Research note 035 — 2026-09-04
Huigan — Tea's Time of Sweetness After Bitterness
Is huigan (回甘) the same thing as a "sweet aftertaste"? The explanation repeated across the sources runs from a faint bitterness and astringency on entering the mouth to sweetness becoming dominant over time. It is read not simply as sweetness that lingers, but as a word that covers after what, where, and how it changes. Next to it stand shengjin, houyun, and huitian, but the boundary among the four words does not agree from source to source. This note does not take up the time course of huigan itself (that is handled by a separate note, as a clock for bitterness in general). Instead, it follows, in the source materials' own words, how this vocabulary is named and how explanations for it are attempted within the single drink that is tea, and how the bitterness and astringency of green tea, oolong tea, pu-erh tea, matcha, gyokuro, and hojicha each move through the processes of cultivation, steeping, firing, and fermentation.
On this page (8 sections)
- What this page establishes
- Huigan, shengjin, houyun, and huitian — four similar terms
- What is not known
- How the delay in sweetness is explained
- Green tea, Tieguanyin, and pu-erh — bitterness by type of tea
- Matcha and gyokuro — what shading moves
- Firing — where sencha and hojicha char their bitterness
- Frequently asked
What this page establishes
- Huigan, shengjin, houyun, and huitian are explained in articles covering tea culture, but the boundary of each word shifts from article to article. Huigan also appears in the background description of a peer-reviewed paper, but that sentence is not an operational definition derived from an experiment.
- In a subject group prone to feeling huigan, one study reports that salivary protein content and lipase activity correlate with the strength of huigan.
- One quantitative study measures that green tea's bitterness correlates with the concentration of EGCG, ECG, and related compounds, and its astringency with the concentration of ECG and flavonol glycosides (bitterness R²=0.7769, astringency R²=0.7878).
- The mechanism itself of why sweetness arrives with a delay after bitterness has not yet been established.
Huigan, shengjin, houyun, and huitian — four similar terms
Rather than fixing the four words as if in a dictionary, this table lays out what the source used for each entry wrote about "when," "where," and "what happens." A blank does not mean that trait is absent — it means the source used does not let us decide it.
| Term | Timing given by the source used | Site mainly described | Center of the source's account | Caution from the source |
|---|---|---|---|---|
| Huigan (tea-culture articles) | After bitterness and astringency | Mouth | Sweetness becomes dominant, ending in a sweet aftertaste | Explanation from an article that is not peer-reviewed |
| Huigan (peer-reviewed background) | After drinking tea | Mouth and throat | A sweet taste persists | Not an operational definition derived from an experiment |
| Shengjin | While drinking tea | Both cheeks, between teeth and cheeks, tongue surface, under the tongue | Saliva arising | The breakdown by site is from tea-trade articles |
| Houyun | After the tea liquid passes through the throat | Throat | A classification covering sweetness, moisture, and discomfort | One article calls a sweet houyun "huigan" outright, overlapping the boundary |
| Huitian | After a faint bitterness | Mouth | Sweetness gradually appears | The distinction from huigan is the organisation of a single article |
| "Sweet aftertaste" | After drinking | Not specified | A general description that sweetness lingers | A general term placed here for comparison, not a formal tasting term |
The huigan that tea-culture articles explain includes not just the sweet outcome but the sequence of moving from bitterness and astringency to sweetness. The background description in the peer-reviewed paper, meanwhile, does not treat bitterness and astringency as a necessary condition, and records it as a sweet taste that follows in the mouth and throat. Some articles call sweetness in the throat huigan as well, so site alone cannot fully separate the four words. The table does not set out the one correct answer; it exists to make the agreements and disagreements among the sources visible.
Huigan (回甘) is repeatedly explained, in articles covering tea culture, as the sensation in which a faint bitterness and astringency on entering the mouth gives way to sweetness over time, ending in a sweet aftertaste.
