Tea processing
Encyclopedia
Tea processing is the method in which the leaves from the tea plant Camellia sinensis
Camellia sinensis
Camellia sinensis is the species of plant whose leaves and leaf buds are used to produce Chinese tea. It is of the genus Camellia , a genus of flowering plants in the family Theaceae. White tea, green tea, oolong, pu-erh tea and black tea are all harvested from this species, but are processed...
are transformed into the dried leaves for brewing tea
Tea
Tea is an aromatic beverage prepared by adding cured leaves of the Camellia sinensis plant to hot water. The term also refers to the plant itself. After water, tea is the most widely consumed beverage in the world...
. The categories of tea are distinguished by the processing they undergo. In its most general form, tea processing involves different manners and degree of oxidation of the leaves, stopping the oxidation, forming the tea and drying it. The innate flavour of the dried tea leaves is determined by the type of cultivar of the tea bush, the quality of the plucked tea leaves, and the manner and quality of the production processing they undergo.
General
Although each type of tea has different taste, smell, and visual appearance, tea processing for all tea types consists of a very similar set of methods with only minor variations:
- 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.
- Withering/ Wilting: The tea leaves will begin to wilt soon after picking, with a gradual onset of enzymatic 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 acid and increases the availability of freed caffeine both of which changes the taste of the tea.
- Bruising: In order to promote and quicken oxidation, the leaves may be bruised by shaking and tossing in a bamboo tray, tumbling in baskets or by being kneaded or rolled over by heavy wheels. The bruising breaks down the structures inside and outside of the leaf cells and allows from 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.
- 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 chlorophyllChlorophyllChlorophyll is a green pigment found in almost all plants, algae, and cyanobacteria. Its name is derived from the Greek words χλωρος, chloros and φύλλον, phyllon . Chlorophyll is an extremely important biomolecule, critical in photosynthesis, which allows plants to obtain energy from light...
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 oolongOolongOolong is a traditional Chinese tea produced through a unique process including withering under the strong sun and oxidation before curling and twisting. Most oolong teas, especially those of fine quality, involve unique tea plant cultivars that are exclusively used for particular varieties...
teas this may be anywhere from 5-40% oxidation, in darker oolong teas 60-70%, and in black teaBlack teaBlack tea is a variety of tea that is more oxidized than the oolong, green, and white varieties.All four varieties are made from leaves of the shrub Camellia sinensis. Black tea is generally stronger in flavor and contains more caffeine than the less oxidized teas. Two principal varieties of the...
s 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. - Fixation / Kill-green: Kill-green or shāqīng (殺青) 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 blacksCrush, Tear, CurlCrush, Tear, and Curl is a method of processing black tea, similar to that of orthodox tea manufacture. Instead of the leaves being rolled as a final stage, they are passed through a series of cylindrical rollers with hundreds of small sharp "teeth" that Crush, Tear, and Curl.CTC was invented by W...
, kill-green is done simultaneously with drying. - Sweltering / Yellowing: Unique to yellow teaYellow teaYellow tea usually implies a special tea processed similarly to green tea, but with a slower drying phase, where the damp tea leaves are allowed to sit and yellow. The tea generally has a very yellow-green appearance and a smell different from both white tea and green tea...
s, 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 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 temperaturesNormal human body temperatureNormal human body temperature, also known as normothermia or euthermia, is a concept that depends upon the place in the body at which the measurement is made, and the time of day and level of activity of the person...
, the amino acids and polyphenols in the processed tea leaves undergo chemical changes to give this tea its distinct briskness and mellow taste. - 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 type of oolong, the rolled strips of tea leaf are then rolled to 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.
- 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, however, baking is usually the most common. Great care must be taken to not over-cook the leaves. The drying of the produced tea are responsible for many new flavour compounds particularly important in green teas.
- Aging / Curing: While not always required, some teas required 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 flavorants.
Without careful moisture and temperature control during its manufacture and life thereafter, fungi will grow on tea. This form of fungus causes real fermentation that will contaminate the tea and may render the tea unfit for consumption.
