The Main Organic Acids in Tea
| Organic Acid | Source in Tea | Concentration (brewed) | Taste Character |
|---|---|---|---|
| Gallic acid | EGCG/ECG hydrolysis, native | 50–500 mg/L | Bitter, dry, astringent at higher conc. |
| Quinic acid | Chlorogenic acid hydrolysis, native | 20–200 mg/L | Sharp, slightly roasted, clean |
| Citric acid | Native in leaf, higher in herbals | 10–100 mg/L | Bright, fresh, lemon-like |
| Malic acid | Native in young leaves | 10–80 mg/L | Fresh, apple-like, clean |
| Oxalic acid | Native, higher in mature leaves | 5–30 mg/L (in brew) | Slightly sour, dry |
| Succinic acid | Fermentation products (pu-erh) | 5–50 mg/L | Mild, slightly fermented |
| Pyruvic acid | Processing by-product | Trace | Slightly sour, apple |
Gallic Acid: The Most Consequential
Gallic acid is quantitatively the most important organic acid in most teas. It is produced in two ways: it is present natively in tea leaves as part of some polyphenol structures, and it is released in increasing quantities during processing as the gallate ester groups of EGCG and ECG are hydrolysed (the gallate linkage being inherently susceptible to hydrolysis under aqueous conditions and heat).
Gallic acid has complex taste properties: at low concentrations (below ~50 mg/L) it contributes to astringency without being perceivably bitter; at higher concentrations it becomes distinctly dry and bitter. The concentration in the cup is therefore sensitive to steeping parameters — longer, hotter steeps produce more gallic acid from hydrolysis, which can push the cup from pleasantly astringent to unpleasantly dry.
🧠 Expert Tip: Brightness vs Astringency
The fine line between "bright acidity" and "dry astringency" in a tea is often determined by the gallic acid concentration and its balance with amino acids. A tea high in both gallic acid and theanine tastes bright. One high in gallic acid but low in theanine tastes dry and astringent. This is why first-flush teas with high theanine "get away with" relatively high acid content.
Oxalic Acid: The Kidney Stone Question
Tea does contain oxalic acid — a concern for people with a history of calcium oxalate kidney stones, who are advised to moderate high-oxalate foods. However, the amount of oxalic acid actually extracted into brewed tea is modest: typically 5–30 mg per 200ml cup, compared to 100–900 mg for a 100g portion of spinach. Current evidence suggests that tea's contribution to oxalate load is clinically relevant only for people who drink very large quantities (8+ strong cups per day) AND have pre-existing oxalate metabolism issues.
Fermentation-Derived Acids in Pu-erh
The microbial fermentation of pu-erh generates a suite of organic acids not typically found in other teas, including succinic acid, acetic acid (low levels, responsible for the slight vinegary top note in some pu-erh), and lactic acid from bacterial activity. These contribute to the distinctive earthy, complex acidity of pu-erh that differs fundamentally from the clean citric/gallic acidity of Darjeeling. The microbial succession in pu-erh is the primary driver of its unique acid profile.
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