Scope: An explanation repeated across Chinese-language tea-culture media articles
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concept-huigan —is_defined_as→ "In Chinese tea tasting, huigan is the sensation of feeling a slight bitterness and astringency immediately after taking a sip, after which sweetness gradually becomes dominant over time, ending in a sweet aftertaste."Shengjin (生津) is explained as the phenomenon in which saliva arises when tea is drunk. The same article also gives an explanation that components of the tea stimulate multiple salivary glands, but this is not the meaning of the word itself — it is a mechanism explanation the article adds.
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concept-sheng-jin —is_defined_as→ "The phenomenon in which, on drinking tea, organic acids and other components in the tea stimulate the submandibular, parotid, and sublingual glands, promoting saliva secretion"This shengjin is named more finely still, depending on where it is felt. Both cheeks, between the teeth and cheeks, the surface of the tongue, and a case felt as if welling up from under the tongue each carry a separate name, set out in tea-trade explainer articles.
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concept-sheng-jin —has_sensory_attribute→ "Described as dividing, by where it is felt, into 4 types: both-cheek shengjin, teeth-and-cheek shengjin, tongue-surface shengjin, and “spring beneath the tongue” (under-the-tongue shengjin)"Houyun (喉韵) is explained as a word for the sensation felt in the throat after the tea liquid passes through it.
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concept-hou-yun —is_defined_as→ "The sensation felt in the throat after the tea liquid passes through it"This houyun is further discussed as dividing into three: a state in which astringency and irritation fade, saliva flows, and the throat feels moist and sweet; a state in which the throat becomes moist and thirst disappears; and a state in which the throat feels uncomfortable and unpleasant.
Scope: As vocabulary for tasting pu-erh tea
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concept-hou-yun —has_sensory_attribute→ "Described as dividing into 3 types: gan (astringency and irritation fade, saliva flows, and the throat feels moist and sweet), run (the throat becomes moist and thirst disappears), and zao (the throat feels uncomfortable and unpleasant)"Huitian (回甜) is explained, in a single article, as the sensation in which sweetness gradually appears in the mouth after a faint bitterness on entering. The same article distinguishes huigan and huitian as separate effects. This, however, is that article's organisation, not an established distinction shared across the four words.
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concept-hui-tian —is_defined_as→ "In ripened pu-erh tea and similar teas, the sensation in which, after feeling a slight bitterness on first taking a sip, sweetness gradually rises up in the mouth"Show data
concept-hui-tian —is_not_synonymous_with→ concept-huiganYet the four words are not cleanly separated across every source. One tea-trade article, at the end of the sentence explaining houyun's "gan" (sweetness), calls that very sensation huigan outright, and another article states at its outset that houyun is an alternative name for huigan. The four words circulate with neighboring terms overlapping here and there.
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concept-huigan —has_unresolved_property→ "Huigan and the sweetness felt as houyun are sometimes explained, in tea-industry materials, as being the same sensation"Huigan is also distinguished from an aftertaste that is simply leftover bitterness. The definition of huigan itself makes explicit a time structure in which sweetness overtakes the bitter-astringent taste as time passes, ending finally in sweetness — and it is discussed as a separate event from an aftertaste in which bitterness merely lingers and fades.
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concept-huigan —differs_from→ concept-bitter-aftertasteWhat is not known
The boundary between the words
- The four words huigan, shengjin, houyun, and huitian all have their definitions explained by tea-culture media articles rather than academic papers, and are not peer-reviewed; the very boundary of each word shifts from article to article. How far huigan and houyun's "gan" (sweetness) refer to the same phenomenon is not settled within this vocabulary. An article containing reprinted or shared wording is not counted as an independent point of agreement.
Mechanism
- The three explanations for huigan — film formation, polysaccharide breakdown, and contrast adaptation — are all presented as conventional accounts introduced by articles, without direct observation in the mouth or primary verification experiments targeting tea.
