Kombucha is a fermented probiotic drink whose beneficial effects were believed to be valuable as early as 200 BC.
When consumed regularly, the compounds in kombucha may support health in a variety of ways.
However, if poorly produced or made under unhygienic conditions, kombucha can also pose health risks.
What is kombucha?
Kombucha is a beverage obtained by fermenting sweetened tea. It was originally produced with black tea, but over time, production has expanded to include green tea, oolong, and other varieties. The sweetened tea acts as the fermentation substrate for a symbiotic culture of bacteria and yeast, known as SCOBY (Symbiotic Colony Of Bacteria and Yeast). The end product is slightly carbonated with a tangy, sour flavour.
Although SCOBY includes certain strains of bacteria and yeast, the composition and properties of this culture and the sweetened tea may not be exactly the same everywhere, but may vary slightly depending on the location of production or even the weather. The fermentation process is then influenced by a myriad of factors, including the hardness of the water used, the final concentration of the tea, the bacterial composition of the fermentation culture and the tea, the surface area where the culture meets the tea, the degree of oxygen access or, of course, the ambient temperature. If any of these factors are disturbed, the nutritional, taste or even safety properties of the resulting kombucha may be adversely affected.
What is the origin of kombucha?
The earliest documented evidence of kombucha consumption dates back to 220 BC in what is now northwestern China. Even then, it was valued for its stimulating and health‑promoting properties, which earned it the nickname “the drink of immortality.” According to legend, in 414 AD, a physician named Dr. Kombu brought the beverage to Japan to treat the emperor’s digestive problems. Kombucha later spread to Russia and Eastern Europe via trade routes, and eventually around the world, especially during and after the Second World War.
Though the name Dr. Kombu may sound like fiction, this is where the drink gets its name. The suffix “-cha”, meaning tea in Japanese, was added to his name, giving us kombucha, the name still used today.
What are the health benefits of kombucha?
While studies have repeatedly shown the positive effects of kombucha, it is important to note that many of these studies are conducted in vitro (i.e. in laboratory conditions, "in a test tube") or on rodents. Research with human subjects also exists, of course, but so far it represents only a minority of the available evidence, so further high‑quality scientific studies with human subjects will be needed to confirm the benefits listed below. The potential positive effects of kombucha are also more likely to be seen if the drink is consumed regularly. As with any other food/beverage, the effect cannot be expected after a single consumption.
1. Probiotic effects
Thanks to fermentation through bacterial and yeast culture, kombucha is a source of health‑promoting bacteria that have a probiotic effect and thus positively influence the composition of the gut microbiome. According to studies, many different strains of probiotic bacteria have been found in kombucha, although the amount and strains can vary considerably from one beverage to another, as mentioned above. The most common genera found are Lactobacillus or Bifidobacterium, while the most common yeasts are Saccharomyces cerevisiae.
To preserve the probiotic cultures, kombucha must be unpasteurised; however, some producers pasteurise the finished kombucha and then add probiotic bacteria to it. In the old days, kombucha was often pasteurised in stores to minimise contamination with pathogenic bacteria, but nowadays production practices are so safe that most commercially available kombucha is also unpasteurised.
2. Antioxidant activity
Laboratory tests show that kombucha contains significantly more components with antioxidant activity than unfermented tea. These include polyphenols, catechins, ascorbic acid and DSL (D‑saccharic acid‑1,4‑lactone). The content of these substances varies, of course, depending on the fermentation time, temperature or raw materials used. For black, green and oolong tea, the highest amount of substances with antioxidant activity seems to be available after 3 days of fermentation, whereas for white tea, it is after 14 days. Green tea kombucha also clearly leads the others in terms of the amount of phenolics contained. Black tea, on the other hand, has the highest amount of organic acids.
