DARJEELING BLACK TEA MANUFACTURE

The Black or Green tea sold commercially is manufactured from the tender leaves of the plant “Camellia sinensis”. A tea plant if left unpruned would grow to a 40ft high tree. It is however pruned every 4-5 years to spread laterally and maintain a harvestable height in plantation agriculture which gives its typical bush shape. The tender apical growing leaves are plucked off at regulated intervals of 5-7 days and manufactured to dry tea through various processes. The moisture of leaf which is about 74- 83% is brought down to 2.5-3% while controlling its oxidation/ fermentation to produce tea of different types. The duration of manufacture varies between a period of a couple of hours in case of green tea till almost 24 hours in case of black tea. 100Kg of green leaf yields roughly 22.5Kg of dried tea.

1.RAW MATERIAL:

The quality of raw material or harvested green leaf, being the sole ingredient is most important and the key to tea quality. Darjeeling plantations vary from elevations of 2500- 7000 ft above sea level. This part of the Himalayan range of mountains are covered with clouds for major part of the year. It is naturally blessed with a variety of dense flora and fauna which thrive in the misty conditions. The tea plant and its leaves imbibe these characters to give Darjeeling tea its unique flavour and taste. These rare geographical conditions give birth to this variety known as “The Champagne of Tea”. Tea is plucked off the bush by the nimble hands of the tea plucker. Through their years of experience they choose the best of leaf quality comprising maximum of two full grown leaves and a growing bud and put it in a traditional “doko” or bamboo basket.

GREEN TEA LEAVES PLUCKING 

GREEN TEA LEAVES PLUCKING

The composition of healthy polyphenols, volatile flavour components and catechins are maximum in the bud till the first 3 leaves, which are the ingridients of good quality Black Darjeeling Tea. Plucking starts from about 8.00 in the morning and carries on till 4.00 in the afternoon with breaks in

between for tea and lunch. During a day, a plucker harvests almost 5-10Kg green leaf. This leaf is weighed in the field and carried off to the factory in motorised vehicles thrice during the course of work. Care is taken that the plucked leaf is kept cool, intact and green as oxidation starts after it is taken off the tea bush which releases heat. Under no circumstance should the temperature rise above 32⁰C.

2.WITHERING:

This is a process of delaying the oxidation of green leaf over a period of about 18 hours. It has two parts- physical wither which is the loss of inherent leaf moisture from 74-83% till 30-40% and chemical wither. With the loss of moisture through leaf stomata, the cell wall weakens and breaks, releasing the intra cellular materials which mix and undergo complex reactions setting off chemical wither. During this stage enzyme activity starts, partial breakdown of proteins to amino acids occur, production of Volatile flavour components happen and there is a reduction of chlorophyll is noticed.

SECTIONAL DIAGRAM OF A TEA WITHERING TROUGH

GREEN LEAF ON WITHERING TROUGH

The green leaf is kept on withering troughs which are huge net top tables/beds with standard dimensions of 4’ x 60’. They are fitted with a duct below and fan on one end. The fan delivers air through the bed of leaf spread on top of the trough to cool it as well as remove moisture. As the climatic conditions can be cold and rainy, provisions of hot air through air heaters or boilers are also provided to be used as necessary. At the end of a duration of 18 hours of withering, the leaf becomes quite dry but remains green and starts to emit a faint sweet flavour.

3.ROLLING:

Rolling of leaf is the process where withered leaf is subjected to twisting action which gives orthodox manufactured tea its unique shape. The leaf is charged into the feed drum of a Rolling Table machine and thereafter twisted between two plates. Generally the bottom plate moves in a circular pattern with relation to the top plate (Single action Rolling Table). The action of the rolling table is akin to putting some leaf between human palms and rolling. The profile of the bottom plate is also shaped likewise.

TEA ROLLING MACHINE

TEA BEING ROLLED

Rolled leaf undergoes rupture in its cells causing intermixing of cellular sap thereby setting off oxidative reactions.