How it is measured
- The studies showing a correlation between huigan and total salivary protein content, lipase activity, and the friction coefficient all targeted small subject groups, and are correlational; what causes what has not been established.
- Most human sensory studies of huigan remain limited to a method of rating intensity at a single point after swallowing, and no example has been found of measuring tea's huigan by a method that follows the passage of time as a continuous curve.
- The study of Tieguanyin's steeping conditions evaluates bitterness and astringency as a single combined attribute, and cannot separate out how much each individual sensation moved.
How the delay in sweetness is explained
More troublesome than the phenomenon of huigan itself is the explanation of why sweetness comes after the bitter-astringent taste. One article introduces the explanation that tea polyphenols bind with salivary proteins to form a film in the mouth, which is felt as astringency and bitter-astringent taste, and that huigan and shengjin arise when this film breaks and the muscles of the mouth relax.
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concept-huigan —has_currently_proposed_mechanisms→ "The hypothesis (the "astringency-conversion" theory) that tea polyphenols bind salivary proteins to form a film in the mouth, perceived as an astringent, bitter-astringent sensation, and that when the film breaks, the oral muscles relax and huigan and shengjin (a moistening, salivating sensation) are felt."Another article gives the explanation that the polysaccharides contained in tea are not themselves sweet, but remain in the mouth owing to their stickiness, and that the time lag before they are broken down by salivary amylase into sweet maltose is what produces huigan.
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concept-huigan —has_currently_proposed_mechanisms→ "The hypothesis that tea polysaccharides, though not themselves sweet, remain in the mouth owing to their viscosity, and that the time lag before they are hydrolyzed by salivary amylase into sweet maltose is what produces huigan"Yet another article introduces a contrast explanation, in which, as sensory adaptation to bitterness and sweetness progresses, the sweetness that was present in the background comes to be felt as relatively stronger. All three explanations place the origin of huigan in separate places — a film in the mouth, an enzyme, and sensory adaptation — and are not unified across the sources.
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concept-huigan —has_currently_proposed_mechanisms→ "The contrast-effect hypothesis, that after sensory adaptation to bitter and astringent stimuli has progressed, the sweetness that was present in the background is perceived as relatively stronger"In a study combining tea with human saliva, the total salivary protein content and lipase activity showed a significant positive correlation with the strength of huigan, in the group of subjects judged to be sensitive to feeling huigan.
Scope: A sensory and biochemical trial with 6 subjects selected as the Huigan-sensitive group, using green-tea-derived compounds (L-theanine, trilobatin, an EC/EGC mixture, with distilled water as control)
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concept-huigan —is_correlated_with→ "Total salivary protein content (TPC) and lipase activity (LP) (in the subject group judged to be highly sensitive to huigan)"In a measurement of the friction coefficient of a saliva and tea-compound mixture, targeting the same subject group, the strength of huigan also correlated strongly with the friction coefficient, particularly under conditions of slow sliding speed.
Scope: In vitro tribology measurements on a sensitive group of 6 and a non-sensitive group of 6, selected after screening 24 people
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concept-huigan —is_correlated_with→ "The friction coefficient of a saliva and tea-compound mixture (particularly at sliding speeds below 0.5 mm/s, in the subject group with high huigan sensitivity)"In an experiment comparing which compounds are most likely to trigger huigan, an aqueous mixture of epicatechin and epigallocatechin showed the strongest huigan rating in the subject group with high sensitivity to huigan, significantly different from the other samples.
Scope: An aqueous mixture of EC 400 ppm and EGC 100 ppm (a 4:1 ratio), compared against L-theanine 200 ppm, trilobatin 30 ppm, and a distilled-water control. In the Huigan-sensitive group, the rating was 5.2±1.3 in the oral stage and 5.2±1.0 in the oral-pharyngeal stage (p<0.05, significantly different from the other samples)
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compound-ec —is_correlated_with→ concept-huiganGreen tea, Tieguanyin, and pu-erh — bitterness by type of tea
In green tea infusion, bitterness and astringency are positioned as separate, main quality attributes.
