Green tea

• 1. Introduction

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  Green tea is almost nothing at all. A regular cup is 99.9 percent water and supplies about 1 kcal per 100 mL, with no meaningful nutrients. Yet this drink starts as the leaves and buds of Camellia sinensis, picked before the withering and oxidation that turn the same plant into oolong or black tea. It has been argued over by scientists, shaped by emperors and monks, and once turned away at a European airport. Which country gave green tea to the world, and how did a single plant split into so many different flavours? Why can a few degrees of water temperature decide whether a cup is sweet or harsh? And how much of the praise for green tea survives contact with clinical research?

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• 2. Books and Legends

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  Legend gives the credit for tea drinking to Emperor Shennong, a mythological ruler of China. The documented story is less colourful. Green tea originated in China in the late 1st millennium BC, and its production later spread to other countries in East Asia.

  Between 618 and 907 AD, Lu Yu wrote The Classic of Tea, a book that historians still treat as important to the story of green tea.

  In 1211, the Zen priest Eisai wrote a Japanese work known as The Book of Tea, or Kissa Yōjōki. The title means Record of Drinking Tea for Nourishing Life. Eisai described the shapes of tea plants, flowers and leaves, and explained how to grow the plant and process its leaves. He also claimed that drinking green tea could affect the five vital organs.

  Lu Yu's classic is even cited as a source for a tea called Cloud tea, named for the mountain clouds around the slopes where it was first cultivated.

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• 3. From Bush to Cup

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  Green tea plants are grown in rows and pruned so that shoots come up in a regular pattern, with most farms picking three times a year. Growers fall into two basic camps, those who grow in full sun and those who grow under shade. The first flush arrives in late April to early May and brings the best leaves, with prices to match. The second harvest runs from June through July, and the third comes in late July to early August. Some farms add a fourth.

  After picking, the leaves are fixed by either artisanal or modern methods. Sun-drying, basket or charcoal firing, and pan-firing are the artisanal choices. Oven-drying, tumbling and steaming are the modern ones. All of them aim to keep as many polyphenols and volatile organic compounds as possible, which shapes both aroma and taste.

  The result at this stage is called aracha, and it is still unrefined. Aracha is kept under low-humidity refrigeration at 0-5 C, in paper bags of 30 or 60 kilograms. Processors re-fire the leaves through the year as orders come in, which stretches shelf life and improves flavour. A May first flush will keep this way until the next harvest. Each batch is then sifted and graded by size, and tasters blend the lots according to a blending order before packing.

  A standard cup starts with roughly 2 g of tea for every 100 mL of water. Steeping temperatures run from 61 C to 87 C, and steeping times from 30 seconds to three minutes. Cheaper green teas are usually steeped hotter and longer. Better teas get cooler, shorter infusions, typically two or three of them in a row. Gyokuro, a high-grade tea, calls for more leaf and several brief steepings.

  Go too hot or too long and the leaves release excess tannins, which makes a bitter, astringent brew whatever the tea's quality. Two habits help. Warming the pot first keeps the tea from cooling instantly, and leaving the leaves in the pot while adding hot water bit by bit keeps the flavour even.

  The country that grew the most green tea in 2014 was China, with 1.42 million tons.

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• 4. China's Pan-Fired Leaves

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  Loose leaf green tea has been the most popular form of tea in China since at least the Southern Song dynasty. Chinese green tea was originally steamed. After the early Ming dynasty, makers switched to pan-firing the leaves in a dry wok, and that remains typical today, alongside oven-firing, basket-firing, tumble-drying and sun-drying.

  In 2013, global green tea production was about 1.7 million tonnes, with a forecast that it would double by 2023. By 2015, China held 80 percent of the world green tea market. Its exports were rising by 9 percent a year, and it shipped 325,000 tonnes abroad in 2015. The United States was the largest buyer of Chinese green tea that year, taking 6,800 tonnes, an increase of 10 percent over 2014. Britain imported 1,900 tonnes, which was 15 percent more than in 2014.

