Green tea

This article is about the type of tea. For other uses, see Green Tea (disambiguation).
The appearance of green tea in three different stages: (from left to right) the infused leaves, the dry leaves, and the liquid. (Notice that the infused leaves look greener than the dry leaves.)
The tea fields in the foothills of Gorreana, Azores Islands, Portugal: the only European region other than Georgia to support green tea production.
Green tea
Traditional Chinese 綠茶
Simplified Chinese 绿茶
Hanyu Pinyin lǜchá

Green tea is a type of tea that is made from Camellia sinensis leaves that have not undergone the same withering and oxidation process used to make oolong and black tea.[1] Green tea originated in China, but its production has spread to many countries in Asia.

Several varieties of green tea exist, which differ substantially because of the variety of C. sinensis used, growing conditions, horticultural methods, production processing, and time of harvest.

History

Main article: History of tea

Tea consumption has its legendary origins in China during the reign of Emperor Shennong.[2]

A book written by Lu Yu in 600-900 AD (Tang Dynasty), "Tea Classic" (simplified Chinese: 茶经; traditional Chinese: 茶經; pinyin: chájīng), is considered important in green tea history. The Kissa Yojoki (喫茶養生記 Book of Tea), written by Zen priest Eisai in 1191, describes how drinking green tea may affect five vital organs, the shapes of tea plants, flowers and leaves, and how to grow and process tea leaves.

Brewing and serving

Green tea leaves steeping in a gaiwan

Steeping is the process of making a cup of tea; it is also referred to as brewing. In general, two grams of tea per 100 ml of water, or about one teaspoon of green tea per five-ounce (150 ml) cup, should be used. With very high-quality teas like gyokuro, more than this amount of leaf is used, and the leaf is steeped multiple times for short durations.

Green tea steeping time and temperature vary with a different tea. The hottest steeping temperatures are 81 to 87 °C (178 to 189 °F) water and the longest steeping times two to three minutes. The coolest brewing temperatures are 61 to 69 °C (142 to 156 °F) and the shortest times about 30 seconds. In general, lower-quality green teas are steeped hotter and longer, whereas higher-quality teas are steeped cooler and shorter. Steeping green tea too hot or too long will result in a bitter, astringent brew, regardless of the initial quality, because it will result in the release of an excessive amount of tannins. High-quality green teas can be and usually are steeped multiple times; two or three steepings is typical. The steeping technique also plays a very important role in avoiding the tea developing an overcooked taste. The container in which the tea is steeped or teapot should also be warmed beforehand so that the tea does not immediately cool down. It is common practice for tea leaf to be left in the cup or pot and for hot water to be added as the tea is drunk until the flavor degrades.

Health effects

Main article: Health effects of tea
Brewed, regular green tea
Nutritional value per 100 g (3.5 oz)
Energy 4 kJ (0.96 kcal)
0 g
0 g
0.2 g
Vitamins
Thiamine (B1)
(1%)

0.007 mg

Riboflavin (B2)
(5%)

0.06 mg

Niacin (B3)
(0%)

0.03 mg

Vitamin B6
(0%)

0.005 mg

Vitamin C
(0%)

0.3 mg

Minerals
Calcium
(0%)

0 mg

Iron
(0%)

0.02 mg

Magnesium
(0%)

1 mg

Manganese
(9%)

0.18 mg

Potassium
(0%)

8 mg

Sodium
(0%)

1 mg

Other constituents
Water 99.9 g
Caffeine 12 mg
Link to Full USDA Nutrient Report
Percentages are roughly approximated using US recommendations for adults.

Regular green tea is 99.9% water, provides 1 Calorie per 100 mL serving, is devoid of significant nutrient content (table) and contains phytochemicals, such as polyphenols and caffeine. Polyphenols found in green tea include epigallocatechin gallate (EGCG), epicatechin gallate, epicatechins and flavanols.[1]

Although numerous claims have been made for the health benefits of green tea, human clinical research has not provided conclusive evidence of any effects.[1][3][4] In 2011, a panel of scientists published a report on the claims for health effects at the request of the European Commission: in general they found that the claims made for green tea were not supported by sufficient scientific evidence.[3] Although the mean content of flavonoids and catechins in a cup of green tea is higher than that in the same volume of other food and drink items that are traditionally considered to promote health,[5] flavonoids and catechins have no proven biological effect in humans.[3][6]

