Scientists from the Wrocław University of Environmental and Life Sciences and Wroclaw Medical University (Associate Professor Helena Moreira, PhD, Associate Professor Ewa Barg, PhD, and Anna Szyjka, MSc Eng.) set out to investigate one key question: Does the type of tea used to make kombucha affect the final product? Their findings revealed much larger differences than expected.

The research team compared kombuchas made from black, green, white, oolong, and pu-erh teas. Their study was published in the journal Food Chemistry.

"The type of tea acts as a specific matrix that shapes the course of fermentation and the final composition of kombucha," explains Associate Professor Helena Moreira, PhD, from the Department of Basic Medical Sciences and Immunology, Wroclaw Medical University. "Individual teas differ in their content of polyphenols, catechins, caffeine, and other bioactive compounds, which are subsequently metabolized by SCOBY microorganisms. As a result, fermentation proceeds with different dynamics, and the final beverages differ in both chemical and aromatic profiles."

How Fermentation Changes Kombucha

Kombucha is made when a SCOBY, a symbiotic culture of bacteria and yeast, ferments sweetened tea. During fermentation, a series of complex biochemical changes takes place.

Yeasts first convert sugars into alcohol and carbon dioxide. Bacteria then transform those compounds into organic acids, primarily acetic acid and gluconic acid. These acids give kombucha its familiar tart flavor.

The process also alters many of the tea's naturally occurring compounds. Researchers observed changes in polyphenols, catechins, and volatile compounds that contribute to flavor and aroma.

"At the same time, transformations of polyphenols and volatile aromatic compounds present in tea take place. As a result, the beverage acquires its characteristic sour, lightly sparkling taste and a more complex aroma," explains Associate Professor Helena Moreira, PhD.

The team found higher levels of compounds associated with floral and fruity aromas, including linalool and 2-phenylethanol. These substances are also found naturally in flowers and essential oils. At the same time, several compounds present in freshly brewed tea disappeared as fermentation progressed, replaced by new metabolites generated by the SCOBY microorganisms.

To examine these changes in detail, the researchers used advanced chromatographic methods and mass spectrometry. This enabled them to track hundreds of chemical compounds and compare the composition of kombuchas made from different tea varieties.

"The most surprising aspect was the scale of changes occurring during fermentation and how strongly they depended on the type of tea used," says the scientist. "Despite identical fermentation conditions, we obtained kombuchas with highly distinct profiles of volatile aromatic compounds."

Green and Oolong Kombucha Showed the Highest Antioxidant Activity

The study also revealed that kombuchas made from different teas can vary in their biological properties.

Among all the varieties tested, kombuchas prepared from green tea and oolong tea demonstrated the strongest antioxidant activity and the greatest capacity to neutralize free radicals.

Free radicals are highly reactive molecules that can damage cells and contribute to aging. Because of this, scientists are actively studying antioxidants and their possible role in supporting health.

"The results of our research indicate that the type of tea influences not only the taste and aroma, but also the biological activity of kombucha," emphasizes Associate Professor Helena Moreira, PhD. "Particularly interesting results were obtained for kombuchas prepared from green and oolong teas, which demonstrated the highest biological potential."

The researchers caution that these findings come from laboratory analyses and should not be interpreted as proof of specific health benefits in people.

"Further clinical studies are necessary to clearly confirm the impact of particular types of kombucha on human health," adds the researcher.

Why Tea Choice Matters

Growing interest in kombucha is part of a larger scientific focus on fermented foods. Researchers are increasingly exploring how fermentation can improve the availability of bioactive compounds, create new metabolites, and influence the gut microbiota.

"Fermented foods are currently at the center of scientific interest because they combine traditional technologies with a modern approach to health and nutrition," says Associate Professor Helena Moreira, PhD. "Kombucha is a very good example of a product in which chemical composition, biological activity, and sensory profile result from complex interactions between the raw material and fermentative microorganisms."

The findings also highlight that kombucha should not be viewed as a single, uniform beverage. The tea used as the starting ingredient can significantly influence both its chemistry and sensory characteristics.

Green tea kombucha tended to have a fresher, more vegetal aroma. Oolong kombucha developed stronger floral and fruity notes. Kombuchas made from black tea and pu-erh, meanwhile, displayed richer, earthier aromas with more pronounced fermentation characteristics.