  The names of Chinese green teas often describe their shapes. Green Snail Spring, from Jiangsu, takes its name from leaves curled like snails. Gunpowder tea, also called pearl tea, is tumble-dried until each leaf becomes a small pellet. Precious Eyebrows is popular outside China and has a plum-like flavour.

  Dragon Well, or Longjing, is grown near Hangzhou in Zhejiang province and is the best-known pan-fired Chinese green tea. Part of its flavour comes from the terroir of its home region.

  Anhui province supplies several distinctive leaves. Yellow Mountain Fur Peak grows in the microclimate of the Huangshan range and is picked as two equal-sized leaves with a bud. Lu'an Melon Seed is plucked as two separate leaves, with no bud and no stem, later in the season, and tastes grassier than most Chinese green teas. Peaceful Monkey Leader uses a cultivar with an unusually large leaf, and its production flattens the leaves into the so-called "two knives and a pole" shape.

  Henan province gives Tippy Green, also called Xinyang Maojian, which is picked as a bud with one leaf. Sichuan's Mengding mountain produces Sweet Dew of Mengding, a yellowish-green tea with a sweet aftertaste. Anji White comes from Anji.

  Another famous Chinese tea, Duyun Maojian, was a favourite of Mao Zedong.

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• 5. Japan's Steamed Teas

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  Early in the 9th century, the Buddhist monks Saicho and Kūkai first brought tea seeds to Japan. During the Heian period, which ran from 794 to 1185, Emperor Saga introduced tea drinking to the imperial family.

  Eisai, who lived from 1141 to 1215 and founded the Rinzai school of Buddhism, later carried tea seeds over from China and had them planted in various places. He argued that everyone, not only monks and the elite, should drink tea for its health benefits.

  The oldest tea-producing region in Japan is Uji, near the former capital of Kyoto, and seeds sent by Eisai are thought to have formed the basis of its tea industry. Japan's most expensive premium teas are still grown in Uji. The largest producing area today is Shizuoka Prefecture, which accounts for 40 percent of all Japanese sencha. Kyushu and the prefectures of Shiga, Gifu and Saitama are other major regions.

  Every commercial tea made in Japan today is green tea. Black tea was briefly produced there in the late 19th and early 20th centuries. Production is heavily mechanized, because labour is expensive, and only the finest teas are still plucked and processed by hand.

  Most Japanese tea is steamed rather than pan-fired, which gives it a thin, needle-like shape, a rich dark green colour and a sweeter, grassier flavour. A mechanical rolling and drying process then sets the final shape. Steamed tea also pours cloudy, because it carries more dissolved solids.

  Japanese growers blend leaves from different regions and care less about terroir than their Chinese counterparts do. Limited supply means most of the crop goes to the premium market. Cheaper bottled teas and tea-flavoured foods usually rely on lower-grade, Japanese-style tea made in China. The vast majority of Japanese tea comes from the Yabukita cultivar, which was developed in the 1950s.

  Sencha is the standard style and makes up 80 percent of all Japanese tea, with 90 percent of it grown from Yabukita. Bancha is a lower-grade tea picked from the same bushes after the sencha season ends, and it tastes bolder. Genmaicha mixes sencha with toasted puffs of rice. Kukicha blends sencha leaves with stems. Hōjicha is made by roasting sencha or bancha leaves along with kukicha twigs.

  Gyokuro is shaded for three weeks before plucking. The shade gives it a sweeter flavour and a richer colour from extra chlorophyll, and it is one of Japan's most exclusive teas. Kabusecha is shaded for just one week, so its taste falls between gyokuro and ordinary sencha.

  Matcha is also shaded. Its processed leaf is called tencha, and grinding tencha into fine powder makes matcha. The powder is very perishable and expensive, so it is sold in small quantities. Matcha is the tea of the Japanese tea ceremony, and it is whisked with hot water in a bowl until the surface turns frothy. Water that is too hot makes it overly bitter.

  Shincha is the earliest harvest, picked from the youngest growth from early April to early May, before the first flush. Because so little is made, shincha is highly prized and expensive.

