The Tea Plant
The tea plant is an evergreen shrub that is kept at a height of approximately 5’ for harvesting (plucking height). If left alone, the tea plant can grow into trees and in some parts of the world, these trees are harvested by climbing and plucking the youngest shoots.
Tea grows in many countries around the world and regions that vary greatly from each other geographically. Temperature, precipitation, soil conditions and altitude are some of the components that lead to a tasty, complicated and healthy beverage. Tea, very much like wine, changes complexity and nuances with the change of each of these factors and the outcomes can be very different year after year,
There are three basic varietals of the tea plant but Camellia Sinensis is the most used and known.
Camellia Sinensis or tea plant, is the plant whose leaves and leaf buds are used to produce all varieties of tea.
The name sinensis means Chinese in Latin. Older names for the tea plant include Thea Bohea, Thea sinensis and Thea viridis.
- Camellia sinensis-sinsensis is native to mainland south and southeast Asia, but is today cultivated across the world, in tropical and subtropical regions. It is an evergreen shrub or small tree that is usually trimmed to below two metres (six feet) when cultivated for its leaves. It has a strong taproot. The flowers are yellow-white, 2.5–4 cm in diameter, with 7 to 8 petals.
- The seeds of Camellia sinensis can be pressed to yield tea oil, a sweetish seasoning and cooking oil that should not be confused with tea tree oil, an essential oil that is used for medical and cosmetic purposes and originates from the leaves of a different plant.
The leaves are 4–15 cm long and 2–5 cm broad. Fresh leaves contain about 4% theaine. The young, light green leaves are preferably harvested for tea production; they have short white hairs on the underside. Older leaves are deeper green. Different leaf ages produce differing tea qualities, since their chemical compositions are different.
- Assamese variety – Camellia Assamica
- The most volume comes from the Assam variety (sometimes called C. sinensis var. assamica or C. assamica), predominantly grown in the Assam region. It is a small tree (single stemmed) with large leaves. In the wild it reaches a height of 6 to 20 meters (20–65 feet) and is native to North-East India, Myanmar, Vietnam, and south China. In tea estates it is kept trimmed to just above waist level. A lowland plant, it requires a high rainfall but good drainage. It does not tolerate extreme temperatures. Discovered in 1823 (though used earlier by local people in their brews), it is one of the two original tea plants. All Assam teas and most Ceylon teas are from this plant. The Assam plant produces malty, earthy drinks, unlike the generally flowery yield of the China plant.
- Cambodian variety
The Cambodian plant is sometimes called C. sinensis var. parvifolia. Its leaves are in size between the Assam and Chinese varieties; it is a small tree with several stems. It is sometimes referred to as a hybrid of the Assam and China plants
Although each type of tea has a different taste, smell, and visual appearance, tea processing for all tea types consists of a very similar set of methods with only minor variations.
1. Plucking: Tea leaves and flushes, which includes a terminal bud and two young leaves, are picked from Camellia sinensis bushes typically twice a year during early spring and early summer or late spring. Autumn or winter pickings of tea flushes are much less common, though they occur when climate permits. Picking is done by hand when a higher quality tea is needed, or where labour costs are not prohibitive. Depending on the skill of the picker, hand-picking is performed by pulling the flush with a snap of the forearm, arm, or even the shoulders, with the picker grasping the tea shoot using the thumb and forefinger, with the middle finger sometimes used in combination. Tea flushes and leaves can also be picked by machine, though there will be more broken leaves and partial flushes reducing the quality of the tea. However, it has also been shown that machine plucking in correctly timed harvesting periods can produce good leaves for the production of high quality teas.
2. Withering/ Wilting: The tea leaves will begin to wilt soon after picking, with a gradual onset ofenzymatic oxidation. Withering is used to remove excess water from the leaves and allows a very slight amount of oxidation. The leaves can be either put under the sun or left in a cool breezy room to pull moisture out from the leaves. The leaves sometimes lose more than a quarter of their weight in water during withering. The process is also important in promoting the breakdown of leaf proteins into free amino acids and increases the availability of freed caffeine, both of which change the taste of the tea.
