Tea is an immemorial crop originally grown and manufactured by peasants in a very primitive manner. Mechanical means of cultivation, the use of fertilisers and power driven machinery in factories of modern design have revolutionised in many respects the primitive technique. But the care of the individual bush and the harvesting of the crop still elude mass treatment. Tea cultivation is in fact a horticultural operation carried out on agricultural and industrial scale now so that we presently talk of Tea Industry employing considerable capital and controlled until recently by the so called “Sterling Companies”.
After his adventurous journey along the orbit, Cosmonant Glenn immediately on his return to earth asked for tea (iced) : But man’s first use of the tea plant as a source of what has become the most popular, cheap and graceously pleasant beverage, is shrowded in the mists of legend and apocryphal history. In china they have been drinking tea since the 4th Century AD and the people of upper Burma along the Indo Burmese border and upper Assam have been used to tea for just as long a period. The tender leaf of the tea shrub which early British writers compared with their native garden box plant, in the course of its romantic rise has altered the course of history, influenced social customs habits, literature and fine arts, shaped economics and politics and altered the directions of trade. Today tea is drunk on the five continents and as each year passes more tea is being produced and consumed the world over. The importance of tea as a world beverage entering international Commerce belongs to the era of Western expansion in the East, after the sixteenth Century.
Tea did not become a popular drink without opposition. Eminent physicians, men of Letters, rulers and philosophers opposed and criticised the drinking of tea. But tea has also its champions who sang its praise claiming for its virtues which would make hardy planters blush today. Dr. Jonquet of the French medical perofession fearlessly proclaimed tea as the “Divine herb” comparing it to nectar and ambrosia.
India is the world’s largest exporter of tea and more cups of tea are drunk throughout the world than any other beverage except water because it is a good tranquilliser and at the same time acts as a mild stimulant. From the distant past, an ancient philosopher has left this image of tea to posterity.
“when I drink tea, I am conscious of peace. The cool breath of heaven rises in my sleeves and blows my cares away.”
The tea plant is an evergreen of the Camellia genus and is known as Camellia sinensis and flourishes in warm tropical and sub tropical rainy regions. It is a hardy plant, yet its demands upon the soil or climate are exacting. It can however be grown in almost any climate but will suffer severely from drought. While tea requires considerable rain it will not grow in swampy areas. The highest yield will be obtained from tea which is grown in tropical climate. Paradoxically, the finest quality teas are produced from leaves grown in the cooler altitudes of 1,000 to 2,000 metres. (Darjeeling Teas grown against the background of Mount Kanchenjunga). Tea lends itself admirably to the Plantation system. Not only is it necessary to employ many workers for tending and harvesting but most of the estates must and do have their factories which require more machinery and skilled supervision than is involved in the exploitation of other tropical products.
FROM GARDEN TO FACTORY
The story starts from the tea seed but of course the seed itself is taken from the tea trees. Many estates have a plot of selected trees which are allowed to grow to their full size of 5 metres to 10 metres. During July to October, the trees blossom and tea flowers appear. But only after a year will the seed be ripe. The seeds are germinate into seedings and green shoots start to grow. In 9 to 12 months the young plants are ready for removal to the tea garden their permanent home.
The tea plant now grows steadily upwards and in the fourth year it attains a height of about 2 metres. If allowed the tea shrub grows into a tree reaching a height from 5 to 10 metres or even more. This makes it unfit for rapid production of leaves, while its shape and height would render the labour of gathering leaves both difficult and expensive. The plant is, therefore, cut back to about 45 cm to 50 cm when it is about 90 cm high. This is called ‘Pruning’, the primary object being to change the tea three into a bush and to encourage a spreading growth of leaf rather than wood. Much care is taken during the period of growth. Shade trees are also grown to provide a canopy and they also supply some of the essential plant nutrients and their roots ventilate the soil provided they are not over grown. Further, excessive shade trees is deleterious to quality.
Normally, the growth of tea plant is not maintained at a continous rate. There are periods periodic appearance of new leaves being called a flush. In South India there are two monsoons and bushes flush all the year round. While in North India when the wind turns during middle of November on the onset of winter season, bushes cease to flush until spring. The practice generally followed is to pluck the two top leaves and a bud as fine plucking but occasionally a third is also plucked which is called medium plucking. An experienced plucker can even gather as much as 56 kg of leaf in one day, enough to make 14 Kg. of finished tea. The era of cheap labour is gone. In Russia a combined pruning and harvesting machine is already in operation in some of the commercial estates while experiments are being carried on at the Research Station at Tocklai. In hand plucking discrimination between mature leaves ready for plucking and immature leaves are to be left over for next round of plucking is easy which is not possible in mechanical plucking. However, plucking as an individual operation now absorbs the highest of labourers spread over about 7 months of a season.
