tea productıon.pdf

Tea Domestication China type domesticated in south China ◦ 4000 years ago? ◦ Spread throughout China and Japan Trading with Europe beginning in early 1600s ◦ Earliest maritime explorations by the Portuguese and Dutch ◦ England enters trade with East India Co in mid to late 1600s East...

Tea Domestication China type domesticated in south China ◦ 4000 years ago? ◦ Spread throughout China and Japan Trading with Europe beginning in early 1600s ◦ Earliest maritime explorations by the Portuguese and Dutch ◦ England enters trade with East India Co in mid to late 1600s East India Trade Co monopoly on tea trade ends in 1833  Tea Domestication Tea growing in India investigated ◦ Seed of China type were planted various locations ◦ Grew best in Assam, NE India - so developed plantations ◦ Tea-like plants grew wild throughout forest in this area - these were the Assam type tea ◦ Initial plantings were mixtures of China and Assam tea plants ◦ Outcrossing plants ◦ Seed propagation ◦ Hybrid tea populations were developed  Tea Domestication Assam region initial area of domestication of Assam tea ◦ Late 1800s ◦ South India ◦ Sri Lanka (esp. after rust destroyed the coffee industry) ◦ Java and Indonesia ◦ 1930s ◦ Equatorial highlands of Central and East Africa Current Assam tea is a hybrid type derived from the initial mixed plantings in NE India Origin and Domestication of Tea Assam China 1833 1930s  Tea Production Major Producing Regions 30 27 25 21 20 Increasing Percent of 15 total 15 production 9 10 5 0 India China Sri Lanka Africa By weight 50% total production of coffee  Tea Production Major Producing Regions 2500 2168 Production (1000 t) 2000 1500 1000 500 395 1 0 57 0 Asia Europe Africa North South America America Much of production consumed locally  Tea Importations Major Importers 350 311 Importations (1000 t) 300 250 227 200 187 150 104 100 50 16 0 Asia Europe Africa North South America America Much of production consumed locally The Tea Plant Perennial evergreen bush/tree Harvest young leaves Understorey trees The Tea Plant Adaptation ◦ Temperature ◦ 18-30°C ◦ Leaf growth stops ◦ Below 13°C ◦ Above 35°C ◦ Shoot replacement cycle related to temp. ◦ Equatorial region ◦ Grown in highlands (1000-3000 m) ◦ At low latitude/altitude need shade for best growth (Assam type) ◦ Rainfall ◦ Soil type  The Tea Plant Understorey trees Adaptation ◦ Rainfall ◦ 1150 mm if evenly distributed ◦ Soil type ◦ Acid soils (pH 4.0 to 5.6) ◦ Good drainage ◦ Good water holding capacity Density of planting Tea Planting ◦ 10,000 to 15,000/ha Use of shade ◦ Initially all tea in Assam with shade ◦ Now many areas without shade ◦ Higher yields without shade ◦ Greater response to fertilizer without shade ◦ Some exceptions ◦ High heat areas (lowlands of north India/Bangladesh) ◦ Low input system, in highlands of Kenya, shaded system is equal or better than unshaded Training Tea Training and Pruning ◦ Head back to 20 cm at planting ◦ Next year to 40 cm ◦ Final year at 60 cm to form a level “plucking table” Pruning ◦ Need to cut back periodically ◦ Plucking table will slowly rise ◦ Periodically need to rejuvenate ◦ Prune below branches ◦ Bring to bear again  Tea Harvesting Harvest - Most done by hand ◦ Tips ◦ Bud only gives best product ◦ Fine plucking - most common ◦ Bud plus 2 leaves ◦ Coarse plucking ◦ Bud plus 3 leaves Important to begin processing quickly Tea Harvesting  Types of Tea Green Tea ◦ Not “fermented” ◦ Only China type tea ◦ Mainly China and Japan Oolong Tea ◦ Semi “fermented” ◦ Produced in Taiwan Black Tea (highest production) ◦ “Fermented” Processing Steps Harvesting Tea harvesting is a delicate process that is difficult to do quickly for fear of damaging the tea leaves. The majority of tea is still harvested by hand but mechanical picking can also be done depending on the tea variety. Manual harvesting allows for discrimination in selection where priority is placed on the younger leaf shoots, as they are the highest in caffeine and antioxidants. This is also the derivation of the saying “two and a bud.” Manual harvesting (by hand) is the preferred method for many cultivators; however, others prefer the large scale production that comes with mechanized harvesting. It’s an issue of quantity versus quality. The scale made possible by mechanical harvesting is often used for teas with which there is much room for error, imperfection, or damaging of tea leaves and absolute quality isn’t a consideration. These include black teas which undergo the CTC (crush, tear, curl) processing as well as powdered teas like matcha.  