What's in Pu'er: An Overview of Its Main Constituents
In a cup of pu'er, the bitterness, astringency, sweetness, savoriness, and mellowness on your palate each correspond to a group of chemical constituents. Getting to know them isn't about memorizing terms; it's about understanding why raw and ripe tea taste so different, why spring tea is more savory, and why a tea kept for ten years becomes gentle.
What a Tea Leaf Is Made Of
Most of the dry leaf is structural material such as fiber and protein that doesn't dissolve in water; what actually goes into the liquor and determines the taste is the soluble part. The main groups most related to flavor:
| Constituent | General role | Relation to taste |
|---|---|---|
| Tea polyphenols (mainly catechins) | One of the most abundant soluble constituents | Bitterness, astringency, a puckering feel |
| Amino acids (mainly theanine) | Not abundant but influential | Savoriness, sweetness |
| Caffeine | About 3%–4% of dry leaf | Bitterness |
| Sugars | Soluble sugars and polysaccharides | Sweetness, thick and smooth body |
| Pigments (theaflavins, thearubigins, theabrownin) | Formed mainly during processing and aging | Liquor color, mellow fullness |
| Organic acids | Such as gallic acid | Slight acidity, layers |
| Aroma compounds | Tiny amounts, many kinds | Floral, honey, aged, pile notes |
| Minerals (ash) | What's left after the leaf is burned | Little effect on taste; one quality indicator |
What Is Water Extract?
Water extract is the percentage of the dry tea made up of substances that dissolve in water when ground leaf is steeped in boiling water, tested according to China's national standard GB/T 8305. Think of it as "how much this tea can give up when brewed": the higher the figure, the fuller and longer-lasting the liquor usually is.
The national standard for pu'er, GB/T 22111-2008, sets the following:
| Item | Raw tea | Ripe loose tea | Ripe compressed tea |
|---|---|---|---|
| Moisture | ≤ 13.0% | ≤ 12.0% | ≤ 12.5% |
| Total ash | ≤ 7.5% | ≤ 8.0% | ≤ 8.5% |
| Water extract | ≥ 35.0% | ≥ 28.0% | ≥ 28.0% |
| Crude fiber | ≤ 14.0% | ≤ 14.0% | ≤ 15.0% |
| Tea polyphenols | ≥ 28.0% | — | — |
The water extract threshold for ripe tea is lower than for raw tea because microbes use up part of the soluble substances during wodui. What each indicator means is covered in Lab Quality Indicators for Tea, and the full standard in GB/T 22111, the National Standard for Pu'er, Explained.
How Raw and Ripe Differ in Composition
How do raw and ripe tea differ in composition? Ripe tea goes through the extra step of wodui fermentation, and its constituents change enormously. In research at Yunnan Agricultural University using special-grade sun-dried maocha for wodui, at the end of processing:
- Tea polyphenols decreased by about 59.74%.
- Free amino acids decreased by about 57.98%.
- Water extract decreased by about 23.36%.
- Theabrownin increased greatly, reaching 7.19% in the finished tea.
- Caffeine and tea polysaccharides increased slightly, while total ash changed little.
A 2026 study comparing five teas made from Yunnan large-leaf tea found the same direction: total catechins were about 103 mg/g in raw tea but only about 9 mg/g in ripe tea; theabrownin made up about 13% of ripe tea; and gallic acid rose from 1.76 mg/g in raw tea to 13.7 mg/g in ripe tea.
Translated into taste: raw tea has more catechins, so it's noticeably bitter and astringent, fresh and punchy; in ripe tea most catechins have turned into pigments, giving a deep red liquor and a mellow mouthfeel. The full comparison is in Raw vs. Ripe Pu'er, and the wodui process in Wodui Fermentation.
What Is Theanine?
Theanine is an amino acid unique to the tea plant, making up more than 60% of free amino acids in tea leaves, the most abundant of them. It's synthesized in the roots of the tea plant and then transported to the buds and leaves, where it accumulates. Theanine has a savory, slightly sweet taste and is an important source of the "fresh, savory" quality of the liquor.
Amino acids dissolve very quickly during brewing, which is why savoriness is usually most noticeable in the first and second infusions.
Why Is Spring Tea More Savory?
Why is spring tea more savory? After winter dormancy, the tea plant's roots store a lot of nitrogen, which is sent to the new buds when they sprout in spring and used to make amino acids. On top of that, spring is cooler and the buds grow slowly, so more amino acids accumulate while relatively fewer tea polyphenols are produced. Studies comparing tea from different seasons in the same garden found spring tea highest in free amino acids, theanine, and water extract; in summer, higher temperatures and stronger sunlight mean more tea polyphenols and caffeine, and a more bitter, astringent taste.
That's why spring pu'er, especially the first flush, is so highly valued. Seasonal differences are covered in Spring Tea, Summer Tea, and Autumn Tea.
How Do Amino Acids Change with Aging?
How do amino acids change with aging? As raw tea is stored, amino acids decrease year by year, partly by taking part in forming aroma compounds and pigments, and partly by being used by microbes. Research tracking a 7542 raw tea over the long term found that tea polyphenols, catechins, and free amino acids all decreased gradually with age, while flavonoids increased; another study following raw tea from the same origin stored for 1–10 years also saw clear turning points around year 3 and year 8.
So aged raw tea is less savory than young tea, and what replaces that savoriness is mellowness, sweetness, and aged aroma. These changes are covered in The Chemistry of Raw Pu'er Aging and Aging and Vintage in Pu'er.
Constituents and Taste
- Bitterness: caffeine and some catechins.
- Astringency: ester catechins (EGCG, ECG) have the strongest puckering effect.
- Savoriness: amino acids such as theanine and glutamic acid.
- Sweetness: soluble sugars and some amino acids.
- Mellow fullness: large-molecule constituents such as polysaccharides and theabrownin.
- Acidity: organic acids; ripe tea has more gallic acid.
Taste comes from the combination and proportions of these constituents, not from any single one. The details of bitterness, astringency, and sweetness are in The Chemistry of Bitterness, Astringency, and Sweetness.
FAQ
What are the main constituents of pu'er? Tea polyphenols (mainly catechins), amino acids (mainly theanine), caffeine, sugars, pigments (theaflavins, thearubigins, theabrownin), organic acids, aroma compounds, and minerals.
What is water extract? The percentage of the dry tea made up of substances that dissolve in boiling water. The national standard requires at least 35.0% for raw tea and at least 28.0% for ripe tea.
How much do raw and ripe tea differ in composition? In research, wodui reduced tea polyphenols by about 60% and free amino acids by nearly 60%, while theabrownin increased greatly, which is why ripe tea has little bitterness or astringency and a deep red liquor.
What is theanine? An amino acid unique to the tea plant, making up more than 60% of free amino acids, with a savory, slightly sweet taste. Spring tea contains more of it.