--- title: 'The chemistry of tea aroma' url: 'https://howtotea.me/science/chemistry/aroma' markdown: 'https://howtotea.me/science/chemistry/aroma.md' lang: en date: '2026-10-25' description: 'Where tea aroma comes from: glycosides, indole, pyrazines, how withering and roasting build them, and how to smell the lid, the steam and an empty cup.' --- # The chemistry of tea aroma 香气 Editors · October 25, 2026 · 9 min read Researchers have found about 600 volatile compounds in tea, but the recognizable smell of a given tea rests on a few dozen. Most of them form in the leaf during processing, and different ones reach you above the cup and in the mouth, so the same tea smells one way on a sniff and another on a sip. ![A tall aroma cup and a drinking cup of oolong on a wooden stand](https://howtotea.me/images/c/o/v/e/r/cover-599ddda8.webp) Illustration 香气 Aroma xiāng qì Volatiles: about 600 found, a few dozen perceptible Fresh leaf: almost no smell, or slightly grassy Oolong: indole, jasmine lactone, nerolidol Roasting: pyrazines and furans, from 110 °C Steam above the cup: light compounds: flowers, greens Liquor in the mouth: heavy and soluble ones: honey, caramel A freshly plucked leaf smells faint: grassy, or of almost nothing. The floral [oolong](https://howtotea.me/teas/oolong), the honeyed [black tea](https://howtotea.me/teas/black) and the roasted, nutty dancong all take shape later, in the workshop. The leaf holds no finished smell. Processing creates it. So talking about aroma means talking about what the tea maker does to the leaf, and what you do with it in the cup. ## Where the smell comes from A 2025 Chinese review sorts tea volatiles by origin into four families: derivatives of [amino acids](https://howtotea.me/science/chemistry/theanine), compounds released from glycosides, derivatives of fatty acids and derivatives of carotenoids[1](#fn:1). Heat products form a group of their own, from the Maillard reaction and the Strecker degradation of amino acids. For floral teas, the route that matters most runs through glycosides. Linalool, geraniol, benzyl alcohol and 2-phenylethanol are stored in the cell vacuoles, each tied to a sugar. The enzyme β-primeverosidase sits close by, but on the other side of the cell wall, so as long as the leaf stays whole the two never meet. Bruise the leaf and the enzyme cuts the sugar away, leaving the alcohol free to smell. Disaccharide glycosides outnumber glucosides in the leaf about three to one, and young leaf, from the bud down to the third leaf, holds the most of them. Hence the old habit of making the best oolongs and black teas from a tender pluck. Fatty acids yield the green notes, (Z)-3-hexenol and hexanal, along with jasmine lactone. Carotenoids yield β-ionone and β-damascenone, with their violet and honey smells. Indole comes from the shikimate pathway. On its own it smells “animalic”, but in a blend it reads as floral. ## What you can smell and what you can't A compound can be present in tea and still have no smell. Chemists gauge its contribution with the odor activity value, OAV: the concentration divided by the odor threshold in water. Anything above one is perceptible. Thresholds vary by orders of magnitude. In water, the figure is 0.01 µg/kg for β-ionone, 0.002 µg/kg for β-damascenone (0.004 in another study), 0.4 for linalool, 7.5 for geraniol, 390 for 2-phenylethanol and 250 for nerolidol. In a 2015 [white tea](https://howtotea.me/teas/white), β-damascenone reached an OAV of about 13,900, while nerolidol fell short of one. So the idea that the most abundant compound dominates the smell is wrong. What you smell is whatever registers at a tiny concentration. Mirror-image forms of a molecule complicate things further. R-linalool smells of flowers and lavender, S-linalool of sweet petitgrain, and their thresholds differ. Methyl jasmonate, the well-known “jasmine” compound of oolong, occurs in tea below its own threshold. The smell actually comes from its relative, methyl epijasmonate, which by the estimate of Acree and colleagues, cited by Kobayashi in a 1988 paper, is 400 times more potent. The ratio of mirror forms in a raw material usually holds steady, which makes it useful as a fingerprint of origin and quality. Which way one form converts into the other under heat is still disputed. ## How processing builds aroma **Oolong.