Scope: Brewed green tea
Note: Intensity depends on the tea leaf and brewing method. / 2026-08-31: Calibrated down from established to supported, because the supporting evidence does not derive from a full-text check. May be re-upgraded after a full-text check.
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ingredient-green-tea —has_sensory_attribute→ sensation-bitterScope: Brewed green tea
Note: Kept separate from bitterness even where the compounds driving the two overlap. / 2026-08-31: Calibrated down from established to supported, because the supporting evidence does not derive from a full-text check. May be re-upgraded after a full-text check.
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ingredient-green-tea —has_sensory_attribute→ sensation-astringentIn Tieguanyin, a type of oolong tea, the steeping conditions themselves — the tea-to-water ratio, water temperature, steeping time, and number of infusions — govern the strength of the combined bitter-astringent attribute. With a combination of a high tea-to-water ratio, low water temperature, and short steeping time, this combined attribute became significantly lower.
Scope: An orthogonal regression design and trained panel using Tieguanyin
Note: The evaluated attribute is the composite "bitterness-astringency." It does not claim to have varied bitterness and astringency separately.
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ingredient-tieguanyin-infusion —has_bitter_astringency_affected_by→ "Tea-to-water ratio, water temperature, steeping time, and number of infusions"In a study tracking the pile fermentation of pu-erh tea, both bitterness and astringency became significantly lower at the endpoint of fermentation, compared with the raw material.
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.
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process-tea-pile-fermentation —was_observed_with→ "Lower bitterness and astringency than the raw material at the 36-day endpoint"At the same fermentation endpoint, sweetness rose significantly, the color changed from yellow-green to reddish-brown, and the aroma changed in the direction the source recorded as from "fresh" to "stale." The process of pile fermentation moves the whole of the tea's taste in a way that lowers bitterness and astringency while raising sweetness at the same time.
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.
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process-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""Matcha and gyokuro — what shading moves
Matcha is made from the new shoots of tea trees grown under shade cultivation. One source records that what falls in content with shading is the weakly bitter-astringent epigallocatechin, and that almost no drop in content is seen for the strongly bitter-astringent epigallocatechin gallate.
Scope: Matcha made from tencha (shading cultivation)
Note: This is background text in the "Purpose" paragraph of a NARO (National Agriculture and Food Research Organization) conference abstract, stated as a summary of prior knowledge rather than new measurement data from the abstract itself (citation numbers are not given in the abstract). Figures such as the rate of change in EGC and EGCG content are not given in this abstract.
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ingredient-matcha —has_composition→ "The source states that the catechin whose content falls with shading cultivation is epigallocatechin (EGC), which has weak bitter-astringency, while epigallocatechin gallate (EGCG), which has strong bitter-astringency, shows almost no drop in content."When matcha is prepared according to the whisking method used for sensory panels, the extraction rate is high for theanine, caffeine, and epigallocatechin, while it is low for epigallocatechin gallate, whose concentration in the infusion was lower than in the sensory-panel infusions of other teas.
Scope: Matcha (prepared according to the method used for sensory panels)
Note: A measured value obtained by directly analyzing the centrifuged supernatant with capillary electrophoresis and high-performance liquid chromatography.
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ingredient-matcha —has_composition→ "In matcha infusion prepared according to the whisking method used for sensory panels, the extraction rate into the infusion was 80% or higher for theanine, caffeine, and EGC, whereas it was 50% or lower for EGCG, and the EGCG concentration in the infusion was lower than in sencha and other sensory-panel infusions."There is also the view that vigorously shaking the tea whisk when preparing matcha sharply lowers the water temperature, which hinders the dissolution into the water of the strongly temperature-dependent epigallocatechin gallate, so that the whisked matcha infusion does not show as much bitter-astringent taste as would be expected from the content of the tea leaf components.
