Green tea
The appearance of green tea in three different stages (from left to right): the infused leaves, the dry leaves, and the liquid.
TypeTea
Country of originChina
Region of originEast Asia
ColourGreen
IngredientsTea leaves
Related productsTea
Green tea
Traditional Chinese綠茶
Simplified Chinese绿茶
Literal meaningGreen tea

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

Several varieties of green tea exist, which differ substantially based on the variety of C. sinensis used, growing conditions, horticultural methods, production processing, and time of harvest. Although there has been considerable research on the possible health effects of consuming green tea regularly, there is little evidence that drinking green tea has any effects on health.[2]

History

The tea fields in the foothills of Gorreana, Azores Islands, Portugal: the only European region other than Georgia to support green tea production.
The tea fields in the foothills of Gorreana, Azores Islands, Portugal: the only European region other than Georgia to support green tea production.

Main articles: History of tea and History of tea in China

Tea consumption has its legendary origins in China during the reign of Emperor Shennong.[3]

A book written by Lu Yu in 618–907 AD (Tang dynasty), The Classic of Tea (simplified Chinese: ; traditional Chinese: ; 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 1211, 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.

Steeping, brewing and serving

Four varieties of green tea prior to brewing
Four varieties of green tea prior to brewing
The color of green tea brewed for 3 minutes at 90 °C (194 °F)
The color of green tea brewed for 3 minutes at 90 °C (194 °F)

Steeping, or brewing, is the process of making tea from leaves and hot water, generally using 2 grams (0.071 oz) of tea per 100 millilitres (3.5 imp fl oz; 3.4 US fl oz) of water (H2O) or about 1 teaspoon of green tea per 150 ml cup. Steeping temperatures range from 61 °C (142 °F) to 87 °C (189 °F) and steeping times from 30 seconds to three minutes.

Generally, lower-quality green teas are steeped hotter and longer while higher-quality teas are steeped cooler and shorter, but usually multiple times (2–3 typically). Higher-quality teas like gyokuro use more tea leaves and are steeped multiple times for short durations. Steeping too hot or too long results in the release of excessive amounts of tannins, leading to a bitter, astringent brew, regardless of initial quality. The brew's taste is also affected by the steeping technique; two important techniques are to warm the steeping container beforehand to prevent the tea from immediately cooling down, and to leave the tea leaves in the pot and gradually add more hot water during consumption.[citation needed]

Extracts

Polyphenols found in green tea include epigallocatechin gallate (EGCG), epicatechin gallate, epicatechins and flavanols,[1] which are under laboratory research for their potential effects in vivo.[4] Other components include three kinds of flavonoids, known as kaempferol, quercetin, and myricetin.[5] 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,[6] flavonoids and catechins have no proven biological effect in humans.[7][8]

Green tea leaves are initially processed by soaking in an alcohol solution, which may be further concentrated to various levels; byproducts of the process are also packaged and used.[citation needed] Extracts are sold over the counter in liquid, powder, capsule, and tablet forms,[4][9] and may contain up to 17.4% of their total weight in caffeine,[10] though decaffeinated versions are also available.[11]

Health effects

Main article: Health effects of tea

Brewed, regular green tea
Nutritional value per 100 g (3.5 oz)
Energy4 kJ (0.96 kcal)
0 g
0 g
0.2 g
VitaminsQuantity
%DV
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
MineralsQuantity
%DV
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 constituentsQuantity
Water99.9 g
Caffeine12 mg

Percentages are roughly approximated using US recommendations for adults.

Regular green tea is 99.9% water, provides 1 kcal per 100 mL serving, is devoid of significant nutrient content (table), and contains phytochemicals such as polyphenols and caffeine.

Numerous claims have been made for the health benefits of green tea, but human clinical research has not found good evidence of benefit.[2][7][12] 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.[7] Although green tea may enhance mental alertness due to its caffeine content, there is only weak, inconclusive evidence that regular consumption of green tea affects the risk of cancer or cardiovascular diseases, and there is no evidence that it benefits weight loss.[2]

A 2020 review by the Cochrane Collaboration listed some potential adverse effects including gastrointestinal disorders, higher levels of liver enzymes, and, more rarely, insomnia, raised blood pressure, and skin reactions.[13]

Cancer

Research has shown there is no good evidence that green tea helps to prevent or treat cancer in people.[13]

The link between green tea consumption and the risk of certain cancers such as stomach cancer and non-melanoma skin cancers is unclear due to inconsistent or inadequate evidence.[14][15]

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.[16]

Cardiovascular disease

Observational studies found a minor correlation between daily consumption of green tea and a 5% lower risk of death from cardiovascular disease. In a 2015 meta-analysis of such observational studies, an increase in one cup of green tea per day was correlated with slightly lower risk of death from cardiovascular causes.[17] Green tea consumption may be correlated with a reduced risk of stroke.[18][19] Meta-analyses of randomized controlled trials found that green tea consumption for 3–6 months may produce small reductions (about 2–3 mm Hg each) in systolic and diastolic blood pressures.[19][20][21][22] A separate systematic review and meta-analysis of randomized controlled trials found that consumption of 5-6 cups of green tea per day was associated with a small reduction in systolic blood pressure (2 mmHg), but did not lead to a significant difference in diastolic blood pressure.[23]