3. Disruption: Known in the Western tea industry as “disruption” or “leaf maceration”, the teas are bruised or torn in order to promote and quicken oxidation. The leaves may be lightly bruised on their edges by shaking and tossing in a bamboo tray or tumbling in baskets. More extensive leaf disruption can be done by kneading, rolling, tearing, and crushing, usually by machinery. The bruising breaks down the structures inside and outside of the leaf cells and allows for the co-mingling of oxidative enzymes with various substrates, which allows for the beginning of oxidation. This also releases some of the leaf juices, which may aid in oxidation and change the taste profile of the tea.
4. Oxidation / Fermentation: For teas that require oxidation, the leaves are left on their own in a climate-controlled room where they turn progressively darker. This is accompanied by agitation in some cases. In this process the chlorophyll in the leaves is enzymatically broken down, and its tannins are released or transformed. This process is sometimes referred to as “fermentation” in the tea industry. The tea producer may choose when the oxidation should be stopped, which depends on the desired qualities in the final tea as well as the weather conditions (heat and humidity). For light oolong teas this may be anywhere from 5-40% oxidation, in darker oolong teas 60-70%, and in black teas 100% oxidation. Oxidation is highly important in the formation of many taste and aroma compounds, which give a tea its liquor colour, strength, and briskness. Depending on the type of tea desired, under or over-oxidation/fermentation can result in grassy flavours, or overly thick winey flavours.
5. Fixation / Kill-green: Kill-green is done to stop the tea leaf oxidation at a desired level. This process is accomplished by moderately heating tea leaves, thus deactivating their oxidative enzymes and removing unwanted scents in the leaves, without damaging the flavour of the tea. Traditionally, the tea leaves are panned in a wok or steamed but with advancements in technology, kill-green is sometimes done by baking or “panning” in a rolling drum. In some white teas and some black teas such as CTC blacks, kill-green is done simultaneously with drying. Sweltering / Yellowing: Unique to yellow teas warm and damp tea leaves from after kill-green are allowed to be lightly heated in a closed container, which causes the previously green leaves to turn yellow. The resulting leaves produce a beverage that has a distinctive yellowish-green hue due to transformations of the leaf chlorophyll. Through being sweltered for 6–8 hours at close to human body temperature, the amino acids and polyphenols in the processed tea leaves undergo chemical changes to give this tea its distinct briskness and mellow taste.
6. Rolling / Shaping: The damp tea leaves are then rolled to be formed into wrinkled strips, by hand or using a rolling machine which causes the tea to wrap around itself. This rolling action also causes some of the sap, essential oils, and juices inside the leaves to ooze out, which further enhances the taste of the tea. The strips of tea can then be formed into other shapes, such as being rolled into spirals, kneaded and rolled into pellets, or tied into balls, cones and other elaborate shapes. In many types of oolong, the rolled strips of tea leaf are then rolled into spheres or half spheres and is typically done by placing the damp leaves in large cloth bags, which are then kneaded by hand or machine in a specific manner.
7. Drying: Drying is done to “finish” the tea for sale. This can be done in a myriad of ways including panning, sunning, air drying, or baking. Baking is usually the most common. Great care must be taken to not over-cook the leaves. The drying of the produced tea is responsible for many new flavour compounds particularly important in green teas.
8. Aging / Curing: While not always required, some teas require additional aging, secondary fermentation, or baking to reach their drinking potential. For instance, a green tea puerh, prior to curing into a post-fermented tea, is often bitter and harsh in taste, but becomes sweet and mellow through fermentation by age or dampness. Additionally, oolong can benefit from aging if fired over charcoal. Flavoured teas are manufactured in this stage by spraying the tea with aromas and flavours or by storing them with their flavourants.
