Brief description about the manufacturing of instant tea/iced tea

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Basura J Jayasundara
Manufacturing process of instant tea
Process of the production of instant tea consists of the following operations.
Raw materials
The criteria for the selection of the raw material include raw material availability, processing
requirements, the market for which the tea is intended and the commercial restrictions placed
upon manufacture. Main types of raw materials used in the industry are processed leaves,
fermented dhools, refuse tea (BMF grade) in either black, green or oolong teas. Fresh leaves
also used as the raw materials in some manufactures of instant tea.
Extraction
The active substances of the tea leaves are extracted by means of aqueous extraction and are
carried out in hot water in batch or continuous extraction systems. Counter current extraction
is commonly used in both batch and continuous forms. Batch-wise countercurrent extraction
is normally used for the processing of small amounts of material and in continuously
operating extractors, the solid material and the liquid (solvent) flow counter currently.
Temperature of extract water, time of extraction, proportion of tea and water, type of tea and
purification of water are the major factors affect on the extraction process.
Raw Materials
Extraction
Decanting
Aroma Stripping
De-creaming
Concentration
Blending
Drying
Packing

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In this process tea leaves are fed into the lower end of the extractor and are conveyed
upwards by the rotation of the screw while the extracting water flows in the reverse direction.
The solution coming from the extractor usually contains 3-5% solids, which is measured as
brix value.
Type of unit operation: Mass transfer operation without phase change
Decanting
The soluble components are responsible for the taste, aroma and effect. In addition to the
soluble components, there are insoluble substances also that are not wanted in the end
product. They have a negative impact on the appearance and therefore have to be removed.
The extracted slurry is subjected to pass through continuous decanters and clarifier to remove
the non-soluble suspended matter from the extract. Decanters are used for the separating large
volumes of insoluble tea leaf components from tea extracts in the pre-clarification process. In
decanters, centrifugal force is used to separate solids from liquid efficiently in a manner that
is easy to control.
Aroma stripping
As tea aroma have important contribution to the acceptability of tea, considerable efforts have
been made to preserve the aroma in the instant product. Therefore, volatile aroma compounds
are stripped from the extract prior or during evaporation and added back to the liquor before
spray drying. If the aroma has not been stripped off the extract before concentration a
proportion of it will be removed with the steam.
De-creaming
Centrifuge is used in the instant tea manufacturing process to remove fine particles from the
extracted tea liquor.
The centrifuge works using the sedimentation principle, where the centripetal acceleration
causes denser substances and particles to move outward in the radial direction. At the same
time, objects that are less dense are displaced and move to the center.
In the centrifugal separator, the effectiveness is increased with a stack of conical disks for
creating a large equivalent clarification area and the force of gravity is replaced with a

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centrifugal force that can be more than 5,000 times stronger than the force of gravity.
Therefore, the separation will be significantly faster.
Concentration
The liquor coming from the de-creaming process is too dilute to pass directly to a drier.
Therefore the liquor has to be concentrated, generally to 20-40% solids. Concentration of tea
extract is carried out by evaporation under reduced pressure.
Type of unit operation: Heat transfer operation
The typical evaporator is made up of three functional sections: the heat exchanger, the
evaporating section, where the liquid boils and evaporates, and the separator in which the
vapour leaves the liquid and passes off to the condenser or to other equipment.
Single effect evaporator or multiple effect evaporators is used for the concentration of tea
extract. Multiple effect evaporator save energy by utilizing steam repeatedly.
Concentration of tea is normally done through reduction of pressure. At high temperatures,
the theaflavins in the solution are converted to thearubigins and carbohydrates caramelize.
Plate heat exchangers can cause the desired evaporation at around 45o
C, with short residence
times that reduce the risk of thermal damage.
Blending
Concentrated tea liquor is blended with previously stripped aroma compounds before drying.
Drying
Drum, spray and freeze drying can be used for the drying of concentrated tea liquor, but spray
drying is most commonly used in the industry because it is cheaper in terms of both capital
and running costs.
In a spray dryer, concentrated solution should be fed into the drying tower by high pressure
homogenizing pump and then sprayed in the form of fine droplet dispersion into a current of
heated air. Air and solids may move in parallel or counter flow. Drying occurs very rapidly,
so that this process is very useful for materials that are damaged by exposure to heat for
higher time. The dry product will be collected at the bottom of the spray dryer, and fines to be
collected in the cyclones.