Tea processing technology

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Presentation Transcript

TEA : 

TEA

Slide 2: 

Tea is the agricultural beverage product of the infusion of processed and dried leaves, leaf buds, and internodes of the Camellia sinensis plant, prepared and cured by various methods. "Tea" also refers to the aromatic beverage prepared from the cured leaves by combination with hot or boiling water and is the common name for the Camellia sinensis plant itself. Although tea contains various types of polyphenols, "contrary to widespread belief, tea does not contain tannic acid". After water, tea is the most widely-consumed beverage in the world. It has a cooling, slightly bitter, astringent flavor which many enjoy. There are at least six varieties of tea: white, yellow, green, oolong, black and pu-erh of which the most commonly found on the market are white, green, oolong and black.

Slide 3: 

All teas are made from the same species of plant, though different varieties may be used, and the leaves are processed differently, and, in the case of fine white tea, grown differently. Pu-erh tea, a post-fermented tea, is also often used medicinally. The term "herbal tea" usually refers to an infusion or tisane of leaves, flowers, fruit, herbs or other plant material that contains no Camellia sinensis. The term "red tea" refers to an infusion made from either black tea (mainly in Chinese, Korean, Japanese and other East Asian languages) or the South African rooibos plant (containing no Camellia sinensis).

AgronomyThe genus Camellia : 

AgronomyThe genus Camellia Comprises evergreen shrubs which, in commercial cultivation are maintained as a low bush in continuous vegetative growth. Contains a large no. of species but only the ‘tea Camellia’ , Cam. sinensis is grown commercially. Other species like Cam. irrawadiensis and Cam. taliensis are of imp. as a source of genetic material.

Slide 5: 

Camellia is a cross-pollinated, heterogenous plant. Leaf size is the chief criterion for the classification of tea plants. 3 principal taxa of cultivated camellia are recognized: -China (Camellia sinensis) used for most Chinese, Formosan and Japanese teas, characterized by the smallest leaves -Assam (Camellia assamica) used in most Indian and other teas, characterized by the largest leaves and -Cambod (Camellia assamica var. lasiocalyx) characterized by leaves of intermediate size.

Cultivation of CamelliaClimate and soil type : 

Cultivation of CamelliaClimate and soil type India, China and Ceylon are the 3 major producers. Also grown in Java, Sumatra, Japan and parts of Africa. Air temp. ranging 18-30˚C are optimal for shoot growth. Mini. air temp. for shoot growth appears to be 13-14 C Net photosynthesis & growth are reduced at temp. in excess of 30 C. Soil temp. between 20-25 C for optimum growth. Max. yield requires long hours of sunshine . Camellia Becomes dormant when day length falls below 12 hours. A high rainfall and high air humidity are required. An annual rainfall of 1800mm is necessary for continuous crop production.

Slide 7: 

Soil types which support commercial tea cultivation include- - alluvial soil - drained peat - sedimentary soil - soil derived from volcanic ash Growth is favored by acidic conditions , a pH value of 5.0-5.6 being optimum. Soils of pH values above 6.5 cannot be used for commercial tea growing. Tea needs high N requirement which cannot be met by soil. Application of N-genous fertilizers is necessary for high yielding clones although they reduce the quality of the made tea.

Slide 8: 

Commercially grown Camellia has a low P and S requirement. K is imp. as an intimate relationship with N metabolism. High requirements for Ca, Zn and Mg and deficiencies can occur. Localized deficiencies for Cu ( Malawi) and B ( north-east India) have been reported. Cu def. is significant in post-harvest behavior of tea. low levels of a Cu-protein enzyme result in failure of fermentation process. Al is also imp. Soil should be deep, well drained, of good water holding capacity.

Agricultural Practice : 

Agricultural Practice Land clearance is required before tea planting. Burning is not recommended as the ash will also raise the soil pH value. Tea plants are normally raised in a nursery before being planted out in fields. Tea seeds are produced by selected plants which are allowed to grow with only minimum pruning. Nursery beds should be of good quality topsoil.

Harvesting : 

Harvesting Tea is harvested by removing the top section , usually 2 or 3 shoots and a bud from an actively growing stem. Only the top 1-2 inches of the mature plant are picked. These buds and leaves are called flushes. A plant will grow a new flush every seven to ten days during the growing season. Harvesting of tea is traditionally a manual operation which involves 80% of the labor employed. Mechanical pluckers range from motor-powered, hand-held shears to self propelled harvesters. In the case of black tea, an important factor in determining the quality of the end product is the no. of leaves plucked during harvesting.

