Biochemistry of kombucha

During fermentation, sweet tea becomes a fresh, tangy drink. Yeasts and bacteria convert sugars and change its aroma, flavour and composition. Here we explore what happens in your kombucha, and what research can and cannot tell us about it.

Yeasts and bacteria work together

Kombucha starts with tea, sugar, water and a living culture. Tea provides compounds such as polyphenols and aromas. Yeasts break down sugars and produce alcohol and carbon dioxide. With oxygen, acetic acid bacteria can convert alcohol into acetic acid and other sugars into organic acids [2, 4].

These conversions keep changing. The compounds present depend on the culture, tea, sugar, temperature, oxygen and time. A favourable result in one experimental setup does not establish a universally best home-brewing recipe.

Which compounds are found in kombucha?

Researchers find a mixture of organic acids, compounds from tea and substances formed or transformed during fermentation. Some are called bioactive because they can produce a biological effect in a test. That alone does not establish what drinking a glass of kombucha does in the human body.

1. Organic acids

Organic acids contribute kombucha’s fresh, tangy taste. Their combination and concentrations vary between batches.

  • Acetic acid: contributes the familiar vinegar-like tang and can form from alcohol.

  • Gluconic acid: can form when bacteria convert glucose.

  • Other acids: depending on the culture and analytical method, researchers also detect compounds such as glucuronic and succinic acid [1, 4, 6].

Acidity can inhibit the growth of some microorganisms. Careful preparation and storage still matter. Detecting glucuronic acid does not prove that kombucha has a detoxifying effect in people.

2. Polyphenols

Tea naturally contains polyphenols, including catechins and theaflavins. Their composition can change during fermentation [1, 4], which helps explain why the choice of tea matters.

Researchers use chemical antioxidant assays to test particular properties of a sample under laboratory conditions. Such a result is not the same as demonstrated protection against disease in people. Improved absorption is also not established for every compound or every brew.

3. Alcohols, esters & aromatic volatiles

Esters, aldehydes, ketones and alcohols contribute to aroma and flavour. Their combination can come across as fruity, floral, spicy or more pronounced. Research using different microorganisms shows how strongly the culture can influence these aromas [2, 4].

Alcohol is also produced. Its final concentration depends on preparation and can change further during bottle fermentation. Home-brewed kombucha is therefore not automatically alcohol-free.

4. Vitamins

Studies report different vitamins and concentrations. Their presence depends on ingredients, culture and analytical method [4, 7]. Without testing your own product, you cannot assume how much a glass contains. Fermentation alone does not establish kombucha as a reliable vitamin or B12 source.

5. Unidentified metabolites

Modern analytical methods let researchers follow many compounds and unidentified signals. An unknown signal is not automatically a newly discovered substance, and the number of detected compounds does not measure how healthy a drink is. Their identities, concentrations and effects need to be investigated separately [3].

Changes in microbes and flavor

A 2025 study compared kombucha made with white, green and black tea. Researchers found differences in acids, phenolics and antioxidant assays. They also tested inhibition of bacterial growth and nitric oxide production in cultured cells [1].

These are interesting laboratory findings. They do not demonstrate that drinking these kombuchas treats infections or inflammation in people.

Home-brew vs commercial

Both home-brewed and commercial kombucha can contain live microorganisms. This depends on processing, filtration, any pasteurisation and storage [5]. Greater microbial variety alone does not establish a greater health benefit. Home brewing offers the chance to choose flavours, learn about your culture and develop careful brewing habits.

Limits of current research

Interpreting research requires distinguishing chemical assays, cultured cells, animal studies and human studies. Kombucha cultures and recipes also vary widely. A result from one study cannot simply be applied to a different product or every home brew.

Containing live microorganisms does not automatically make a drink a proven probiotic. Specific health benefits require research on the relevant product, a known amount and suitable human studies.

At BiomeBrew we enjoy sharing what we learn about fermentation. We distinguish measurements, possible explanations and demonstrated effects in people, and update our explanations when new knowledge calls for it.

Ready to brew? Explore our living starter cultures or send your question to info@biomebrew.nl.