阿波晩茶 (Awa-bancha) of Tokushima Prefecture, 碁石茶 (Goishicha) of Kochi Prefecture, and 石鎚黒茶 (Ishizuchi-kurocha) of Ehime Prefecture are all post-fermented teas, finished after the tea leaves are fermented. The way each is fermented, however, is not the same across the three. Goishicha and Ishizuchi-kurocha both go through two stages, packing the leaves into a barrel for anaerobic fermentation by lactic acid bacteria after an aerobic fermentation by mold; Awa-bancha, after boiling the leaves to halt oxidative fermentation, brings about only lactic acid fermentation in a single stage. This difference in process also shows up as separate axes -- astringency and sourness -- in taste-sensor measurements of the infusion. This note lays the processes of the three teas side by side, reads the microbes involved and the taste-sensor results, and then compares them with the change pu-erh tea undergoes through pile fermentation.
What this page establishes
Goishicha and Ishizuchi-kurocha are recorded as being made through a two-stage process, in which anaerobic fermentation by lactic acid bacteria follows an aerobic fermentation by mold.
Awa-bancha is recorded as a process in which the tea leaves are heat-treated to halt oxidative fermentation, after which only lactic acid fermentation is brought about, in a single stage.
In taste-sensor measurements, one report shows a result in which Goishicha has weaker astringency and umami and stronger sourness than other teas or coffee.
For all three teas, no taste-sensor measurement or sensory evaluation targeting bitterness itself has yet been carried out.
Goishicha — Two-Stage Fermentation, and the Microbes Involved
Goishicha is a tea passed down in Otoyo, Kochi Prefecture, made by steaming the leaves and then putting them through two stages of fermentation.
goishi-cha two-stage fermentation is prepared by: The raw tea leaves are steamed for about 2 hours, then piled to a height of about 50-70cm on straw mats on an earthen floor for 7-10 days of aerobic fermentation (mold inoculation, pre-fermentation). The leaves are then packed into a barrel with a weight placed on top for 10-20 days of anaerobic fermentation (post-fermentation), after which they are cut and dried in the sun for 2-3 days to finish the product.supported
Scope: Goishicha of Otoyo, Kochi Prefecture
Note: Process description by Ukeda (2015). Not a peer-reviewed original paper but a lecture record; included as an account compiled by a regional-collaboration researcher.
The microbes involved in this fermentation are reported through isolation and identification by rDNA analysis. The source reports that the two fermentation stages -- mold inoculation and pickling -- each involve separate microbes, and that each is involved in producing separate aroma compounds.
goishi-cha two-stage fermentation is prepared by: Isolation and identification by rDNA analysis reports 3 microbial species involved in the fermentation of Goishicha: Aspergillus niger, Pichia manshurica, and Lactobacillus plantarum. The source reports that A. niger is involved in producing ethyl furaneol and thiazoline compounds; P. manshurica in esters, alcohols, and phenols (including 4-ethylphenol and 4-ethyl-2-methoxyphenol); and L. plantarum in organic acids such as hexanoic acid and butanoic acid, and lactones.supported
Scope: Aroma-compound analysis of Goishicha (sample of unspecified origin) by GC-O/AEDA, and identification of isolated microbes.
Note: Only the abstract has been confirmed. Ukeda's (2015) lecture record names Aspergillus fumigatus as the main organism in pre-fermentation (mold inoculation), while Koyama et al.'s (2019) isolation and identification names Aspergillus niger — the reported species does not agree between the two sources. This entry adopts Koyama et al. (2019), who performed the isolation and identification, and records the discrepancy explicitly. Whether this is due to a difference in identification method or collection timing has not been confirmed.
Isolates and identifies Aspergillus niger, Pichia manshurica, and Lactobacillus plantarum by rDNA analysis, and reports the aroma compound groups each microbe produces.
Limitations: Only the abstract has been confirmed. Details of origin, lot, and number of replicates have not been confirmed.
Context: Quantitatively confirms the top aroma-contributing compounds (FD factors) in Goishicha: hexanoic acid (fermented odor) is highest at FD=1,024, followed by furfural (almond odor), furaneol (caramel odor), and ethyl furaneol (sweet burnt odor) at FD=512. The source also reports, as a mechanism by which A. niger produces ethyl furaneol, a compound characteristic of Goishicha, that an NCBI BLAST homology search confirmed A. niger to possess a secreted protein showing 40.3% homology with an enone oxidase from Zygosaccharomyces rouxii — going beyond simple species identification to a proposed production mechanism.
