Yes, kombucha naturally contains some alcohol, because it is made by fermenting sweetened tea with a culture of yeast and bacteria, and the yeast turns part of the sugar into alcohol. Kombucha sold in the U.S. as a non-alcoholic drink has to stay below 0.5% alcohol by volume (ABV) and is then regulated as a food by the FDA. Under federal law, if a kombucha reaches 0.5% ABV or more at any point—during production, at bottling or afterward—it is legally an alcohol beverage regulated by the Alcohol and Tobacco Tax and Trade Bureau (TTB), with alcohol taxes and a government health warning label. Because fermentation can continue in the bottle, a kombucha that was under 0.5% when bottled can climb past that limit later, and it is then treated as an alcohol beverage.
Source: U.S. Alcohol and Tobacco Tax and Trade Bureau (TTB), “Kombucha”
Image: Kombucha with SCOBY (photo: Mgarten, CC BY-SA 3.0), via Wikimedia Commons.