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• 6. Korea and Vietnam

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  A text called the Record of Gaya, cited in Memorabilia of the Three Kingdoms, tells of Queen Heo Hwang-ok. She was a princess of Ayodhya who married King Suro of Gaya, and she supposedly brought the tea plant from India and planted it on Baegwolsan, a mountain in present-day Changwon. A more widely held view says that systematic tea planting began around the 4th century, when Buddhist monks introduced Chinese tea culture.

  Three of Korea's earliest temples claim to be the birthplace of its tea culture. Bulgapsa in Yeonggwang and Bulhoesa in Naju were both founded in 384, and Hwaeomsa in Gurye was founded in 544. Green tea was offered to the Buddha and to the spirits of ancestors. During the Goryeo period, tea offerings were part of the largest national ceremonies, and tea towns grew up around temples.

  The Joseon period brought secularization. The Korean ancestral rite jesa, also called charye, meaning "tea rite", grew out of darye, a practice in which the royal family and aristocracy offered tea in simple ancestral rituals.

  Between 1910 and 1945, during the Japanese forced occupation, Korean tea culture was actively suppressed. The Korean War of 1950-1953 made survival harder still. The revival began in the 1970s, around Dasolsa, and commercial green tea production in South Korea began in the same decade. By 2012, the industry produced 20 percent as much tea as Taiwan and 3.5 percent as much as Japan.

  In 2016, South Koreans drank just 0.16 kg of green tea per person, against 3.9 kg of coffee. Then the coffee market reached saturation, and tea production doubled between 2010 and 2014. Imports of tea also doubled between 2009 and 2015, despite a tariff of 513.6 percent on green tea. Black tea faces 40 percent, processed or roasted coffee 8 percent, and raw coffee beans 2 percent.

  Korean green tea is classified mainly by flush. Ujeon, made from hand-picked leaves plucked before gogu on the 20th or the 21st of April, steeps best at 50 C. Sejak is picked after gogu and before ipha on the 5th or the 6th of May. It is also called jakseol, because its leaves are about the size of a sparrow's tongue. Jungjak is plucked after ipha until mid-May. Daejak, picked in late May and after, usually goes into tea bags or cooking.

  Roasting is the most common and traditional processing method, and pan-fried deokkeum-cha is richer in flavour. Steaming is less popular but survives in temple cuisine, and steamed jeungje-cha has a more vivid colour. Boseong in South Jeolla Province, Hadong in South Gyeongsang Province and Jeju Island are famous for high-quality leaves. Banya-cha, a steamed tea developed by Buddhist monks in Boseong, takes its name from the Korean transliteration of the Buddhist concept prajñā. Hyeonmi-nokcha blends green tea with brown rice tea.

  Vietnam makes a very different story. In 2011, green tea accounted for over 63 percent of all retail tea volume sales there, making it the country's most popular tea. Large-scale cultivation arrived in the late 19th century, when French colonists ran the first plantations in the Phú Thọ area. Vietnam ranks fifth in the world for tea production today.

  The Thái Nguyên area, north of Hanoi, has been called the cradle of Vietnamese tea and ships its green tea internationally. Many Vietnamese teas are scented with flower petals, including lotus, jasmine and chrysanthemum. One of them, trà sâm dứa, is a herbal mix of green tea, jasmine, Aglaia duperreana flower, basil and pandan leaves.

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• 7. What Science Says

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  In 2011, a panel of scientists published a report on green tea health claims at the request of the European Commission. In general, it found the claims were not supported by sufficient scientific evidence. Human clinical research has not found good evidence of benefit. The caffeine in green tea may sharpen mental alertness. Evidence that regular drinking affects the risk of cancer or cardiovascular disease is weak and inconclusive, and there is no evidence it helps with weight loss or weight maintenance.

