TeaClear

How is tea made?
Green tea and black tea are the same leaf. Crush it and an enzyme turns it copper in an hour; heat it first and it stays green. Run the factory, stop the oxidation at the right minute, then brew it: caffeine rushes out first, the bitter tannins keep coming, and a pan of chai shows why milk makes it smooth.

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1. One plant, kept in two rooms. All tea comes from Camellia sinensis. Pluckers take two leaves and a bud. In each cell the bitter catechins sit in the vacuole and the enzyme polyphenol oxidase sits in the chloroplasts, so a living leaf stays green.
2. The factory breaks the wall. The leaf is withered from about 77% water to about 70%, then rolled or cut by CTC rollers so the cells tear. Catechins, enzyme and oxygen meet and the leaf oxidises: orange theaflavins rise, then red-brown thearubigins. Hot air then dries it to about 3% water and kills the enzyme. About 100 kg of leaf makes 23.7 kg of tea.
3. Six teas from one leaf. Heat the leaf first and the enzyme dies: green tea. Oxidise it all the way: black tea. Stop halfway: oolong. Only wither and dry it: white. Wrap a green tea warm and damp: yellow. Pile it damp with microbes for weeks: dark tea, the only one that is truly fermented.
4. The brew is a race. Caffeine is small and leaves the leaf fast: half is out of whole black leaf in under two minutes at 80 °C (measured). Tannins are bigger, come out more slowly and keep coming, so a long brew adds bitterness, not much caffeine. Hotter water and smaller leaf speed everything up.
5. Why chai is boiled with milk. CTC granules in boiling water give up nearly all their caffeine within a minute and their tannins soon after. Casein, the main milk protein, binds tannins, so fewer are left to dry your mouth. Sugar covers the rest. A strong Assam CTC can take the boiling and the milk.
6. India's cup, and yours. India made about 1,285 million kg of tea in 2024, half of it in Assam, and drinks about four fifths of it. ICMR-NIN advises keeping caffeine within 300 mg a day and tea an hour away from meals, because tannins hinder iron absorption. IARC classes drinks above 65 °C as probably carcinogenic, so let the cup cool.

From a wild leaf in the hills where China, Myanmar and Assam meet to a billion cups of chai a day.

• 760 · Lu Yu writes The Classic of Tea (Lu Yu, Tang dynasty China)
• 1610 · Dutch ships carry tea towards Europe (Dutch East India Company, Macao, Hirado and Amsterdam)
• 1823 · Assam's own tea plant is shown to the British (Robert Bruce, Maniram Dewan and the Singpho chief Bessa Gam, Upper Assam)
• 1839 · The first Assam tea is sold in London (The Tea Committee and the Assam Company, Chabua, Assam, and London)
• 1863 · Indentured labour and its cost (Recruited workers of the Assam gardens, Assam)
• 1903 · A campaign teaches India to drink tea (Tea Cess Committee and Indian Tea Association, Railways, mills and bazaars of India)
• 1908 · The tea bag (Roberta Lawson and Mary McLaren; Thomas Sullivan, Milwaukee and New York, USA)
• 1930 · CTC: crush, tear, curl (William McKercher, Amgoorie tea garden, Assam)

The full story, with 30 moments, charts, people and 39 sources: glassbox.how/e/teaclear/history. The data lives in history.json.

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