Kombucha as a Functional Fermented Beverage: Emerging Clinical Evidence, Proposed Mechanisms, Sensory Dimensions, Cultural Context, and Implications for Global Health

1. Introduction

Kombucha is a fermented tea beverage produced by a SCOBY, which generates a complex matrix of organic acids, polyphenols, microbial metabolites, and live microorganisms [1,2]. Tea, prepared from the leaves of Camellia sinensis, is the world's most widely consumed beverage after water, consumed by more than two-thirds of the global population [3]. Its deep cultural significance across Asia, the Middle East, and beyond provides kombucha with a uniquely broad and familiar consumer foundation. The rising popularity of kombucha reflects not only growing interest in functional foods, the human microbiome, and low-glycaemic beverage alternatives, but also the way in which fermentation transforms the sensory profile of the tea base into a distinctive, often preferred beverage experience.

Fermentation is one of the oldest food-processing technologies and has been utilized across virtually all human societies [4]. In addition to preservation, fermentation enhances nutritional value, reduces antinutritional factors, and produces bioactive compounds that can influence human health [5]. These processes also facilitate exposure to diverse microbial communities, which are increasingly recognised as important for immune function, metabolic regulation, and overall health.

The complex nature of kombucha distinguishes it from many modern food products, which are typically industrially produced and microbiologically simple in composition. Contemporary dietary patterns are characterised by high consumption of ultra-processed foods and sugar-sweetened beverages (SSBs), which have been strongly linked to obesity, insulin resistance, type 2 diabetes, and cardiovascular disease [6,7]. Metabolic syndrome, defined by a cluster of risk factors including impaired glucose metabolism, dyslipidaemia, hypertension, and central adiposity, represents a major global health challenge [8].

Within this context, there is increasing interest in functional foods and beverages that offer sensory appeal while producing a favourable metabolic response. Kombucha has emerged as a strong candidate in this category, supported by a growing body of preclinical and clinical evidence and driven in part by the sensory diversity that fermentation introduces to the tea base. This review aims to provide an integrated overview of the current literature, incorporating sensory, clinical, mechanistic, cultural, and future perspectives.

2. Methods

This manuscript is a narrative review and was not subject to systematic review protocols or PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) reporting guidelines, which are designed for systematic reviews and meta-analyses rather than for integrative narrative syntheses. The narrative review format was chosen deliberately: the human RCT evidence base for kombucha is currently too small and heterogeneous for pooled meta-analysis, and the scope of this review, encompassing fermentation biochemistry, sensory science, clinical evidence, cultural history, and public health implications, extends substantially beyond what a single, narrowly defined systematic review question could accommodate.

A targeted literature search was conducted across PubMed/MEDLINE, Scopus, and Google Scholar using the following search terms in combination: ‘kombucha’, ‘fermented tea’, ‘SCOBY’, ‘functional beverage’, ‘tea polyphenols’, ‘L-theanine’, ‘organic acids’, ‘glycaemic index’, ‘probiotics’, ‘microbiome’, and ‘sugar-sweetened beverages’. Searches were conducted without date restrictions but prioritised publications from 2010 onwards, with earlier foundational studies included where directly relevant. All human randomised controlled trials (RCTs) identified as investigating the health effects of kombucha consumption were included regardless of sample size. Mechanistic, compositional, and sensory studies were selected to represent the principal domains of fermentation science relevant to kombucha. Review articles were included where they provided authoritative synthesis of primary evidence in areas where direct citation of primary sources would be impractical given the breadth of the review. Evidence from animal or in vitro studies is cited where human clinical data are absent, and is clearly distinguished as preclinical throughout. The quality and limitations of included clinical studies are discussed explicitly in Section 5 and Section 10.

3. Composition and Functional Properties of Kombucha

Kombucha is produced using a SCOBY to ferment sweetened tea, typically derived from Camellia sinensis. The SCOBY is a living microbial consortium that is propagated and shared across individuals and communities, reflecting both biological continuity and cultural transmission [10]. A kombucha SCOBY is a dynamic rather than a fixed microbial consortium that can include species of Acetobacter, Gluconobacter, Lactobacillus, and various yeasts [9]. Metagenomic analyses have revealed hundreds of microbial taxa, highlighting the complexity of the SCOBY ecosystem [10].

During fermentation, sucrose is metabolised by yeast into glucose and fructose and then to ethanol, which is subsequently converted by bacteria into organic acids, including acetic, gluconic, and glucuronic acids [11]. These organic acids contribute to the acidity of the beverage and are thought to play a role in its biological activity, including antimicrobial effects and modulation of metabolic processes [12]. In addition, kombucha contains tannins and other tea-derived polyphenols, which undergo transformations during fermentation that may enhance their bioavailability and bioactivity [13].

In the clinical studies reviewed below, the green tea kombucha used had a pH of 3.41 ± 0.09, total acidity of 0.20 ± 0.02 (w/v acetic acid), antioxidant capacity of 3.24 ± 0.43 µmol TE/mL, and total phenolic content of 0.32 ± 0.003 mg/mL in gallic acid equivalents. Microbiological characterisation identified lactic acid bacteria (1.98 × 10⁷ CFU/mL), acetic bacteria (1.07 × 10⁷ CFU/mL), and yeast (1.57 × 10⁷ CFU/mL). A total of 92 phenolic compounds were identified, predominantly from the flavonoid class (70.7%) [14,15]. In addition to phenolic compounds, kombucha retains caffeine and L-Theanine from the tea substrate, both of which have clinically relevant biological activities. Caffeine (a methylxanthine alkaloid) acts via adenosine receptor inhibition to promote alertness and thermogenesis. While kombucha usually retains a substantial portion of the original tea caffeine, the fraction varies widely and is not consistently established across studies [13,16]. L-Theanine (a non-proteinogenic amino acid found in Camellia sinensis) promotes relaxed alertness by modulating GABA, dopamine, and serotonin pathways, and may counteract the anxiogenic effects of caffeine, producing a synergistic effect on sustained cognitive performance that is particularly pronounced in green tea kombucha [3,17,18,19,20,21,22,23].

The composition of kombucha can vary widely depending on the SCOBY ecosystem, tea substrate, sugar source, temperature, fermentation time, local handling practices, and production methods. This biological complexity distinguishes kombucha from industrially produced beverages and is best understood as a living system in which chemical and biological processes continuously interact. Table 1 provides a comprehensive overview of the principal bioactive components of kombucha, including their chemical class, origin, mechanisms of action, sensory contribution, and health-related effects.

4. Sensory Properties and Consumer Appeal

Kombucha's global popularity is inseparable from its distinctive and versatile sensory profile, which emerges from the fermentation of one of the world's most culturally significant beverages. Tea is the most widely consumed beverage on earth after water, with an estimated 3.7 billion cups consumed daily worldwide [3]. This extraordinary reach provides kombucha with an immediately recognisable base ingredient and a built-in cultural familiarity across diverse populations.