Human ingenuity cannot better the quality and tastefulness of tea when once the leaves are plucked. On the contrary inefficient and careless handling of leaf in manufacture can only spoil the inherent qualities. The plain fact is that good tea is the product of good leaf.
The Tea Act of 1953 provides for regulation of production and export of tea by the Tea Board. The regulation was a consequence of the International Tea Agreement of 1933, whereby an, agreed limit was placed on the exports from each of the contracting producer countries of which India was one. But the agreement lapsed in 1955 and has not been renewed so far.
The Tea Board originally concentrated on the promotion of tea habit domestically but now the necessary, is no longer there. It concentrates on overseas buyers by encouraging exports and the Tea Board has its office in important centres around the globe. Many an India tea chest like famous Dick Whittington finds its way to London : unlike Dick who failed to find any gold on London streets, Indian tea strikes gold the minute it strikes London and what is more, it sends the gold back home (valuable foreign exchange). A world body known as International Tea Promotion Association has been formed aimed at expanding the consumption of tea on a global basis with the mutual Cooperation of tea exporting and importing countries.
The production of Tea in India hovers around 550 million Kg. of which roughly 75% is manufactured in North India. Indian production of tea forms roughly 30% of world production with Sri Lanka and China as close second (around 12% each) of India’s production nearly 200 million Kg. will be exported earning around Rs. 400 cross of valuable foreign exchange. The state-wise production of tea will be roughly as under :
Assam 52 Tamil Nadu 13
West Bengal 24 Others 2
The tea exports are channelized through the ports of Calcutta, 68% Cochin, 21% and Bombay 10%, and Kandla is beginning to handle to relieve the congestion at Bombay.
After a long period during which tea machinery changed comparatively little, recently lot of improvements have been made. The Scientific Research Station and Analytical Laboratory at Tocklai plays a significant role. Great progress has been made in the chemistry of made tea and engineering developments have been remarkable. Thus we have moved a long way from the old fashioned planters who used to say that a dirty fermenting floor encouraged bacteria and so gave a fine flavour to tea:
There are more than 13,000 tea gardens in India. It may be of interest for the student to note that although Assam and West Bengal contribute nearly 50% and 25% of total country’s production, they are having nearly 75 and 300 gardens only. On the other hand, the production of Tamil Nadu and kerala is 13% and 9% of total production, while they have 6600 and 4100 gardens respectively. This means that North Indian gardens are able to reap benefits of large scale operations while fragmentation of holding is a phenomenon in South Indian sphere. On the other hand North East India tea grown in Assam and Darjeeling has to come all the way to Calcutta. South India tea enjoys the advantage of close proximity to Cochin port and in many cases only a matter of hours where road services are available.
The broker plays an unique role in the marketing of tea. In fact he acts as a principal and guarantee full payment to the sellers. He is an expert on tea and is trained in the art of “feeling, seeing, smelling, tasting and valuing” tea. He must also be an accomplished auctioneer.
The different types of manufacture employed in India can be broadly classified into orthodox, C.T.C. (crushing, tearing, curling all in one) Legg cutt, Rotovane and Chaff cut. Orthodox manufacture is by conventional Gank rollers while in other forms, C.T.C. or other machines described above will be used individually or in suitable combination.
Commercially tea may be divided into two well defined classes (1) Black or fermented (2) Green or unfermented. Black tea is most important commercially. After sorting grading tea is given various names such as orange Pekoe, Pekoe, Fannings, dust etc. but the student should note that arte only indicative of size and not of quality.
The following major processes are involved in the manufacture of conventional black tea :
(4) Firing or Drying
We shall take up these individual items of processing in the following chapters.
In the manufacture of tea, the governing idea should be the quality of the leaf. The leaf is the starting point in the processing chain. The different operations are intended to bring out the best from the leaf but if the leaf itself lacks the quality to give the whole proceeding will be wasteful. One authority on tea manufacture describes the possible effect of indifferent plucking on manufacture in these words: “An even wither can be traced to poor leaf; low out turn of fine mal can be due to coarse leaf; a dull infusion is a natural contribution will not improve infusions from coarse leaf; a plain liquor and poor appearance are two other contributions from leaf of a low standard”.
