goishi-cha two-stage fermentation
process / process-goishi-cha-fermentation
碁石茶の二段階発酵
Goishi-cha two-stage fermentation is a two-stage fermentation in the production of (goishi-cha). Steamed tea leaves are piled on an earthen floor for aerobic initial fermentation (mold growth), then submerged in tea barrels for anaerobic lactic acid fermentation in the subsequent stage.
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Production of 「碁石茶」 (goishi-cha) begins by steaming the raw tea leaves for about 2 hours and piling them about 50–70 cm high on mats over an earthen floor for aerobic fermentation (mold growth, the initial fermentation). This stage lasts 7–10 days. The leaves are then submerged in a tub under weights for 10–20 days of anaerobic fermentation (subsequent fermentation). Finally, the leaves are cut and sun-dried for 2–3 days. This account of the process comes from a lecture record, not a peer-reviewed original research paper.
Sources disagree on the fungal species responsible for the initial fermentation (mold growth). A lecture record by Ukeda (2015) describes Aspergillus fumigatus as the main species, whereas a 2019 study using rDNA analysis to isolate and identify organisms reports Aspergillus niger. Whether this difference reflects identification methods or sampling time remains unconfirmed, so both accounts must be retained. The same 2019 study also isolated and identified Pichia manshurica and Lactobacillus plantarum as organisms involved in the subsequent fermentation.
The 3 isolated species have each been reported to contribute to the production of different aroma compounds. A. niger is described as contributing to ethyl furaneol and thiazoline compounds; P. manshurica to esters, alcohols, and phenols (including 4-ethylphenol and 4-ethyl-2-methoxyphenol); and L. plantarum to organic acids such as hexanoic and butanoic acids, and lactones.
The same 2019 study also quantified FD factors indicating contribution to aroma. The highest was hexanoic acid, with a fermented odor, at FD=1,024, followed by furfural with an almond odor, furaneol with a caramel odor, and ethyl furaneol with a sweet burnt odor, each at FD=512. For a possible mechanism by which A. niger produces the characteristic aroma compound ethyl furaneol, the study also identified a secreted protein in the fungus showing 40.3% homology to an enone oxidase from Zygosaccharomyces rouxii in an NCBI BLAST homology search. It thus goes beyond species identification to infer a production mechanism.
In another peer-reviewed paper on goishi-cha, compared with unfermented green tea, the caffeine concentration in hot-water extracts of goishi-cha after two-stage fermentation was lower, 11.6 mg/100 mL versus 43.7 mg/100 mL, as was total catechin concentration, 7.1 mg/100 mL versus 87.8 mg/100 mL. This goishi-cha sample was a single product blended from leaves of some producers, not a matched observation before and after fermentation of a single lot.
Sources for this overview
Checked for this overview: Confirmed the stated times and scale for steaming, initial fermentation, subsequent fermentation, and sun-drying.
後発酵茶・碁石茶の特徴香気成分とその生成に関与する微生物の解析
Checked for this overview: Confirmed the discrepancy between Ukeda (2015) and the isolated identification regarding the main species in the initial fermentation. / Confirmed the groups of aroma compounds whose production was associated with each of the 3 isolated species. / Confirmed the quantified FD factors and the homology-search result concerning the mechanism of ethyl furaneol production by A. niger.
Comparison of antioxidant activities among four kinds of Japanese traditional fermented tea
Checked for this overview: The measured values in the comparison of caffeine and catechin concentrations with the green-tea control.
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goishi-cha two-stage fermentation →reduces→ tea catechins →are main contributors to→ astringency
Hypotheses and recipe candidates for this entry are on the Japanese page.
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How processing and cooking change it (3)
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.
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process-goishi-cha-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."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.
Show data
process-goishi-cha-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."Scope: Layer: Food. Green tea (unfermented, control) and Goishicha (two-stage fermented) extracted under identical conditions (hot water 100 mL, 1.5 g leaf, 5 minutes), n=5 comparison.
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process-goishi-cha-fermentation —reduces→ compound-catechins