Fermentation fundamentally transforms the sensory characteristics of sweetened tea, producing a beverage that is markedly different in taste, aroma, and mouthfeel from the original infusion. The sensory profile of conventional kombucha is typically described as lightly effervescent, mildly sour, subtly sweet, and pleasantly fruity, with a characteristic vinegary note [24]. These attributes arise from multiple fermentation-derived compounds acting in combination.

4.1. Organic Acids

The production of organic acids is the primary driver of kombucha's characteristic acidity and tartness. Acetic acid, produced by acetic acid bacteria from ethanol, is the dominant acid and imparts the sharp, vinegar-like note that defines the base flavour [24]. Gluconic acid, formed by the oxidation of glucose, and glucuronic acid, produced from gluconic acid by Gluconobacter species, contribute milder, more complex acidic notes that soften and round the overall flavour profile [11]. Lactic, citric, and malic acids, present in smaller quantities, further contribute to the fruity-sour character of the beverage [16]. Research has shown that fermentation temperature and duration strongly influence organic acid production and thus the perceived sourness and astringency of the final product; higher acid concentrations are associated with lower consumer liking, underscoring the importance of controlled fermentation in optimising sensory quality [25].

4.2. Tannin and Polyphenol Biotransformation

Tea leaves are naturally rich in tannins, catechins, and other polyphenolic compounds that contribute to the astringency and bitterness of an unfermented tea infusion [17]. During kombucha fermentation, the SCOBY microorganisms, particularly Acetobacter, Saccharomyces, and lactic acid bacteria, secrete tannases, glycosidases, esterases, and other polyphenol-associated enzymes that hydrolyse and depolymerise these complex compounds [13]. This biotransformation converts high-molecular-weight tannins and flavonoid glycosides into smaller, lower-astringency phenolic acids and aglycones, meaningfully reducing the perception of bitterness and harshness relative to an unfermented tea infusion [16]. Concurrently, the production of simpler phenolic compounds including gallic acid, epicatechin, and epigallocatechin increases the total free phenolic content of the beverage and enhances its antioxidant capacity [26,27]. The result is a beverage with a more mellow, complex flavour than the unfermented tea base, with reduced astringency and enhanced fruity and fermented notes.

4.3. Ethanol, Esters, and Volatile Compounds

Yeast metabolism during fermentation produces trace amounts of ethanol (typically 0.5–3% ABV in unpasteurised products), which contributes to mouthfeel and the perception of body and warmth [24]. Ethanol also serves as a substrate for bacteria, which oxidise it to acetic and other organic acids, linking alcohol production directly to the characteristic acidic notes described above. Beyond ethanol, yeast metabolism generates a diverse array of volatile compounds, including esters, higher alcohols, and aldehydes, that collectively contribute to the fruity, floral, and fermented aromatic complexity of kombucha [11,16]. These volatile compounds are highly sensitive to fermentation conditions, meaning that the aroma profile of kombucha can vary substantially across producers and products.

4.4. Sugar, Carbonation, and Flavouring

Sucrose is added at the outset of fermentation as a substrate for microbial metabolism. While most is consumed during primary fermentation, residual sugars remain in the final product, contributing sweetness that counterbalances the acidity and sourness from organic acids. The relative balance of sweetness and sourness is a key determinant of overall consumer appeal [25]. Natural carbonation, generated by yeast-produced CO² during primary fermentation and enhanced during secondary fermentation in sealed containers, provides effervescence that further distinguishes kombucha from conventional tea and contributes to a refreshing mouthfeel comparable to that of carbonated soft drinks [24].

Commercial kombucha producers routinely add fruit juices, botanical extracts, herbs, spices, and other flavourings during secondary fermentation to create diverse flavour profiles that appeal to a broad consumer base. Flavoured varieties dominate the market, accounting for an estimated 80% of global kombucha sales in 2024, reflecting strong consumer preference for flavour variety alongside the perceived health benefits of the beverage [41]. This flavour innovation strategy has been central to the beverage’s transition from a niche health food product to a mainstream functional beverage category.

4.5. Sensory Appeal as A Driver of Adoption

The sensory transformation achieved through fermentation has important public health implications. A beverage that consumers find intrinsically appealing, and that can be offered in a wide range of flavour formats, is more likely to achieve sustained adoption than one that relies purely on perceived health benefits. The global kombucha market was valued at approximately USD 4.26 billion in 2024 and is projected to reach USD 9.09 billion by 2030, reflecting a compound annual growth rate of around 13.5%, driven by both health awareness and the sensory novelty of the product [41,42]. This intersection of sensory appeal and functional benefit is central to kombucha’s potential as a population-level dietary alternative to SSBs and distinguishes it from many other functional food supplements that lack comparable consumer acceptance. The full sensory architecture of kombucha, covering six taste dimensions (sourness, sweetness, spicy/pungent, bitterness/astringency, umami, and saltiness) [28] alongside aroma, effervescence, and colour, is summarised in Table 3.

5. Clinical Evidence

5.1 Glycaemic Regulation

Experimental animal models have consistently reported reductions in blood glucose, improved glucose tolerance, favourable changes in lipid metabolism, and improvements in pancreatic or hepatic markers after kombucha administration [29]. Early observational and non-randomised clinical research also reported improvements in glycaemic control among individuals with diabetes following kombucha consumption [30], though these findings predate rigorous RCT methodology and this pre-RCT observational study used unstandardised preparations and lacked blinded controls. Human clinical evidence from rigourous controlled trials is emerging. In a randomized, placebo-controlled crossover trial in healthy adults, live kombucha consumed with a high-glycaemic index meal significantly reduced postprandial glycaemia and insulinaemia, lowering the glycaemic index from 86 to 68 [31]. This finding is clinically relevant because postprandial glucose excursions are associated with insulin resistance and broader cardiometabolic risk. A randomized, double-blind, placebo-controlled crossover pilot study in adults with type 2 diabetes found that four weeks of kombucha consumption was associated with a reduction in fasting blood glucose (164 to 116 mg/dL, p = 0.035) [32]. In the 10-week RCT by Bonifácio et al. [14], a notable sex-related interaction was observed: men in the kombucha group significantly reduced glycated haemoglobin compared with men in the control group (p = 0.010).

5.2. Lipid Profile and Uric Acid

The 10-week RCT by Bonifácio et al. [14] provides the first dedicated clinical evidence for kombucha's effects on the lipid profile in humans with excess body weight. Participants in the kombucha group (energy-restricted diet + 200 mL/day green tea kombucha) achieved significant within-group reductions in total cholesterol (p = 0.024), LDL-c (p = 0.035), VLDL-c (p = 0.011), triglycerides (p = 0.012), Castelli index II (p = 0.002), and uric acid (p = 0.027) compared with baseline. These improvements were not observed in the control group, yet these findings must be interpreted cautiously given that no significant between-group differences were detected for these markers.

