Kombucha has skyrocketed in popularity around the world in recent years, becoming one of the most widely consumed fermented beverages. Many people choose it for its unique flavor, but researchers are taking a closer look at what happens inside the drink during fermentation and how its ingredients affect its properties.
Scientists from the Wrocław University of Environmental and Life Sciences and the Wrocław Medical University (Associate Professor Helena Moreira, PhD; Associate Professor Eva Barg, MSc) set out to investigate one important question: Does the type of tea used to make kombucha affect the final product? Their findings revealed a much larger difference than expected.
The research team compared kombucha made from black, green, white, oolong, and puerh teas. Their research was published in the journal food chemistry.
“The type of tea acts as a specific matrix that shapes the fermentation process and the final composition of kombucha,” explains Associate Professor Helena Moreira, PhD, from the Department of Basic Medicine and Immunology, Wrocław Medical University. “Individual teas differ in their content of polyphenols, catechins, caffeine and other bioactive compounds, which are then metabolized by the SCOBY microorganisms. As a result, fermentation proceeds with different dynamics and the final beverages differ in both chemical and aroma profiles.”
How fermentation changes kombucha
Kombucha is made by fermenting sweet tea by SCOBY, a symbiotic culture of bacteria and yeast. During fermentation, a series of complex biochemical changes occur.
Yeast first converts sugar into alcohol and carbon dioxide. Bacteria then convert those compounds into organic acids, primarily acetic acid and gluconic acid. These acids give kombucha its familiar sour taste.
This process also changes many of the natural compounds found in tea. The researchers observed changes in polyphenols, catechins, and volatile compounds that contribute to taste and aroma.
“At the same time, changes occur in the polyphenols and volatile aromatic compounds contained in tea. As a result, this beverage acquires its characteristic sourness, light bright taste and more complex aroma,” explains Associate Professor Helena Moreira, PhD.
The researchers found high levels of compounds associated with floral and fruity aromas, such as linalool and 2-phenylethanol. These substances are also found naturally in flowers and essential oils. At the same time, some compounds present in the brewed tea disappeared as fermentation progressed and were replaced by new metabolites produced by the SCOBY microorganism.
To study these changes in detail, the researchers used advanced chromatography techniques and mass spectrometry. This allowed them to track hundreds of chemical compounds and compare the composition of kombucha made from different types of tea.
“The most surprising thing was the scale of the changes that occur during fermentation and how strongly it depends on the type of tea used,” says the scientist. “Despite identical fermentation conditions, we obtained a kombucha with a very distinct profile of volatile aromatics.”
Green kombucha and oolong kombucha showed the highest antioxidant activity.
The study also revealed that kombucha made from different teas can have different biological properties.
Of all the varieties tested, kombucha prepared from green and oolong teas showed the strongest antioxidant activity and the greatest ability to neutralize free radicals.
Free radicals are highly reactive molecules that can damage cells and cause aging. For this reason, scientists are actively researching antioxidants and their potential role in maintaining health.
“Our findings show 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 with kombucha prepared from green tea and oolong tea, which showed the highest biological potential.”
The researchers cautioned that these findings came from laboratory analysis and should not be interpreted as evidence of specific health benefits for humans.
“Further clinical studies are needed to definitively confirm the effects of specific types of kombucha on human health,” the researchers added.
Why tea selection is important
The growing interest in kombucha is part of a larger scientific focus on fermented foods. Researchers are increasingly studying how fermentation improves the availability of bioactive compounds, generates new metabolites, and influences the gut microbiome.
“Fermented foods are currently at the center of scientific interest because they combine traditional techniques with modern approaches to health and nutrition,” says Associate Professor Helena Moreira, PhD. “Kombucha is a very good example of a product whose chemical composition, biological activity, and sensory profile result from complex interactions between raw materials and fermenting microorganisms.”
The findings also emphasize that kombucha should not be viewed as a single, one-size-fits-all drink. The tea used as a starting material can significantly influence both its chemical and sensory properties.
Green tea kombucha tended to have a fresher, more vegetal aroma. Oolong kombucha produced stronger floral and fruity aromas. On the other hand, kombucha made from black tea and pu-erh exhibited a richer, earthier aroma with more pronounced fermentation characteristics.
