The principal objective of leaf maceration is to undertake cell rupture carried out in a rolling machine where progressive disintegration of cellular organelles takes place. The process results in exposure of cell sap leading to intermixing of chemical constituents and enzymes in the presence of atmospheric oxygen to form the important chemical constituents responsible for characteristics of tea. From the moment the maceration starts, the 'fermentation', which is primarily an oxidation process, begins. The shoot with different degree of tenderness is subjected to considerable deformation during rolling, and, during the process of gradual rupture of leaf, the epidermis is torn up in pieces, cells are crumpled, the cuticle wrinkled and the intercellular space is increased.

The mechanical breaking of shoots at this stage also results in the formation of particles of various shapes and sizes depending on the method adopted and the extent of cell damage. These factors have strong effect on the processing steps that would follow as well as market choices for the made teas. Therefore, leaf maceration is also a key step in tea manufacture.

The following processes carry out maceration in North East India:

• Orthodox
• CTC (Crush, Tear and Curl)

Orthodox process of manufacture

In the orthodox process of manufacture maceration or disruption of the leaf cells is carried out in a Rolling Table. During rolling juice from the leaf is wrung out and the leaf is also twisted and broken into smaller particles.

The process objectives during orthodox rolling are therefore

• To rupture the cell walls and expose their contents
• To bring the contents of leaf cells in contact of air to start the process of oxidation
• To twist the leaf and give it the desired shape or appearance
• To break the larger twisted leaf into smaller particles

Rolling

Before the advent of tea machinery, the most convenient method for cell rupture was to rub the leaf in between palms. The Rolling table is simple equipment that emulates the hand rolling method in a commercial level operation. The process of rolling applies pressure and twist between leaves as well as between leaf and surface of the equipment used for rolling. The degree of pressure depends upon the quantity of leaf charged as well as the position of the pressure cap. Resulting friction causes heat, which in excess will hasten the chemical reactions to result in the formation of undesirable constituents detrimental to the quality.

The cell rupture in the small and tender shoots is completed faster and chemical reactions set in earlier while the coarser leaves require a little more time. Also the leaf, which has already undergone size reduction and twisting after some amount of rolling, impedes twisting of larger leaf, which may extend the period of rolling. Segregation of such leaves is carried out after an appropriate period (30-45m). The leaf is discharged and then passed through a Sifter or a Ghoogie. The Ghoogies and Sifters have perforations of different sizes. The particles passing through the perforation are called fines and the spill is known as 'Coarse' leaf, which is sent for further rolling. The fine leaf is taken for 'fermentation'. The coarse leaf after second roll is subjected to similar process to get the 2nd fine and if need be the 2nd coarse leaf may further be subjected to 3rd rolling. It may be noted that major portion of the leaf grades come from the coarse leaf.

Dual manufacture

During the early manufacturing season (up to second flush) when the leaf is of better quality, there is demand for orthodox teas and dual manufacture may be adopted. The first fine as described above goes for orthodox manufacture and the coarse goes for CTC manufacture. It is to be remembered that for dual manufacture the wither should be appropriate for CTC. An extraction up to 10% of fines does not affect the quality of the CTC tea.

The following machines are used for conventional orthodox rolling.

• Rolling Table
• Boruah Continuous Roller (BCR)

Rolling Table

Essential parts

• A circular table with a depression (asymmetric well) at the centre closed by a door below.
• A cylindrical hood to hold leaf and having a feed hopper at the upper end.
• A pressure plate or cap.
• Three cranks placed at 120° apart, one with the drive to give the eccentric motion either to table or to the hood or to both. The length of the crank is 23 cm (9 inch).

Types of rollers available are:

• Single acting table moving types - only the table moves
• Single acting hood moving type - only the hood moves (popular in Sri Lanka)
• Double acting type - both the hood as well as the table move, driven by 11.5 cm (4.5 inch) cranks opposed to each other.
  Speed

The speed may vary according to market requirements. A higher rpm results in more broken and lower rpm in more leaf grades. The rpm given are indicative and can be varied by using variable gear drive etc.

The process

Two to three rolls, each lasting between 30-50 minutes, are given for manufacture of orthodox tea in the plains. When tip is not a consideration the period of 1st rolling can be extended. The rolling program should be planned judiciously and it should be dictated by the drying capacity of the factory. The output of the Rolling table should be match the requirement to produce as much fermented leaf per hour as to keep the dryers full.