The lipid-lowering effects were attributed to the beverage's rich flavonoid content (70.7% of 92 identified phenolic compounds), which may stimulate sirtuin-1, activate AMPK, inhibit SREBP, reduce lipogenesis, and inhibit lipid absorption through catechins [14]. The uric acid reduction was consistent with prior evidence that polyphenols, particularly gallic acid, inhibit xanthine oxidase and decrease renal urate transporter expression [14].

5.3. Oxidative Stress and Endothelial Health

A further 10-week RCT by Bonifácio et al. [33] examined oxidative stress and endothelial health markers in adults with excess body weight. Participants in the kombucha group demonstrated a significant reduction in plasma hydrogen peroxide (H₂O₂), a pro-oxidant marker, compared with the control group (p = 0.007). Mean H₂O₂ levels declined from 18.14 to 14.67 µmol/mL in the kombucha group versus 16.50 to 15.09 µmol/mL in the control group. This represents the first human clinical evidence for a reduction in a pro-oxidant marker following kombucha consumption in an overweight population, consistent with the beverage's well-established antioxidant capacity [33,34].

5.4. Gastrointestinal Health, Gut Microbiota, and Serum Metabolome

A parallel RCT by Fraiz et al. [15] examined gastrointestinal symptoms, intestinal permeability, gut microbiota, and serum metabolomics. The kombucha group reported significantly lower gastrointestinal symptom scores, including lower reflux (p = 0.043), hard stools (p = 0.001), and incomplete bowel emptying (p = 0.027), compared with the control group. Worsening of intestinal permeability markers was observed only in the control group. Serum metabolomics identified discriminant metabolites unique to the kombucha group, including taurine, diethyl malonate, and asperuloside, associated with antioxidant, anti-inflammatory, and anti-obesity effects [15].

5.5. Summary of Clinical Evidence

Taken together, available RCT evidence suggests that daily consumption of approximately 200 mL of green tea kombucha for 4–10 weeks may produce biologically meaningful improvements across multiple cardiometabolic domains, including glycaemic regulation, lipid profile, uric acid, pro-oxidant markers, and gastrointestinal function. The open-label design of the Bonifácio/Fraiz trials [14,15,33] and limited sample sizes (n = 29–30 per arm for the Bonifácio/Fraiz series; n = 11 for Atkinson et al.; n = 12 for Mendelson et al.) represent important limitations that preclude definitive efficacy claims and require confirmation in larger, blinded studies. A summary of all key human RCTs, including study design, population, intervention, outcomes, and limitations, is provided in Table 2.

Table 2. Summary of human randomised controlled trials of kombucha: study design, population, intervention, outcomes, and limitations.

Study (year)	Design	Population	Intervention	Duration	Key outcomes	Limitations	Ref
Atkinson et al. (2023) [31]	Randomised, placebo-controlled, crossover	Healthy adults; n = 11	330 mL of live (unpasteurised) kombucha, diet lemonade soft drink, or soda water (control) consumed with a standardised high-GI Jasmine rice meal; three conditions tested in crossover sequence	Single acute meal	↓ Glycaemic index from 86 (soda water) to 68 with live kombucha (p = 0.041); ↓ insulin index from 85 to 70 (p = 0.041); no significant difference between soda water and diet lemonade; suggests live microbial/polyphenol components drive the effect beyond pH or acidity alone	Very small sample (n = 11); single-meal acute design; no chronic follow-up; mechanism not directly investigated; healthy population limits generalisability to metabolic disease	[31]
Mendelson et al. (2023) [32]	Randomised, double-blind, placebo-controlled crossover pilot	Adults with type 2 diabetes mellitus; n = 12	240 mL kombucha/day vs. matched placebo beverage; crossover with 8-week washout period between arms	4 weeks per arm	↓ Fasting blood glucose in kombucha period: 164 → 116 mg/dL (p = 0.035); placebo period: 162 → 141 mg/dL (p = 0.078, NS); note: 2 participants with well-controlled baseline glucose showed slight increases that remained within normal range	Very small sample (n = 12); underpowered for HbA1c and other secondary outcomes; short duration; single commercially donated kombucha product; two participants with well-controlled baseline glucose confound mean estimates	[32]
Bonifácio et al. (2026) [14] Cardiometabolic RCT	Open-label, parallel-arm RCT	Adults with excess body weight (BMI >27 kg/m²), no chronic disease; n = 29 (control), 30 (kombucha)	200 mL green tea kombucha/day + −500 kcal/day energy-restricted diet vs. energy-restricted diet alone	10 weeks	Kombucha group (intragroup): ↓ TC (p = 0.024), ↓ LDL-c (p = 0.035), ↓ VLDL-c (p = 0.011), ↓ TG (p = 0.012), ↓ Castelli index II (p = 0.002), ↓ uric acid (p = 0.027). Men in kombucha group: ↓ HbA1c vs. control (p = 0.010). Control only: ↑ HbA1c (within normal range). No statistically significant intergroup differences in Δ values for any marker.	Open-label design (no blinding); Brazilian adult cohort limits generalisability; small n; no power for between-group lipid significance; single GTK product; energy-restricted diet in both arms makes kombucha-specific attribution difficult	[14]
Fraiz et al. (2024) [15] Intestinal health & metabolomics RCT	Open-label, parallel-arm RCT (substudy of above cohort)	Same cohort as Bonifácio et al. 2026; n = 29/30 per arm	As above: 200 mL green tea kombucha/day + energy-restricted diet vs. diet alone	10 weeks	Kombucha group: ↓ Total GSRS score (p = 0.035), ↓ reflux (p = 0.043), ↓ hard stools (p = 0.001), ↓ incomplete bowel emptying (p = 0.027). Control group only: ↑ L/M ratio (p = 0.019), ↑ fecal pH (p = 0.004), ↑ zonulin (p = 0.031). Discriminant serum metabolites in kombucha group only: taurine, diethyl malonate, asperuloside, and several tripeptides with anti-obesity and antioxidant properties.	Same limitations as above; insufficient biological samples for LBP and zonulin analysis in full cohort; no significant microbiota differences after FDR adjustment; metabolomics identifications are putative; small sample size for metabolome analysis	[15]
Bonifácio et al. (2025) [33] Oxidative stress RCT	Open-label, parallel-arm RCT (substudy of same programme)	Same cohort; n = 29/30 per arm	As above: 200 mL green tea kombucha/day + energy-restricted diet vs. diet alone	10 weeks	↓ Plasma H₂O₂ in kombucha group vs. control (p = 0.007): kombucha 18.14 → 14.67 µmol/mL; control 16.50 → 15.09 µmol/mL. No significant between-group differences in any other oxidative stress or endothelial health markers.	Same cohort limitations; only one of multiple oxidative stress markers showed significant intergroup difference; endothelial markers unaffected; open-label; single GTK product	[33]