Type specific processing
Tea is traditionally classified based on the degree or period of "fermentation" the leaves have undergone:
White tea
White tea is a lightly oxidized tea grown and harvested almost exclusively in China, primarily in the Fujian province.White tea comes from the delicate buds and younger leaves of the Chinese Camellia sinensis plant. These buds and leaves are allowed to wither in natural sunlight before they are...
: Young leaves or new growth buds that have undergone minimal oxidation through a slight amount of withering before halting the oxidation with heat. Withering of the leaves can last from around one to three days depending on the season and temperature of the processing environment.. Though Chinese sources state that the young leaf buds processed into white tea are usually dried immediately after withering, some Western sources state that the tea is dried directly without withering. 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
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...
, though this is changing with increased western interest in the tea.
Green tea
Green tea
Green tea is made solely from the leaves of Camellia sinensis that have undergone minimal oxidation during processing. Green tea originates from China and has become associated with many cultures throughout Asia. It has recently become more widespread in the West, where black tea is traditionally...
: 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
Steam
Steam is the technical term for water vapor, the gaseous phase of water, which is formed when water boils. In common language it is often used to refer to the visible mist of water droplets formed as this water vapor condenses in the presence of cooler air...
, 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
Gunpowder tea
Gunpowder tea is a form of green Chinese tea produced in Zhejiang Province of China in which each leaf has been rolled into a small round pellet. It is believed to take its English name from the fact that the tea resembles blackpowder grains...
. 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.
Oolong tea
Oolong
Oolong is a traditional Chinese tea produced through a unique process including withering under the strong sun and oxidation before curling and twisting. Most oolong teas, especially those of fine quality, involve unique tea plant cultivars that are exclusively used for particular varieties...
: 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. In Chinese, semi-oxidized teas are collectively grouped as blue tea (青茶, literally: blue-green tea / "celadon tea"), while the term "oolong" is used specifically as a name for certain semi-oxidized teas. 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.
Black tea
Black tea
Black tea is a variety of tea that is more oxidized than the oolong, green, and white varieties.All four varieties are made from leaves of the shrub Camellia sinensis. Black tea is generally stronger in flavor and contains more caffeine than the less oxidized teas. Two principal varieties of the...
: The tea leaves are allowed to completely oxidize. Black tea is the most common form of tea in southern Asia
South Asia
South Asia, also known as Southern Asia, is the southern region of the Asian continent, which comprises the sub-Himalayan countries and, for some authorities , also includes the adjoining countries to the west and the east...
(Sri Lanka
Sri Lanka
Sri Lanka, officially the Democratic Socialist Republic of Sri Lanka is a country off the southern coast of the Indian subcontinent. Known until 1972 as Ceylon , Sri Lanka is an island surrounded by the Indian Ocean, the Gulf of Mannar and the Palk Strait, and lies in the vicinity of India and the...
, India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...
, Pakistan
Pakistan
Pakistan , officially the Islamic Republic of Pakistan is a sovereign state in South Asia. It has a coastline along the Arabian Sea and the Gulf of Oman in the south and is bordered by Afghanistan and Iran in the west, India in the east and China in the far northeast. In the north, Tajikistan...
, Bangladesh
Bangladesh
Bangladesh , officially the People's Republic of Bangladesh is a sovereign state located in South Asia. It is bordered by India on all sides except for a small border with Burma to the far southeast and by the Bay of Bengal to the south...
, etc.) and in the last century many African countries including Kenya
Kenya
Kenya , officially known as the Republic of Kenya, is a country in East Africa that lies on the equator, with the Indian Ocean to its south-east...
, Burundi
Burundi
Burundi , officially the Republic of Burundi , is a landlocked country in the Great Lakes region of Eastern Africa bordered by Rwanda to the north, Tanzania to the east and south, and the Democratic Republic of the Congo to the west. Its capital is Bujumbura...