The following essential points should be remembered for the application of correct principles in orthodox manufacture. (1) Withering should be done under correct temperature with a correct spread of the leaf; (2) In rolling, circulation of leaf must not be hampared under pressure; (3) Right timing usually a maximum of 4 ½ hours and a minimum of 2 ½ hours should be observed in fermentations; (4) In firing both inlet and exhaust temperatures should be properly recorded. Each of the operations from withering to firing forms a link in the chain of manufacture, making a complete whole. For the sake of the whole, therefore, the links must be properly forged. A weak link is likely to make the whole snap this means that the factory equipment must always be kept on tip-top condition, factory organisation must be efficient, supervision very scrupulors, experience as large as possible and labour dutiful.
OBJECT OF WITHERING
After the plucked leaf has moved from the field to the factory, the first process in the chain of manufacturing is withering. In the withering process, there are no appreciable chemical changes in the leaf if not kept over 18 hours, but a degree of physical change is necessary to give appearance to the finished product. This physical change under modern conditions of manufacture is brought about by withering. It has an added importance in that all subsequent operations in manufacture are more or less dependent on the degree of wither. The degree of wither is determined by the objective development of character in the made tea.
Three main factors influence withering. They are :
In the withering process tea leaf loses water and becomes flaccid. The sap in the leaf becomes concentrated, and the leaf proteins change their physical state. Some chemical changes take place whether the leaf withers physically or not. How all these changes exactly affect the tea is not known, but if quality is in the leaf, withering develops it.
But physical wither is essential for the leaf to be properly rolled.
The tea leaf is sensitive to heat and too high temperature destroys the enzyme, hampering fermentation. The lower the temperature at which withering is don the better for quality. In Ceylon temperature as low as 50*F has been found to be beneficial.
DURATION AND TEMPERATURE
In natural withering, the rate at which leaf loses moisture so as to be fit for rolling without being fragmented, completely depends on the temperature and atmospheric humidity. If the rate is slow, withering takes a longer time and vice versa. This rate varies from region to region and even from day to day during the wet months. In Assam, withering is easier in the mid Brahmaputra Valley than at the foot of the hills.
These difficulties in withering have initiated investigation in to the possibility of artificial withering by means of heated air. It is now known that some sort of chemical action takes place in the leaf if it is stored for more than 18 hours. But during the rains natural withering is not completed within even 48 hours in the wet regions. For them, artificial withering will be a boon. During the early part of the season, leaf in these places can be properly rolled within 7 to 8 hours from the time of spreading. By artificial methods this period can be reduced to 2 to 3 hours. In normal manufacture, withered leaf enters the Rolling table in about 18 hours time from the time of plucking. Leaf should not be kept over 24 hours or it loses quality. Kept beyond 24 hours leaf is badly infected by foreign bacteria and makes dull tea. In upper Assam, Cachar and some parts of Dooars it is difficult to get more than 80 to 85 percent wither during the monsoon.
In China freshly plucked leaf is spread in the sun for a couple of hours and then placed in a cool place for half-an-hour, before manufacture. The pioneers in India got their training from the Chinese in the early days, and the Chinese process was adopted. But gradually outturn increased and less cumbersome method was needed. Instead of spreading the leaf on the ground bamboo racks in tiers was introduced but the sun remained in the moisture-removing medium. When the bad effect of heat on the physical and chemical changes in the leaf was realised, leaf houses with racks of bamboo trays were constructed. Subsequently, bamboo trays were replaced by wire netting and bamboo chungs covered with hessian.
In Assam Davidson claimed that the drier he invented could be used for limping the leaf and in 1895 he patented a withering machine with air of 90*F to 100*F. In 1910 Ceylon loft, was developed for use in Ceylon gardens.
This consists in passing heated air from the Drying Chamber or a mixture of the heated air and outside air over the spread leaf in the loft. In 1927, Marshalls produced a machine like an oversized drier which submitted leaf to air at a temperature of 100*F for 30 minutes. This machine has not gained popularity in the plains district of North East India.
But these mechanical devices could not satisfy the needs of some of the tea districts and the latest innovations are Drum Withering and Tunnel Withering.