Cancer

There is no conclusive evidence that green tea helps to prevent or treat cancer in people.[4][7] A review of existing studies concluded that while suggestive evidence existed, it did not amount to a clear indication of benefit.[7]

Daily consumption of black tea (but not green tea) has been associated with a significant reduction in death from all cancers.[8] There is limited evidence to suggest that green tea consumption may be associated with a slightly lower risk of esophageal cancer in the Chinese population, a lower risk of lung cancer in women, and a lower risk of oral cancer in Asian people.[9][10][11] A 2015 meta-analysis of nine prospective cohort studies concluded that a high amount of green tea consumption may be associated with a lower risk of liver cancer in Asian women.[12] This association was not seen in Asian men or when one cup of green tea was consumed daily.[12] Similarly, another analysis of observational data conducted in 2012 suggested that green tea consumption may have a favorable effect on lung cancer risk. The observed effect was strongest in those who consumed more than seven cups of green tea daily.[13] A 2011 meta-analysis of epidemiological studies found limited evidence that green tea consumption may be associated with a moderately reduced risk of liver cancer in Chinese and Japanese people.[14] Limited evidence suggests that green tea consumption is not associated with the risk of developing pancreatic cancer or prostate cancer.[15][16] The link between green tea consumption and stomach cancer risk is unclear due to inconsistent evidence.[17]

Green tea interferes with the chemotherapy drug bortezomib (Velcade) and other boronic acid-based proteasome inhibitors, and should be avoided by people taking these medications.[18]

Cardiovascular disease

Daily consumption of green tea has been associated with a lower risk of death from cardiovascular disease. In a 2015 meta-analysis of observational studies, an increase in one cup of green tea per day was associated with a 5% lower risk of death from cardiovascular causes.[8] Green tea consumption may be associated with a reduced risk of stroke.[19][20][21] A 2013 Cochrane review of randomized controlled trials concluded that green tea consumption for 3–6 months appears to lower systolic and diastolic blood pressures a small amount (about 3 mm Hg each).[21][22] Additional analyses examining the effects of long-term green tea consumption on blood pressure have reached similar conclusions.[23][24][25]

Glycemic control

Green tea consumption lowers fasting blood sugar but in clinical studies the beverage's effect on hemoglobin A1c and fasting insulin levels was inconsistent.[21][26][27]

Hyperlipidemia

Drinking green tea or taking green tea supplements decreases the blood concentration of total cholesterol (about 7 mg/dL), LDL cholesterol (about 2 mg/dL), and does not affect the concentration of HDL cholesterol.[21][28] A 2013 Cochrane review performed a meta-analysis of longer-term randomized controlled trials (>3 months duration) and concluded that green tea consumption lowers total and LDL cholesterol concentrations in the blood.[21][22]

Inflammation

A 2015 systematic review and meta-analysis of 11 randomized controlled trials found that green tea consumption was not significantly associated with lower plasma levels of C-reactive protein levels (a marker of inflammation).[29]

Mortality risk

Daily consumption of green tea is significantly associated with a lower risk of death from any cause; an increase of one cup of green tea per day is linked with a 4% lower risk of death from any cause.[8] A separate analysis found an increase of three cups of green tea per day was associated with a lower risk of death from any cause.[19]

Weight loss

There is no conclusive evidence that green tea aids in weight loss.[30]

Toxicity

Moderate, regular, and habitual consumption of green tea is safe;[4] however, there are reports of liver toxicity in humans after consuming high doses (10–29 mg/kg/day) of green tea extract dietary supplements.[31]

Production

Growing, harvesting and processing

Hand-rolling green tea after steaming

Green tea is processed and grown in a variety of ways, depending on the type of green tea desired. As a result of these methods, maximum amounts of polyphenols and volatile organic compounds are retained, affecting aroma and taste. The growing conditions can be broken down into two basic types − those grown in the sun and those grown under the shade. The green tea plants are grown in rows that are pruned to produce shoots in a regular manner, and in general are harvested three times per year. The first flush takes place in late April to early May. The second harvest usually takes place from June through July, and the third picking takes place in late July to early August. Sometimes, there will also be the fourth harvest. It is the first flush in the spring that brings the best-quality leaves, with higher prices to match.