Abbreviations: RCT = randomised controlled trial; GI = glycaemic index; HbA1c = glycated haemoglobin; TC = total cholesterol; LDL-c = low-density lipoprotein cholesterol; VLDL-c = very low-density lipoprotein cholesterol; TG = triglycerides; L/M ratio = lactulose/mannitol ratio (intestinal permeability marker); GSRS = Gastrointestinal Symptom Rating Scale; FDR = false discovery rate; GTK = green tea kombucha; H₂O₂ = hydrogen peroxide; BMI = body mass index; DB = double-blind; NS = not significant. All trials used green or fermented tea-based kombucha. The Bonifácio/Fraiz 2024–26 studies are subseries of the same cohort (Brazilian adults with excess body weight, Universidade Federal de Viçosa). Sample sizes: Atkinson et al. n = 11; Mendelson et al. n = 12 (crossover); Bonifácio/Fraiz series n = 29/30 per arm.

Table 2. Summary of human randomised controlled trials of kombucha: study design, population, intervention, outcomes, and limitations.

Study (year)	Design	Population	Intervention	Duration	Key outcomes	Limitations	Ref
Atkinson et al. (2023) [31]	Randomised, placebo-controlled, crossover	Healthy adults; n = 11	330 mL of live (unpasteurised) kombucha, diet lemonade soft drink, or soda water (control) consumed with a standardised high-GI Jasmine rice meal; three conditions tested in crossover sequence	Single acute meal	↓ Glycaemic index from 86 (soda water) to 68 with live kombucha (p = 0.041); ↓ insulin index from 85 to 70 (p = 0.041); no significant difference between soda water and diet lemonade; suggests live microbial/polyphenol components drive the effect beyond pH or acidity alone	Very small sample (n = 11); single-meal acute design; no chronic follow-up; mechanism not directly investigated; healthy population limits generalisability to metabolic disease	[31]
Mendelson et al. (2023) [32]	Randomised, double-blind, placebo-controlled crossover pilot	Adults with type 2 diabetes mellitus; n = 12	240 mL kombucha/day vs. matched placebo beverage; crossover with 8-week washout period between arms	4 weeks per arm	↓ Fasting blood glucose in kombucha period: 164 → 116 mg/dL (p = 0.035); placebo period: 162 → 141 mg/dL (p = 0.078, NS); note: 2 participants with well-controlled baseline glucose showed slight increases that remained within normal range	Very small sample (n = 12); underpowered for HbA1c and other secondary outcomes; short duration; single commercially donated kombucha product; two participants with well-controlled baseline glucose confound mean estimates	[32]
Bonifácio et al. (2026) [14] Cardiometabolic RCT	Open-label, parallel-arm RCT	Adults with excess body weight (BMI >27 kg/m²), no chronic disease; n = 29 (control), 30 (kombucha)	200 mL green tea kombucha/day + −500 kcal/day energy-restricted diet vs. energy-restricted diet alone	10 weeks	Kombucha group (intragroup): ↓ TC (p = 0.024), ↓ LDL-c (p = 0.035), ↓ VLDL-c (p = 0.011), ↓ TG (p = 0.012), ↓ Castelli index II (p = 0.002), ↓ uric acid (p = 0.027). Men in kombucha group: ↓ HbA1c vs. control (p = 0.010). Control only: ↑ HbA1c (within normal range). No statistically significant intergroup differences in Δ values for any marker.	Open-label design (no blinding); Brazilian adult cohort limits generalisability; small n; no power for between-group lipid significance; single GTK product; energy-restricted diet in both arms makes kombucha-specific attribution difficult	[14]
Fraiz et al. (2024) [15] Intestinal health & metabolomics RCT	Open-label, parallel-arm RCT (substudy of above cohort)	Same cohort as Bonifácio et al. 2026; n = 29/30 per arm	As above: 200 mL green tea kombucha/day + energy-restricted diet vs. diet alone	10 weeks	Kombucha group: ↓ Total GSRS score (p = 0.035), ↓ reflux (p = 0.043), ↓ hard stools (p = 0.001), ↓ incomplete bowel emptying (p = 0.027). Control group only: ↑ L/M ratio (p = 0.019), ↑ fecal pH (p = 0.004), ↑ zonulin (p = 0.031). Discriminant serum metabolites in kombucha group only: taurine, diethyl malonate, asperuloside, and several tripeptides with anti-obesity and antioxidant properties.	Same limitations as above; insufficient biological samples for LBP and zonulin analysis in full cohort; no significant microbiota differences after FDR adjustment; metabolomics identifications are putative; small sample size for metabolome analysis	[15]
Bonifácio et al. (2025) [33] Oxidative stress RCT	Open-label, parallel-arm RCT (substudy of same programme)	Same cohort; n = 29/30 per arm	As above: 200 mL green tea kombucha/day + energy-restricted diet vs. diet alone	10 weeks	↓ Plasma H₂O₂ in kombucha group vs. control (p = 0.007): kombucha 18.14 → 14.67 µmol/mL; control 16.50 → 15.09 µmol/mL. No significant between-group differences in any other oxidative stress or endothelial health markers.	Same cohort limitations; only one of multiple oxidative stress markers showed significant intergroup difference; endothelial markers unaffected; open-label; single GTK product	[33]

Abbreviations: RCT = randomised controlled trial; GI = glycaemic index; HbA1c = glycated haemoglobin; TC = total cholesterol; LDL-c = low-density lipoprotein cholesterol; VLDL-c = very low-density lipoprotein cholesterol; TG = triglycerides; L/M ratio = lactulose/mannitol ratio (intestinal permeability marker); GSRS = Gastrointestinal Symptom Rating Scale; FDR = false discovery rate; GTK = green tea kombucha; H₂O₂ = hydrogen peroxide; BMI = body mass index; DB = double-blind; NS = not significant. All trials used green or fermented tea-based kombucha. The Bonifácio/Fraiz 2024–26 studies are subseries of the same cohort (Brazilian adults with excess body weight, Universidade Federal de Viçosa). Sample sizes: Atkinson et al. n = 11; Mendelson et al. n = 12 (crossover); Bonifácio/Fraiz series n = 29/30 per arm.

Table 3. Sensory properties of kombucha: fermentation origin, key compounds, modifiable determinants, and consumer impact.