Limitations: A sample from a single origin (Otoyo). The 40.3% enone oxidase homology is interpreted by the authors as 『高い相同性』 (in translation: "high homology"), but this has not been experimentally demonstrated to be a functionally identical enzyme, and remains an inference from sequence homology. Descriptions of physiological effects and functional-food components were excluded as out of scope for this entry.
As for when Goishicha first began to be made, Edo-period records are cited.
Goishi tea — historical origin: The oldest known surviving record is a description found in the 1745 (Enkyo 2) work of Anyoji Kamaro: 『長岡郡豊永郷 碁石茶 六蔵茶とあわせ茶高30斤入り3154丸』 (in translation: "Nagaoka District, Toyonaga area: Goishicha, together with Rokuzo tea, 3,154 balls in cases of 30 kin"), and a description in 『南路志』 (in translation: "Nanroshi") (compiled around 1815): 『茶 韭生郷 大抜茶 本川郷 碁石茶』 (in translation: "Tea: Nirao area, Otsunuki tea; Honkawa area, Goishicha"). From these, Goishicha is inferred to have already been in production before 1745.contextual
Scope: Otoyo, Kochi Prefecture
Note: As recorded by Ukeda (2015). The works cited as the source, 『土佐幽考』 (in translation: "Tosa Yuko") (of the Tani Taizan school) and 『南路志』 (in translation: "Nanroshi"), have not themselves been checked this time, and are included here as a secondary citation via Ukeda (2015).
Context: Quotes the 1745 work of Anyoji Kamaro and the description in 『南路志』 (in translation: "Nanroshi"), inferring production before 1745.
Limitations: A secondary citation via Ukeda (2015); the cited Edo-period source materials themselves have not been checked this time.
Show dataingredient-goishi-cha —has_historical_origin→ (the claim sentence above)
claim: clm-goishicha-history-record / type: cultural / updated: 2026-09-01
Ishizuchi Kurocha — Following the Same Two Stages, Now a Designated Technique
Ishizuchi-kurocha, passed down in the Ishizuchi district of Saijo, Ehime Prefecture, also goes through the same two-stage fermentation as Goishicha.
ishizuchi kurocha two-stage fermentation is prepared by: Made through the processes of plucking, kill-green (fixation), mold inoculation (aerobic fermentation by filamentous fungi, about 1 week), rolling, pickling (anaerobic fermentation by lactic acid bacteria, about 2 weeks), sun-drying, and sorting. Mainly produced in July and August.supported
Scope: the Ishizuchi district of Komatsu, Saijo, Ehime Prefecture
Note: As recorded on Saijo City's official website.
Records: 『おもに７、８月の期間に製造され、摘採、殺青、カビ付け、揉捻、漬け込み、乾燥、選別の各工程がある。発酵に適した冷涼な山中の建物に茶葉を運び込み、二段階に分けて自然発酵させる』 (in translation: "Mainly produced during July and August, going through the processes of plucking, kill-green, mold inoculation, rolling, pickling, drying, and sorting. The tea leaves are carried into a cool mountain building suited to fermentation, and are naturally fermented in two stages.")
Limitations: No identification of the fungal species is given.
This manufacturing technique is designated as an Important Intangible Folk Cultural Property.
ishizuchi kurocha two-stage fermentation is registered as Designated as an Important Intangible Folk Cultural Property under the name 『石鎚黒茶の製造技術』 (in translation: "Manufacturing technique of Ishizuchi-kurocha") on March 22, 2023. The area of transmission is the Ishizuchi district of Komatsu, Saijo, Ehime Prefecture. The preserving body is the Ishizuchi Kurocha Manufacturing Technique Preservation Society.contextual
Scope: Saijo, Ehime Prefecture
Note: Included after directly checking the original record in the Agency for Cultural Affairs' 「文化遺産オンライン」 (in translation: "Cultural Heritage Online") (heritage id 589236).
Records the designated name, designation category, date of designation, area of transmission, and preserving body.
Limitations: None (a direct confirmation of an institutional/administrative fact).
