Can one compound ratio predict flavour?

Start with the essentials

Three key points

1. A ratio provides a relationshipCompare within matching samples and measurement methods.
2. Perceived strength has other conditionsExtraction, thresholds and interactions affect sensations.
3. Processing and brewing change expressionAroma and texture still require attention to the actual liquor.

Try it while tasting

The three leads and their tastes

Absolute amounts set strength; the ratio between them sets the style. But “polyphenols bitter-astringent, amino acids fresh-sweet” is only the beginning — inside each substance there are distinct characters worth separating.

Catechins: the skeleton of astringency and bitterness

In fresh leaves and many green teas, catechins account for a large share of tea polyphenols, often cited as roughly 70–80%. Processing changes this share, so it is not a fixed proportion across all tea types. Catechins fall into two families[1]:

• Galloylated (ester-type) catechins: EGCG, ECG, GCG and others, carrying a galloyl group;
• Non-galloylated (simple) catechins: EGC, EC, GC and others, without that group.

Galloylation affects catechin interactions with oral components. Galloylated catechins often contribute strongly to bitterness and astringency, but this does not make every non-galloylated catechin mild or sweet[1][3]. Astringency is an oral drying, rough or contracting sensation rather than a primary taste. Hydrogen bonding and hydrophobic interactions between polyphenols and salivary proteins, including proline-rich proteins (PRPs), can alter lubrication and friction. Aggregation depends on concentration, pH and oral conditions; it does not require assuming that the compounds always carry opposite charges or instantly precipitate the entire lubricating film[1][3].

German sensory chemists Scharbert and Hofmann gave black tea taste a “molecular dissection” using quantitative analysis, taste reconstitution and omission experiments: they first quantified a dozen-plus tastants in black tea, then dissolved them back into pure water at their measured concentrations — a panel judged the reconstitute almost indistinguishable from real infusion; omitting compounds one by one showed the largest contributions came from caffeine and a group of astringent compounds (galloylated catechins, flavonol glycosides, etc.)[12]. Concentration–intensity research found that EGCG and ECG correlated strongly with bitterness in the studied green-tea infusions, while ECG and some flavonol glycosides contributed to astringency[3]. This helps explain composition differences without classifying all summer or large-leaf teas as harsh.

Theanine: where umami comes from, and how it is tuned

L-theanine is a non-protein amino acid nearly unique to the tea plant, often accounting for about half of the total free amino acids in tea[1]. Its metabolic pathway is itself the key to understanding the polyphenol/amino-acid ratio:

1. Synthesised in the roots: theanine is formed from glutamic acid and ethylamine in the roots;
2. Transported to the shoots: it travels up through the stem and accumulates in young buds and leaves — one reason buds taste the freshest;
3. Converted in the leaf: theanine participates in carbon and nitrogen reuse; light, development and nitrogen supply affect both amino-acid and polyphenol metabolism. An observed fall in amino acids and rise in polyphenols does not establish a fixed direct conversion of theanine into catechins[1][5].

Theanine synthesis, transport and conversion depend on cultivar, development and cultivation. Comparative transcriptomic work on tea and oil tea examines synthesis regulation[5]. Shading changes light and metabolism; additional nitrogen is not an unlimited route to higher quality. See leaf chemistry for cultivation context.

Kaneko et al. (2006) studied matcha, rather than sencha. Fractionation and sensory experiments identified theanine, succinic acid, gallic acid and theogallin as compounds that enhanced the umami intensity of sodium glutamate[4]. This makes the mixture and concentration important, rather than establishing theanine alone or total amino acids as a universal green-tea quality predictor.

Caffeine: beyond bitterness — the “complexation” plot

Caffeine brings bitterness and stimulation — common knowledge[1]. Less known is its mechanistic subplot: caffeine molecules form complexes with catechins and theaflavins through hydrophobic association and hydrogen bonding.

Jöbstl et al. (2005) studied black-tea “creaming” (tea cream) — the milky haze that appears as a strong infusion cools — using small-angle X-ray scattering and NMR: theaflavins first self-associate into nanoclusters about 3 nm across, and caffeine then fills the gaps within the clusters, together forming the bulk of the haze[6]. Two aspects should be distinguished:

• A clue to solution conditions: concentration, polyphenol composition, temperature and calcium affect creaming. Higher concentration can cause earlier onset and larger particles, but visible tea cream alone does not establish caffeine content, grade or quality[6];
• Separate association from taste: association affects distribution between solution and colloids, but X-ray scattering and NMR do not establish that bitterness must decrease. A sensory comparison at controlled brewing and drinking conditions is needed; entry into a cluster does not mean a tastant becomes completely imperceptible[3][6].

In the same cup: orders of magnitude of taste thresholds

A compound’s concentration must be considered alongside a threshold for the same sensory attribute and comparable conditions. Bitterness, astringency and umami enhancement are different questions; the following comparison explains how to read the research[3][4][12].