Sensory attribute	Fermentation origin	Key compounds responsible	Modifiable by	Consumer impact and acceptance
Sourness / tartness	Organic acid production by acetic acid bacteria and yeast; pH drops from ~5.5 to 3.0–3.5 over fermentation	Acetic acid (dominant), gluconic acid, lactic acid, citric acid, malic acid	Fermentation duration (longer = more acidic); temperature (higher = faster acidification); SCOBY inoculation rate; sugar concentration	Key driver of consumer liking; optimal balance (pH 3.0–3.5) preferred; excess acidity significantly reduces acceptance; lower temperature fermentation produces preferred acidity balance [25]
Sweetness	Residual sucrose and simple sugars not fully consumed during fermentation; secondary fermentation additions (fruit juices, flavourings)	Sucrose, glucose, fructose (residual); added fruit sugars in flavoured varieties	Initial sucrose concentration; fermentation duration (longer = lower residual sugar); secondary fermentation flavour additions (fruit juices, honey, agave)	Critical counterbalance to sourness; flavoured varieties (around 80% of global sales) use secondary additions to optimise sweet-sour balance; reducing sugar for health guidelines can alter balance requiring compensatory adjustments [25]
Spicy / pungent	Not a product of primary tea fermentation; introduced entirely through secondary fermentation additions — herbs, spices, and botanical infusions added to the base kombucha after primary fermentation	Gingerols and shogaols (ginger); piperine (black pepper); capsaicin (chilli); allicin (garlic); menthol and carvacrol (mint and herbs); eugenol (cloves)	Secondary fermentation additions: ginger (most common), chilli, black pepper, turmeric, herbs (mint, basil, lemongrass), or botanical extracts; spice concentration, contact time, and temperature during secondary fermentation determine intensity	Strong driver of product differentiation and consumer novelty; ginger kombucha is consistently among the best-selling commercial variants globally; spice additions add warmth, complexity, and heat that broaden appeal and mask excessive sourness; relevant anti-inflammatory (gingerols) and antimicrobial (allicin, carvacrol) properties are additive to kombucha's own bioactive profile [16,24]
Bitterness / astringency	Derived from tea polyphenols (tannins, catechins, caffeine) in the substrate; partially reduced during fermentation through tannin depolymerisation by SCOBY-secreted tannase and glycosidase enzymes; caffeine contributes bitterness independently	Condensed tannins, catechins (EGCG, ECG), gallic acid, caffeine; caffeine is not substantially reduced by fermentation	Tea type and concentration (black tea > green tea astringency at equal concentration); fermentation duration (longer fermentation reduces tannin-derived astringency); tannase enzyme activity of SCOBY strains; caffeine content of base tea	Mild astringency perceived as pleasant by regular kombucha consumers; excessive astringency (from high-tannin black tea at short fermentation) associated with lower acceptance; fermentation reduces tannin-derived harshness but does not substantially reduce caffeine-derived bitterness; important for caffeine-sensitive consumers [16,24]
Umami	Derived from free amino acids released during microbial proteolysis and autolysis, particularly glutamic acid and aspartic acid from tea proteins; also contributed by L-Theanine (amino acid naturally present in tea) which may exhibit umami-adjacent glutamate-like qualities at higher concentrations; certain yeasts contribute nucleotide degradation products (IMP, GMP) with umami-potentiating properties	Glutamic acid, aspartic acid, L-Theanine; nucleotides (inosine 5′-monophosphate, guanosine 5′-monophosphate from yeast autolysis); 5-L-Glutamyl-L-alanine (a discriminant serum metabolite identified in the Fraiz et al. 2024 RCT, detected in the kombucha group after intervention)	Tea type and protein content; SCOBY microbial composition and protease activity; fermentation duration (longer fermentation → ↑ free amino acids); yeast autolysis extent; secondary additions (miso, seaweed-based flavourings in some artisan formulations)	Umami in kombucha is subtle compared to purpose-fermented umami foods (soy sauce, aged cheese); contributes to the perception of depth, roundness, and complexity that distinguishes well-fermented kombucha from a simple acidic beverage; L-Theanine may add a smooth, savoury quality especially in green tea kombucha — potentially contributing to perceived 'body'; the presence of 5-L-Glutamyl-L-alanine as a serum metabolite unique to the kombucha group in the Fraiz et al. 2024 RCT suggests systemic absorption of amino acid fermentation products [15,28]
Saltiness	Mineral ions (sodium, potassium, magnesium, calcium) extracted from tea leaves and source water during brewing; mineral salts are not produced by fermentation per se but concentrations are modified by the ionic environment of the acidic kombucha matrix; organic acid anions paired with mineral cations create salts that contribute a mild electrolyte character	Sodium ions (Na⁺), potassium ions (K⁺), magnesium ions (Mg²⁺), calcium ions (Ca²⁺); chloride (Cl⁻) from source water; potassium acetate, potassium gluconate, and other organic acid mineral salts formed in the acidic fermentation environment	Source water mineral content (hard water → ↑ calcium, magnesium); tea leaf mineral content; fermentation duration (longer fermentation → greater mineral extraction from SCOBY biomass); secondary additions (sea salt added in some commercial 'electrolyte kombucha' formulations)	Saltiness in standard kombucha is very low and typically imperceptible as a discrete sensation; at trace levels, mineral ions contribute to perceived mouthfeel fullness and electrolyte roundness rather than overt saltiness; electrolyte content supports the beverage's positioning as a functional hydration alternative; some commercial producers explicitly add electrolytes (sodium, potassium, magnesium) for post-exercise or sports recovery positioning, making saltiness a more prominent, intentional sensory attribute in those products [29,38,40]
Aroma / fragrance	Volatile compound production by yeast metabolism: esters, higher alcohols, aldehydes (partially degraded), ketones; tea-derived volatile terpenoids from substrate	Ethyl acetate, isoamyl alcohol, acetaldehyde (degraded), ethyl hexanoate, linalool (tea terpenoid), diethyl malonate	Yeast strain composition; fermentation temperature; tea substrate (green vs. black vs. oolong); secondary fermentation additions (fruit, herbs, spices)	Aroma complexity and fruity/floral notes are major drivers of positive consumer response; perceived as refreshing and distinctive; differentiates kombucha from plain fermented vinegar; central to brand differentiation in the commercial market [11,24]
Effervescence	CO₂ produced by yeast metabolism during primary and secondary fermentation; retained in sealed packaging or generated on draught	Carbon dioxide (CO₂) produced stoichiometrically with ethanol from glucose/fructose by yeast	Secondary fermentation conditions (added sugar/juice, sealed vessel, temperature); carbonation can also be added artificially in commercial production	Light sparkling mouthfeel analogous to carbonated soft drinks is a key consumer appeal feature, especially for SSB replacement; contributes to perceived freshness and palatability; strong differentiator from plain tea [24]
Colour	Derived from tea substrate; modified by fermentation-induced polyphenol oxidation and tannin transformations; additional colour from secondary fermentation flavourings	Theaflavins, thearubigins (black tea — amber to reddish-brown); catechins and chlorophyll (green tea — pale gold to amber); anthocyanins (berry additions — pink/red)	Tea type (black tea darker than green tea); fermentation duration; secondary flavour additions; pH (anthocyanins shift colour with pH)	Visual appeal important for first purchase decision; amber/golden colour associated with quality and naturalness; innovative colours from botanical additions drive product differentiation and social media appeal [26,27]