Awa Bancha — Halted by Boiling, Then Only Lactic Acid Fermentation Through Pickling
Awa-bancha, passed down in Kamikatsu, Naka, and Minami, Tokushima Prefecture, combines fermentation differently from Goishicha and Ishizuchi-kurocha. The tea leaves are heat-treated in advance so that oxidative fermentation does not occur, and only lactic acid fermentation through pickling is brought about.
awa bancha boil-then-lactic fermentation is prepared by: Hard tea leaves picked in the late part of summer are given heat treatment, such as boiling in a large kettle, to prevent oxidative fermentation from occurring, after which they are packed into barrels or vats to promote a new lactic acid fermentation. The process goes through tea picking, tea boiling, tea rubbing, pickling, tea drying, and sorting.supported
Scope: Kamikatsu, Naka, and Minami, Tokushima Prefecture
Note: Included after directly checking the original record in the Agency for Cultural Affairs' 「文化遺産オンライン」 (in translation: "Cultural Heritage Online") (heritage id 541631).
Records a manufacturing method in which heat treatment halts oxidative fermentation, after which pickling promotes lactic acid fermentation.
Limitations: None (a direct confirmation of an institutional/administrative fact).
Awa-bancha's manufacturing technique is likewise designated as an Important Intangible Folk Cultural Property.
awa bancha boil-then-lactic fermentation is registered as Designated as an Important Intangible Folk Cultural Property under the name 『阿波晩茶の製造技術』 (in translation: "Manufacturing technique of Awa-bancha") on March 11, 2021. The area of transmission is Kamikatsu (Katsuura District), Naka (Naka District), and Minami (Kaifu District), Tokushima Prefecture. The preserving body is the Awa Bancha Manufacturing Technique Preservation Society (the preservation societies of each town).contextual
Scope: Kamikatsu, Naka, and Minami, Tokushima Prefecture
Note: Included after directly checking the original record in the Agency for Cultural Affairs' 「文化遺産オンライン」 (in translation: "Cultural Heritage Online") (heritage id 541631).
Records the designated name, designation category, date of designation, area of transmission, and preserving body.
Limitations: None (a direct confirmation of an institutional/administrative fact).
What the Taste Sensor Shows — Weak Astringency and Strong Sourness
There is a report that measured the infusion of Goishicha with a taste sensor and compared it with green tea, black tea, hojicha, coffee, and red wine. The result showed weaker astringency and umami and stronger sourness than the other teas or coffee, and the source states that this pattern closely resembled red wine.
Goishi tea — sensory attribute: Comparing Goishicha with green tea, black tea, hojicha, coffee, and red wine using a taste sensor (a radar chart made up of astringency, bitterness, umami, sourness, bitterness aftertaste, astringency aftertaste, and umami aftertaste) brought out the characteristic that Goishicha has weaker astringency and umami and stronger sourness than the other teas and coffee. Among the palatable beverages compared, this pattern was extremely similar to that of red wine.observation
Scope: Taste-sensor comparison of Goishicha (sample of unspecified origin) against 6 reference beverages
Note: A taste-sensor measurement performed by Ukeda (2015) himself. No mention of panel size or number of replicates. This is a comparison of single samples, and is not generalized to tea types in general, pu-erh tea included.
A radar chart from the taste sensor shows Goishicha exhibiting a pattern similar to red wine.
Limitations: No detail given on panel or replicates. A single-sample comparison.
In a report comparing the four teas -- Ishizuchi-kurocha, Awa-bancha, sencha, and black tea -- with the same taste sensor, the sourness output value was highest for Ishizuchi-kurocha, followed by Awa-bancha. The report discusses this sourness as resulting from the anaerobic fermentation becoming more vigorous on the nutrient source generated by microbes during aerobic fermentation, increasing metabolites such as lactic acid.
Ishizuchi kurocha — sensory attribute: In a taste-sensor (SA402B) measurement of the infusion, the sourness output value was highest for Ishizuchi-kurocha among the 4 teas — Awa-bancha, Ishizuchi-kurocha, sencha, and black tea — followed by Awa-bancha. The report discusses this as resulting from the tea leaves being enzymatically broken down by the aerobic mold fermentation that precedes anaerobic fermentation, generating a nutrient source for microbes, which made the anaerobic fermentation more vigorous and increased metabolites such as lactic acid.observation
Scope: Comparison of infusions of Ishizuchi-kurocha, Awa-bancha, sencha, and black tea (Tokushima Prefectural Industrial Technology Center, taste sensor SA402B)
Note: A comparison between single samples, with no mention of replicate count or statistical testing. The description that sourness comes to the fore is included as stated, without bending it toward a bitterness axis.