The programme should be such that the rollers are neither overcharged nor under charged and leaf is going to the fermenting room every 15 minutes.

For the sake of convenience rolling time is taken as commenced from the time of last leaf enters the roller and fermentation begins when the first roller has been failed. Rollers should not be filled once the rolling starts.

Dual manufacture

In the dual process, the fines containing the valuable tips are extracted as first fines after a normal 30 minutes roll. An extraction of up to 10% fines can be adopted without any detectable adverse effect on the cup character of CTC teas. Extraction of higher percentage of fines will not only result in the production of quite an amount of not so attractive grades like Orthodox BP, Fanning and Dusts but will also adversely affect the liquor of CTC teas.

With tippy and pubescent leaf available throughout the year it is possible to adopt dual manufacture throughout provided adequate withering facilities are available, otherwise dual manufacture may be restricted to second flush period only. As has already been mentioned the wither for dual manufacture should be suitable for CTC manufacture.

Boruah Continuous Roller (BCR)

The BCR consists of a reciprocating cylinder, with both ends open, inside serrated, one and wall with an opening fitted with a hopper to feed the leaves; stroke length 24.13 cm. The other components are an oscillating rotor, frusto-conical in shape fitted with a number of vanes and pins and on the straight portion an adjustable pressurising sleeve with battens, oscillating 180° at half the speed of the cylinder, a cylindrical block with closed ends fixed to the frame concentrically inside the cylinder at the hopper end and the driving mechanism with gearbox, roller chain, cranks, connecting rod etc. Expressed in terms of diameter of the cylinder; 37 cm, 40 cm and 45 cm sizes have been prescribed.

The CTC Process

The CTC machine achieves the three actions of Crushing, Tearing and Curling in the same machine at one go. Instead of working on large volumes of leaf, the CTC takes a fast, thin, but steady stream of leaf to pave the way to continuous processing in place of the batch mode of orthodox rollers. Leaf appearance, make, grade percentage, fibre content, liquor and infusion depend on the cut obtained in the CTC machine.

Preconditioning for the CTC Process

Leaf is preconditioned by making use of orthodox rollers or Rotorvane/BLC Preconditioning of leaf aims at imparting twist to the withered leaf in order that the CTC rollers can give adequate treatment. When flat leaf is fed to the CTC machines considerable quantity of made tea may have flaky appearance. The cells of the flat leaf do not undergo correct maceration and as such their cells cannot be exposed to atmosphere for proper fermentation resulting in poorer liquor quality.

Preconditioning in Rolling Table

Correctly withered leaf will have the required twist after 20 minutes of rolling without pressure provided the Rollers are properly charged. A 91 cm (16 inch) roller should be charged between 110-145 kg of leaf while a 117 cm (46 inch) Roller should be charged with around 300 kg of leaf. The Rolling programme should be arranged to coincide with the output of driers. It is important to see that the Rollers giving best twist are employed.

Preconditioning in Continuous Preconditioning Machines

• Rotorvane
• Barbora Leaf Conditioner (BLC).

Essential Parts

A cylinder, one end closed and the other end open, with feed hopper near the closed end. The processing zone inside is fitted with either resistors (Rotorvane) or pins (in BLC).

A rotor fitted concentrically inside the cylinder consists of a feed worm, with a number of vanes (in case of Rotorvane) disposed slightly at a angle and at right angles to the next, and an end device, which in case of Rotorvane is commonly an Iris plate or cone with battens, and in case of BLC, a cone with vanes and battens. In case of Rotorvane using a cone, a sleeve is fitted at the discharge end of the cylinder for pressure adjustment.
Working

Withered leaf fed through the hopper is pressed by the feed worm and brought to the processing zone where the leaf is worked upon mechanically by the rotor elements like vanes or battens over the cone against the cylinder inside surface and the elements thereon, all under pressure produced on the leaf by the feed worm. The pressure can be adjusted by releasing it by opening out the Iris plate or by moving the pressure sleeve and vice versa.

Being continuous, the machines can easily be regulated to supply leaf at the same rate as the input of the dryers. It is merely necessary to supply the required quantity of withered leaf that permits a continuous feed into the Rotorvane with minimum delay after removal from troughs. Leaf should not be piled up for feeding into the Rotorvane or BLC.