Abbreviations: SSB = sugar-sweetened beverage; EGCG = epigallocatechin-3-gallate; ECG = epicatechin gallate; CO₂ = carbon dioxide; ABV = alcohol by volume; IMP = inosine 5′-monophosphate; GMP = guanosine 5′-monophosphate. Reference numbers correspond to the manuscript reference list. Consumer acceptance data are drawn from published sensory studies; individual preferences vary and flavour profiles are highly product- and producer-specific. 'Secondary fermentation' refers to the bottling phase during which additional flavourings (fruit juices, herbs, spices) may be added and CO₂ generation continues in sealed vessels. The six taste dimensions (sourness, sweetness, spicy/pungent, bitterness/astringency, umami, and saltiness) are presented alongside aroma, effervescence, and colour as the full sensory architecture of kombucha. Spicy/pungent and umami are not products of primary fermentation but arise from secondary additions and amino acid liberation respectively. Saltiness is typically at sub-threshold levels in standard kombucha but may be elevated in electrolyte-fortified commercial products.

Table 3. Sensory properties of kombucha: fermentation origin, key compounds, modifiable determinants, and consumer impact.

Sensory attribute	Fermentation origin	Key compounds responsible	Modifiable by	Consumer impact and acceptance
Sourness / tartness	Organic acid production by acetic acid bacteria and yeast; pH drops from ~5.5 to 3.0–3.5 over fermentation	Acetic acid (dominant), gluconic acid, lactic acid, citric acid, malic acid	Fermentation duration (longer = more acidic); temperature (higher = faster acidification); SCOBY inoculation rate; sugar concentration	Key driver of consumer liking; optimal balance (pH 3.0–3.5) preferred; excess acidity significantly reduces acceptance; lower temperature fermentation produces preferred acidity balance [25]
Sweetness	Residual sucrose and simple sugars not fully consumed during fermentation; secondary fermentation additions (fruit juices, flavourings)	Sucrose, glucose, fructose (residual); added fruit sugars in flavoured varieties	Initial sucrose concentration; fermentation duration (longer = lower residual sugar); secondary fermentation flavour additions (fruit juices, honey, agave)	Critical counterbalance to sourness; flavoured varieties (around 80% of global sales) use secondary additions to optimise sweet-sour balance; reducing sugar for health guidelines can alter balance requiring compensatory adjustments [25]
Spicy / pungent	Not a product of primary tea fermentation; introduced entirely through secondary fermentation additions — herbs, spices, and botanical infusions added to the base kombucha after primary fermentation	Gingerols and shogaols (ginger); piperine (black pepper); capsaicin (chilli); allicin (garlic); menthol and carvacrol (mint and herbs); eugenol (cloves)	Secondary fermentation additions: ginger (most common), chilli, black pepper, turmeric, herbs (mint, basil, lemongrass), or botanical extracts; spice concentration, contact time, and temperature during secondary fermentation determine intensity	Strong driver of product differentiation and consumer novelty; ginger kombucha is consistently among the best-selling commercial variants globally; spice additions add warmth, complexity, and heat that broaden appeal and mask excessive sourness; relevant anti-inflammatory (gingerols) and antimicrobial (allicin, carvacrol) properties are additive to kombucha's own bioactive profile [16,24]
Bitterness / astringency	Derived from tea polyphenols (tannins, catechins, caffeine) in the substrate; partially reduced during fermentation through tannin depolymerisation by SCOBY-secreted tannase and glycosidase enzymes; caffeine contributes bitterness independently	Condensed tannins, catechins (EGCG, ECG), gallic acid, caffeine; caffeine is not substantially reduced by fermentation	Tea type and concentration (black tea > green tea astringency at equal concentration); fermentation duration (longer fermentation reduces tannin-derived astringency); tannase enzyme activity of SCOBY strains; caffeine content of base tea	Mild astringency perceived as pleasant by regular kombucha consumers; excessive astringency (from high-tannin black tea at short fermentation) associated with lower acceptance; fermentation reduces tannin-derived harshness but does not substantially reduce caffeine-derived bitterness; important for caffeine-sensitive consumers [16,24]
Umami	Derived from free amino acids released during microbial proteolysis and autolysis, particularly glutamic acid and aspartic acid from tea proteins; also contributed by L-Theanine (amino acid naturally present in tea) which may exhibit umami-adjacent glutamate-like qualities at higher concentrations; certain yeasts contribute nucleotide degradation products (IMP, GMP) with umami-potentiating properties	Glutamic acid, aspartic acid, L-Theanine; nucleotides (inosine 5′-monophosphate, guanosine 5′-monophosphate from yeast autolysis); 5-L-Glutamyl-L-alanine (a discriminant serum metabolite identified in the Fraiz et al. 2024 RCT, detected in the kombucha group after intervention)	Tea type and protein content; SCOBY microbial composition and protease activity; fermentation duration (longer fermentation → ↑ free amino acids); yeast autolysis extent; secondary additions (miso, seaweed-based flavourings in some artisan formulations)	Umami in kombucha is subtle compared to purpose-fermented umami foods (soy sauce, aged cheese); contributes to the perception of depth, roundness, and complexity that distinguishes well-fermented kombucha from a simple acidic beverage; L-Theanine may add a smooth, savoury quality especially in green tea kombucha — potentially contributing to perceived 'body'; the presence of 5-L-Glutamyl-L-alanine as a serum metabolite unique to the kombucha group in the Fraiz et al. 2024 RCT suggests systemic absorption of amino acid fermentation products [15,28]
Saltiness	Mineral ions (sodium, potassium, magnesium, calcium) extracted from tea leaves and source water during brewing; mineral salts are not produced by fermentation per se but concentrations are modified by the ionic environment of the acidic kombucha matrix; organic acid anions paired with mineral cations create salts that contribute a mild electrolyte character	Sodium ions (Na⁺), potassium ions (K⁺), magnesium ions (Mg²⁺), calcium ions (Ca²⁺); chloride (Cl⁻) from source water; potassium acetate, potassium gluconate, and other organic acid mineral salts formed in the acidic fermentation environment	Source water mineral content (hard water → ↑ calcium, magnesium); tea leaf mineral content; fermentation duration (longer fermentation → greater mineral extraction from SCOBY biomass); secondary additions (sea salt added in some commercial 'electrolyte kombucha' formulations)	Saltiness in standard kombucha is very low and typically imperceptible as a discrete sensation; at trace levels, mineral ions contribute to perceived mouthfeel fullness and electrolyte roundness rather than overt saltiness; electrolyte content supports the beverage's positioning as a functional hydration alternative; some commercial producers explicitly add electrolytes (sodium, potassium, magnesium) for post-exercise or sports recovery positioning, making saltiness a more prominent, intentional sensory attribute in those products [29,38,40]
Aroma / fragrance	Volatile compound production by yeast metabolism: esters, higher alcohols, aldehydes (partially degraded), ketones; tea-derived volatile terpenoids from substrate	Ethyl acetate, isoamyl alcohol, acetaldehyde (degraded), ethyl hexanoate, linalool (tea terpenoid), diethyl malonate	Yeast strain composition; fermentation temperature; tea substrate (green vs. black vs. oolong); secondary fermentation additions (fruit, herbs, spices)	Aroma complexity and fruity/floral notes are major drivers of positive consumer response; perceived as refreshing and distinctive; differentiates kombucha from plain fermented vinegar; central to brand differentiation in the commercial market [11,24]
Effervescence	CO₂ produced by yeast metabolism during primary and secondary fermentation; retained in sealed packaging or generated on draught	Carbon dioxide (CO₂) produced stoichiometrically with ethanol from glucose/fructose by yeast	Secondary fermentation conditions (added sugar/juice, sealed vessel, temperature); carbonation can also be added artificially in commercial production	Light sparkling mouthfeel analogous to carbonated soft drinks is a key consumer appeal feature, especially for SSB replacement; contributes to perceived freshness and palatability; strong differentiator from plain tea [24]
Colour	Derived from tea substrate; modified by fermentation-induced polyphenol oxidation and tannin transformations; additional colour from secondary fermentation flavourings	Theaflavins, thearubigins (black tea — amber to reddish-brown); catechins and chlorophyll (green tea — pale gold to amber); anthocyanins (berry additions — pink/red)	Tea type (black tea darker than green tea); fermentation duration; secondary flavour additions; pH (anthocyanins shift colour with pH)	Visual appeal important for first purchase decision; amber/golden colour associated with quality and naturalness; innovative colours from botanical additions drive product differentiation and social media appeal [26,27]