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.[24][25][26]

Hyperlipidemia

Drinking green tea or taking green tea supplements decreases the blood concentration of total cholesterol (about 3–7 mg/dL), LDL cholesterol (about 2 mg/dL), and does not affect the concentration of HDL cholesterol or triglycerides.[23][24][27] A 2013 Cochrane meta-analysis of longer-term randomized controlled trials (>3 months duration) concluded that green tea consumption lowers total and LDL cholesterol concentrations in the blood.[24]

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).[28]

Weight loss

There is no good evidence that green tea aids in weight loss or weight maintenance.[2][29]

Potential for liver toxicity

Excessive consumption of green tea extract has been associated with hepatotoxicity and liver failure.[30][31][32] In 2018, a scientific panel for the European Food Safety Authority reviewed the safety of green tea consumption over a low-moderate range of daily EGCG intake from 90 to 300 mg per day, and with exposure from high green tea consumption estimated to supply up to 866 mg EGCG per day.[33] Dietary supplements containing EGCG may supply up to 1000 mg EGCG and other catechins per day.[33] The panel concluded that EGCG and other catechins from green tea in low-moderate daily amounts are generally regarded as safe, but in some cases of excessive consumption of green tea or use of high-EGCG supplements, liver toxicity may occur.[33]

Production

In 2013, global production of green tea was approximately 1.7 million tonnes, with a forecast to double in volume by 2023.[34] As of 2015, China provided 80% of the world's green tea market, leading to its green tea exports rising by 9% annually, while exporting 325,000 tonnes in 2015.[35] In 2015, the US was the largest importer of Chinese green tea (6,800 tonnes), an increase of 10% over 2014, and Britain imported 1,900 tonnes, 15% more than in 2014.[35]

Growing, harvesting and processing

Hand-rolling green tea after steaming
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 a fourth harvest. The first flush in the spring brings the best-quality leaves, with higher prices to match.

Green tea is processed after picking using either artisanal or modern methods. Sun-drying, basket or charcoal firing, or pan-firing are common artisanal methods. Oven-drying, tumbling, or steaming are common modern methods.[36] 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.[37]

Import of radioactive Japanese tea

On 17 June 2011, at Charles de Gaulle airport in Paris, France, radioactive cesium of 1,038 becquerels per kilogram was measured in tea leaves imported from Shizuoka Prefecture, Japan as a result of the Fukushima Daiichi nuclear disaster on 11 March, which was more than twice the restricted amount in the European Union of 500 becquerels per kilogram. The government of France announced that they rejected the leaves, which totaled 162 kilograms (357 lb).[38]

In response, the governor of Shizuoka Prefecture, Heita Kawakatsu, stated: "there is absolutely no problem when they [people] drink them because it will be diluted to about 10 becquerels per kilogram when they steep them even if the leaves have 1,000 becquerels per kilogram;" a statement backed by tests done in Shizuoka.[39] Japanese Minister for Consumer Affairs and Food Safety Renhō stated on 3 June 2011 that "there are cases in which aracha [whole leaves of Japanese green tea] 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."[40]

In 2018, the US Food and Drug Administration updated its import status on Japanese products deemed to be contaminated by radionuclides, indicating that tea from the Ibaraki prefecture had been removed from the list by the Government of Japan in 2015.[41]

Green tea in East Asia

China

Chinese name
Longjing, a green tea from Zhejiang, China
Traditional Chinese綠茶
Simplified Chinese绿茶
Hanyu Pinyinlǜchá

Further information: History of tea in China, Chinese tea, and Chinese tea culture

See also: zh:中國茶

Loose leaf green tea has been the most popular form of tea in China since at least the Southern Song dynasty.[42][43] While Chinese green tea was originally steamed, as it still is in Japan, after the early Ming dynasty it has typically been processed by being pan-fired in a dry wok.[44] Other processes employed in China today include oven-firing, basket-firing, tumble-drying and sun-drying.[45] Green tea is the most widely produced form of tea in China, with 1.42 million tons grown in 2014.[46]

Popular green teas produced in China today include:

Japan

Sencha green tea, the most popular form of tea in Japan.
Sencha green tea, the most popular form of tea in Japan.