4.OXIDATION:

During oxidation the polyphenols in tea undergo enzymatic oxidation to form more complex polyphenols. The six different forms of catechins are oxidised by Polyphenol Oxidase to initially form orthoquinones, which further combine in pairs to form theaflavins (TF). The theaflavins are responsible for imparting flavour, brightness and briskness of liquor in the tea. Extended oxidation produces further complex thearubingins (TR) which have deleterious effect on quality. Experience and skill in controlling this oxidation (called fermentation commonly) for right combination of TF and TR imparts the flavour and liquor characters to Black Tea.

OXIDATION ON METAL RACK

OXIDATION ON FLOOR

The rolled tea is spread on metal racks or on the floor with a thickness of 0.5”- 1”. They are kept in a room with almost 16 air changes and a relative humidity of 95%- 98%. The desirable ambient temperature is 28°C. Retention time under these conditions for the tea is 15 mins- 2.5 hours depending on the season and requirement of tea. The colour of the tea changes during this stage from green to golden brown over time. Development of smell intensifies.

5.DRYING:

During this process, the oxidation of tea is brought to a stop by application of hot air at about 230- 250°F. During this process the moisture content of tea drops from about 26%- 3%. The chain reactions which attribute the tea with healthy polyphenol and antioxidant content completely stop at desired levels, only to be savoured by the consumer upon brewing.

Drying is carried out majorly in triple circuit chain supported tray type Endless Chain Pressure (ECP) driers. It resembles a heat chamber with enclosed sides and open top. Hot air fed from Air Heaters or radiators are blown in from below. The tea is fed one end at the top and is carried on perforated trays moving on guides at the side. The trays move in a zig-zag fashion from top to bottom and the tea is dried during this time of about 24 minutes.

SECTIONAL DIAGRAM OF A TEA DRYER 

E.C.P. TYPE TEA DRYER

6.SORTING:

The stock of tea which comes out of the dryer is a mix of various sizes of leaf. Some pieces of dried stalky stem is also present which is not so desirable. The process of sorting cleans the stalks from tea bulk and separates the aggregates as per mesh size for evenness.

The following grades of tea are sorted as finished grades which are packed in multiwall paper sacks or wooden chests.

Machines used in sorting are:

FIBRE & STALK EXTRACTORS:

FIBRE EXTRACTOR

3T STALK EXTRACTOR:

While the leafy part of the raw material forms black tea, the stem gives stalk and fibre. Presence of these in large quantity decreases saleability. The tea bulk is cleaned from these stalks by passing through one of these machines. In a typical Fibre Extractor the tea flows through a vibrating steel tray. Mounted at a height of 3” across the tray are a set of rotating PVC rollers with felt pads pressed against them. The rubbing action generates static electricity which pulls up the lighter stalks out of tea bulk, thereby cleaning it.

In a 3T Stalk Extractor the rollers are stacked vertically and the electricity is controlled by a electric separate unit. Tea falls vertically and the lighter stalks stick to roller surface and are cleaned off.

MYDDLETON SORTER:

Two sets of Aluminium trays with 3/16” perforation are oscillated at about 210 RPM. Bulk tea from dryer mixed with all grades and stalk are fed through one side. It gets separated into larger well twisted leaf grades and smaller broken and dust grades. This machine does the primary grading of orthodox tea.

BALANCED TEA SORTER & ARNOTT SORTER:

BALANCED TEA SORTER

ARNOTT SORTER

The Balanced Tea Sorter machine has five sets of Stainless steel mesh stacked vertically. The mesh numbers are 8, 10, 12, 16, 20, 24, 30 and 40. The meshes move up and down in vertical motion by a asymmetric drive at about 300 RPM. Each mesh separates out tea as per its grain size.

The Arnott Sorter machine has similar 5 sets of mesh, but these ocillate horizontally causing the mesh to vibrate. The RPM is higher than the Pucca Sorter at about 500. The tea is sorted out as per mesh size.

ANDREWS TEA BREAKER & SAVAGE CUTTER MACHINES:

ANDREWS TEA BREAKER

SAVAGE CUTTER

The Andrew’s Breaker machine is used to reshape larger size unsaleable orthodox tea grades. It has two fluted Rollers rotating at about 60 RPM. Tea is crushed to smaller size when it passes through.

The Savage Cutter machine also reshapes larger leafy tea grades. It has two multicelled rollers rotating at 30RPM through which oversized tea grades are passed.