Slide 11: 

The actively growing bud gives the highest quality tea, quality deteriorating with the position of each leaf down the stem. The lowest quality tea is obtained from the stem itself. Picking first 2 leaves and the unopened bud – quality tea. Plucking 3 or more leaves and a bud - quantity. Plucking round may be as short as 4-5 days to a month. Long plucking intervals lead to poor leaf standard with a large no. of mature leaves.

Slide 12: 

A tea's type is determined by the processing which it undergoes. Leaves of Camellia sinensis soon begin to wilt and oxidize, if not dried quickly after picking. The leaves turn progressively darker as their chlorophyll breaks down and tannins are released. This process, enzymatic oxidation, is called fermentation in the tea industry, although it is not a true fermentation. It is not caused by micro-organisms, and is not an anaerobic process. The next step in processing is to stop oxidation at a predetermined stage by heating, which deactivates the enzymes responsible. With black tea, this step is executed simultaneously with drying.

Slide 13: 

Without careful moisture and temperature control during manufacture and packaging, the tea will grow fungi. The fungus causes real fermentation that will contaminate the tea with toxic and sometimes carcinogenic substances, as well as off-flavors, rendering the tea unfit for consumption. Tea is traditionally classified based on the techniques with which it is produced and processed. White tea: Wilted and unoxidized Yellow tea: Unwilted and unoxidized, but allowed to yellow Green tea: Unwilted and unoxidized Oolong: Wilted, bruised, and partially oxidized Black tea: Wilted, sometimes crushed, and fully oxidized Post-fermented tea: Green tea that has been allowed to ferment/compost

Technology Black Tea : 

Technology Black Tea Black (fermented) tea is technically the most complicated of the teas.

Slide 16: 

Withering Leaves lose moisture resulting changes in the permeability of the cell membranes. This conditions the leaf for maceration & fermentation stages , known as the physical wither. At the same time biochemical changes occur – the chemical wither. It is imp. that air should circulate as freely as possible around the leaf. This can be done by use of a withering trough, a long, low, narrow rectangular box fitted with a perforated floor through which a fan blows air upward through a shallow bed of leaves. Air heated may be fitted but avoid overheating.

Slide 17: 

Load the withering trough full so as to facilitate adequate withering. Withering improves the quality of tea but is often poorly controlled. A correct level of withering is achieved taking into consideration external factors such as humidity, temperature and standard of leaf. Optimum withering time is 12-16 h. Decrease in quality if withering time is extended beyond 20 h. Physical withering occurs concurrently with chemical withering.

Leaf Disruption : 

Leaf Disruption It is a physical process whose function is to reduce the size of the leaf material and some degree of cell disruption. This helps in exposure of new material to air during fermentation process. The choice of method of leaf disruption affects the requirements for both withering and drying. Rolling - Orthodox rolling is the most common method, where the green leaf is rolled in Rollers. This method of rolling is achieved by feeding withered leaf into a machine which appears like a large mixing bowl, on a circular, hard-surfaced table, on which brass or wooden battens are fitted. During the process the leaf is torn apart to a certain degree and also crushed. Orthodox teas tend to be lighter and less full bodied, compared to CTC manufactured teas.

Slide 19: 

Rollers occupy the ground floor of the factory and the withered leaf is fed through openings on the ceiling into the roller cylinder. This cylinder is adjustable to give the required pressure on the leaf during rolling.

Slide 20: 

Cut, Twist & Curl (CTC) In the CTC manufacture process, the tea is sent through a CTC Machine which makes small balls of tea. The withered leaf passes through two large rollers that revolve opposite to one another. On each roller are a multitude of sharp blades set at an angle that mesh with the opposing roller. As the tea passes through this series of blades the tea is cut, torn apart and is compressed or curled into little balls. This is a popular variety of processing for higher yields of crop. CTC teas are more suitable for tea bagging since they are easily fed into bagging machines.

Fermentation or Oxidation : 

Fermentation or Oxidation The rolled leaves, now called Dhools, are collected and spread over Fermenting Tables, where exposure to warm air makes it fermented. During Fermentation, the tea acquires its quality, flavor, strength and color depending on fermenting period, degree of rupture of leaf, humidity and temperature. The period can vary from twenty minutes to five hours. Due to the chemical process, the leaf changes from greenish to a bright coppery color. The fermented leaf is then sent through the firing chambers where hot air will quickly dry the Dhools to prevent further chemical reaction taking place.

FIRING OR DRYING : 

FIRING OR DRYING Firing technology itself is highly technical, as the process involves firing temperature, volume of air, load of leaf on to dryer trays, period of drying and the inlet and exhaust temperatures. The machinery used for firing is called a Drier. There are different types (batch/semi-continuous, belt, fluidized bed, plug flow fluidized bed dryers) and sizes of Driers in use.