Scope: Matcha (whisked according to the method used for sensory panels)
Note: The authors' own interpretation; the abstract does not present an experiment that directly measured the water temperature itself, nor a causal experiment involving sensory evaluation of the bitter-astringent taste. An interpretation derived from measured extraction-rate data (in which only EGCG is low).
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ingredient-matcha —has_perceived_bitterness_suppressed_by→ "The sharp drop in water temperature brought on by vigorously whisking the tea whisk when preparing matcha. Because this hinders the dissolution into the water of the strongly temperature-dependent EGCG, the authors reason that the whisked matcha infusion does not show as much bitter-astringent taste as would be expected from the content of the tea leaf components."In gyokuro, the opposite movement is observed. The longer the exposure time after the shading material is removed, the more the content of free amino acids and theanine falls, and the more the content ratio of catechins rises. Sensory evaluation by the standard panel method also tilted toward inferior internal quality as exposure time lengthened. While matcha keeps its shading and reduces the weakly bitter-astringent catechin, gyokuro moves, from the moment the shading is removed, in the direction of increasing the strongly bitter-astringent catechin.
Scope: Fukuoka Prefectural Agriculture and Forestry Research Center, Yame Branch; gyokuro cultivars 'Yabukita' and 'Okuyutaka'; a 2006 field trial (3 replicates)
Note: The subject is gyokuro, not tencha (the raw material for matcha) itself. However, gyokuro and tencha belong to the same family of shading-cultivation techniques and involve the same mechanism -- shading changing amino acid / catechin composition. Note that the sensory evaluation uses overall items such as "flavor" from the standard tasting method, not a scale that isolates bitterness alone.
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ingredient-gyokuro —has_composition→ "The longer the exposure time (0/1/2/4/6 hours) after removing the shading material, the more the free amino acid and theanine content in the crude tea fell, while the catechin content (the sum of EC+ECG+EGC+EGCG) rose. In the 'Yabukita' cultivar, theanine fell from 2224 mg/100g under shading to 1983 mg/100g after 6 hours of exposure, and catechins rose from 9.4% to 10.3% (dry weight). Dimethyl sulfide (DMS), the main component of the covering aroma, fell to about 55% of the shaded level after 1 hour of exposure ('Yabukita') and to about 88% after 2 hours of exposure ('Okuyutaka'). Sensory evaluation by the standard tasting method (internal quality such as flavor) tended to worsen the longer the exposure time ('Yabukita' total difference: -0.7 points at 1 hour of exposure, -3.2 points at 6 hours)."Firing — where sencha and hojicha char their bitterness
In hojicha, the deeper the degree of roasting, the more the total amount of catechins decreases, in first flush, cut-leaf tea, and second flush alike. For individual components, however, some show a mountain-shaped change — rising once from crude tea to a light roast, then decreasing as the roast is deepened further.
Scope: Kochi Prefectural Agricultural Technology Center Tea Experiment Station; crude teas of first flush, cut-leaf, and second flush with a 50-second steaming time. Roasted 2 times with an automatic continuous hojicha roaster (exhaust temperature 90 C for the 1st roast, 100 C for the 2nd roast, with drum rotation speed adjusted for each flush and roasting degree).
Note: Direct quantification by HPLC (JASCO X-LC system). Only 1 sample per condition; the number of replicates is not stated.
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process-hojicha-roasting —reduces→ compound-catechinsThe finish processing of sencha goes through the stages of grading, sorting, firing, and blending. The temperature and time of firing are changed according to the grade of the crude tea: crude tea for high-grade tea is given a light firing that makes the most of its original character, while crude tea of middle and ordinary grade is given a firing that strengthens the taste and aroma distinctive of fired tea. It is also recorded that excessive firing produces a burnt smell that masks the sweet aroma.
Scope: Crude ordinary steamed sencha produced within Kochi Prefecture.
