leaf. Presently, many factories use the rotor vane, which acts like the common domestic mincing machine, to pre-condition the withered leaf prior to feeding to CTC machine. CTC maceration improves theaflavin and thearu¬bigin content, and briskness, brightness and thickness of black teas, whereas the orthodox process produces more caffeine and volatile flavor compounds which make tea with superior flavor. CTC teas, being more economic, are popular in India.
A different method, Leg Cut manufacture, is used in certain tea estates in Dooars in West Bengal. The fresh leaf is directly processed and the liquor made from this tea compares well with those from withered teas but possesses a characteristic brassy or metallic taste. The green-leaf-processing can also be made continuous by using the rotor vanes in conjunction with the Leg Cut manufacture.
The main operation in the manufacture of black tea is enzymic oxidation, originally termed ‘fermentation’ which still continues. Fresh shoots contain about 25% solid matter, nearly half of it as insoluble substances like crude fiber, cellulose, protein and fats. The water-soluble portion contains, apart from caffeine, about 30 different polyphenolic substances, many amino acids, sugars and some organic acids. Within the leaf, but spatially sepa¬rated from the polyphenolic bodies, are present enzymes called polyphenolic oxidizes. Fermentation brings about a series of en¬zyme-catalyzed reactions by bringing the polyphenolic bodies (mainly epigallocatechin and its gallate) in contact with the enzyme. The polyphenolic bodies undergo change to theaflavins and thearu-bigins. The concentration of yellow-colored theaflavins and the red-and-brown thearubigins in the manufactured tea have remark¬able influence on the color, strength, brightness and briskness of liquor. Fermentation also imparts mellowness to the brew. The proportion of theaflavins and thearubigins can be brought to an optimum level by proper control of the conditions of fermentation. Various fractions of the rolled leaf are spread on clean cement floors or other suitable platforms to a thickness of 2.5-10.0 cm, depending upon the season and condition of the leaf, and allowed to ferment for 2-4 hrs depending upon the type of roller used under high humidity and low temperature (24.0- 26.5°)C. The color of the leaf also changes from green to a bright coppery red. Too high a temperature results in over-fermentation and inferior product. Recently, a new method of fermentation using rotating drums has been introduced which yields uniformly good grade of tea.
4. Drying or firing
The fermented leaf is dried with hot air (82-93°) C for 30-40 min to arrest further changes and to make the product fit for packing and keeping. The dried product contains 3-4 % moisture, and can withstand long storage and transit.