In the conventional orthodox process, the leaf distortion is achieved by rolling, during which the withered leaf is subjected to the motions of conventional rolling machine. The purpose of rolling is to primarily break up the leaf cells and to mix up the chemical components of the leaves with the enzymes. In orthodox method of manufacture, these chemical constituents are ‘wrung’ out by subjecting the leaves to twisting or ‘rolling’ that imparts the leaf a twisted appearance and a special character to the liquor of made tea.
The simultaneous Wisting and rupturing of the leaf cells allow the chemical contents of the leaf to be mixed up in presence of air (i.e. oxygen). This starts off the chemical changes necessary for production of black tea characteristics through the fermentation process. During rolling, tender leaf parts are tom off, leaves are detached, stalks are broken up into smaller parts, and the leaf juice is forced to come over the surface of the broken leaf particles. The expression of juice is dependent on the physical condition of the leaf after wither during which the cell membranes become more permeable. The thorough mixing of the catechins present in leaf and the enzyme under exposure to oxygen facilitate initiation of the fermentation process
The twisted appearance in the leaf during the rolling process can be imparted with a lighter roll in a rolling table with very little breaking up of the leaf into pieces. Hard rolling on the other hand breaks the leaf into small pieces with little rolled appearance in the product. For the sake of efficiency of brewing, the orthodox tea traded all over the world comprises of small leaf particles with leaf juice dried on its surface. The requirement of the rolling machine as well as the process is, therefore, a compromise between the twisted appearance and liquor. The number of rolls and the period of rolling are dependent on the following factors (Tankariwala.N.F, 1999):
- Type of leaf.
- Degree of wither.
- Roller charge and speed
- Pressure.
- Temperature.
- Type of tea required.
Generally a roll of 20-30 minutes is given in the orthodox roller without or with light pressure, and the leaf is then passed through a shifter to extract fines. The length of rolling var1es from factory to factory, but it should not be shorter than 15 minutes to avoid fonnation of flaky leaf appearance. The question whether two or three passes are necessary is usually decided by the plucking standard and the withering facilities prevailing in a particular factory. With fine plucking two passes through Rollers are known to have yielded desired results, but with coarse plucking third cut may be necessary.
CTC tea Manufacture
The CTC (crushing, tearing and curling) manufacture is the contribution from Sir William Mckercher, an ex-Superintendent of Amgoorie T.E., Assam (Griffits.P, 1977).
He invented the ere machine in 1930. The ere machine consists of two stainless steel engraved rollers with circumferential helical grooves. They are meshed closely and made to rotate in opposite directions at a speed differential of 1:10. The rolled leaves are allowed to pass through the zone between the two rollers. The teeth of the rollers perform the crushing tearing and cutting operations simultaneously. The following three parts of a tooth are responsible for the CTC process. The ‘Tooth Body’ or shoulder length is responsible for crushing. The ‘Milling Groove’ which creates the flanks of the teeth helps in curling of the leaf The ‘Sharp Edges’ of the teeth are responsible for cutting and tearing of the leaf.
Processing of leaf in a ere machine requires that the leaf be rolled or conditioned prior to feeding in the CTC machine. Therefore, the rolling table has to be used which is to be synchronized to be able to feed the CTC machine continuously. Meanwhile, Rotorvane, invented at T ocklai initially as continuous roller, proved to be an ideal machine for rolling/conditioning the leaf for ere manufacture. The throughput through a 15inch rotorvane varies between 550-1600 kg of processed leaf per hour. Its speed varies from 15 to 45 rpm. The throughput is 37 kg of processed leaf per hour. Thus with good plucking standard the capacity of a 15 inch rotorvane matches with that of a 36 inch ere machine.
Dual tea Manufacture
Though CTC machine was developed in 1930, it did not catch on for next two decades because the early users failed to produce quality CTC tea as they did not shorten the time for fermentation. (Dutta. A.K., 1992). Thus the CTC manufacturing method commercially started in the fifties. After just ten years of time, more than two-thirds of the Teas manufactured were CTC tea. It was however; observed that from time to time there has been a greater demand for Orthodox tea. This led to the development of a new concept of tea manufacture popularly known as dual manufacture. The attractive benefit derived from this process in that: the fines, containing much of the valued tips are extracted from the normally rolled leaf and subsequently fermented and fired conventionally, while the coarse leaf is put through a CTC machine. This method of.manufacture has been carried out by the industry with mixed leaf i.e. clones and jats as well as from only seed jats. However, some estates adopt the method of dual manufacture at a particular season depending upon the market demand.