  Cancer Council Australia and Cancer Research UK both say there is not enough reliable evidence that green tea prevents cancer. The National Cancer Institute says "the evidence regarding the potential benefits of tea consumption in relation to cancer is inconclusive at present". One interaction is firmer. Green tea interferes with the chemotherapy drug bortezomib, sold as Velcade, and with other boronic acid-based proteasome inhibitors. People taking these medications should avoid it.

  For the heart, a meta-analysis of observational studies linked one extra cup of green tea a day to a slightly lower risk of death from cardiovascular causes. Drinking it may also be tied to a lower stroke risk. Meta-analyses of randomized controlled trials found that three to six months of green tea may lower systolic and diastolic blood pressure by about 2-3 mm Hg each. A separate review found a systolic drop of 2 mmHg and no significant diastolic change.

  Green tea lowers fasting blood sugar, but its effect on haemoglobin A1c and fasting insulin has been inconsistent. Green tea and its supplements reduce total cholesterol by about 3-7 mg/dL and LDL cholesterol by about 2 mg/dL, with no effect on HDL or triglycerides. A 2013 Cochrane meta-analysis of trials lasting longer than three months reached the same conclusion on cholesterol. A 2015 review of 11 randomized controlled trials found no significant link with lower C-reactive protein, a marker of inflammation.

  The chemistry behind the interest is real. Green tea holds the polyphenols epigallocatechin gallate, known as EGCG, and epicatechin gallate, plus the flavonoids kaempferol, quercetin and myricetin. A cup contains more flavonoids and catechins than the same volume of other foods and drinks traditionally thought to promote health. Even so, these compounds have no proven biological effect in humans.

  Extracts are made by soaking the leaves in an alcohol solution, which can be concentrated to various levels. They are sold over the counter as liquids, powders, capsules and tablets. Some contain up to 17.4 percent caffeine by weight, though decaffeinated versions exist. The Food and Drug Administration has approved a green tea extract ointment as a prescription drug for treating genital warts.

  Extracts also carry risk. In some cases of excessive intake, green tea extract is hepatotoxic, meaning it damages the liver, and has been associated with liver failure. A 2020 Cochrane review listed possible adverse effects including gastrointestinal disorders and higher liver enzymes. More rarely it listed insomnia, raised blood pressure and skin reactions.

  In 2018, a panel of the European Food Safety Authority reviewed intake from 90 to 300 mg of EGCG a day, with heavy tea drinking estimated to supply up to 866 mg. Supplements can provide up to 1000 mg of EGCG and other catechins daily. The panel judged low-to-moderate daily amounts generally safe, while warning that liver toxicity may occur with excessive tea or high-EGCG supplements.

  Outside the pharmacy, green tea extract has found another job as a clean label food preservative that protects fats from rancidity. Its oil-soluble form, palmitoylated green tea catechins, was ruled generally recognized as safe in 2020.

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• 8. Radioactive Leaves in Paris

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  On the 17th of June 2011, at Charles de Gaulle airport in Paris, inspectors measured radioactive caesium at 1,038 becquerels per kilogram in tea leaves imported from Shizuoka Prefecture, Japan. The contamination followed the Fukushima Daiichi nuclear disaster of the 11th of March. The reading was more than twice the European Union limit of 500 becquerels per kilogram. France announced that it was rejecting the shipment, which totalled 162 kg.

  Heita Kawakatsu, the governor of Shizuoka Prefecture, answered that drinkers faced "absolutely no problem". Steeping, he said, would dilute the figure to "about 10 becquerels per kilogram", even if the dry leaves held 1,000. He added that tests done in Shizuoka backed up the statement.

  The Japanese Minister for Consumer Affairs and Food Safety, Renhō, had struck a more cautious note on the 3rd of June 2011. She pointed out that some whole aracha leaves are sold as furikake, a condiment sprinkled on rice, and eaten as they are. For that reason she called inspection of tea leaves, aracha included, important "from the viewpoint of consumers' safety".

  The story had a long tail. In 2018, the US Food and Drug Administration updated its import status for Japanese products deemed contaminated by radionuclides. Tea from Ibaraki prefecture, it noted, had been removed from the list by the Government of Japan back in 2015.

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