Black Tea Processing Withering ◦Thin layers of leaves in trays ◦Leaves allowed to dry to lose turgidity ◦18-24 hours ◦50% weight loss Withering - Reduction of water content The goal of all tea undergoing withering is to reduce water content by 50-70%, allow for amino acid degradation, and the development of antioxidants. The leaves can be withered in a variety of ways, such as outdoors in sunlight or in dark, hot rooms. Teas withered in the sun dehydrate faster than those dried indoors because chlorophyll still active in the leaves metabolizes and exhausts the water supply. The range of withering times for different teas is rather large due to the initial water content of the leaves and the desired flavor development. For example, the chlorophyll content falls as withering time increases. Chlorophyll is associated with the vegetal, earthy flavor in many teas and is the source of “green” in green tea. Withering times for different teas: White: 12-36 hours Yellow: 2-4 hours Chinese Green: 2-4 hours Japanese Green: 30-60 min* Oolong: 30 min - 2 hours Black: 4-18 hours Leaf Maceration - Physical breakage of leaves The following four stages are different methods of leaf maceration. They differ in their intensity of maceration, but all of them similarly induce the release of oxidative enzymes by physical means. This results in biochemical changes within the leaves and the creation of new flavors. Leaf Bruising (oolong and sometimes black teas) - Leaf maceration The goal of leaf bruising is to create tears in the leaf epidermis, releasing oxidation enzymes. Leaf bruising is done by shaking the leaves in a basket or by machinery, which kneads and tears the leaves (just a little). The bruising can be likened to bruising a fruit, causing the leaves to brown. Rolling-Shaping - A gentle form of leaf maceration In this stage, the leaves are shaped into fashionable tea leaf shapes, such as the needle and pearl. Rolling-shaping also brings about a light breakage in cell structure and activates enzymes, re-starting and promoting the oxidation process. Traditionally speaking, all tea leaves were manually rolled- shaped; however, machines are now most oftenly used to economically create more tea shape varieties. Crushing - A strong form of leaf maceration Crushing is another leaf maceration technique in which the leaves are bluntly cut into smaller pieces, usually by machine, triggering a greater release of oxidative enzymes. Crushing, unfortunately, also results in the exposure of a leaf’s essential oils, which hold many of the antioxidants, vitamins, and other nutraceuticals found in tea. Exposure of these oils to oxygen may potentially lead to oxidative damage subsequently neutralizing these health compounds. Crush, Tear, and Curl (CTC) - An intense form of leaf maceration CTC was a developed in the 1930’s as a means to reduce the amount of tea leaves required for a cup of tea; however, it could easily be argued that this sacrificed quality for quantity. The leaves are literally crushed, torn, and curled by a machine. This intense maceration technique increases the exposed surface area of the leaves, thus reducing the amount of tea required for brewing. Oxidation - A chemical reaction involving oxygen In tea and food, this reaction results not only in a physical browning of the substance (like a banana peel) but also in the creation and unlocking of new compounds at a molecular level. Passive Oxidation This is a natural oxidation lacking an outside stimulus, such as the greening of copper or the rusting of metal. This process is excruciatingly slow in comparison to active oxidation. In regards to tea, the moment the leaf is plucked, the oxidase (oxidative enzymes) are activated, resulting in passive oxidation. During this passive oxidation/withering