Pressure applied n the Rotorvane/BLC should be just sufficient so as to express just enough juice for spreading over the cut leaf. Excessive heating during Rotorvane processing must be avoided and leaf temperature should not be allowed to go beyond 32°C (90°F).

Excessive heating in the rotorvaned leaf may result from any of the following reasons.

• Heating up of leaf in basket or in heaps after removal from the withering trough
• Overfeeding of leaf into the Rotorvane
• Uneven feeding
• Feeding over-withered leaf

The rotorvaned leaf is fed directly to CTC (in tandem) with the help of conveyor for further processing.

The CTC Machine

Essential Parts

Two stainless steel rollers with circumferential as well as helical grooves machined to certain definite specification, meshed closely, rotated in opposite directions at a speed differential of 1:10. The diameter of the roller varies between 20.3 cm (8 inch) - 20.95 cm (8.25 inch). The larger 33 cm (13 inch) diameter CTC machines are gaining popularity now a days.

Three or four CTC machines in tandem are connected to each other with the help of conveyors made of non-toxic, food grade and hygienic rubber belt discharging onto the slow speed roller.

Principle of Working

The triple process of Crushing, Tearing and Curling is done by the teeth on the two rollers moving against each other at differential speeds. Preconditioned leaf is fed to the slow speed roller of the first cutting unit by a feed conveyor and is processed between the rollers adjusted with a gap of about 0.050 mm (2 thou). The sharp edges of the teeth cut and tear up the leaf while the leaf is crushed between the shoulder of teeth and the matched meshing groove, and curled due to rubbing action between the flanks of the teeth. The processed leaf is discharged below the pair of the rollers on to a moving conveyor belt, which carries the leaf to the next cutting units slow speed roller. The shape, size and differential speed of these teeth are of vital importance in CTC processing.

Sharpening of rollers to accurate specification and proper meshing assume great significance considering their influence on the quality of made tea.

• Tearing action is related to closeness of setting and the speed ratio. Closer the setting and higher the speed ratio more are the smaller grades.
• Curling and Crushing - The two simultaneous processes depend on the available surface area on the teeth, closeness of setting and linear differential speed.
• Capacity - Capacity drops with the reduction in the roller diameter and also due to reduction in discharge area when milling angle is reduced. The reduction in the milling angle increases tooth shoulder area that will help in producing more grainy teas. With reduction of roller diameter, there is also deterioration in style.

Basic Requirements for Manufacturing of CTC Tea

• Good Leaf: The CTC machine is capable of handling coarse leaves but teas produced from such leaf are more fibery and flaky with poor liquor characters. It is therefore advisable to use standard to medium plucked leaves (fine leaf and 70%).
• Optimum Wither: In North East India a light wither of 72-75% (68-69% moisture) has been found suitable. The variation in wither will depend on the texture of the leaf. Coarser the leaf, lighter the wither.
• Temperature in Rolling Room: The rolling room should be cool and humid. There should be enough exchange of air so that heat developed during processing is easily dissipated - minimum 10 air changes per hour is recommended.
• Machine with Correct Specification: The CTC machine used should conform to correct specifications given below:

Roller Tooth Profile: The machining of the rollers to form the chased as well as milled grooves results in multiple numbers of teeth appearing all over the circumference of the roller. The following checks are very essential:

• The depth of the chased groove must be minimum of 2.03 mm (80 thou).
• There should be no serrations or chatter marks over the surface.
• The chased groove is 0.03 mm (12 thou) deeper than the milling groove.
• The shoulder to slope ratio is between 3:5 and 1:1.
• The depth of milling must be equal throughout.
• There should be no multiple lines over the milled surface.
• Speed and Alignment of Rollers: The CTC machine must have the correct specifications. The conventional CTC machine must have the speed maintained at 70:700 rpm at the ratio of 1:10. At higher speeds, excessive heat developed yields poorer quality of tea and at low speeds the cut is poor. The Rollers must be correctly set and properly meshed. This can be easily checked by viewing the enmeshed rollers from the top against light projected from below. In a correctly meshed CTC machine no tooth will touch another. Incorrectly set rollers will adversely affect the bloom and the style.
• Sharpness of Teeth: Roller teeth must be maintained sharp. The machining i.e., chasing and milling should be accurate and there should be no bluntness on the edges of the teeth or burrs on the tooth surface. Rollers with blunt teeth or burred surface produce flaky and fibrous teas. Liquors of such teas are poorer. Such rollers must be changed immediately. For CTC machine with 21 cm dia rollers need to be resharpened after processing 50,000 kg of leaf.
• Rate of Feed : The rate of feed should be such that the leaf does not get heated and match the maximum output allowed in the third cut. The rate of feeding should be such that continuous flow of leaf is possible.
• Severity of Treatment : This will depend on the type and texture of raw material used. This will also be dictated by the market requirement.
• Power Transmission : For running the machine whenever V-belts are used, they should be used in exact numbers and in exact size and specifications as recommended by the manufacturer. The following important points are to be taken care of:
  • Use of correct numbers of V-belts.
  • Correct section of V-belts with matching V-pulley groove. The top of the belt should be flush with the rim of the pulley and there should be a small clearance between the bottom of the belt and the groove.
  • Tension of all the belts in a set should be equal.
  • The pulley grooves should not be worn.
  • Polished groove indicates slippage of belt.

  However, the present day CTC's are run on direct drive and the above problems have been eliminated.

• Magnets: There is every possibility of iron filings being picked up by the leaf from mechanical process. Even nuts and bolts are picked up. These cannot only damage the CTC rollers but beyond a certain limit, are also not permissible under PFA act. It is, therefore, recommended to mount powerful magnets on the feed conveyors.
• Cleanliness: Bacterial contamination at the green leaf processing stage will affect the liquors particularly in briskness. The machine must be kept clean. Quite often, plenty of over fermented leaf remain deposited under the top cover of the CTC machine and in the not commonly accessible areas in the machine. Such deposits must be brushed free from machinery and conveyor belts as frequently as possible. Leaf should not be allowed to fall on the floor. Washing of the machine should be done as and when necessary but it is essential to wash the machinery at the end of the day.
• Resharpening of Rollers: The tooth surface and the roller itself have to be in the perfect condition to make good CTC tea. Rollers must be free of worn out or blunt teeth and must be resharpened as soon as wear exceeds 0.015 mm (6 thou) of the teeth depth or 0.030 mm (12 thou) of the diameter. Damaged rollers must be replaced immediately.
• Sharpening Intervals: The rollers should sharpened -
  • Every 60-80 hours if the cut is hard and the leaf is coarse
  • Every 80-100 hours for a normal hard cut and when the leaf is medium
  • Every 130-140 hours and 180-200 hours in the large dia CTC under the above conditions (a) and (b).
• Tooth Surface : Tooth surfaces are the processing surfaces. During sharpening, it must be ensured that the surfaces are absolutely smooth and without any chatter marks. The lack of smoothness may result from (I) Reduction of sharpness of the cutting tool, (ii) High speed of rotation, (iii) Worn out or damaged bearings and (iv) High rate of tool feed.
• Perfect Meshing : The pair of rollers must mesh perfectly. The clearance between Rollers when hard cut settings are used is 0.050mm (2 thou). Hence the degree of accuracy must be very high.

  Rollers usually wear more at the middle than at the ends and a 'waist' is formed. This has to be corrected at each sharpening; otherwise even cuts will not be possible.

  Once the diameter is made even throughout, and, final chasing is complete, each pair of rollers must mesh perfectly. With an accurately operating lathe, the problem of meshing will be less. Digital read-out with electronic scale attachment (DRO) help in achieving perfect meshing every time.

• 'U' Profile and 'V' Profile: Both U as well as V profiles are used either alone or in combination. V-profile gives a sharper cut and therefore it can process leaf at lower temperature. The U-profile gives a less sharp cut and there is some rise in the leaf temperature. However, V-profile lasts for a shorter length of time, which may be 60-70% of the life of the U-profile. Also, after some use the V-profile loses its sharpness and nearly turns into U-profile. Depending upon the end product aimed at a combination of V and U profile can be used e.g., sharper cuts with V-profile teeth (in the first and second cut) followed by somewhat loose cut in U-profile (in the third cut) will give more brokens.
• CTC Ghoogies : Passing the leaf after CTC cut through the rotary ghoogies induces an increase in broken grades and also the floating fibres get embedded. However, the process deteriorates the liquors. Wherever appearance and size are most important than liquor it is useful to pass the CTC processed leaf through 'ghoogie'.