Introduction of Drum Withering by Messrs. Davidson & Co., Belfast, has revolutionised the whole withering process. In the first place, there is much economy in space and labour and our present day elaborate leaf houses may be done away with. It has been found by experience that it is difficult to distinguish between the naturally withered and the drum withered teas by tasting. The leaf retains its qualities under both the process. Durm-withering has made control over quality and percentage of withering possible under perfect scientific conditions. The process is described here in the words of the inventors. Green leaf from the field is stored in the loft over the drum house and spread in banks of 6” to 8” thick. Each bank would contain sufficient quantity of leaf to feed a drum and the leaf is chuted to the drum. Each drum is capable of dealing with 5000 to 6000 1bs of green leaf in 3 hours depending upon the size and degree of wither required. The withered leaf can be discharged into trolleys or conveyor belt for transport to the rolling room.
This consists of a large tunnel chamber in which trolleys with built-in withering trays are placed so as to completely fill the chamber. Leaf is spread by hand on the trays outside the tunnel and then the mounted trolleys are moved into the chamber. When the chamber is completely filled with required number of trolleys, air is evenly passed over the leaf on the trays at a regulated speed. The hygromatric difference of this air, required to evaporate moisture from leaf is controlled by the application of heated air mixed with air at ambient temperature, and an even wither to the required degree is obtained in a comparatively short period of 3 to 4 hours according to the percentage of moisture to be removed from the leaf.
NO WITHER MANUFACTURE
Earlier we have referred to two systems of manufacture practised in some tea district with unwithered and partly withered leaf. The one is the Legg Cut Process and the other is C.T.C. in the legg cut system, the plucked leaf is passed through the Legg Cutter and cut leaf is then rolled in a specially designed roller. In the C.T.C. system the leaf is first rolled lightly for about 30 to 40 minutes and the rolled leaf is then treated in the Crushing, Tearing and Curling machine, two, process the leaf cells are completely smashed and the sap is evenly spread and distributed, accelerating fermentation. In the Legg cut, the leaf is first cut and then rolled. In the C.T.C. the leaf is first rolled and then cut. The speed of the gap between the rollers can be veried by means of adjusters according to the amount of bruising and tearing desired. In both the systems, either unwithered or partly withered leaf may be used. Sometimes, even a mixture of the two is used.
This type of manufacture requires a much stricter supervision than orthodox manufacture. In C.T.C. system of manufacture, usually fermentation is completed within about two hours and so conditions in the fermenting room are to be closely watched.
If withering can be described as the process for concentrating the cell-sap in the leaf, rolling may be considered as the process for breaking the self-same cells. An essential operation for releasing the elements which go to make for quality. On successful breaking up of the cells depends, to a considerable extent the quality all desire in the end product.
The rollers green sifters, C.T.C. machines trollies, which constitute equipments of the rolling room, as well as its floor, must be kept meticulourly clean to avoid contamination by harmful moulds and bacteria. Bacteria kills the enzymes which help the process of fermentation.
It has been observed that if the leaf can be given the twist characteristic of a good roll, the quality of its liquor is greatly improved. This can be treated by comparing the brews obtained from the leaf immersed in boiling water before-rolling and after rolling. Twist is also necessary for appearance. The tea industry has to cater to fastidious tastes in respect of its custom. The industry has to exert its best efforts to retain as many qualities of the leaf as is possible during processing. The role which rolling occupies in developing quality in tea, is an important link in the chain of processing.
Both withering and a successful roll contributes to the superior liquoring characters of a normally manufactured tea as compared with those of a nonwither tea. In the latter case the brassy or metallic character persists, as the breaking up cannot be satisfactorily done by a standard roller. The change occuring in fermentation is influenced by the efficiency with which the roller has been able to rupture the leaf cells and to distribute the sap over the surface of the leaf. To bring about the ideal condition in case of unwithered leaf, Legg cutter and C.T.C machines have been developed.
IMPROTANT FACTORS IN ROLLING
In rolling, three factors play prominent part. These are :-
TIME IN ROLLING
Rolling time is regulated in different factories and in different regions from experience of local conditions and the adequacy or inadequacy of firing capacity of the driers. As a general rule, rolling should not be extended beyond the time absolutely necessary for quick oxidation of the smashed leaf cells. Extended oxidation gives dull or flat tea, wanting in briskness. In Assam, longer roll was the practice sometime back, but now the time has been reduced to two rolls of 30 minutes each, to make increased allowance for the leaf to cool down from the heat generated by mechanical contact, as well as from bio-chemical changes started by rolling.