The taste sensor's sourness output value was highest for Ishizuchi-kurocha among the 4 tea types. The report discusses this as due to the generation of a microbial nutrient source accompanying aerobic fermentation, and the resulting more vigorous anaerobic fermentation.
Limitations: No mention of sample number, replicates, or statistical testing. The original report explicitly states that the sourness and saltiness sensor outputs were judged to be below the no-taste point, and adopts them as reference values on the basis of their correlation with lactic acid analysis.
Source: 阿波晩茶の成分特性に関する研究 (有澤隆文; 西岡浩貴; 池田絵梨; 横山直人; 吉本春奈, 2024) · full text checked
Show dataingredient-ishizuchi-kurocha —has_sensory_attribute→ (the claim sentence above)
In the same comparison of the four teas, Awa-bancha had lower output values for astringency stimulus and umami than sencha or black tea, and its sourness output value was the second highest, after Ishizuchi-kurocha.
Awa bancha — sensory attribute: Measuring infusions with a taste sensor (SA402B), awa-bancha showed lower output values for astringency stimulus and umami than sencha and black tea. Its sourness output value was the second highest, after Ishizuchi-kurocha. These results are reported to show that awa-bancha has a sour, clean-tasting profile.observation
Scope: A comparison of infusions of awa-bancha, Ishizuchi-kurocha, sencha, and black tea (Tokushima Prefectural Industrial Technology Center, taste sensor SA402B)
Note: A comparison between single samples; the number of replicates and statistical testing are not stated.
Awa-bancha's astringency-stimulus and umami output values were lower than sencha's and black tea's, and its sourness output value was the second highest, after Ishizuchi-kurocha.
Limitations: Sample size, replicates, and statistical testing are not stated. The original report explicitly notes that the sensor outputs for sourness and saltiness were judged to be at or below the taste-threshold point, and adopts them as reference values on the basis of their correlation with lactic acid analysis.
Source: 阿波晩茶の成分特性に関する研究 (有澤隆文; 西岡浩貴; 池田絵梨; 横山直人; 吉本春奈, 2024) · full text checked
Show dataingredient-awa-bancha —has_sensory_attribute→ (the claim sentence above)
There is also an analysis that tracked the main chemical components involved in astringency numerically. Analyzing the leaves of Awa-bancha, Ishizuchi-kurocha, sencha, and black tea, tannin content was highest in sencha, lower in Awa-bancha and Ishizuchi-kurocha, and lower still in black tea. Caffeine content was highest in black tea, followed by sencha, and low in Awa-bancha and Ishizuchi-kurocha.
Awa bancha — composition: In an analysis conducted under the Food Labeling Standards (Cabinet Office Ordinance No. 10 of Heisei 27), tannin content was 8.1 g/100g for awa-bancha, 7.5 g/100g for Ishizuchi-kurocha, 11.4 g/100g for sencha, and 6.5 g/100g for black tea; caffeine content was 1.5 g/100g for awa-bancha, 1.4 g/100g for Ishizuchi-kurocha, 2.1 g/100g for sencha, and 3.0 g/100g for black tea. Awa-bancha had less protein, caffeine, and tannin than sencha, and less protein and caffeine than black tea.supported
Scope: Leaf analysis of awa-bancha and Ishizuchi-kurocha (both post-fermented teas), sencha (an unfermented tea), and black tea (a fermented tea)
Note: Included after checking the full text (Table 2) from the Tokushima Prefectural Industrial Technology Center. Details of sample size and origin/lot are not given.
Presents a nutrient composition table for the 4 tea types (moisture, protein, fat, carbohydrate, ash, sodium, caffeine, tannin, salt equivalent, and energy).
Limitations: Details of sample size and origin/lot are not given.
Source: 阿波晩茶の成分特性に関する研究 (有澤隆文; 西岡浩貴; 池田絵梨; 横山直人; 吉本春奈, 2024) · full text checked
Show dataingredient-awa-bancha —has_composition→ (the claim sentence above)
For Goishicha, there is an analysis comparing the total amount of catechins and gallic acid in a hot-water extract against other teas, with a result far lower than green tea, oolong tea, or black tea.