stage, aromatic compounds are likely to develop. This method of oxidation continues throughout withering until it is halted by the enzyme kill stage, where the tea leaves are briefly flashed with heat. Controlled Oxidation Controlled oxidation is where the conditions for oxidation have been manipulated by raising room temperature, humidity. The degree of oxidation can be measured in various parameters. For example, in black tea, this process is usually controlled to maintain a specific ratio of theaflavins to thearubigins (usually around 1:10 to 1:12). Enzyme Kill - Reduction of enzyme activity The goal of the enzyme kill stage is to halt oxidative enzyme activity from the previous stages of tea processing. This is performed by exposing the leaves to high levels of heat for a very short amount of time (60 seconds or less), similar to blanching vegetables. This step is especially important in preserving the desired aromatic and antioxidant compounds of tea. There are four popular methods of enzyme kill: baking, steaming, pan-frying, and GABA. The enzyme kill stage is also referred to as “firing”, “fixation”, and “kill green”. Baking: Tea leaves are arranged in a thin layer on a conveyer belt where they are baked as they pass through an oven (similar to a pizza oven). Steaming: Tea leaves will be rotated through a metal cylinder where they will be flushed with steam. This process is the most effective in preserving the green color and vitamin content in the leaves. Pan-frying: Tea leaves are tossed around in a dry, hot wok by hand, where the tea processor must fry them until they give back just the right amount of “bounce.” The skill of tea gurus really shines through in pan-frying, as they must not allow the leaves to burn. GABA: Enzyme fixation by nitrogen In 1987, Japanese researchers developed a new technique for the enzyme kill stage where, instead of the traditional heat treatment, the tea was given a nitrogen treatment. In doing so, they increased gamma-Aminobutyric acid (GABA); therefore, some teas have gained the acronymed prefix “GABA” (i.e. GABA oolong, GABA green, etc.). GABA is naturally found in the brain and functions as neurotransmitter, stimulating mental activity as well as regulating muscle tone. GABA also creates an interesting purple hue on oolong leaves. TROPICAL HORTICULTURE - TEXAS A&M UNIVERSITY Drying - Reduction of water content to 3-6% The goal of the last step is to reduce the water content of the tea leaves down to 3-6%. This will cease all enzymatic activity and preserve the chemical and flavor compounds for the tea’s shelf life. Drying occurs in oven-like rooms where the leaves are laid out in thin layers and dried at 212-248°F (100-120°C). The exact time of drying varies depending on the water content of the leaves prior to drying. For example, Taiwanese-styled oolong tea requires only 5-10 minutes of drying while Indian black teas require up to 20-30 minutes. Black Tea Processing Rolling ◦ Twists and breaks up leaf ◦ Expresses leaf sap ◦ Good contact with flavanols and polyphenol oxidase ◦ Done 3-5 times ◦ 1st roll = dhools, most tender parts of the leaves ◦ 2nd and 3rd rolls = mahls and fines ◦ Sticks left over = big bulk ◦ Need to keep temp between 27 - 32 C ◦ Mechanical heat ◦ Heat generated by oxidation  Black Tea Processing Fermentation = oxidation ◦ Begins with rollers, dhool stages ◦ Flavor and aroma develops ◦ Leaves turn dark ◦ Flavanols >> colored theaflavins, thearubigins ◦ Limit of 4-5 hours Black Tea Processing Drying = stops oxidation ◦Time of fermentation ◦ Subjective ◦ Important in quality ◦In at 82 - 94 C and finish at 53 C ◦Moisture level ◦ 54% to 3% moisture  Black Tea Processing Grading and Sorting ◦ Broken Orange Pekoe (high % buds) ◦ Broken Pekoe ◦ Orange Pekoe (twisted tender stalk) ◦ Pekoe - compact and dense  Green Tea Processing Prevent “fermentation” ◦ Initial heating to destroy polyphenol oxidase ◦ Rolled at 90-100 C for 45-50 min - 50% moisture ◦ Rolled without heat for 15 min ◦ Dried at 50-60 C (30-40 min) - 30% moisture ◦ Rolled on heated pan (80-90 C), 40 min. ◦ Dried at 80 C - > reduce risk of cancer Much of benefits not experimentally confirmed