Time of rolling is also determined by the degree of wither in the leaf. Hard wither leaves require longer roll than light-withered.
EFFECT OF TEMPERATURE
Temperature above the prescribed limit affects flavour adversely. Temperature both in the rolling room and inside the roller should be controlled. Air should occasionally be allowed inside the rolling table by releasing the pressure cap so that the charge may not be overheated. Rolling tables should also be installed in the coolest part of the factory and should be partitioned off form all heat generating equipments. There is generally a difference of 10*F between the temperature of the following room and of the leaf under hard roll inside a roller. To avoid overheating the temperature of the room should not be allowed to go beyond 70* to 80*F.
EFFECT OF PRESSURE
It is a good practice to apply very light pressure during the first roll, if the plucking is fine. Pressure should be exerted only to bring out that much juice sufficient to cover the bud. In case of medium plucking however, a lignt pressure may be necessary to bruise the coarse leaf. Too much pressure in the first roll destroys the buds which form tips. Tippy teas have a market of their appearance although quality is not necessarily associated with tips. After sifting the fine leaf the residual course leaf may be subjected to hard pressure as to bruise it completely to ensure an even fermentation. Whenever pressure is applied it should never be continuous but cap should be raised and lowered at intervals to allow the heat inside the roller to escape.
The essential requirements to get the best results when flavour is present in the leaf is hard rolling. But some people erroneously entertain the idea that falvour is lost by hard rolling and for this reasons they change the rolling programme for ‘flavoury’ season. Even the time of rolling is shortened so that the flavour may not be ruined by the slightest rise in temperature during rolling. The pressure cap of the rolling table can thus make or mar the quality in tea.
The C.T.C. system of manufacture is an effort to reduce the cost of production and to increase in-take by foreign buyers. It must not be forgotten that the system cannot provide what is not already in the leaf. It however, been established, that the system is more efficient than the orthodox method in enhancing both the flavour and the strength of the brew provided the raw leaf possesses the necessary properties. When desirable properties are lacking in the leaf, the method has a tendency to dull down the liquor. The taste for C.T.C product has not yet developed as widely as the taste for orthodox tea and so the market is also limited now. It may be that with the increased popularity of the tea bag and instant brew the demand of C.T.C tea will increase.
SPEED OF ROLLERS
Another factor generally overlooked is the speed of the rollers. In normally withered leaves, 60 to 70 revolutions per minute are satisfactory. With underwithered leaf, higher speed is productive of good result. In regions where hard wither is practice, slower rolling is the rule. Slow rolling is associated with the lengthening of the rolling period to facilitate complete break-up of the leaf cells. It is not possible to adjust the speed every hour of the day, but speed can be regulated during dry and wet spells by maintaining two sets of pulleys.
Fermentation starts with the rolling of the leaf. Tea fermentation consists in the oxidation of tannin bodies in the leaf with the help of an enzyme which is present in the leaf. When leaf cells are broken, this enzyme takes oxygen from the air, passes it on to the tannin to form red and brown substances, making for colour and strength. In this phase, enzymatic actions are more pronounched and the properties of black tea are attributed to this phase first decomposed into alcohol and carbon dioxide. In over-fermentation this decomposition proceeds further than desirable and alcohol is decomposed further into acid. If fermentation is carried too far, the fermented leaf develops a sour smell which is reflected in the cup.
The following factors influence the quality of the tea during fermentation :
TIME IN FERMENTATION
As fermentation starts with the first roll, fermenting time is calculated from the time first rolling is set into motion. Time required for complete fermentation various with climate, temperature, quality of leaf, intensity of wither and nature of rolling. Any one of these factors is sufficient to affect the time of fermentation. Flush leaf takes less time to ferment than the rains leaf and autumnal tea requires longer fermentation than the rains tea.
While plucking is coarse, a certain percentage of hard coarse leaf and coarse banjhis get mixed with the tender leaf. The tender leaf ferments in due course but the coarse leaf is difficult of fermentation and remains green. No time should be lost over the fermentation of this green stuff, because this will never take proper colour owing to its physical charcter. But in the meantime, the tender leaf will lose its quality by this prolonged fermentation. This coarse leaf, when dried and cut, will present a rugged appearance by its flakly character. Provided the leaf is properly rolled a good wither will give quicker fermentation than imperfect wither.