** Oolong processing keeps the leaf alive and under constant strain: plucking, sun withering, indoor withering, shaking. Each stress triggers the leaf’s defenses, and defense has a smell. It is during shaking that indole, jasmine lactone and (E)-nerolidol build up. The gene that switches on indole synthesis is active at that stage, and repeated wounding of the leaf makes it more active still. Light [Tie Guan Yin](https://howtotea.me/teas/oolong/tie-guan-yin) and Taiwanese high-mountain oolongs smell of terpene alcohols and nerolidol. Taiwan’s Oriental Beauty takes this to the extreme. Leafhoppers bite the leaf in the field, the leaf mounts a defense, and after long withering and five rounds of shaking, geraniol rises about 24-fold, benzyl alcohol 38-fold and 2-phenylethanol 41-fold. **Black tea.** Rolling ruptures the cells and the β-primeverosides all but disappear, as the enzyme frees the floral alcohols during oxidation. Black tea has far less indole than oolong, since its synthesis stops once the leaf is rolled. Terpene alcohols are only part of the story in Darjeeling. Vanillin, furaneol and (E,E,Z)-2,4,6-nonatrienal, which smells of oatmeal, were among the 18 compounds German chemists used to rebuild an aroma model of the liquor that matched the real tea. Chinese papers link geraniol to the “Qimen aroma” (祁门香) of [Qimen](https://howtotea.me/teas/black/qimen) black tea. **[Green tea](https://howtotea.me/teas/green).** Fixation kills the enzymes, and its temperature shapes the smell. In trials, leaf fixed at 270 °C smelled more noticeably of grass; at 320 °C sweet, chestnut and bean notes appeared; at 370 °C a floral note joined them. Green tea contains little Maillard product, and one explanation is that [catechins](https://howtotea.me/science/chemistry/polyphenols) suppress the formation of glyoxal from glucose. In Japanese [sencha](https://howtotea.me/brewing/methods/sencha-gyokuro), the final drying and firing (hiire) soften the green smell and add a toasty note. Once the leaf surface reaches 130 °C, the tea already smells like hojicha. **Roasting.** It creates new aroma rather than masking the old. In model reactions of amino acids with sugars, pyrazines climb noticeably above 110 °C and peak at 130 °C. In Wuyi rock tea, 61–86% of the nitrogen in newly formed alkylpyrazines comes from the leaf’s free alanine, and 72–86% of the carbon in new furans from its free glucose. The caramel smell of [Dong Ding](https://howtotea.me/teas/oolong/dong-ding) rests on three pyrazines: remove them from the aroma model and the caramel is gone. Roasting does strip away some of the fresh green notes. Aging shifts the smell even without fire. In aged white tea, β-damascenone goes up while cedrol, methyl salicylate and linalool go down. **Shou pu-erh.** The “stored” smell comes from 1,2,3- and 1,2,4-trimethoxybenzene, which microbes make from gallic acid. Spontaneous fermentation produced about seven times as much of them as sterile fermentation, where only moisture and heat were at work. With moist heat and no microbes, the tea smelled of plum and honey instead. So the smell of [shou pu-erh](https://howtotea.me/teas/dark/puer) is born in the fermentation pile and has nothing to do with spoilage. ## What brewing does to the smell Hotter water and a stronger liquor send more volatiles into the air above the mug, and each compound follows its own curve. In one green tea study, volatiles in the steam rose from the first minute to the third and dropped by the fifth, while in the liquor itself they kept climbing. Over those five minutes the liquor cooled from 92 to 62 °C. The authors found two to three minutes of steeping best for aroma in the steam. Steam and liquor smell different because each picks up its own set of compounds[2](#fn:2). Researchers found 42 odorants in Darjeeling leaf, and nine of them, including geraniol, were significantly higher in the liquor than in the dry leaf, since water releases them. Compounds with high vapor pressure rise into the air, while soluble and heavy ones stay in the liquor. Furaneol dissolves readily in water but hardly evaporates, so