Young leaves or new growth buds that have undergone minimal oxidation through a slight amount of withering before halting the oxidative processes by being baked dry, with the optimal withering conditions at 30 degrees Celsius (65% relative humidity) for 26 hours. Withering of the leaves can last from around one to three days depending on the season and temperature of the processing environment. There is an international disagreement on definition of white tea between China and other producing countries. The buds may be shielded from sunlight to prevent the formation of chlorophyll. White tea is produced in lesser quantities than most other styles, and can be correspondingly more expensive than tea from the same plant processed by other methods. It is less well known in countries outside of China, though this is changing with increased western interest in the tea.
This tea has undergone the least amount of oxidation. The oxidation process is halted by the quick application of heat after tea picking, either with steam, the Japanese method, or by dry cooking in hot pans, the traditional Chinese method. Tea leaves may be left to dry as separate leaves or they may be rolled into small pellets to make Gunpowder tea. This process is time consuming and is typically done with pekoes of higher quality. The tea is processed within one to two days of harvesting, and if done correctly retains most of the chemical composition of the fresh leaves from which it was produced. Variation in steaming time for fixation or processing from additional stages of rolling and drying are sometimes used to improve or alter the flavour for types of green tea.
This tea is processed in a similar manner to green tea, but instead of immediate drying after fixation, it is stacked, covered, and gently heated in a humid environment. This initiates oxidation in the chlorophyll of the leaves through non-enzymatic and non-microbial means, which results in a yellowish or greenish-yellow colour.
This tea’s oxidation is stopped somewhere between the standards for green tea and black tea. The processing typically takes two to three days from withering to drying with a relatively short oxidation period of several hours. Common wisdom about lightly oxidized teas in Taiwan (a large producer of Oolong) is that too little oxidation upsets the stomach of some consumers. Even so, some producers attempt to minimize oxidation in order to produce a specific taste or allow the tea leaves to be easily rolled into the spherical or half-sphere form demanded by buyers in the market.
The tea leaves are allowed to completely oxidize. Black tea is first withered to induce protein breakdown and reduce water content (68-77% of original). The leaves then undergo a process known in the industry as “disruption” or “leaf maceration”, which through bruising or cutting disrupts leaf cell structures, releasing the leaf juices and enzymes that activate oxidation. The oxidation process takes between 45–90 minutes to 3 hours and is done at high humidity between 20-30 degrees Celsius, transforming much of the catechins of the leaves into complex tannin. Orthodox processed black teas are further graded according to the post-production leaf quality by the Orange Pekoe system, while Crush, Tear, Curl (CTC; or “Cut, tear, curl”) teas use a different grading system. Orthodox tea leaves are heavily rolled either by hand or mechanically on a cylindrical rolling table or a rotorvane. The rolling table consists of a ridged table-top moving in an eccentric manner to a large hopper of tea leaves, of which the leaves are pressed down onto the table-top. The process produces a mixture of whole and broken leaves, and particles which are then sorted, oxidized, and dried. The rotorvane consisted of an auger pushing withered tea leaves through a vane cylinder which crushes and evenly cuts the leaves. CTC black teas is a production method developed by William McKercher in 1930 and consists of machines with contra-rotation rotors with surface patterning that cut and tear the leaves producing a product popular for use in tea bags. The rotorvane is often used to precut the withered tea prior to the CTC and to create broken orthodox processed black tea.
Post-fermented tea (Pu-Erh)
Teas that are allowed to undergo a second oxidation after the fixation of the tea leaves, such as Pu-erh, Liu`àn, and Liubao, are collectively referred to as secondary or post-fermentation teas in English. In Chinese they are categorized as Dark tea or black tea. This is not to be confused with the English term Black tea, known in Chinese as red tea. Pu-erh, also known as Póu léi (Polee) in Cantonese is the most common type of post-fermentation tea in the market.