Green tea is processed using either artisanal or modern methods.[32] Sun-drying, basket or charcoal firing, or pan-firing are common artisanal methods.[32] Oven-drying, tumbling, or steaming are common modern methods.[32] Processed green teas, known as aracha are stored under low humidity refrigeration in 30- or 60-kg paper bags at 0–5 °C (32–41 °F). This aracha has yet to be refined at this stage, with a final firing taking place before blending, selection and packaging take place. The leaves in this state will be re-fired throughout the year as they are needed, giving the green teas a longer shelf-life and better flavor. The first flush tea of May will readily store in this fashion until the next year's harvest. After this re-drying process, each crude tea will be sifted and graded according to size. Finally, each lot will be blended according to the blending order by the tasters and packed for sale.[33]

Production by country

2006 Green tea production and export (in thousands of metric tons)[34]
Country Production Export
 China782.4 (80.8%)218.7 (83.0%)
 Japan91.8 (9.5%)1.6 (0.6%)
 Vietnam66.0 (6.8%)26.0 (9.9%)
 Indonesia20.0 (2.1%)9.1 (3.5%)
World968.1 (100%)263.5 (100%)

Import of Japanese tea

On 17 June 2011, radioactive cesium of 1,038 becquerels per kilogram was detected at Charles de Gaulle airport in France in tea leaves imported from Shizuoka Prefecture, Japan as a result of the Fukushima Daiichi nuclear disaster, which was more than twice as much as the restricted amount of 500 becquerels per kilogram designated by the European Union, and the government of France announced that they rejected the tea leaves, which amounted to 162 kilograms (357 lb).[35] The governor of Shizuoka Prefecture Heita Kawakatsu stated that "there is absolutely no problem when they [people] drink them because it will be diluted to about ten becquerels per kilogram when they steep them even if the leaves have 1,000 becquerels per kilogram," which was a consequence of own examinations of the prefecture.[36] Minister for Consumer Affairs and Food Safety Renhō stated on 3 June 2011, that "there are cases in which aracha are sold as furikake [condiments sprinkled on rice] and so on and they are eaten as they are, therefore we think that it is important to inspect tea leaves including aracha from the viewpoint of consumers' safety."[37]

Green tea by country

China

Green tea is the most popular form of tea in China. Chinese green teas are made from over 600 different cultivars of the Camellia sinensis plant, giving plenty of variety and regional teas. Chinese green teas are traditionally pan-fired, unlike the Japanese steaming process. Other processes in China include oven-dried and sun-dried. Due to the different production process, Chinese teas are said to have a more "earthy" taste than Japanese teas.

