Kombucha is an effervescent fermented drink usually made with black or green tea. The process of brewing kombucha starts with sweetened tea and SCOBY—a symbiotic culture of bacteria and yeast—often called a mushroom or mother.
The combination is left to ferment for a couple of weeks before it undergoes the second fermentation in the bottle. Kombucha is then usually refrigerated to slow down the fermentation and carbonation process. During the second fermentation, the brew can be flavored with fruit, fruit juices, spices, or herbs.
It probably spread with the tea trade, primarily to Korea and Japan. The word kombucha is possibly a Japanese loan (kombu stands for kelp, while cha translates as tea), but it is still not certain how it originated.
Kombucha has been homebrewed for centuries, but it became a household name in Western civilizations in the 1990s, which went along with a massive upsurge in popularity. It is still brewed at home, but it is also widely available as a bottled, commercially produced drink.
Kombucha is generally marketed as a non-alcoholic drink, with an alcohol content less than 0.5% ABV. However, since kombucha continues to ferment in the bottle, this percentage can be exceeded, sometimes intentionally, and these varieties need to be labeled accordingly.