SORTING AND GRADING : 

SORTING AND GRADING Once the tea passes through the firing process, it will be ready for Grading. The Graded Tea is final product. The tea particles are separated into different shapes and sizes, by sifting through a progressively finer series of meshes. The various grades denote only the size and appearance of the leaf and bear no relation to the quality or flavor. The major grades of tea are – Leaf Grades and Broken Grades. Leaf grades have larger and longer pieces of leaf giving lighter colored liquor and the Broken grades consist of smaller pieces which normally gives a darker liquor and stronger flavor. The smallest particles come under Dust grade, valued for its strength and quick infusion. Within these grades there are sub-divisions such as Orange Pekoes from Leaf Grades, and Fannings from Broken Grades.

PACKING : 

PACKING Once Grading is complete the Teas are now weighed and packed into Tea Chests or Paper Sacks ready for dispatch. All sorted and graded teas are now ready for packing in tea chests or bags. Pics show made tea being filled in large bins and packed teas in bags ready for dispatch.

Flavored Teas : 

Flavored Teas The most famous is Earl Grey flavored with the essence of citrus fruit. Flowers like – jasmine- flavor some China teas. Flavoring is added either as an essential oil or as a water –soluble concentrate. Natural, synthetic or natural-identical flavorings may be used. Synthetic flavor gives a long shelf life. Natural flavoring give a better quality.

Green Teas : 

Green Teas The fermentation stage is completely omitted from processing and enzymic activities in the leaves is inhibited by heating (steaming or pan-firing) . The character of green tea is largely determined by the endogenous components of the leaves at the time of plucking rather than by compounds formed in post –harvest reaction .

Slide 28: 

Processing of green & Semi-fermented tea

The Sen-cha process : 

The Sen-cha process Produced from the leaves of unshaded plants. Freshly plucked leaves are steamed for 45-60s before being dried and curled in the roller in air at a temperature of 100˚C. This primary drying and rolling lasts 40-50min and reduces the leaf moisture from 76% to 50%. The leaves are rolled, pressed and pass to a secondary drying stage involving heat at 50-60˚C for 30-40min. Moisture content reduces to 30 %. Further subjected to rolling before being dried by direct heating at 80-90˚C. Process lasts for 40min. Leaves are subjected to twisting by pressing and rolling using a “curling hand” Finally the moisture content is reduced to 6% by drying. After refining , the green tea is usually redried to improve the aroma of the made tea.

The Kamairi-cha Process : 

The Kamairi-cha Process Pan-firing is used in the production of ‘Chinese’ green tea. Process differs from Sen-cha in the use of dry heat (parching) instead of steaming. It involves heating in a pan at temp. 250-300˚C for 10-15 min. Slow agitation (5cycles/min) must be employed to prevent burning. During heating the tea develops the characteristic pan fired aroma. Leaves are then passed to a roller and processed without heating for 10-15min before final drying in a pan at 100-150˚C The rolling shape determines the final stage of the tea and 3 end-product variants can be produced: - gun tea (small pellets) - chun-mee & sow-mee (fine, twisted) - pan fired (flat, polished leaves, pale white in color)

Semi-fermented tea : 

Semi-fermented tea Characterized by oolong and pouchong teas, difference lying in the intensity of fermentation. Semi-fermented teas have flowery characteristics and specially selected clones are used. The 1st stage involves outdoor withering in the sunlight imp. in initiating biochemical reactions. Done on bamboo baskets, the temp. increases to 35-40˚C for 30-60 min. Indoor withering is done at room temp. This lasts 6-7 h in case of oolong tea and 3-4 h for pouchong tea. Every hour leaf is manually agitated. The withered leaves are pan-fired at 250-300˚C for 15 min. Pan firing inactivates enzymes and terminates biochemical changes. Rest processing is same as green tea.

Pickled Tea : 

Pickled Tea Pickling involves a fermentation in which indigenous micro-organisms play a significant role. It is made from fresh tea leaves steamed for up to 1.5 h . Steamed mass is buried in a pit / packed in bamboo baskets & allowed to ferment for 2-4 months. NaCl is added to suppress undesirable MO. MO give sour and flowery flavor. Pickled tea to be consumed as a beverage is dried after pickling.