If space permits, thickness of the spread of leaf on the fermenting floor, or aluminium or glass sheets, should not exceed one inch. In Ceylon, good result has been obtained by spreading leaf half-an inch thick. Thick spreading prevents aeration of the leaf inside the spread, hampering fermentation. Thicker spreading, however, does not reduce the amount of oxygen absorption, but helps conserving the heat already generated in the rolling table by fermentation to the deteriment of quality.
EFFECT OF TEMPERATURE
Colour and aroma have their appeals to consumer. Both of these develop during fermentation under favourable conditions. So the temperature of the fermenting room and the rolling room must be kept constant and uniform between 70* to 75*F. It has been observed that with a much higher temperature, tannin oxidation is too rapid and by the time aroma can be developed, oxidation is far ahead and the colour is lost. Conversely, with a much lower temperature, aroma exhauts itself by the time colour develops under very low rate of oxidation.
Dry air on dry leaf surface spoils the colour of the leaf and blackens it. It also impedes the progress of fermentation. It is therefore, necessary of fermentation. It is therefore, necessary to keep both the leaf surface and the air moist, to obtain proper fermentation. Formerly, this used to be done by spraying water on the fermenting beds and by sprinkling water on hessians suspended along the outer walls. This primitive arrangement has now been replaced by a more scientific method of evaporative cooling by means of mist chambers. Humidification is not uniformly effective in all regions at all times. In some parts hot dry spells are of considerable length during the early part of the year. Humidification is a necessity for those. In other parts, where rainfall is low, humidification is of immense benefit. The crude method of sprinkling is pregnant hot-bets of bacteria which are inimical to fermentation. It is really a matter of great regret that the importance of humidification is not great regret that the importance of humidification is not realised in Cacher, Tripura and other common tea producing areas, where it would have contributed to the improvement of quality to some extent.
OBJECTS OF FIRING
The principal object of firing is to make the fermenting enzymes inoperative so as to arrest further fermentation and to develop the keeping quality of the product. Tea is required to be stored, at times by the intermediaries in distribution, even for a year after being packed. Moisture content plays significant part in deciding how long the quality of the tea can be preserved.
The firing process needs constant supervision for in North East India, the moisture content of the fermented leaf varies according to the wither and with a Kutcha wither the moisture in the leaf will be higher and the dryer will consequently have more work to do. Similarly, the nature of the machine, for every fine mal or soft, flakly unwithered leaf will pack more closely on the trays than coarse mal or well twisted leaf through which the air can pass more freely.
NUMBER OF FIRINGS
Firing may be done in one or two operations. Both the processes have their merits and demerits. In single firing equipments have to be ircreased to one and half times the equipments necessary for double firing. In considering the length of firing we should consider that firing and fermentation are delayed, leaf is likely to be ove-fermented. On the other hand, if the firing is done under unusually high temperature tea is likely to lose its properties. Moreover, it may not be possible to obtain even firing by the single operation system.
Single firing is widely practised in Ceylon, Java and other places where moisture content of the leaf is kept constant by controlled withering. In North East India, where withering is still done under normal conditions this moisture content in the leaf varies according to the degree of the wither and seasonal variations in climate. Here the usual practice is to do the firing in two operations the first being done varying from 75% to 90% and second, to complete the process.
Of late, some firing machines, have been improved to a degree of efficiency for single firing. But here too, strict supervision and control are necessary. In very recent years, Dryers have been equipped with thermometers which automatically record the day’s firing temperatures.
For the first fire or in case of single firing, an inlet temperature of 190*F may be appropriate. In this case, the exhaust temperature will be naturally higher than 120*F. An inlet-temperature lower than 180*F may improve the liquoring qualities but will reduce the keeping quality. A higher inlet temperature increases the output or a dryer, but it results in loss of liquoring qualities, which loss becomes more pronounced in the second firing. The inlet temperature should be kept constant at 190*F as far as possible.
The exhaust temperature should not be allowed to drop below 120*F as this will render the air moist and reduce its drying capacity. Fermentation does not stop even at high temperature if fermented leaf is placed on the top tray under humid conditions. This prolonged fermentation causes stewing with the characteristic dull colour in cup and soft liquor. Loss of moisture in the upper part of the dryer under these conditions is slight.
If the exhaust temperature is substantially above 120*F, the fermented leaf will be dried will be dried more rapidly than is desireable. Rapid drying will result in the outside tissues of the fermented leaf becoming crusted and in the inside moisture remaining pent up within the crust. Excessive heat may also make the internal moisture vaporize, forming blisters on the surface of the leaf.
