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A fresh leaf houses two substances of “opposite character”: the polyphenols and caffeine that make tea astringent and bitter, and the theanine that makes it fresh and sweet. Whether a cup tastes good is essentially the balance between them.
Below, meet each molecule and its taste; to dial the proportions yourself and watch flavour change, head to the interactive chart in “Composition & Flavour · the ratio”.
L2 · Deep DiveThe main taste compounds of the fresh leaf
The main components of fresh tea leaf (by dry weight) are roughly:
| Component | Amount (approx.) | Taste / role |
|---|---|---|
| Polyphenols (mainly catechins) | 18–36% | astringent, bitter; core antioxidants. Higher in large-leaf cultivars, summer leaf, strong sun |
| Caffeine | 2–5% | bitter and stimulating; with trace theobromine, theophylline |
| Theanine & free amino acids | theanine ~4%, amino acids 1–5.5% | umami and sweetness, calming, softening bitterness |
| Aroma compounds | trace | source of aroma (see oolong zuoqing) |
| Others | — | carbohydrates, chlorophyll, organic acids, vitamins, minerals |
Flavour is a tug-of-war: polyphenols and caffeine pull toward “bold and astringent,” amino acids toward “fresh and gentle.” Green tea has the most catechins, so it is brisk yet bitter-astringent; in black tea catechins oxidise into theaflavins and thearubigins, lowering astringency and raising body.
The “magic” of shading
Shading the plant before harvest does something interesting: with less light, the leaf’s conversion of amino acids into polyphenols is suppressed, so theanine and other amino acids rise while astringent polyphenols fall.
Japan’s gyokuro and matcha are shade-grown for exactly this — rich umami and the seaweed-like note of “covered” teas. It shows that leaf chemistry is not fixed: cultivation can actively tune it — a bridge between “the plant” and “the taste.”
How composition decides taste
The levels and ratio of polyphenols, caffeine and amino acids set a tea’s style. One key index is the polyphenol/amino-acid ratio — how it shapes flavour and how it is tuned by tender plucking and shading is explored with an interactive chart in the Flavour chapter:
👉 Composition & Flavour · the ratio
See also
- The Botany of the Tea Plant — the plant this leaf grows on
- The Flavour Wheel — how composition finally becomes “taste”
References
- Chemical Composition of Tea. Herbs & Kettles. https://www.herbsandkettles.com/blogs/blog/chemical-composition-of-tea
- Tea Components. O-CHA / World Green Tea Association. https://www.o-cha.net/english/cup/pdf/38.pdf
Composition figures are common ranges and vary with cultivar, season, tenderness and origin — for understanding only.