Note: Extension technology information from the Kochi Prefectural Agricultural Technology Center Tea Experiment Station (research period: Heisei 30 to Reiwa 2).
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process-tea-hiire —is_prepared_by→ "Finish processing of crude tea produced within the prefecture (ordinary steamed sencha) proceeds through the stages of grading → sorting → firing (hiire) → blending. After the crude tea is graded by inspection into Grade A (for high-grade tea), Grade B (for mid-grade tea), and Grade C (for ordinary tea), Grade A crude tea, whose appearance and internal quality are superior, is fired to make the most of that character, at around 90°C for 30 minutes in a rotary-drum firing machine, or, when adding an even lighter roast aroma, around 100°C for 20-30 minutes. Grade B and Grade C are fired with a medium-to-strong roast aroma, to generate the taste and aroma distinctive of fired tea and emphasize its toastiness, at around 100°C for 30-40 minutes in a rotary-drum firing machine. Firing is a heating process that generates the aroma and taste distinctive of fired tea, and excessive firing masks the sweet aroma with a burnt smell."Frequently asked
What does huigan mean?
Huigan is repeatedly explained, in Chinese-language tea-culture articles, as a word for the sensation in which a faint bitterness or astringency is felt right after taking tea into the mouth, after which sweetness becomes dominant over time, ending in a sweet aftertaste. Similar words — shengjin, houyun, and huitian — are also used alongside it, but their boundary with huigan overlaps and circulates differently from article to article, and no rigorous definition from an academic paper has been confirmed. As for the mechanism behind why sweetness is felt with a delay, a theory that a film forms in the mouth and then breaks, a theory that polysaccharides are slowly broken down by a salivary enzyme, and a theory that sensory adaptation to bitterness relatively strengthens sweetness have all been proposed, but none is accompanied by a direct verification experiment targeting tea.
Why is matcha unlikely to become astringent?
The tea leaf that is the raw material for matcha is grown under shading, and it is reported that what falls with the shading is the weakly bitter-astringent epigallocatechin, while the strongly bitter-astringent epigallocatechin gallate falls little. Furthermore, when prepared according to the whisking method used for sensory panels, it has been confirmed that the extraction rate of epigallocatechin gallate is lower than that of theanine or caffeine, and its concentration in the infusion is also lower than in the sensory-panel infusions of other teas. There is also the view that shaking the tea whisk vigorously sharply lowers the water temperature, making it harder for the temperature-sensitive epigallocatechin gallate to dissolve out, but this is the authors' own interpretation, not a verification that directly measured the drop in water temperature itself.
Does pu-erh tea become sweeter with fermentation?
In one time series fermenting maocha from old-tree tea for 36 days, both bitterness and astringency are reported to have dropped significantly at the endpoint of fermentation, while sweetness rose significantly at the same time. It is also recorded that the color changed from yellow-green to reddish-brown, and the aroma changed from a fresh impression to one with a fermented smell. However, this is an observation of a single batch without a control fermentation vessel, and which process factor is causing this change has not been separated out.
Related entries:sweet aftertaste / sheng jin (tea salivation sensation) / hou yun (tea throat feel) / hui tian (tea rising sweetness) / green tea infusion / Tieguanyin oolong tea infusion / ripe Pu-erh tea / matcha / gyokuro / Hojicha / tea pile fermentation / tea finishing fire (hi-ire)
Related research notes: Bitterness Has a Clock / How Bitterness, Astringency, and Egumi Differ / The Map of "Bitter" — From One Word to East and West
Source ledger: Source list
How to cite this page
Aoki, M. (NIGAMI LAB) (2026). Huigan: Sweetness After Bitterness in Tea. https://nigamilab.com/en/notes/huigan-tea-time/
Each claim card has a stable anchor (#clm-…). The dataset is CC BY 4.0; see the data page. Dataset DOI: 10.5281/zenodo.22739101