Goishi tea — composition: HPLC analysis of hot-water extracts found the total amount of the main catechins and gallic acid in goishicha to be extremely low compared with other teas -- about 1/7 that of green tea and about half that of oolong and black tea, the source reports. Because catechins are the components involved in tea astringency, the source describes goishicha, whose catechins decrease during fermentation, as having mild astringency.contextual
Scope: A comparison of hot-water extracts across several teas including goishicha
Note: As described by Ukeda (2015); the original is given as Moriyama, Katayama, Nakabayashi, Ukeda, and Sawamura, Nippon Shokuhin Kagaku Kogaku Kaishi 49, 679 (2002). The primary source (the 2002 paper) itself was not checked this time, so it is included as a secondary citation.
Cites the result of a 2002 paper that the total amount of catechins and gallic acid in goishicha is extremely low -- about 1/7 that of green tea and about half that of oolong and black tea.
Limitations: A secondary citation via Ukeda (2015); the original (Moriyama et al. 2002) was not checked this time.
The Aromas Overlap, but Bitterness and Astringency Go Unmentioned
An analysis comparing the aroma compounds of hot-water extracts of Goishicha and Awa-bancha confirms an aroma pattern common to both. However, this analysis deals only with aroma compounds, and no mention of bitterness or astringency is found.
Goishi tea — sensory attribute: A GC analysis of the aroma compounds in hot-water extracts of Goishicha and Awa-bancha newly identified 12 compounds (2 esters, 5 alcohols, 4 phenols, and acetoin), and the source reports that an aroma pattern seen as characteristic of what both share, described as 『漬物茶』 (in translation: "pickled tea"), was confirmed.observation
Scope: Comparison of aroma compounds in Goishicha and Awa-bancha (both samples of unspecified origin)
Note: Only the abstract has been confirmed. The abstract makes no mention of bitterness or astringency.
GC-MS analysis of hot-water extracts of Goishicha (from Otoyo, Kochi Prefecture, made August 1985) and Awa-bancha (from Aioi, Tokushima Prefecture, made August 1985) identified 12 new compounds (methyl lactate, acetoin, 2-methyl-1-penten-3-ol, 3-methyl-2-buten-1-ol, 2-heptanol, 3-octanol, (E)-2-octenol, 4-methylguaiacol, 1,2,3-trimethoxybenzene, 4-ethylphenol, and others). The source reports a fermentation aroma pattern characteristic of pickled tea shared by both (a pleasant fermented odor accompanied by an acetic-acid-like sour odor), and describes Goishicha as having more microbial metabolites and a stronger pickled-tea aroma than Awa-bancha.
Limitations: The samples are a single-lot comparison from one origin each (Goishicha: Otoyo, Kochi Prefecture; Awa-bancha: Aioi, Tokushima Prefecture; both made August 1985), and variation across origins or years has not been examined. No mention of bitterness or astringency could be confirmed throughout the text (a paper dealing only with aroma compounds).
Source: 漬物茶碁石茶と阿波晩茶の香気特性 (川上美智子; 小林彰夫; 山西貞, 1987) · full text checked
Context: The samples are Goishicha (Otoyo, Kochi Prefecture; made August 1985; a pickled-plum-like aroma) and Awa-bancha (Aioi, Tokushima Prefecture; made August 1985; a dead-leaf-like aroma), both from a native landrace. The source's English abstract states that Goishicha has more microbial metabolites and a stronger pickled-like aroma. Verbatim: 「碁石茶;高知県大豊町,1985年8月製,黒紫色,梅漬様香気.阿波晩茶;徳島県相性町,1985年8月製,褐色,枯葉様香気.いずれも原茶は,在来種var.sinensisである。」 (in translation: "Goishicha; Otoyo, Kochi Prefecture, made August 1985, blackish-purple, a pickled-plum-like aroma. Awa-bancha; Aioi, Tokushima Prefecture, made August 1985, brown, a dead-leaf-like aroma. In both cases the raw tea is the native landrace var. sinensis.")
Limitations: No mention of bitterness or astringency.
Source: 漬物茶碁石茶と阿波晩茶の香気特性 (川上美智子; 小林彰夫; 山西貞, 1987) · full text checked
Show dataingredient-goishi-cha —has_sensory_attribute→ (the claim sentence above)
Pu-erh tea from China is also a tea that undergoes fermentation by piling, and there is a study that tracked its fermentation time series. The source reports that at the endpoint of fermentation, both bitterness and astringency were lower than in the raw material.
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.
