Quality of tea is dependent upon the filed to factory. Quality of tea mainly depends on the raw material and method of plucking . So care should be taken both in field and during transportation and within factory before operating the withering process. Tea leaves are damaged at various stage from plucking of leaves. Therefore care must be done as follows,
1. There is tendency that the plucker hold the greater quantity of plucked leaves in their hands. This should be avoided.
2. Plucked shoots collected in smaller or larger container such as bamboo basket, sacks and nets should never be compressed compact. It causes burising of tea leaves, generation of excessive heat and early fermentation.
3. Plucked tea leaves should not be exposed to sun.
4. Heat is the enemy of plucked leaf. Therefore temperature should not exceed more than 49°C which turns the plucked leaf red and breaks down the cell structure. Such tea leaves produce dull liquor and loss of brightness in fused tea.
5. Contamination of plucked leaves with foreign matters like dust, sand, twigs, rodent droppings and insects should be avoided.
6. Plucked tea leaves should be transported immediately to factory before they overfill. The stored tea leaves in lorry should not exceed 8 kg/m2.
7. Suitable framework is needed in lorry to permit free passage of air during transportation. Care should be taken mainly in rainy season when leaf is wet.
8. Upon receiving of tea leaves in industry, leaves should be spread on trays or mat for 10 minutes to remove field heat.
9. Damaged tea leaves should not be stored more than 8 hours after harvesting the tea leaves. It should be transferred immediately to the factory as soon as possible.
10. Tea leaves have predominant green color due to carbonyl compounds but short term storage of plucked leaf before processing reduce green color and grassy odor which is replaced by fruity odor due to increased linallol and linalool oxide.
Processing of black tea:Packaging of tea leaves: After tea leaves has been manufactured and graded, it is necessary to pack in suitable container so that its quality doesn’t deteriorate. Bulk packaging container should be from a hopper at regular rate. The tea never should be forced down, compressed or stuffed compact to save loss of bloom damage and prevent dust formation.
Sortened and graded tea is normally packed in plywood tea-chest. The chest are assembled using various component like iron nails, paper linings or aluminium foils. Recently, multi wall paper sacks and polythene lined jute bags are being popularly used.
The moisture content of tea and its shelf life is closely related. Maximum amount of tea should be packed in the container. Otherwise moisture and oxygen of free space promotes bacterial growth and enzymes are regenerated affecting the Theaflavins (TFs). After filling, tea in container should be closed promptly.
Tea should contain not more than 4 % moisture. For packaging 3 % moisture is preferable. There is no harm in bringing the moisture down to 2.5 % but there is no extra benefit. Reducing the moisture much below 3 % is costly operation s the rate of loss of moisture becomes very slow.
Process control in tea processing:
Withering: There should be microprocessor based control system in different point in the sequence of processing. The electric moisture meter would help optimize the system of withering. Microprocessor indicate the moisture content of the tea leaves at any time during withering. A controlled timer attached to the withering fan would be advantageous in automatic control of withering. The microprocessor based moisture meter and timer are forward going steps toward the automation of system of withering. The system will also provide for automatic switching off the process once optimum withering is achieved.
Rolling: Rolling is the complex operational stage. The cell rupture and release of enzyme under a set of pressure . Pressure during rolling needs more controlled system. Properly programmed electronic control with timer coupled with pressure gauze help in determining the optimal pressure at various time sequence.
Fermentation: during the fermentation, an electric sensor can greatly help in determining level of fermentation. Parameters like humidity and temperature can be evaluated and and standardized in relation to quality of leaves to be processed. An electronic color sensor would be ideal to indicate the desired degree of fermentation as color is most reliable parameter that changes linearly with degree of fermentation.
Drier: Electronic thermometers with large visual display can give instant inlet and outlet temperature of the drier. Automatic temperature control system also help save economy. A closed loop microprocessor system not only stabilize the inlet and outlet temperature but also help in determining the moisture content of final product tea at the end of drier. A major breakthrough in drying is the development of computerized drier with appropriate software to accurately predict the drying time.
Grading: For sorting out unwanted stalk, twigs or foreign particles from processed tea, an electronic color sensing separator is ideal. But the separation of tea particles according to size, shape and volume is based on advanced electronic image processing system.
An important parameter that needs continuous monitoring in almost every step of manufacturing is temperature because temperature determines not only the quality of final product but also optimization of energy conservation particularly during drying.
Name : Pratiksha Shrestha
Ms. Shrestha holds masters degree in food engineering and bioprocess technology from Asian Institute of Technology (AIT) Thailand. She is currently working for Government of Nepal at Department of Food Technology and Quality Control (DFTQC), Kathmandu. She is also a teaching faculty in College of Applied food and Dairy Technology (CAFODAT) affiliated to Purbanchal university, Nepal.