Taste activity value (TAV) = concentration ÷ corresponding threshold, using the same units and comparable conditions. A hypothetical 100 mg/L divided by 50 mg/L gives 2. Above 1 suggests possible contribution, rather than guaranteed recognition in a mixture; compounds below 1 can still influence overall perception through interactions[3][4][12].

Absolute amounts set strength, while the ratio between them sets the style — and the most-used yardstick is the polyphenol/amino-acid ratio.

The TP/AA ratio: what does it include and miss?

The polyphenol/amino-acid ratio (TP/AA) divides total tea polyphenols by total free amino acids. Total amino acids are not interchangeable with theanine alone. Both quantities must share a mass basis and compatible analytical methods[1][2].

For example, 20% polyphenols and 4% amino acids on a dry-weight basis give a ratio of 5. Raising only amino acids to 5% lowers it to 4; raising only polyphenols to 25% increases it to 6.25. The number describes a relative relationship.

However, two samples can have the same ratio at different absolute amounts. Compare hypothetical A and B below, then move one slider and watch both the amount and ratio.

The concept is abstract; three typical scenarios make it concrete:

• Early-spring, bud-only fine green tea: slow growth in cool weather and tender plucking push amino acids up to 3–4.5% of dry weight with moderate polyphenols (18–22%), roughly 4–7.3 across those independent ranges; an actual ratio requires paired measurements from one sample — the material basis of freshness combined with body. Wang and Ruan (2009), analysing Longjing and other green teas, found amino-acid content positively correlated with sensory quality scores, while the polyphenol/amino-acid ratio correlated negatively within the studied Longjing samples[7].
• Summer tea: strong light and heat raise polyphenols (especially galloylated catechins) and lower amino acids; the ratio can climb to 10–15 or beyond, giving a harsh, bitter-astringent cup which can contribute to a bold style rather than making all summer tea suitable only for commodity use or extraction[1][2].
• Yunnan large-leaf (assamica): polyphenols often exceed 30%–35% of dry weight, and the ratio is markedly higher than in small- and medium-leaf varieties — a clue to taste and processing substrates rather than a substitute for cultivar-specific processing trials[1].

Important scope reminder: The TP/AA ratio is a commonly used reference tool for unfermented green teas. For semi-oxidized oolong and oxidized/post-oxidized black and dark teas, catechins undergo dramatic oxidation and condensation. Oxidation products, aroma, extraction and sensory results also matter. TF and TR can be informative in black tea, but TF/TR/TB is not a universal quality formula for oolong, black and dark teas.

Note: absolute ratios depend on the analytical method (total amino acids by ninhydrin vs individual amino acids by HPLC use different measures) and on sampling, so numbers from different sources should not be compared directly. The examples above are typical magnitudes common in textbooks and studies — meant for building a sense of direction, not for judging any specific tea[1][7].

Related to green-tea style, not a universal quality score

In the Longjing samples studied by Wang and Ruan (2009), free amino-acid content correlated positively with sensory scores, while the polyphenol/amino-acid ratio correlated negatively with taste scores[7]. This describes a relationship within a particular sample set, not a rule that every tea below a fixed ratio must be good.

Cultivar, tenderness, season and cultivation affect composition, while processing alters individual polyphenols and aroma compounds. Two teas with the same ratio can differ in catechin composition, caffeine and aroma. Use this index alongside other evidence rather than to rank all six tea categories.

Dry-tea composition is not the same as perceived taste

Compounds must first extract into the infusion, and their extraction rates differ. Thresholds, interactions, drinking temperature and individual perception also matter. Follow composition → brewing conditions → tasting, rather than deriving bitterness, astringency or freshness scores from one ratio.

Analytical methods matter too: a total-content assay and individual-compound analysis may use different measures. The diagram’s invented examples explain the ratio; they do not establish suitability, tea grades or infusion concentrations.

What lowers the ratio

Anything that relatively raises amino acids and curbs polyphenols lowers the ratio and makes tea fresher:

• Tender plucking: buds and young leaves are higher in amino acids, lower in polyphenols (early-spring buds taste fresher)[2].
• Shading: changes light and carbon–nitrogen metabolism, often increasing free amino acids and lowering the ratio in particular samples (gyokuro, matcha) — see leaf chemistry[1].
• High altitude / low temperature / spring: slower growth lets amino acids accumulate[2].
• Sound nitrogen management: nitrogen is the raw material for amino-acid synthesis — the heavy nitrogen regime of gyokuro gardens applies exactly this principle[1].

Conversely, strong sun, heat, summer and large-leaf cultivars tend to give a higher ratio, better for bold black tea.

Where does aroma come from? A teaser

Polyphenols, amino acids and caffeine contribute to taste; trace volatiles contribute to aroma[10]. Some aroma precursors are glycosidically bound and may release volatile compounds under suitable enzymatic or thermal conditions. Processing also involves new synthesis and losses, so aroma formation is not simply the release of every bound precursor. Follow the flavour wheel for the aroma side of the story[10].

Composition across the six tea types

The diagram compares processing routes and retained or transformed compound groups. It does not encode amounts. The table keeps eight component groups across the six categories without assigning universal concentration ranges or quality ranks[1][14].