ADJUSTMENT OF TEMPERATURE
From the above it is evident that the exhaust temperature should be kept steady between 120* to 130*F. This can be done by a number of adjustments. If the exhaust temperature is too low, it can be raised by one of these adjustments: (1) by thinning out the spread of the leaf in the tray; (2) by decreasing the speed of the tray; (3) increasing of all these methods. Should the exhaust temperature be too high a reversal of the above methods is called for.
RECIRCULATION OF EXHAUST AIR
One of the frequent causes why dryers cannot fulfill their estimated outturn of finished tea even with correct inlet and exhaust temperature is the insufficient supply of clean fresh air to the fan. In most of the factories there is no suitable outlet for the hot moist exhaust air to pass quickly out of the drying room and as a result it recirculates to the inlet fan. This defect can be remedied by providing ventilators in the roof of the drying room and by separating furnaces from driers by a partition. But at the same time, fresh air should not be shut-off from the drying chamber.
ESSENTIAL PREREQUISITES OF CORRECT FIRING
In order to ensure correct and efficient firing a complete knowledge about the driers installed in the factory is essential. The different adjustments are to be studied carefully and their functions thoroughly watched. Theremometers both in the duct and above the top tray should be kept in perfect order and should give correct readings. Exact knowledge by the leaf to traverse the dryer at each pulley speed should be acquired operating in the thorough grasp of the dryers operating in the factory grasp of the dryers operating in the factory is essential. Above all factory equipments factory is essential. Above all factory equipments must be commensurate with the crop to be dealt with.
1. Cleanliness strictly to be observed.
2. Arrangements for passing out of exhaust air.
3. Capacity ratio of first to second drier to be maintained if firing is done in two operations.
4. Provision for supply of fresh air from outside to be kept.
5. Thermometers at both sides of the drier indicating even firing to be checked up as frequently as possible.
6. Exhaust temperature in first firing to be kept as constant as possible.
7. Constant feed of driers for economy.
8. Fermentation does not stop at high temperature if humid conditions are allowed to prevail inside the drier.
9. Thin spreading is of special importance in the first firing but not so in the second.
10. The second firing should be as quick as possible to avoid overfiring.
11. Drier-mouth mal should never be stacked hot from the drier but first allowed to be cooled. Any thickness of this spread above 6” has an adverse effect on liquor.
12. All equipments to be maintained in tip-top condition.
FIRING OF C.T.C. TEA
It is unfortunate that in recent years there has been a considerable changeover to C.T.C. system of manufacture without first equipping the factories with the number of Driers adequate for firing the leaf after C.T.C. treatment. C.T.C. teas, due to their fine cut, are to be spread very thinly on the trays to prevent packing and naturally, the firing capacity of the factory which was designed for orthodox, tea has to be enlarged to meet the increased demand. The trays of the firing machine, where necessary, have to be changed so that small sized C.T.C. may not fall through the meshes resulting in uneven firing. Drying process is now universally acknowledged by all as the most important process in the chain of manufacture, whatever be the system employed. Far less margin of error is permissible in this process than in any other. Maintenance of correct temperatures is a vital thing to drying under any system of manufacture but it is all the more important in the C.T.C. system. Criticism is levelled against C.T.C. teas regarding their keeping properties. But it can be said without fear of contradiction, that C.T.C. teas will hold their own against any other tea provided the drying process is correct and the moisture content is checked before packing.
SORTING AND PACKING
OBJECTS OF SORTING
Sorting merely changes the size and shape of the manufactured tea, but cannot influence the development of quality as the manufacturing processes do.
In the rolling process the leaf is broken up into different sizes according to the flaccidity imparted by wither. Some leaves remain unbroken and get twisted in the process. These whole leaves are passed through a cutter or breaker to bring those into line with the broken leaves as far as possible. But even then, uniformity in size cannot be established. We have seen that the manufactured tea becomes brittle/after firing. This brittleness is reflected in the conversion of the tea into powder form in course of the breaking operation. The aim of sorting is to retreive the different sizes from the bulk and to classify them into grades, it is expected that grading according to sizes will give everness to the brew, when the leaf is infused.