Maybe the most well-known green tea in China; originates from Hangzhou (杭州), the capital of Zhejiang Province. Longjing in Chinese literally means dragon well. It is pan-fired and has a distinctive flat appearance. The tasteless frying oil is obtained from tea seeds and other plants. There are many fake Longjings on the market[38] and in less-scrupulous tea houses around the country.
  • 景宁惠明茶 Huiming
Named after a temple in Zhejiang.
  • 开化龙顶 Kaihua Longding
A tea from Kaihua County known as Dragon Mountain.
  • 华顶云雾 Hua Ding
A tea from Tiantai County, named after a peak in the Tiantai mountain range.
  • 天目青顶 Qing Ding
A tea from Tian Mu, also known as Green Top.
This popular tea is also known as zhuchá, originates in Zhejiang but is now grown elsewhere in China. This tea is also the quintessential ingredient in brewing Maghrebi mint tea, which is brewed green tea with fresh mint.
A plate of Bi Luo Chun tea, from Jiangsu Province in China
A Chinese famous tea also known as Green Snail Spring, from Dong Ting. As with Longjing, inauthentic Bi Luo Chun is common and most of the tea marketed under this name may, in fact, be grown in Sichuan.
  • 南京雨花茶 Rain Flower
A tea from Nanjing.
  • 金坛雀舌 Que She (Tongue of golden altar sparrow)
originate in Jin Tan city of Jiangsu Province.
  • 太湖白云 White Cloud
Camellia sinensis, the tea plant
A tea with added jasmine flowers.
Meaning "furry peak".
  • 翠剑 Cui Jian
Meaning "jade sword".
  • 玉露 Yu Lu
A steamed tea also known as Gyokuro (Jade Dew) in Japanese, made in the Japanese style.
An example of a Chinese green tea, called Mao Jian.
A Chinese famous tea also known as Green Tip, or Tippy Green.
Meaning "precious eyebrows"; from Jiangxi, it is now grown elsewhere.
  • 狗牯 Gou Gu Nao
A well-known tea within China and recipient of numerous national awards.
  • 云雾 Yun Wu
A tea also known as Cloud and Mist.
A tea from Huangshan also known as Big Square suneet.
A Chinese famous tea from Huangshan
A Chinese famous tea also known as Melon Seed
A Chinese famous tea also known as Monkey tea
  • 屯绿 Tun Lu
A tea from Tunxi District.
  • 火青 Huo Qing
A tea from Jing County, also known as Fire Green
  • 雾里青 Wuliqing
Wuliqing was known since the Song dynasty. Since 2002, Wuliqing is produced again according to the original processing methods by a company called Tianfang (天方). Zhan Luojiu a tea expert and professor at the Anhui Agricultural University who revived its production procedure.
A medium-quality tea from many provinces, an early harvested tea.
  • 竹叶青茶 Zhu Ye Qing
Also known as Meng Ding Cui Zhu or Green Bamboo
A yellowish-green tea with sweet after taste.
  • 百美绿茶 Baimei Green Tea
  • 汉中仙毫 Han Zhong Xian Hao
A green tea from the Han Zhong.

Japan

Japanese green tea
Genmaicha
Aracha

Green tea (緑茶 Ryokucha) is ubiquitous in Japan and is commonly known simply as "tea" (お茶 ocha). Tea was first used in China, and in 1191, was brought to Japan by Myōan Eisai, a Japanese Buddhist priest who also introduced the Rinzai school of Zen Buddhism. Teas from Japan may be referred to as "Japanese tea" (日本茶 nihoncha).

Japanese green teas are mainly made from Yabukita (やぶきた), a cultivar of the camellia sinensis plant. Unlike Chinese green teas which are pan-fired, Japanese green teas are steamed giving them a more "vegetative" or "leafy" taste. The exception is hōjicha, a Japanese roasted tea. Japanese green teas are categorized by the age of the leaves: young leaves are called sencha and the more mature, larger leaves are called bancha. Types of tea are commonly graded depending on the quality and the parts of the plant used as well as how they are processed.[39] There are large variations in both price and quality within these broad categories, and there are many green teas that fall outside this spectrum. Here shows well-known tea-growing districts in Japan; Shizuoka Prefecture (Shizuoka-cha, the largest yield in Japan), Uji tea (宇治茶 Uji-cha) from Uji region of Kyoto Prefecture, Yame (八女 yame) region of Fukuoka Prefecture (Yame-cha), Kagoshima Prefecture (Chiran-cha).