At the same endpoint, the source reports that sweetness rose, the color changed from yellow-green to reddish-brown, and the aroma changed in the direction the source text recorded as from "fresh" to "stale."
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.
There is also a report that tracked this change in terms of components. In the same fermentation time series, the content of tea polyphenols and catechins is reported to have decreased significantly as fermentation progressed.
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.
Another report tracking the pile fermentation of a different shou (ripe) pu-erh tea likewise states that tea polyphenol content decreased greatly as fermentation progressed.
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.
Among the words used to talk about pu-erh tea is huigan (回甘). Tea-trade articles explain this word with pu-erh tea as their main subject. Where the sources on Awa-bancha, Goishicha, and Ishizuchi-kurocha talk about astringency and sourness in taste-sensor output values, the sources on pu-erh tea talk about taste through huigan, a word that carries the passage of time -- even for the same 「発酵した茶」 (in translation: "fermented tea"), where the telling is placed differs.
Note: The group of tea-trade articles explaining pu-erh tea's tasting vocabulary (huigan, shengjin, houyun, and huitian) all explain huigan with pu-erh tea as their main subject.
Under the title 「普洱茶品茶术语解读」 (in translation: "Interpreting Pu-erh Tea-Tasting Terminology"), the source explains huigan, shengjin, houyun, and suohou, treating pu-erh tea as its main subject and huigan within it.
Limitations: A tea-trade article, not an academic paper.
Under the title 「关于普洱茶的回甘、生津、回甜」 (in translation: "On Pu-erh Tea's Huigan, Shengjin, and Huitian"), the source treats pu-erh tea as its main subject and discusses huigan within it.
Limitations: A tea-trade article, not an academic paper.
Show dataingredient-puer-tea —has_defining_sensory_theme→ concept-huigan
claim: clm-puer-huigan-defining-theme / type: cultural / updated: 2026-09-02
What is not known
For none of Goishicha, Awa-bancha, or Ishizuchi-kurocha is a report of taste-sensor measurement or sensory evaluation targeting bitterness itself to be found. Astringency, sourness, and umami output values have been measured, but there is no material comparing bitterness output values across the three teas.
The analysis comparing the aroma compounds of Goishicha and Awa-bancha does not touch on bitterness or astringency, and whether the overlap in aroma and the overlap in taste come from the same cause cannot be told from this material alone.
The taste-sensor measurements of Ishizuchi-kurocha and Awa-bancha are treated as reference values by the report itself, after positioning the sourness and saltiness output as below the no-taste point, and there is no mention of sample number, replicates, or statistical testing either.
Goishicha's fermentation microbes and their involvement in aroma production are based on a sample from a single origin, and it has not been confirmed whether the same microbes and the same aroma pattern occur when the origin or lot changes.
The study of pu-erh tea's pile fermentation is a time-series observation without a control fermentation vessel, and the drop in bitterness and astringency cannot be separated out as an effect of the process of pile fermentation itself.
Frequently asked
How do Awa-bancha and Goishicha differ?
Goishicha is recorded as being made by steaming the raw material and then, after about 2 hours of heat treatment, layering two fermentations -- about 7-10 days of aerobic fermentation by mold and about 10-20 days of anaerobic fermentation by lactic acid bacteria. Ishizuchi-kurocha is likewise recorded as following the same two-stage fermentation, while Awa-bancha differs in that heat treatment stops oxidative fermentation beforehand, and only lactic acid fermentation through pickling is brought about, in a single stage. In reports that measured the infusion with a taste sensor, Ishizuchi-kurocha and Awa-bancha each have a higher sourness output value than sencha or black tea, while Goishicha shows weaker astringency and umami and stronger sourness -- different results for each. However, these measurements have no mention of sample number or replicates, and remain reports at the level of reference values.
Does fermentation lower the bitterness of Goishicha or pu-erh tea?
In one time-series study tracking pu-erh tea's pile fermentation, both bitterness and astringency are reported to have become significantly lower than in the raw material at the endpoint of fermentation, with sweetness rising at the same time. For Goishicha, Awa-bancha, and Ishizuchi-kurocha, on the other hand, while there are taste-sensor reports measuring astringency, sourness, and umami, no measurement targeting bitterness itself is found. For Goishicha, there is an analysis showing the total amount of catechins and gallic acid to be considerably lower than green tea, and a description stating that its astringency is mild, but this too is not a direct measurement of bitterness.