3. Antimicrobial activity
Kombucha shows antimicrobial activity against some Gram‑positive and Gram‑negative bacteria (the differences are due to the composition of the cell wall), which is probably due to the presence of substances such as polyphenols, organic acids and other bioactive compounds. In addition, black tea also appears to have an antifungal effect, i.e., it inhibits the growth of certain types of fungi and moulds. Green tea and oolong, on the other hand, have shown the best activity against pathogenic intestinal bacteria that can cause alimentary diseases and digestive problems. It should be noted, however, that the above research was conducted in vitro and is therefore more of a baseline for future research with human subjects.
4. Anti‑inflammatory effects
Due to the content of the substances already mentioned above, kombucha also shows anti‑inflammatory effects. Although the ability to induce inflammation is one of the body's most effective mechanisms to defend itself against infection, when chronically persistent, inflammation has a rather negative impact on health and increases the risk of developing many diseases such as type II diabetes, cardiovascular disease and even cancer.
In the context of cancer in particular, some of the bioactive substances found in kombucha show promise in inhibiting the growth of cancer cells, especiallywhen dried lemon balm leaves are added to kombucha. However, these findings are so far mainly based on research under laboratory conditions, and further research is needed for application and potential effectiveness in real‑life situations.
Can kombucha have negative effects?
Cases of nausea and dizziness after consuming kombucha have been reported in the literature. There is even a case of lead poisoning after six months of consuming kombucha; however, it has been shown that this compound was released into the kombucha from a damaged container intended for its fermentation. When kombucha is prepared in unhygienic conditions, there is a risk of overgrowth of pathogenic bacteria, which in some cases has caused a shift in the acid‑base balance of the body or damage to the kidneys.
In terms of pre‑existing diseases or other conditions, kombucha consumption may not be suitable to a greater extent for people with a tendency to disturb the acid‑base balance, such as those with acute renal failure. This also includes people with immune deficiencies or who are taking immunosuppressants.
Therefore, the health risks from kombucha in 99% of cases include improper hygienic conditions during preparation or pre‑existing diseases or conditions for which it is recommended not to consume kombucha for safety reasons. However, for healthy people, and when properly prepared, it is assessed as safe and beneficial to health. In general, consumption of about 120ml of kombucha per day is not considered to be risky even in the long term.
Kombucha in pregnancy
Scientists warn about the potential risks of consuming kombucha during pregnancy. This is due to the possibility of small amounts of alcohol being produced during fermentation or contamination of the drink with pathogenic bacteria that may not be dangerous to the mother but may endanger the fetus. However, the main cause for concern is the effect of heparin, which may be present in trace amounts in kombucha as part of the glycosaminoglycans in the tea. In other circumstances, beneficial substances can affect blood clotting, which can lead to complications in pregnancy. Although the direct presence of heparin in kombucha has not been recorded, researchers warn that increased drinking of kombucha may encourage its own production in the body, and therefore, extra caution should be taken, which translates to not consuming kombucha during pregnancy.
Clear evidence on the safety of kombucha for breastfeeding is not currently available. However, the potential risk is lower than during pregnancy, and it is therefore recommended to consult a doctor if kombucha is consumed in small quantities during breastfeeding.
Is it possible to prepare kombucha at home?
Kombucha can be prepared at home. You need the mother culture of scoby itself (it can be bought in a pharmacy or even grown), a small amount of ready‑made unpasteurised kombucha, loose tea of your choice, sugar, and water.
However, as mentioned above, unhygienic conditions during production, too long fermentation time or other factors can negatively affect not only the taste of kombucha but its safety. For this reason, before making kombucha at home, we recommend attending a fermentation course, where the instructors will explain everything in detail and teach you how to work with kombucha to minimise any health risks.
Bottom line
Kombucha is a pungent, mildly fizzy probiotic drink that has been around since 200 BC. It's made by fermenting sweetened tea together with bacterial and yeast cultures, giving it substances with a range of health benefits when consumed regularly.
However, it does come with its risks, especially if you suffer from a disease that increases the risk of acid‑base imbalance in the body or if you prepare kombucha in unhygienic conditions. Pregnant women should also consult a doctor.