Abbreviations: SSB = sugar-sweetened beverage; EGCG = epigallocatechin-3-gallate; ECG = epicatechin gallate; CO₂ = carbon dioxide; ABV = alcohol by volume; IMP = inosine 5′-monophosphate; GMP = guanosine 5′-monophosphate. Reference numbers correspond to the manuscript reference list. Consumer acceptance data are drawn from published sensory studies; individual preferences vary and flavour profiles are highly product- and producer-specific. 'Secondary fermentation' refers to the bottling phase during which additional flavourings (fruit juices, herbs, spices) may be added and CO₂ generation continues in sealed vessels. The six taste dimensions (sourness, sweetness, spicy/pungent, bitterness/astringency, umami, and saltiness) are presented alongside aroma, effervescence, and colour as the full sensory architecture of kombucha. Spicy/pungent and umami are not products of primary fermentation but arise from secondary additions and amino acid liberation respectively. Saltiness is typically at sub-threshold levels in standard kombucha but may be elevated in electrolyte-fortified commercial products.

6. Mechanisms of Action

The cardiometabolic effects of kombucha are likely mediated through multiple, interacting pathways arising from its diverse bioactive components (summarised in Table 1). Organic acids, particularly acetic acid, inhibit carbohydrate-digesting enzymes while improving insulin sensitivity [35,36]. Glucuronic acid, produced during fermentation, may conjugate with phenolic compounds, enhancing their bioavailability [14].

The polyphenols present in tea undergo transformation during fermentation, generating additional metabolites with antioxidant, anti-inflammatory, and metabolic effects [34,37]. In the clinical studies reviewed, these compounds may account for the observed reductions in lipid markers, uric acid, and H₂O₂. Notably, microbial biotransformation not only enhances polyphenol bioactivity but also modulates the sensory properties of the beverage, reducing astringency and bitterness through tannin depolymerisation, as discussed in Section 4.

The microbial components of kombucha may indirectly influence host metabolism through gut microbiota interactions. In the Fraiz et al. [15] trial, discriminant metabolites including taurine and diethyl malonate correlated with specific microbiota changes, suggesting that kombucha reshapes the host metabolome in clinically meaningful ways. These mechanisms are unlikely to act independently, representing a synergistic system in which organic acids, polyphenols, and live microbial metabolites produce emergent biological effects.

7. Kombucha Versus Sugar-Sweetened Beverages

SSBs typically contain high levels of rapidly absorbable sugars without fibre or bioactive compounds, leading to rapid postprandial glycaemic and insulinaemic responses and contributing to metabolic syndrome, obesity, type 2 diabetes, and cardiovascular disease [6]. Compared with these beverages, kombucha may offer a more favourable metabolic profile, given its evidence for attenuating postprandial glycaemia [31], improving lipid markers [14], and reducing pro-oxidant burden [33]. Crucially, kombucha's sensory complexity—its effervescence, mild acidity, residual sweetness, and flavour variety—provides a consumer experience comparable to carbonated soft drinks, making it a genuinely appealing and sustainable alternative for consumers seeking to reduce SSB intake. Many commercial products are available in a wide range of fruit and botanical flavours, broadening their appeal across age groups and cultural contexts [24].

However, any public health interpretation must remain product-specific. Many commercial kombuchas have been pasteurised, potentially eliminating the live microbial constituents implicated in health effects, and sugar content varies widely across products. From a population health perspective, replacing SSBs with fermented alternatives such as kombucha may reduce glycaemic load and improve metabolic outcomes at scale [8], a hypothesis supported by emerging clinical evidence but requiring further investigation.

8. Hydration, Electrolytes, and Recovery Physiology

Hydration and electrolyte balance are critical for maintaining physiological homeostasis, particularly during physical activity and heat exposure [38,39]. Electrolytes such as sodium, potassium, and magnesium are essential for cellular function, neuromuscular activity, and glucose transport [40]. Kombucha contains organic acids, trace minerals, and bioactive compounds and its composition and palatability suggest potential utility as a functional hydration beverage that may support hydration and recovery. Yet, its ability to confer meaningful hydration benefit in humans is currently untested and warrants formal investigation.

9. Cultural and Public Health Implications

Kombucha's cultural relevance is intertwined with its sensory identity. Fermentation is a universal practice embedded in food heritage, intergenerational knowledge, and local microbial ecologies across virtually all human cultures [4]. Because kombucha begins with tea, one of the most culturally universal of all beverages [3], it carries a particular resonance across Asian, Middle Eastern, European, and African cultures where tea is already central to daily life. The global spread of kombucha reflects both renewed consumer interest in tradition and fermentation culture, and the sensory appeal of a novel, health-oriented beverage with perceived functionality. This cultural dimension may help explain both the beverage's rapid global adoption and its strong positioning within microbiome-oriented wellness narratives [5].

