Kombucha has gained popularity around the world in recent years, becoming one of the most consumed fermented beverages. While many people choose it for its distinctive flavor, researchers are taking a closer look at what happens inside the drink during fermentation and how its ingredients may influence its properties.
Scientists from Wrocław University of Environmental and Life Sciences and Wrocław Medical University (Associate Professor Helena Moreira, PhD, Associate Professor Ewa Barg, PhD, and Anna Szyjka, MSc Eng.) set out to investigate a 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 with 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 the kombucha,” explains Associate Professor Helena Moreira, PhD, of the Department of Basic Medical Sciences and Immunology at the Medical University of Wroclaw. “Different teas are differentiated by their content of polyphenols, catechins, caffeine and other bioactive compounds, which are subsequently metabolized by SCOBY microorganisms. As a result, fermentation develops with different dynamics and the final drinks 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 occur.
Yeasts first convert sugars into alcohol and carbon dioxide. Bacteria then transform these compounds into organic acids, mainly acetic acid and gluconic acid. These acids give kombucha its familiar sour flavor.
The process also alters many of the tea’s natural compounds. The 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 the tea occur. As a result, the drink acquires its characteristic acidic, slightly sparkling flavor 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 the freshly brewed tea disappeared as fermentation progressed, being 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 allowed them to track hundreds of chemical compounds and compare the composition of kombuchas made with different varieties of tea.
“The most surprising thing was the magnitude of the changes that occurred during fermentation and to what extent they depended on the type of tea used,” says the scientist. “Despite the same fermentation conditions, we obtained kombuchas with very different profiles of volatile aromatic compounds.”
Green and Oolong Kombucha showed the highest antioxidant activity
The study also revealed that kombuchas made with different teas can vary in their biological properties.
Among all the varieties tested, kombuchas made with green tea and oolong tea demonstrated the highest antioxidant activity and the greatest ability 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 flavor and aroma, but also the biological activity of kombucha,” highlights Associate Professor Helena Moreira, PhD. “Particularly interesting results were obtained with kombuchas prepared from green and oolong tea, which demonstrated the greatest biological potential.”
The researchers caution that these findings come from laboratory analyzes and should not be interpreted as evidence of specific health benefits for people.
“More clinical studies are needed to clearly confirm the impact of certain types of kombucha on human health,” adds the researcher.
Why the choice of tea is important
The growing interest in kombucha is part of a broader 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 the 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 seen as a single, uniform drink. The tea used as the initial ingredient can significantly influence both its chemistry and sensory characteristics.
Green tea kombucha tended to have a fresher, more vegetal aroma. The kombucha oolong developed stronger floral and fruity notes. Meanwhile, kombuchas made with black tea and pu-erh displayed richer, earthier aromas with more pronounced fermentation characteristics.