Leaf Distortionis that step in the process of tea manufacture where the withered leaf is subjected to some kind of mechanical operation whereby the leaf cells are ruptured to give the desired style and appearance to the made tea. During this operation the leaf undergoes the process of size reduction with a degree of cell disruption to allow the exposure of new surfaces to air during the fermentation process.
This is achieved either by rolling or putting the leaves in CTC machine.
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 squeezed 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 twisting 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 torn 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 polyphenols present in leaf and the enzyme under exposure to oxygen, facilitates initiation of the fermentation (oxidation) 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 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:
i) Type of green leaf
ii) Degree of withering
iii) Roller charge and speed
vi) Type of tea required
Generally, a roll of 20-30 minutes is done in the orthodox roller with or without light pressure, and the leaf is then passed through a shifter to extract fines. The length of rolling may vary, but it should not be shorter than 15 minutes to avoid formation of flaky leaf appearance. The question on 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 the rollers is known to have yielded desired results, but with coarse plucking, third cut may be necessary.
CTC stands for crushing, tearing and curling. CTC tea is made through the Crush, Tear, and Curl (CTC) process of manufacture producing a granular leaf particle and it is characterised by its strong liquor.CTC teas had revolutionisedthe tea trade after its introduction. In this type of manufacture, fermentation being intense, the cuppage is much higher than the orthodox tea. Cuppage refers to number of cups of liquid tea that can be prepared from one kg of made tea. One kg CTC tea normally yields 550 cups (one cup is 114 ml of liquid tea) as against 275 cups from orthodox tea.
The CTC manufacture is the contribution from Sir William Mckercher, an ex-Superintendent of Amgoorie T.E., Assam. He invented the CTC machine in 1930. The CTC 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 three parts of a tooth of the CTC roller 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 CTC machine requires the leaf to be rolled or conditioned prior to feeding in the CTC machine. Therefore, before feeding the leaves into the CTC machine, withered leaves are either rolled in the rolling table or leaves are conditioned by passing through Rotorvane, invented at Tocklai Experimental Station, Assam initially as continuous roller which proved to be an ideal machine for rolling/conditioning the leaf for CTC manufacture. Some other machine like BLC (Barbora Leaf Conditioner) were also used.
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. 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 in many factories of the industry. However, some estates adopt the method of dual manufacture at a particular season depending upon the market demand.