What Is Kombucha?

What Is Kombucha?

Kombucha is a fermented tea drink made by combining sweetened tea with a SCOBY — a symbiotic culture of bacteria and yeast. The fermentation gives the finished drink its light sourness and natural fizz.

The culture itself is sometimes mislabeled a "tea fungus," but it is not a fungus: it is a colony of acetic acid bacteria and yeast living together in a cellulose mat on the surface of the tea.

The Fermentation Science Behind the Sourness

Fermentation runs in two microbial steps. Yeast first breaks down the sugar into simpler sugars and converts them into ethanol, then acetic acid bacteria oxidize that ethanol into acetic acid — the source of kombucha's characteristic tang and low pH.

The longer the fermentation runs, the more the balance shifts from sweet toward sour; a short ferment stays sweeter and lightly fizzy, while an over-fermented batch turns closer to vinegar.

Tea, Sugar, and the Two-Stage Brew

Kombucha is built on two ingredients: tea (most often black or green) and sugar. The sugar isn't there to sweeten the finished drink — it's the fuel the yeast needs to start fermenting, and most of it is consumed as the process runs.

Production happens in two stages: an open primary fermentation with the SCOBY, followed by a sealed secondary fermentation in the bottle, where trapped carbon dioxide gives the drink its carbonation.

Safety Notes for Home Brewers

Home-fermented kombucha carries real risks if equipment and workspaces aren't properly sanitized, since it can pick up contamination from unwanted microorganisms. Kombucha also contains a low but real amount of alcohol, which builds up over fermentation time.