kombucha, beverage made of fermented green or black tea, usually consumed as a health food. Kombucha is often brewed at home, though commercial products are increasingly available in many places. The fermentation process involves a number of microorganisms, including a variety of yeasts and bacteria, and the resultant probiotic drink is slightly effervescent with a mild sour or vinegar flavour. The tea has a number of reported health benefits, though there is little research to back many of those claims.
The exact origin of kombucha is uncertain, though it likely originated in China and spread with tea along the Silk Road. It is widely brewed in parts of eastern Europe, particularly in rural Russia, and is common in China and Korea. In the United States kombucha initially gained popularity during the HIV/AIDS epidemic in the late 1980s and early ’90s, as it was hoped that the drink could increase T-cell counts and support compromised immune systems. However, it fell out of favour following a report by the Centers for Disease Control and Prevention (CDC) in 1995 that linked the drink to two cases of severe metabolic acidosis, one of which was fatal. With greater awareness of probiotics and the possible health benefits of fermented foods, it resurged as a health product in the early 21st century, and home-brewing kits and commercial brews were soon readily available in many places.
In small-scale and home brewing, kombucha is typically made in glass jars topped with fabric. Black or green tea leaves are steeped in hot water with sugar, then removed. When the sweetened tea has cooled, it is mixed with a bit of kombucha from a previous batch to make the liquid more acidic. A gelatinous mat of symbiotic culture of bacteria and yeast (SCOBY) is then added, and the brew is covered with a tight-weave fabric or paper coffee filter and left to ferment at room temperature for 7–30 days.
The living components of SCOBY can vary widely but generally include strains of Saccharomyces cerevisiae and other yeasts, as well as a number of bacteria, including Gluconacetobacter xylinus. Fresh or dehydrated SCOBY can be bought from suppliers, or a “mother” can be taken from a previous batch of kombucha. In the fermentation process, the alcohols produced by the yeasts are converted by the bacteria into organic acids. The final kombucha product contains vitamin C, vitamins B6 and B12, thiamin, acetic acid, and lactic acid, as well as small amounts of sugar and ethanol, depending on the length of fermentation. The drink can be consumed plain or mixed with fruit or fruit juices and fermented for a few more days for additional effervescence. It can also be flavoured with spices and herbs. Many commercial brews are sweetened and flavoured. The SCOBY itself can be eaten fresh or dried and is sometimes used as a meat substitute.
Kombucha is said to be beneficial for a wide variety of conditions, including hair loss, arthritis, hypertension, inflammation, cancer, hangovers, and many other ailments, though few formal studies have been conducted to verify any of those claims. As a probiotic beverage with live cultures, there is some evidence that the drink may contribute to a healthy gut microbiome and support digestion and immune system functioning, though further empirical studies are needed.
The consumption of large amounts of kombucha has been linked to a number of serious illnesses, notably several cases of metabolic acidosis and liver damage. Additionally, there have been instances of food poisoning or other infections from contaminated home brews. The pasteurization of commercial brews limits this risk significantly, though the process renders any probiotic properties of the drink inert. Kombucha is not recommended for people with compromised immune systems, as the drink has been associated with severe bacteremia (bacterial infection of the blood) and fungemia (fungal infection of the blood) in such people.