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Green, black and oolong teas are transformed by the leaf’s own enzymes. Dark tea is different — it hands the lead role to microbes. This is fermentation in the true sense of the word.
Black tea’s “fermentation” is really enzymatic oxidation, with no microbes involved. Dark tea’s wodui (渥堆, “wet piling”), by contrast, takes sun-dried maocha, piles it up, sprays it with water and keeps it warm and humid so that fungi and bacteria multiply and remake the leaf with the enzymes they secrete. Because this happens after primary processing (fixation, etc.), it is called post-fermentation.
Wodui: microbes, heat, and the making of theabrownins
Drag through the ~50-day pile; watch pile temperature, microbes and theabrownins ↓
Schematic. Unlike green/black/oolong (the leaf’s own enzymes), this is true microbial fermentation.
Microbial metabolism gives off heat, so the pile’s core naturally climbs to around 50–65 °C; makers periodically “turn the pile” to cool it, add oxygen, even out the fermentation, and prevent overheating (“pile-burning”). After roughly 40–60 days, dark-green maocha becomes glossy red-brown ripe tea — deep red liquor, mellow taste, much less bitterness. This is ripe (shou) pu-erh.
L2 · Deep DiveThe main line of dark tea (ripe pu-erh)
1. Who does the work: microbes and their enzymes
Research shows that Aspergillus niger is the dominant fungus in wodui, with the highest detection frequency and abundance [1][2]. It (along with other fungi, bacteria and yeasts) secretes a range of extracellular enzymes that remodel the leaf [2]:
- glycoside hydrolases and tannases — hydrolyse ester catechins and flavonoid glycosides;
- catechol oxidases, peroxidases and laccases — oxidise, condense and polymerise phenolic compounds into theabrownins [2].
In other words, theabrownins — the core compounds behind dark tea’s colour and mellow taste — are produced by microbial enzymes transforming and polymerising polyphenols. Microbes also degrade some caffeine and generate compounds such as gallic acid [2]; overall, bitterness and astringency fall and the mouthfeel turns smooth.
2. Moist-heat action: not only microbes
The hot, humid pile also drives a set of non-enzymatic moist-heat oxidation and degradation reactions. Dark tea’s transformation is therefore usually understood as the combined result of microbial action + moist-heat action, with the microbial enzymatic contribution dominant.
3. Raw vs. ripe pu-erh
Both belong to dark tea / post-fermentation, but pu-erh has two routes:
| Raw (sheng) | Ripe (shou) | |
|---|---|---|
| Process | maocha pressed, slow natural aging (years) | wodui accelerated fermentation (~40–60 days) |
| Origin | traditional | wodui established by Kunming Tea Factory around 1973 [3] |
| Style | brisk and astringent early, mellowing with age | deep, red and mellow from the start |
Dark tea is not only pu-erh. Fu brick tea, for instance, grows beneficial “golden flowers” (Eurotium cristatum) during fermentation — another prized form of dark-tea post-fermentation.
Key processing parameters
| Item | Typical range | Notes |
|---|---|---|
| Pile height | ~50–70 cm [4] | affects heat/moisture retention and airflow |
| Moisture | ~30–50% [4] | water for the microbes |
| Pile temp | rises to ~50–65 °C [4] | from microbial metabolism |
| Turning | every ~7–14 days [4] | cool, oxygenate, even out, prevent burning |
| Duration | ~40–60 days [4] | then dried |
Methods and materials vary widely by factory; the table shows representative ranges for understanding the mechanism.
Typical flavour
Ripe pu-erh · flavour sketch
See also
- The Science of Black-Tea “Fermentation” — where “fermentation” is really enzymatic oxidation; a clarifying contrast
- The Science of Green-Tea Fixation · Oolong “Bruising”
The full process & parameters
| Step | Parameters | Role |
|---|---|---|
| Kill-green | hotter, longer | deactivates enzymes (less fully than green) |
| Rolling | while warm | ruptures cells, creates the pile interface |
| Wodui ⭐ | pile ~50–65 °C, high humidity; ripe pu-erh ~40–60 days | microbe-driven (Aspergillus niger, etc.) deep transformation: theabrownins form, astringency drops, aged aroma develops |
| Dry / age | drying or natural storage | ends wodui; can keep transforming with age |
Representative ranges; they vary widely by cultivar, origin and process.
References
- Enhanced Fermentation of Pu-Erh Tea with Aspergillus niger: Quality and Microbial Community Analysis. Molecules / PMC, 2024. https://pmc.ncbi.nlm.nih.gov/articles/PMC11643846/
- Pile-fermentation mechanism of ripened Pu-erh tea: Omics approach, chemical variation and microbial effect. Trends in Food Science & Technology, 2024. https://www.sciencedirect.com/science/article/abs/pii/S0924224424000554
- Pu’er tea. Wikipedia (wodui established ~1973 by Kunming Tea Factory). https://en.wikipedia.org/wiki/Pu’er_tea
- The technology / process of ripe pu-erh (process-parameter overview, popular source). https://teadaocultivation.com/blogs/blog/what-is-the-technology-for-producing-ripe-puer