you can't detect it above sencha, though it matters in the mouth. β-damascenone dissolves poorly and is barely volatile, but its threshold is so low that you still pick it up in the liquor. In the mouth, smell takes a different route. When you inhale, it reaches the nose from outside, the orthonasal route. When you drink, it rises from inside, from the throat, and you smell it retronasally. In a Japanese experiment, participants rated this aroma of an oolong after each of ten sips, and their sense of smell warmed up instead of tiring: the aroma came across weaker after the first sip than after the later ones. This matters at the tea table. In light floral teas the key compounds go into the steam, so the lid of the [gaiwan](https://howtotea.me/teaware/brewing-vessels/gaiwan) and the cup tell you the most. Teas whose aroma leans heavy (sencha, hojicha, roasted oolongs) open up in the mouth, and a sniff above the cup won't do them justice. How water and time pull flavor from the leaf is a question of [extraction](https://howtotea.me/science/water-and-extraction/extraction). ## How to smell The Chinese tea evaluation standard [GB/T 23776-2018](https://howtotea.me/science/evaluation/shenping) calls for smelling the aroma three times[3](#fn:3): hot, with the lid at about 75 °C; warm, at about 45 °C; and cold, at room temperature. Hold the lid to your nose for two to three seconds and repeat once or twice. Under the standard, dry leaf is judged by appearance, and aroma only after brewing. The group standard for dancong uses the same three stages: the lid at about 80 °C, at about 50 °C, and once it no longer feels warm. At home, a simpler sequence will do. Brew [gongfu cha](https://howtotea.me/brewing/methods/gongfu-cha) style and [preheat](https://howtotea.me/brewing/basics/preheating-and-rinsing) the vessels before adding the leaf. Smell the inside of the lid right after you pour, then again once it cools. After that, the surface of the liquor in the cup, a sip, a breath out through the nose, and the empty cup. Save the spent leaf for last. You don't need a wen xiang bei, the tall, narrow [aroma cup](https://howtotea.me/traditions/china/living-traditions/taiwan-chayi). The liquor goes into it, gets flipped into a low [tasting cup](https://howtotea.me/teaware/brewing-vessels/cups), and you smell the empty tall one. Cai Rongzhang writes that you can manage without it. ## Common questions Why does dry leaf smell different from the liquor? In dry leaf, some of the fragrant compounds are still bound to sugars or have not yet been washed out. Hot water frees them, and the steam and the liquor each take different molecules: light ones go into the air, heavy and soluble ones into the water. That is why the standards judge dry leaf by appearance and leave aroma until after brewing. Do I need an aroma cup? No. The Taiwanese tea master Cai Rongzhang writes that you can smell the surface of the liquor before a sip, the aroma in your mouth as you drink, and the empty cup afterward. The wen xiang bei appeared in Taiwan in the 1980s, and it had more to do with hygiene than with smell. Does the “stored” smell of shou pu-erh mean the tea has spoiled? No. It comes from methoxybenzenes that microbes make out of the leaf’s gallic acid during wet piling. It is the typical smell of shou pu-erh, not a sign that the tea went bad. Notes 1. Li Lu et al., “Progress in research on tea aroma components” (茶叶香气成分研究进展), China Tea Processing (中国茶叶加工), 2025, no. 2. The same paper is the source for the class profiles, fixation temperatures and the role of catechins. [↩](#fnref1:1) 2. Y. Mizukami, “Odorants in the headspace and infusion of sencha” (煎茶のヘッドスペースと浸出液に含まれる香気寄与成分), 茶業研究報告 116, 2013. Furaneol: logP 0.34, vapor pressure 4.27 Pa; β-damascenone: logP 4.4, 2.67 Pa. [↩](#fnref1:2) 3. GB/T 23776-2018, “Methodology for sensory evaluation of tea” (茶叶感官审评方法), adopted 6 February 2018, in force since 1 June 2018. [↩](#fnref1:3) --- ## Navigation - Parent: [Tea leaf chemistry](https://howtotea.me/science/chemistry.md) - Previous: [Theanine, amino acids and umami](https://howtotea.me/science/chemistry/theanine.md) - Next: [Is tea safe? What is in the cup](https://howtotea.me/science/chemistry/tea-safety.md)