Decaffeinated tea : 

Decaffeinated tea Tea is mixed with an organic solvent which dissolves the caffeine. Solvent is removed from the tea as completely as possible. Caffeine is recovered for sale and the solvent cleaned for re-use. 3 solvents are used – ethyl acetate, methylene chloride and supercritical CO2. Decaffeination involves treatment of the dried black leaf. Decaffeination of the green leaf before drying is used on a small scale and appears to improve product quality.

Instant tea : 

Instant tea Both black and green instant teas are produced. The liquor (tea brew) itself is further concentrated and dried to form a powdered or granular product. Tea Cream Processing When a solution of tea cools down it becomes opaque and changes color to pale brown in a phenomenon known as 'creaming'. The cream essentially consists of caffeine, theaflavins and thearubigins and teas can be characterized by the amount of cream formed on cooling. In the manufacture of instant tea, tea cream is processed either by maintaining the temperature above 65 C or by removal by cooling and precipitation or centrifugation.

Slide 36: 

Since tea cream contains may flavor compounds removal by precipitation decreases the quality of the tea and incidentally, decreases the yield of solids from the leaf, so solubilisation by maintaining the temperature is a preferred method. Cold soluble tea, is required to be clear and bright when reconstituted and the cream causes an unacceptable haze, hence solubilisation of the cream is crucial. The cream is separated from tea extract and is oxidized at 70 C at a pH of 9 - 10 with molecular oxygen. Use of enzyme tannase has also been documented in dissolving the tea cream. Cold soluble teas are produced by allowing the tannins in the cream to react with anaqueous solution of natural plant catechines extracted from other plants such as green tea.

Slide 37: 

Processing of Instant Tea

Other Tea Products : 

Other Tea Products Utilized for production of by-products such as caffeine and polyphenols. Ready-to-drink tea flavored with lemon and other fruit. Tea flavored mineral water.

Composition of tea : 

Composition of tea Contain polyphenols (catechin): – 25% of dry weight of fresh tea leaves – Mostly in white and green tea – Antioxidants: May protect against cancer, heart disease.

Content : 

Content Tea contains catechins, a type of antioxidant. In a freshly-picked tea leaf, catechins can compose up to 30% of the dry weight. Catechins are highest in concentration in white and green teas, while black tea has substantially fewer due to its oxidative preparation. Research by the U.S. Department of Agriculture has suggested that levels of antioxidants in green and black tea do not differ greatly, with green tea having an Oxygen Radical Absorbance Capacity (ORAC) of 1253 and black tea an ORAC of 1128 (measured in μmolTE/100g).

Slide 41: 

Tea also contains theanine and the stimulant caffeine at about 3% of its dry weight, translating to between 30 mg and 90 mg per 8 oz (250 ml) cup depending on type, brand and brewing method. Tea also contains small amounts of theobromine and theophylline, as well as fluoride, with certain types of brick tea made from old leaves and stems having the highest levels. Dry tea has more caffeine by weight than coffee; nevertheless, more dried coffee is used than dry tea in preparing the beverage, which means that a cup of brewed tea contains significantly less caffeine than a cup of coffee of the same size. Tea has no carbohydrates, fat, or protein.

Caffeine content of beverages : 

Caffeine content of beverages Caffeine per 6-oz. cup Espresso (2oz.) 60-90mg Drip coffee 60-165mg Black tea 25-110mg Oolong tea 12-55mg Green tea 8-16mg

Health Benefits of Tea : 

Health Benefits of Tea

Slide 44: 

Reduce risk of Coronary Heart Disease – Epidemiological studies – Lowers blood levels of LDL cholesterol Flavonoids are antioxidants – 95%polyphenols in tea are flavanoids – Higher anti oxidant activity than Vitamin A, C or E but with less bioavailability – Combat free radicals >> reduce risk of cancer • Much of benefits not experimentally confirmed

The Components and Healthy Effects of Green Tea : 

The Components and Healthy Effects of Green Tea Components of Green Tea Catechins (Main component) Caffeine Vitamin C Vitamin B Complex r-Amino Butyric Acid(GABA) Flavonoids Polysaccharides Fluoride Vitamin E Theanine(a kind of amino acid) Healthy Effects Reduces incidence of cancer Reduces tumorsReduces mutations Reduces oxidation by active oxygenLowers blood cholesterol Inhibits increase of blood pressureInhibits increase of blood sugar Kills bacteriaKills influenza virus Fights cariogenic bacteria Prevents halitosis Stimulates wakefulness (removes fatigue and sleepiness)Acts as diuretic Reduces stress Prevents flu Aids carbohydrate metabolism Lowers blood pressure Strengthen blood vessel wallsPrevents halitosis Lowers blood sugar Prevents cavities Acts as antioxidant and regulates aging Gives green tea its delicious taste

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