, Rwanda
Rwanda
Rwanda or , officially the Republic of Rwanda , is a country in central and eastern Africa with a population of approximately 11.4 million . Rwanda is located a few degrees south of the Equator, and is bordered by Uganda, Tanzania, Burundi and the Democratic Republic of the Congo...
, Malawi
Malawi
The Republic of Malawi is a landlocked country in southeast Africa that was formerly known as Nyasaland. It is bordered by Zambia to the northwest, Tanzania to the northeast, and Mozambique on the east, south and west. The country is separated from Tanzania and Mozambique by Lake Malawi. Its size...
and Zimbabwe
Zimbabwe
Zimbabwe is a landlocked country located in the southern part of the African continent, between the Zambezi and Limpopo rivers. It is bordered by South Africa to the south, Botswana to the southwest, Zambia and a tip of Namibia to the northwest and Mozambique to the east. Zimbabwe has three...
. The literal translation of the Chinese word is red tea, which is used by some tea lovers. The Chinese, Japanese, and Koreans call it red tea because the actual tea liquid is red. Speakers of many other languages call it black tea because the tea leaves used to brew it are usually black. However, red tea may also refer to rooibos
Rooibos
Rooibos is a broom-like member of the legume family of plants growing in South Africa's fynbos.The generic name comes from the plant Calicotome villosa, aspalathos in Greek. This plant has very similar growth and flowers to the redbush...
, an increasingly popular South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
n tisane
Tisane
A herbal tea, tisane, or ptisan is a herbal or plant infusion and usually not made from the leaves of the tea bush . Typically, herbal tea is simply the combination of boiling water and dried fruits, flowers or herbs. Herbal tea has been imbibed for nearly as long as written history extends...
. Black tea is first withered to induce protein breakdown and reduce water content (68-77% of original), heavily rolled or torn to bruise and disrupt the leaf cell structures and 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. Black tea is further classified as either orthodox or as Crush, Tear, Curl
Crush, Tear, Curl
Crush, Tear, and Curl is a method of processing black tea, similar to that of orthodox tea manufacture. Instead of the leaves being rolled as a final stage, they are passed through a series of cylindrical rollers with hundreds of small sharp "teeth" that Crush, Tear, and Curl.CTC was invented by W...
(CTC), a production method developed around 1932. Unblended black teas are also identified by the estate they come from, their year and the flush (first, second or autumn). Orthodox processed black teas are further graded according to the post-production leaf quality by the Orange Pekoe
Orange Pekoe
Orange pekoe , also spelled "pecco" is a term used in the Western tea trade to describe a particular genre of black teas . Despite a purported Chinese origin, these grading terms are typically used for teas from Sri Lanka, India and countries other than China; they are not generally known within...
system, while CTC teas use a different grading system.
Post-fermented tea
Post-fermented tea
Post-fermented teas are a class of teas that have undergone a period of "aging" in open air, from several months to many years. The exposure of the tea to microflora, humidity and oxygen in the air causes it to undergo further oxidation through auto-oxidation, fermentation, and possibly some...
: Teas that are allow to undergo a second oxidation after the fixation of the tea leaves, such as Pu-erh
Pu-erh tea
Pu'er, Pu-erh, Puer, also Po Lei or Bolay is a variety of post-fermented tea produced in Yunnan province, China. Post-fermentation is a tea production style in which the tea leaves undergo a microbial fermentation process after they are dried and rolled. This is a Chinese specialty and is sometimes...
, Liu'an, 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-fermetation tea in the market.
Yellow tea
Yellow tea
Yellow tea usually implies a special tea processed similarly to green tea, but with a slower drying phase, where the damp tea leaves are allowed to sit and yellow. The tea generally has a very yellow-green appearance and a smell different from both white tea and 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
Chlorophyll
Chlorophyll is a green pigment found in almost all plants, algae, and cyanobacteria. Its name is derived from the Greek words χλωρος, chloros and φύλλον, phyllon . Chlorophyll is an extremely important biomolecule, critical in photosynthesis, which allows plants to obtain energy from light...
of the leaves through non-enzymatic and non-microbial means, which results in a yellowish or greenish-yellow colour.