Biochemistry of kombucha

During fermentation, your sweet tea transforms into a lively kombucha full of organic acids, vitamins, and antioxidants. Sugar is consumed, tea flavors evolve, and hundreds of organic compounds are formed — substances that together shape the aroma, flavor, freshness, and potential health effects of your kombucha.
In this article, you’ll learn how yeasts and bacteria work together, why every batch is unique, and which compounds may have effects in the body.

Ready, set... brew!

The basics of kombucha are simple: tea, sugar (or honey for Jun), water, and a living culture (the SCOBY). But the exact type of tea you use [1] and how much sugar you add largely determine what ends up in your drink.

Tea — black, green, or white — naturally contains plant compounds (flavonoids and polyphenols) that change during fermentation. Some break down into smaller pieces; others transform into more stable or more soluble variants. This makes the flavor softer, more complex, and may increase the antioxidant capacity of the drink.

During fermentation, your kombucha is constantly evolving. In the beginning, it contains mostly sugar and polyphenols extracted from tea. After a few days, dozens to hundreds of new compounds begin to appear [1–4].
Bacteria convert sugars into acids, and yeasts convert sugars into alcohol and carbon dioxide (COâ‚‚). The alcohol produced by yeasts is then further converted into acids by the bacteria, giving the drink its fresh acidity and helping preserve it [2, 4].
These processes are similar to how vinegar is made — the difference is that in kombucha, these conversions happen at the same time.

Microbes also produce vitamins and release volatile compounds that contribute to aroma [2, 4]. Altogether, this results in a rich mixture of more than 400 different compounds.

The exact balance depends on factors like temperature, fermentation time and sugar concentration. A 2024 study showed that fermenting at 20°C with 100 g/L sugar resulted in the highest levels of bioactive compounds [3].

Below, we summarize which compounds you can expect in your drink.

Bioactive compounds in kombucha

Although kombucha is not an officially recognized probiotic, it is rich in bioactive compounds — substances produced by the microbes in your SCOBY that may have beneficial effects on the body.
They originate from the sugars, tea extracts (polyphenols, amino acids, minerals), and the breakdown of the microbes themselves. Microorganisms live only briefly: once they die, they serve as building blocks for the next generations.
Step by step, yeasts and bacteria convert these building blocks into aromas, acids, vitamins, and more.

1. Organic acids

Organic acids are the main end products of fermentation. They make kombucha tangy, stable, and easy to digest.
Some of the most common are acetic acid, gluconic acid, succinic acid, and glucuronic acid [1–6], formed when bacteria convert sugars and alcohol.

  • Acetic acid contributes most to the sour taste and has antibacterial effects. In mice, it supports lower blood glucose in hyperglycaemia, improves insulin sensitivity, and may improve mitochondrial function [1].

  • Gluconic acid has antibacterial properties [1].

  • Succinic acid shows activity against Salmonella [1].

  • Glucuronic acid is linked to detoxification processes in the liver, helping bind and eliminate waste products. It is also involved in the production of vitamin C, supports insulin sensitivity, and has antibacterial activity. The highest glucuronic acid levels were found in kombucha made from white tea [1, 4].

2. Polyphenols

Polyphenols are plant compounds naturally present in tea (such as catechins and theaflavins) that contribute to kombucha’s bioactive properties. During fermentation, microbes break down these larger molecules into smaller, more absorbable ones.

  • Gallic acid and similar phenolic acids act as powerful antioxidants. They neutralize free radicals produced during metabolism and may help protect cells from oxidative stress. Phenols are also known for anti-inflammatory effects [1].

  • Flavonoids are also found in kombucha, most abundant in black-tea kombucha, followed by green and white tea. Flavonoids show anti-inflammatory, antioxidant, neuroprotective and even anti-cancer properties. Flavonoid intake is linked to reduced risk of chronic diseases such as diabetes, cancer, and cardiovascular disease [1, 3].

3. Alcohols, esters & aromatic volatiles

During fermentation, up to 28 aroma compounds develop. These volatile molecules (esters, aldehydes, ketones, and higher alcohols) are responsible for kombucha’s fragrance and flavor — ranging from exotic fruit and marzipan to spicy, grassy, or floral notes.
Which aromas appear depends on the tea you use, how the fermentation progresses, and can even vary between SCOBYs [2, 4].

4. Vitamins

During fermentation, microbes produce small amounts of B vitamins (B1, B2, B5, B6, B12) and vitamin C [4, 7].

  • B vitamins support energy metabolism and enzymatic processes.

  • Vitamin C supports immune function and acts as an antioxidant.

5. Unidentified metabolites

Thanks to modern analysis techniques, we now know kombucha is even more complex than expected: researchers have found more than thirty unknown compounds, whose roles are still being investigated [3].

Changes in microbes and flavor

The type of tea you start with seems to influence the composition of the final drink. A 2025 study found the highest glucuronic acid levels in white-tea kombucha. Both white- and green-tea kombucha contained high levels of antioxidants. Additionally, kombucha has been shown to inhibit the growth of various pathogenic bacteria such as E. coli, Salmonella, and Vibrio cholerae. Green-tea kombucha reduced inflammation markers in in-vitro studies by lowering the production of nitric oxide (NO), a compound released during inflammation. Acetic acid, DSL, citric acid, glucuronic acid, and total phenol content were particularly important in these antioxidant and anti-inflammatory effects.

Home-brew vs commercial

Home-brewed kombucha typically contains a richer microbial ecosystem than commercial versions, which are often filtered or pasteurized for stability and shelf life [5].
This means homemade kombucha usually contains a more vibrant living culture and a broader spectrum of metabolites — but good hygiene is essential to prevent contamination.

Limits of current research

What begins as sweet tea becomes a fresh, tangy drink full of natural acids, vitamins, antioxidants, and aromas. Much of what we know about kombucha still comes from laboratory and animal research. Few studies have been conducted in humans, and kombucha composition varies by brand, brewer, and even individual batch. As a result, we don’t yet know precisely how these compounds act in the body or how much is absorbed.

What is clear: the natural acids in foods and drinks help maintain a healthy pH balance in the gastrointestinal system and may help inhibit unwanted bacteria.

With modern analytical tools, researchers are mapping kombucha in increasing detail — more than 400 compounds, including over 30 entirely new ones, have been identified so far. Their full relevance for human health still needs further investigation.

At BiomeBrew we believe that sharing knowledge begins with reliable and traceable information. Our articles are based on recent scientific literature and, where possible, include references. We aim to translate complex research into accessible language — without exaggeration or poorly supported health claims.
That way, you can trust that what you read is accurate.