Pile fermentation moistens and stacks tea leaves, then allows them to ferment over time; bitterness, astringency, sweetness, color, and aroma may all change together. A 2023 study followed one 36-day fermentation time series of sun-dried green maocha from old trees. At the fermentation endpoint (day 36), the sample had significantly lower bitterness and astringency than the unfermented starting material. This was a time series of one fermentation, however, without a control fermentation vessel, so it does not isolate the general effect or magnitude of fermentation as a process.
Other changes occurred during the same 36-day fermentation alongside the changes in bitterness and astringency. A trained panel of 9 people rated sweetness higher; color shifted from yellow-green to reddish-brown, and aroma shifted from what the original describes as fresh to stale. The original word stale cannot be replaced by a favorable term such as an aged aroma. Nor can this observation alone establish whether changes in sweetness, color, or microbes individually caused the sensory changes.
Wang QP; Li X; Liu Y; Chen J; Bo T; Wang J; Xiao X; Sha S; Chen Y; Lei J; Lu C; Ma S; Zhao G / 2023 / journal article / full text checked
Checked for this overview: Confirmed the observation of lower bitterness and astringency at the endpoint of a 36-day fermentation. / Confirmed the simultaneous changes in sweetness, color, and aroma and the handling of the original word stale.
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tea pile fermentation — observed together with: In the same 36-day fermentation time series, tea polyphenol content decreased significantly (p<0.05) from 21.59% in the raw material (RM) to 10.58% at the fermentation endpoint (F4). The 5 catechins — epicatechin gallate, epigallocatechin gallate (EGCG), gallocatechin gallate, catechin, and catechin gallate — also decreased significantly (p<0.05). The source reports that theaflavin and thearubigin content also decreased during fermentation.observation
Scope: One shou (ripe) pu-erh fermentation made from sun-dried green maocha from old-tree tea (the same time series as the existing claim on pu-erh fermentation and bitterness)
Over a 36-day fermentation time series, tea polyphenol content decreased significantly (p<0.05) from 21.59% in the raw material (RM) to 10.58% at the fermentation endpoint (F4). The 5 catechins — epicatechin gallate, epigallocatechin-3-gallate, gallocatechin gallate, catechin, and catechin gallate — also decreased significantly (p<0.05). Theaflavin and thearubigin content also decreased significantly during fermentation (p<0.05), while theabrownin content increased from 2.13% to 12.28%.
Limitations: Not a factorial experiment with a control fermentation vessel, so the causal effect or effect size of fermentation in general cannot be separated out.
Show dataprocess-tea-pile-fermentation —was_observed_with→ "In the same 36-day fermentation time series, tea polyphenol content decreased significantly (p<0.05) from 21.59% in the raw material (RM) to 10.58% at the fermentation endpoint (F4). The 5 catechins — epicatechin gallate, epigallocatechin gallate (EGCG), gallocatechin gallate, catechin, and catechin gallate — also decreased significantly (p<0.05). The source reports that theaflavin and thearubigin content also decreased during fermentation."
tea pile fermentation — observed together with: In one pile-fermentation batch of shou (ripe) pu-erh tea made from the small-leaf cultivar grown in Yunnan Province (fermentation days 0-30, 15 time points, with samples taken in 6 groups from the middle layer of the tea pile at each time point), tea polyphenol content is reported to have shown "marked reductions, by 56.8% (107.22 mg/g)" (the source's own wording) as fermentation progressed.observation
Scope: Shou (ripe) pu-erh tea from the small-leaf cultivar grown in Yunnan Province, the middle layer of a single pile-fermentation batch
Note: An additional connection to the existing entry for tea pile fermentation (no duplicate entry created). This is a time series from a single batch and a single layer, so the causal effect or effect size cannot be separated out. Whether the source's 107.22 mg/g refers to the amount of decrease or the endpoint value has not been determined this time. This report itself makes no mention of astringency or bitterness.
In the pile fermentation of shou (ripe) pu-erh tea from the small-leaf cultivar grown in Yunnan Province (day 0 on August 19, 2022, ending on day 30 on September 18; 15 sampling time points from the middle layer, 6 groups per time point), Section 3.1 and Figure 1d show tea polyphenol content decreasing with "marked reductions, by 56.8% (107.22 mg/g)" (the source's own wording) as fermentation progressed. At the same time, free amino acids decreased by 35.5% (13.61 mg/g) and cellulose by 33.9% (108.33 mg/g), while soluble polysaccharides, total flavonoids, theabrownins, protein, and lignin increased (13.89→22.31, 8.79→18.45, 18.36→60.90, 275.63→333.96, and 316.67→558.33 mg/g, respectively).
Limitations: The sampling is from a single batch and a single layer (the middle layer), and the authors themselves make explicit the limitation that, since "tea samples were collected exclusively from the middle layer of the fermentation pile," vertical non-uniformity cannot be captured. There is no direct mention of astringency or bitterness in this Section 3.1 reporting.
Show dataprocess-tea-pile-fermentation —was_observed_with→ "In one pile-fermentation batch of shou (ripe) pu-erh tea made from the small-leaf cultivar grown in Yunnan Province (fermentation days 0-30, 15 time points, with samples taken in 6 groups from the middle layer of the tea pile at each time point), tea polyphenol content is reported to have shown "marked reductions, by 56.8% (107.22 mg/g)" (the source's own wording) as fermentation progressed."
tea pile fermentation — observed together with: Lower bitterness and astringency than the raw material at the 36-day endpointobservation
Scope: A 36-day fermentation time series of one sun-dried green maocha from old-tree tea
Note: A comparison between RM and F4. This is a time series from a single fermentation batch, not the causal effect or effect size of fermentation in general.
In a 36-day fermentation time series (9 trained sensory assessors, 5 men and 4 women, aged 24-48), the fermentation endpoint (F4) scored 3.73 for bitterness and 3.57 for astringency compared with the raw material (RM), both significantly lower (p<0.05). Meanwhile, sweetness (6.97), thickness (7.23), sourness (0.73), redness (a*, 34.91), and yellowness (b*, 78.77) were significantly higher (p<0.05), and lightness (L*, 56.32) was significantly lower (p<0.05).
Limitations: This is not a factorial experiment with a control fermentation vessel, so the causal effect or effect size of fermentation in general cannot be isolated.
tea pile fermentation — observed together with: A rise in sweetness, a shift to a reddish-brown color, and a change in aroma to what the source called "stale aroma"observation
Scope: The same 36-day fermentation, evaluated by a trained panel of 9
Note: Multiple attributes were observed at the same time. Do not convert the correlation of sugars, pigments, and microorganisms into the sole cause of each individual change.
At the endpoint of the same time series, sweetness rose, the color changed from yellow-green to reddish-brown, and the aroma changed from "fresh" to "stale."
Limitations: Do not replace the source's "stale" with a quality judgment or an "aged aroma." The cause of each change cannot be separated out from this observation alone.
Show dataprocess-tea-pile-fermentation —was_observed_with→ "A rise in sweetness, a shift to a reddish-brown color, and a change in aroma to what the source called "stale aroma""