|
Tea (Camellia Sinensis) is an evergreen shrub or tree, which grows wild from India to China. There are about 45 species of Camellia of which sinensis considered native to India and is the important one from which tea of commerce is made. Tea is a beverage prepared by pouring boiling water over dry processed leaves. It is the most popular refreshing drink in many countries.
Fresh tea leaves contain carotenes, riboflavin, niacin, pantothenic acid and ascorbic acid. But during manufacture of black tea they are lost. No change takes place in green tea as its manufacturing does not involve fermentation.
Tea as a beverage is consumed for its stimulating effect. The important constituents of tea contributing to the flavour are caffeine, polyphenols and essential oils.
Antioxidant activity
Polyphenols present in tea have antioxidant activity. Antioxidant activity of tea is much higher than spinach and other vegetables. A cup of tea supplies around 200mg of flavonoids. The antioxidant potency in a tea is 400 per cent greater than a cup of orange juice.
Studies have shown that higher the flavonoid intake lower the risk of death from coronary heart disease.
Types of tea
There are three types of tea depending on the processing of tea leaves. They are
- Black produced by a fermentation process
- Green or unfermented tea and
- Oolong or semi-fermented teas.
Black tea is the most popular among the three.
Black tea
Various processing steps involved in the manufacture of black tea are withering, rolling, fermentation, drying, grading and packing.
- Withering
It is carried out by spreading tea leaves thinly on racks or shelves. Air is blown to make them soft and flexible. They are dried till the moisture content is lowered to 40 %.
- Rolling
The withered leaves are then rolled to break open the cells and release the juices and the enzymes. The flavour characteristic inherent in various teas partially depends on the technique used.
- Fermentation
After rolling the leaves are spread out thinly on suitable platforms and allowed to ferment for 2-6 hours at temperature between 21 and 270 C. Two of the important polyphenols that undergo oxidative changes are catechin and gallocatechin. The colour of the leaves changes to black. When the fermentation has proceeded to the desired degree further change is arrested by drying and firing.
- Drying or firing
The fermented leaf is passed through the drier. The leaf is dried at 87.7-93.30 C for 30-40 min.
- Sorting and grading
Grading of tea is done according to its size.
- Blending
Different teas are blended to produce a product with uniform character. Blending is an art and demands skill and experience.
- Packing
In India, the blended tea is packed in plywood boxes lined with aluminium foil and parchment paper.
Green tea
Green tea is produced in Japan. Here withering and fermentation are completely omitted. It is made by first steaming the leaves to prevent the leaves from changing colour and to inactivate the enzymes. Steaming is then followed by rolling and drying. The leaves retain much of its original green colour especially the finer leaves. The older leaves often have a blackish gray colour. The beverage made from green tea has a greenish yellow colour and is distinctly bitter and astringent.
Oolong tea
This has special market in America and almost exclusively produced in Borneo. Oolong tea is partially fermented. The fermentation period is too short to change the colour of the leaf completely.
- Colour of tea
The bright orange colour in black tea beverage is due to theoflavin. The high phenolic content gives a tea with a high colour.
-
Factors affecting the quality of tea
- The polyphenol and the enzyme content of leaves used in processing affects the quality of tea. The polyphenol and the enzyme content is maximum in buds and the first and second leaf and the tea obtained from these is most desirable.
- The finest tea comes from higher elevations of 900-2100 meters.
- Mechanical pluckers are common in countries with flat land but tea of high quality are generally produced from leaves that have been hand plucked.
- Soil in which the plant is grown.
- Best tea comes from plants grown at low temperature where the air is warm.
- Processing techniques used.
- Orange pekoe has the largest leaves and is the best quality.
Tea is a stimulating and refreshing drink. The principal flavour components of tea are caffeine, tannin yielding compounds and small amounts of essential oils. Caffeine provides the stimulating effect, tannin the colour, body and taste to the extract and the essential oils the aroma.
- Instant tea
The process consists of the following steps.
- Extraction and concentration of the extract
- Recovery of the volatile flavour components
- Drying of the extract and
- Addition of flavour concentrates to the final product.
- Adulteration
The commonest adulterants are spent leaves, grit and sand. Leaves of other plants like agathi, avaral and husk of black gram are used as adulterants.
|