The first and second flushes of green tea made from leaves that are exposed directly to sunlight. This is the most common green tea in Japan. The name describes the method for preparing the beverage.
  • Fukamushicha (深蒸し茶, long-steamed green tea)
Sencha, which, in the processing of the leaves, has been steamed two times longer than usual Sencha, giving it a deeper color and producing a fuller flavor in the beverage.
Gyokuro is a fine and expensive type that differs from Sencha (煎茶) in that it is grown under the shade rather than the full sun for approximately 20 days.[40] The name "Gyokuro" translates as "jade dew" and refers to the pale green color of the infusion. The shading causes the amino acids (Theanine) and caffeine in the tea leaves to increase, while catechins (the source of bitterness in tea, along with caffeine) decreases, giving rise to a sweet taste.[41] The tea also has a distinct aroma.
Kabusecha is made from the leaves grown in the shade prior to harvest, although not for as long as Gyokuro. It has a more delicate flavor than Sencha. It is sometimes marketed as Gyokuro.
Tamaryokucha has a tangy, berry-like taste, with a long almondy aftertaste and a deep aroma with tones of citrus, grass, and berries. It is also called Guricha.
Lower grade of Sencha harvested as a third- or fourth flush tea between summer and autumn. Aki-Bancha (autumn Bancha) is not made from entire leaves, but from the trimmed unnecessary twigs of the tea plant.
Kamairicha is a pan-fired green tea that does not undergo the usual steam treatments of Japanese tea and does not have the characteristic bitter taste of most Japanese tea.
A tea made from stems, stalks, and twigs. Kukicha has a mildly nutty, and slightly creamy sweet flavor.
  • Mecha (芽茶, buds and tips tea)
Mecha is green tea derived from a collection of leaf buds and tips of the early crops. Mecha is harvested in spring and made as rolled leaf teas that are graded somewhere between Gyokuro and Sencha in quality.
  • Konacha (粉茶, (coarse) powdered tea)
Konacha is the dust and smallest parts after processing Gyokuro or Sencha. It is cheaper than Sencha and usually served at Sushi restaurants. It is also marketed as Gyokuroko (玉露粉) or Gyokurokocha.
A fine ground tea made from Tencha. It has a very similar cultivation process as Gyokuro. It is expensive and is used primarily in the Japanese tea ceremony. Matcha is also a popular flavor of ice cream and other sweets in Japan.
  • Tencha (碾茶, milling tea)
Half-finished products used for Matcha production. The name indicates its intended eventual milling into matcha. Because, like gyokuro, it is cultivated in shade, it has a sweet aroma. In its processing, it is not rolled during drying, and tencha, therefore, remains spread out like the original fresh leaf.
Bancha (sometimes Sencha) and roasted genmai (brown rice) blend. It is often mixed with a small amount of Matcha to make the color better.
A green tea roasted over charcoal (usually Bancha).
  • Aracha (荒茶, raw green tea)
Half-finished products used for Sencha and Gyokuro production. It contains all parts of the tea plant.
First flush tea. The name is used for either Sencha or Gyokuro.
  • Funmatsucha (粉末茶, instant powdered tea)
Milled green tea, used just like instant coffee.　Another name for this recent style of tea is "tokeru ocha," or "tea that melts."

Korea

Green tea

Korean Green tea in Boseong.
Hangul 녹차
Hanja 綠茶
Revised Romanization Nokcha
McCune–Reischauer Nokch'a

Other countries

See also

References

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  31. ↑ Lambert JD, Sang S, Yang CS (April 2007), "Possible controversy over dietary polyphenols: benefits vs risks", Chem Res Toxicol, 20 (4): 583–5, doi:10.1021/tx7000515, PMID 17362033
  32. 1 2 3 Heiss, Mary Lou; Heiss, Robert J. (2007), Hardcover, ed., The Story of Tea: A Cultural History and Drinking Guide, Ten Speed Press, pp. 56–69, ISBN 978-1-60774-172-5
  33. ↑ Green Tea Processing, O-cha.com, retrieved 2013-01-13
  34. ↑ Current situation and medium-term outlook (PDF), Intergovernmental Group on Tea, UN Food and Agriculture Organization, May 2008, p. 9
  35. ↑ "日本からの緑茶に基準超えるセシウム パリの空港で検出." (Japanese) Asahi Shimbun. 2011-06-18. Retrieved 2011-06-19.
  36. ↑ "静岡知事「飲用茶にすれば問題ない」 仏での検出受け." (Japanese) Asahi Shimbun. 2011-06-18. Retrieved 2011-06-19.
  37. ↑ "蓮舫内閣府特命担当大臣記者会見要旨（平成23年６月３日（金））." (Japanese) Consumer Affairs Agency. 2011-06-03. Retrieved 2011-06-19.
  38. ↑ http://www.chinadaily.com.cn/business/2010-02/23/content_9489252.htm
  39. ↑ Heiss, Mary Lou; Heiss, Robert J. (2007), The Story of Tea: A Cultural History and Drinking Guide, Ten Speed Press, pp. 179–185, ISBN 1-58008-745-0
  40. ↑ Illustrated explanation of the process for producing gyokuro tea, Ippodo-tea.co.jp, retrieved 2013-01-13
  41. ↑ About the effects of the shading process, and the components of this tea compared to others, Ippodo-tea.co.jp, retrieved 2013-01-13

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