METHODS OF GRADING
The method of grading has undergone many changes from hand chulney to the most up-to-date sorting machines, Grading is the most mechanised single operation in a tea factory. In progressive factories the bulk is passed automatically to the different strong machines by means of conveyors and the residual coarse leaf is similarly passed/through cutters and breakers before reconveyed to the desired machines, Although saving in labour cost may not be anything astounding the tendency in greying is minimized to a considerable extent, A high premium is now placed on the appearance of tea. It is therefore desirable that all intermediate processes, which involve too much handling should be avoided as far as possible. Many factories are capable, of effecting this improvement with their present installations while reshuffling of plants machineries may be necessary in other factories.
Science is greatly helping the Industry to simplify all processes of manufacture. In Soviet Russia extensive work is in progress in the All Union Tea Industry Research Institute on the sorting of the half-finished black tea product. The problem of creating a combined sorting machine in which all the operations will be mechanised is also thought of. Already a pneume-sorting table, which separates different grades of tea on the basis of their respective specific weights, has been adopted by the Industry there. Our own Research Institutes are also doing research on continuous mechanical rolling and sorting. The smaller units can avail the modernisation methods by collective operations.
NUMBER OF GRADES
As almost all tea is blended before being offered to consumers, buyers are always particular about known garden marks so that they may not grope in the dark as to the suitability of their purchase for the particular blend or blends they have in view. Buyers have been habituated to these marks so much so that they have come to associate certain standards with the teas under those marks. This standard may not be an all round quality of the tea but its superiority in some respects and the constancy of that superiority. One other factor that counts with the buyers is the availability of that particular tea in quantities according to their requirements. If a tea fails to answer to these two essential demands big buyers in the auction room can never be attracted, and unless big buyers become interested in the tea, it cannot be expected to fetch the best price. This is why it is necessary to stick to a particular standard of grading and to confine the grades to as low a number as possible, so that buyers may always be interested in the offers. In small units, grading of teas into Golden Flowery Orange Pekoe (F.F.O.P) Flowery Orange Pekoe (F.O.P) Flowery Broken Orange Pekow (F.B.O.P) etc. is done at the sacrifice of quality of the other normal grades of O.P., B.O.P. Pekoe (p) Broken Pekoe souchoug (B.P.S.) Orange Fannings (O.F.) Pekoe Fannings (P.F.) and Dust. The classification into Flowery grades as mentioned above may be necessity with the bigger units but it is a luxury with the smaller ones and may be called a ‘Vanity’ grading to show a semblance of parity justified in the bigger units. This classification can be justified in the smaller units if the individual grades are big enough in proportion to its total output to be offered independently for sale and it does not detract from the value of other grades both of which are outside the mark.
In the no-wither system of manufacture, only three grades namely B.O.P., Fannings and dust are produced. B.O.P., makes the highest percentage between 60 to 70%.
With the increased popularity of packet sales of tea bags consumer might forget the appearance of tea. There is a possibility of the/numerous grades now in fashion to be reduced to two or three as in non-wither teas and a time may come when a few of the ultra-fastidious may call for Flowery Orange Pekoe or Golden Flower Orange – Pekoe.
Grading should always be true to the standard established by a particular estate, close to the type to which buyers have become accustomed. Constant variations from the type will drive away the traditional buyers and the tea will be left at the mercy of new buyers. Buyers resent a mixture broken grades with whole leaf grades and specially dislike the presence of Dust tea in any other grade. It should be the aim of the producers to standardise the grades in the different estates. Where quality fails, characteristics count. Appearance of tea and evenness of size are two of the most important characteristics, which have an appeal value.
It is very difficult to detect the presence of sand and other alien materials in Dust tea. Unless the floor of the sorting room is kept scrupulously clean, the risks of this mixing up becomes considerable. The atmosphere of the sorting room remains surcharged with fluff and dust released during the process of shifting and these have a tendency of setting down on the tea under processing as well as on the tea lying in heaps and in packing boxes on the floor of the storing room. Labourers are prone to sweep back these undesirable materials to the piles if the supervision is slack.
At one time it was the rule rather than an exception to press down the tea in the packing box by trampling. But now in progressive factories packing is being done by machines, although in less progressives ones, the old system continues. The trampling system causes abrasion much more than machine packing and the result is an admisture of dust with other grades. This admixture is likely to detract from the value of the original grade. The moisture content of all teas should be estimated before submission to final firing for packing. No foreign material such as bits of wood and bamboo, nails, small pieces of aluminimum foil etc., should remain mixed up with the packed tea.