How should measurements be compared? Wang et al. (2019) processed one cultivar, Longjing 43, using six methods and compared targeted and untargeted chromatographic results. Grouping by total catechins differed from grouping by the whole metabolome, showing why one constituent cannot stand for every processing difference[14].

Jiang et al. (2020) used UHPLC to analyse 24 samples covering six tea types, measuring 21 free amino acids, six catechins, two alkaloids and gallic acid. The abstract reports these measured ranges across the entire sample set[15]:

A/B/C in the calculator are hypothetical dry-weight percentages; this table reports measured mg/g. Align units and analytical definitions before comparing. The range endpoints may belong to different samples and cannot be cross-divided to invent a real TP/AA ratio. No category ranking is reconstructed from these pooled ranges.

See also

• The Flavour Chemistry of the Fresh Leaf — where the three substances come from
• The Flavour Wheel — how composition becomes specific aroma and taste
• Brewing Basics — how brewing also shifts the bitter/sweet balance

References

1. R-029 — 宛晓春 主编 (2003).《茶叶生物化学》(第3版). 中国农业出版社. ISBN: 978-7109066274.

2. R-030 — 陈宗懋 主编 (2000).《中国茶叶大辞典》. 中国轻工业出版社. ISBN: 978-7501925094.

3. R-253 — Xu, Y.-Q., et al. (2018). Quantitative analyses of the bitterness and astringency of catechins from green tea. Food Chemistry, 258, 16–24. https://doi.org/10.1016/j.foodchem.2018.03.042

4. R-254 — Kaneko, S., Kumazawa, K., Masuda, H., Henze, A., & Hofmann, T. (2006). Molecular and sensory studies on the umami taste of Japanese green tea. Journal of Agricultural and Food Chemistry, 54(7), 2688–2694. https://doi.org/10.1021/jf0525232

5. R-152 — Tai, Y., Ling, C., Wang, H., et al. (2019). Comparative Transcriptomic Analysis Reveals Regulatory Mechanisms of Theanine Synthesis in Tea (Camellia sinensis) and Oil Tea (Camellia oleifera) Plants. Journal of Agricultural and Food Chemistry, 67(36), 10235–10244. https://doi.org/10.1021/acs.jafc.9b02295

6. R-255 — Jöbstl, E., et al. (2005). Creaming in black tea. Journal of Agricultural and Food Chemistry, 53(20), 7997–8002. https://doi.org/10.1021/jf0506479

7. R-069 — Wang, K. B., & Ruan, J. Y. (2009). Analysis of chemical components in green tea in relation with perceived quality, a case study with Longjing teas. International Journal of Food Science & Technology, 44(12), 2476–2484. https://doi.org/10.1111/j.1365-2621.2009.02040.x

8. R-032 — Chen, G.-H., et al. (2009). Comparison of major chemical components in different kinds of tea. Journal of Agricultural and Food Chemistry, 57(15), 7325–7330. — Legacy entry: title, authors and pages remain unverified; not used here to establish concentration ranges.

9. R-033 — Wang, K., et al. (2010). Comparison of catechins and amino acids in white, green, oolong, black, and pu-erh teas. Food Chemistry, 121(2), 338–344. — Legacy entry: title, authors and pages remain unverified; not used here to establish concentration ranges.

10. R-235 — Ho, C.-T., Zheng, X., & Li, S. (2015). Tea aroma formation. Food Science and Human Wellness, 4(1), 9–27. https://doi.org/10.1016/j.fshw.2015.04.001

11. R-034 — Xu, Y.-Q., et al. (2018). Chemical compositions and biological activities of different types of tea. Comprehensive Reviews in Food Science and Food Safety, 17(2), 432–452. — Legacy entry: title, authors and pages remain unverified; not used here to establish concentration ranges.

12. R-252 — Scharbert, S., & Hofmann, T. (2005). Molecular definition of black tea taste by means of quantitative studies, taste reconstitution, and omission experiments. Journal of Agricultural and Food Chemistry, 53(13), 5377–5384. https://doi.org/10.1021/jf050294d

13. R-355 — 農業部茶及飲料作物改良場. 臺灣特色茶分類及加工製程簡介. https://www.tbrs.gov.tw/ws.php?id=4748

14. R-359 — Wang, Y., Kan, Z., Thompson, H. J., Ling, T., Ho, C.-T., Li, D., & Wan, X. (2019). Impact of Six Typical Processing Methods on the Chemical Composition of Tea Leaves Using a Single Camellia sinensis Cultivar, Longjing 43. Journal of Agricultural and Food Chemistry, 67(19), 5423–5436. https://doi.org/10.1021/acs.jafc.8b05140

15. R-360 — Jiang, H., Zhang, M., Wang, D., Yu, F., Zhang, N., Song, C., & Granato, D. (2020). Analytical strategy coupled to chemometrics to differentiate Camellia sinensis tea types based on phenolic composition, alkaloids, and amino acids. Journal of Food Science, 85(10), 3253–3263. https://doi.org/10.1111/1750-3841.15390