Kombucha also represents a form of intergenerational microbial transmission, in which SCOBY cultures are shared and propagated, linking human culture with microbial ecology [10]. This practice reflects broader interactions between human behaviour and microbial environments and positions kombucha not only as a health product but as a participatory cultural artifact.

10. Limitations

Despite the emerging body of clinical evidence, several limitations must be acknowledged. First, while three new RCTs [14,15,33] substantially advance the field, all were conducted in the same cohort of Brazilian adults with excess body weight using the same green tea kombucha preparation. Generalisability to other populations, age groups, health conditions, and kombucha formulations remains uncertain. Second, all cardiometabolic RCTs were open-label, introducing risk of performance and detection bias. Third, sample sizes (n ≈ 29–30 per group) and 10-week durations were insufficient to detect modest between-group differences for several outcomes and did not provide adequate power to establish clinical efficacy. Fourth, kombucha products vary substantially in their polyphenol profiles, organic acid composition, microbial content, sugar content, and flavouring, making extrapolation across products difficult [12]. Fifth, the optimal dosage for therapeutic effects remains undefined [14]. Sixth, pasteurisation of many commercial products likely eliminates or substantially reduces live microbial components, meaning that the health effects documented in research using live kombucha may not be replicated by commercial products.

10.1. Safety Considerations and Undesirable Compounds

A balanced evaluation of kombucha must consider not only its potential benefits but also its potential risks and undesirable components, yet, the absence of standardised composition across commercial products, particularly for alcohol content, sugar content, viable microbial counts, and organic acid profiles, makes it difficult for consumers, clinicians, and researchers to make informed assessments of any specific product.

Alcohol is an inherent product of yeast fermentation in kombucha and represents one of the most significant regulatory and safety considerations. Live-culture kombucha typically contains between 0.5% and 3% alcohol by volume (ABV) at the point of production, with continued post-bottling fermentation capable of increasing this further if products are stored at ambient temperatures or for extended periods. Under the Australia New Zealand Food Standards Code (Standard 2.6.2), beverages containing more than 0.5% ABV are classified as alcoholic and require appropriate labelling and regulatory oversight. Many commercially available kombuchas are formulated or pasteurised to remain below this threshold, but product variability is substantial and consumer awareness of alcohol content is often low. It is worth noting that many everyday foods naturally contain comparable trace levels of alcohol as a consequence of fermentation or ripening, including ripe bananas (0.4–0.9% ABV), fresh fruit juices (0.1–0.5% ABV), and some bread and bakery products, providing regulatory and biological context for the 0.5% threshold. Producing genuinely low-alcohol, low-sugar kombucha presents significant technical challenges. Within conventional production parameters, reducing residual sugar necessarily reduces the substrate available for carbonation and flavour development, while reducing alcohol requires careful management of fermentation duration, temperature, and microbial ecology. One approach is to allow fermentation to proceed to completion, until all fermentable sugars and ethanol are consumed by the acetic acid bacteria, yielding an alcohol-free and sugar-free probiotic base that can be carbonated naturally or sweetened with non-fermentable sweeteners such as monk fruit extract, stevia, erythritol, or xylitol, or sweetened with small amounts of sugar to produce natural carbonation without exceeding 0.5% ABV. Alternatively, pasteurisation arrests fermentation at a defined point but at the cost of viable microbial populations.

Beyond alcohol, several other safety considerations warrant attention. The high organic acid content of kombucha (pH typically 2.5–3.5) poses a theoretical risk of dental erosion with frequent consumption, particularly when consumed without dilution or between meals, and may cause gastrointestinal discomfort in sensitive individuals. Home-brewed kombucha, produced without the quality controls of commercial production, carries additional risks of contamination by pathogenic fungi or bacteria if the SCOBY culture is unhealthy or the fermentation environment is compromised. Rare but serious adverse events have been reported in the medical literature following excessive kombucha consumption, including hepatotoxicity and lactic acidosis, though these are predominantly associated with very high intake volumes or compromised home-brew preparations. Kombucha should therefore be approached with caution by immunocompromised individuals, pregnant women, those with alcohol sensitivities or liver disease, and those taking medications that interact with alcohol or acetic acid.

11. Future Implications

Future research is required to establish whether kombucha’s observed health associations represent genuine causal effects and to define the product characteristics, doses, and population subgroups most likely to benefit. Such research should prioritise larger, longer-term, blinded randomised controlled trials with standardised product definitions, diverse populations, and direct comparisons between live and pasteurised products. Studies are also required to examine whether the observed effects on glycaemia, lipids, oxidative stress, and gastrointestinal health are driven primarily by organic acids, polyphenols, live microbial metabolites, or their interactions, and whether effects differ between live and pasteurised products, which is critical for translating research findings to commercial products. Standardised composition reporting, including alcohol content, organic acid profile, total phenolics, and viable microbial counts, should be mandated for future trials to allow meaningful comparison across studies. Sensory research is also needed to assess whether flavour preferences and product acceptability affect long-term adherence and, in turn, health outcomes.

The serum metabolomics findings from Fraiz et al. [15] represent a particularly promising avenue for identifying novel biomarkers of kombucha response and elucidating systemic effects. From a public health standpoint, kombucha may be most useful as a lower-glycaemic, antioxidant-rich, and sensorially appealing substitute for SSBs, particularly for populations with elevated cardiometabolic risk. Its scalability, low cost, adaptability to diverse flavour preferences, and basis in the world's most widely consumed beverage after water make it a compelling candidate for population-level dietary strategies. Until stronger evidence is available, kombucha should be described as a promising functional fermented beverage with plausible cardiometabolic benefits, not as a proven therapeutic agent.

12. Conclusions

Kombucha integrates traditional fermentation practices with modern scientific insights and represents a promising functional beverage with a growing clinical evidence base. Beginning with tea, the world's most widely consumed beverage after water, fermentation transforms the sensory profile of the base infusion through the production of organic acids, the biotransformation of tannins and polyphenols, the generation of trace ethanol and volatile esters, and through the commercial addition of sugars and flavourings. The resulting beverage has a distinctive, complex, and widely appealing sensory character that has driven its rapid global adoption and positions it as a credible and acceptable alternative to sugar-sweetened beverages.

Emerging clinical evidence suggests that kombucha may also offer meaningful cardiometabolic benefits, including improvements in lipid profile, glycaemic regulation, oxidative stress markers, and gastrointestinal health. These effects are mechanistically plausible given the beverage's organic acid, polyphenol, and live microbial content. Continued rigorous investigation of its composition, mechanisms, sensory properties, and population-level effects will be essential to establish kombucha's role within evidence-based dietary recommendations and preventive healthcare strategies.