Further information: History of tea in Japan

See also: ja:日本茶

Tea seeds were first brought to Japan in the early 9th century by the Buddhist monks Saicho and Kūkai. During the Heian period (794–1185), Emperor Saga introduced the practice of drinking tea to the imperial family. The Zen Buddhist priest Eisai (1141–1215), founder of the Rinzai school of Buddhism, brought tea seeds from China to plant in various places in Japan. Eisai advocated that all people, not just Buddhist monks and the elite, drink tea for its health benefits.[54]

The oldest tea-producing region in Japan is Uji, located near the former capital of Kyoto.[54] It is thought that seeds sent by Eisai were planted in Uji, becoming the basis of the tea industry there.[55] Today, Japan's most expensive premium teas are still grown in Uji.[56] The largest tea-producing area today is Shizuoka Prefecture, which accounts for 40% of total Japanese sencha production.[57][56] Other major tea-producing regions include the island of Kyushu and the prefectures of Shiga, Gifu, and Saitama in central Honshu.[56]

All commercial tea produced in Japan today is green tea,[58] though for a brief period black tea was also produced in the late 19th and early 20th centuries. Japanese tea production is heavily mechanized, and is characterized by the use of modern technology and processes to improve yields and reduce labor. Because of the high cost of labor in Japan, only the highest quality teas are plucked and processed by hand in the traditional fashion.[59]

Japanese green teas have a thin, needle-like shape and a rich, dark green color. Unlike Chinese teas, most Japanese teas are produced by steaming rather than pan firing. This produces their characteristic color, and creates a sweeter, more grassy flavor. A mechanical rolling/drying process then dries the tea leaves into their final shape.[58] The liquor of steamed Japanese tea tends to be cloudy due to the higher quantity of dissolved solids.[60]

Most Japanese teas are blended from leaves grown in different regions, with less emphasis on terroir than in the Chinese market. Because of the limited quantity of tea that can be produced in Japan, the majority of production is dedicated to the premium tea market. Cheaper bottled teas and tea-flavored food products usually use lower-grade Japanese-style tea produced in China.[61]

Although a variety of commercial tea cultivars exist in Japan, the vast majority of Japanese tea is produced using the Yabukita cultivar developed in the 1950s.[62]

Popular Japanese green teas include:

Korea

Korean name
Korean name
Hangul
녹차
Hanja
綠茶
Revised Romanizationnokcha
McCune–Reischauernokch'a
IPA[nok̚.tɕʰa]

Further information: Traditional Korean tea and Korean tea ceremony

Gakjeochong, a Goguryeo tomb, shows a knight drinking tea with two ladies (5-6th century)
Gakjeochong, a Goguryeo tomb, shows a knight drinking tea with two ladies (5-6th century)
Tea leaves: sejak (green tea), ujeon (green tea), and hwangcha (yellow tea) from Hadong County
Tea leaves: sejak (green tea), ujeon (green tea), and hwangcha (yellow tea) from Hadong County

According to Record of Gaya cited in Memorabilia of the Three Kingdoms, the legendary queen Heo Hwang-ok, a princess of the Ayodhya married to King Suro of Gaya, brought the tea plant from India and planted it in Baegwolsan, a mountain in current Changwon.[71]: 3 However, it is a widely held view that systematic planting of tea bushes began with the introduction of Chinese tea culture by the Buddhist monks around the 4th century.[72] Amongst some of the earliest Buddhist temples in Korea, Bulgapsa (founded in 384, in Yeonggwang), Bulhoesa (founded in 384, in Naju) and Hwaeomsa (founded in Gurye, in 544) claim to be the birthplace of Korean tea culture.[72] Green tea was commonly offered to Buddha, as well as to the spirits of deceased ancestors.[72] Tea culture continued to prosper during the Goryeo Dynasty, with the tea offering being a part of the biggest national ceremonies and tea towns were formed around temples.[73] Seon-Buddhist manners of ceremony prevailed.[73] During the Joseon Dynasty, however, Korean tea culture underwent secularization, along with the Korean culture itself.[73] Korean ancestral rite jesa, also referred to as charye (차례; 茶禮, "tea rite"), has its origin in darye (다례; 茶禮, "tea rite"), the practice of offering tea as simple ancestral rites by the royal family and the aristocracy in Joseon.[73]

Tea culture of Korea was actively suppressed by the Japanese during the Japanese forced occupation period (1910‒1945), and the subsequent Korean War (1950‒1953) made it even harder for the Korean tea tradition to survive.[74] The restoration of the Korean way of tea began in the 1970s, around Dasolsa.[74] Commercial production of green tea in South Korea only began in the 1970s,.[75] By 2012 the industry was producing 20% as much tea as Taiwan and 3.5% as much as Japan.[76][77] Green tea is not as popular as coffee or other types of Korean teas in modern South Korea. The annual consumption per capita of green tea in South Korea in 2016 was 0.16 kg (0.35 lb), compared to 3.9 kg (8.6 lb) coffee.[78] Recently however, as the coffee market reached saturation point, South Korean tea production doubled during 2010‒2014,[79] as did tea imports during 2009–2015,[80] despite very high tariff rate (513.6% for green tea, compared to 40% for black tea, 8% for processed/roasted coffee, and 2% for raw coffee beans).

Korean green tea can be classified into various types based on several different factors. The most common is the flush, or the time of the year when the leaves are plucked (and thus also by leaf size).

The mode of preparation also differs:

Leaf teas are processed either by roasting or steaming.

Southern, warmer regions such as Boseong in South Jeolla Province, Hadong in South Gyeongsang Province, and Jeju Island are famous for producing high-quality tea leaves.[92]

Green tea can be blended with other ingredients.

See also

References

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