How to brew it, and what to do when it goes wrong

The shape of the process

Home kombucha is four steps and one of them is waiting. Brew sweetened tea and cool it. Add the culture and its starter tea. Cover with cloth and leave it somewhere warm for one to two weeks. Bottle it, optionally with fruit, and leave the bottles sealed for a few days to carbonate.

That is the whole thing. Almost everything written about kombucha is an elaboration of one of those four steps, and almost every problem is a temperature problem, a starter tea problem, or a seal problem in disguise.

Why there are two fermentations

The first fermentation is open to the air, in a jar covered with cloth. The culture needs oxygen, and the carbon dioxide it produces simply escapes. This is where the sourness comes from.

The second is sealed, in a bottle, usually with a little fruit or juice for the yeast to work on. Now the gas cannot escape, so it dissolves into the liquid, and that is the fizz. Understanding this distinction resolves most confusion at once: a first fermentation is not supposed to be fizzy, and a second fermentation cannot happen in anything that is not sealed. Second fermentation is the full version.

The three things that actually go wrong

• It stalls. Almost always cold. A jar at 66 F can sit for three weeks and taste like sweet tea. Temperature is the fix.
• It will not carbonate. Almost always a seal, sometimes not enough sugar in the bottle, occasionally too cold again. Why kombucha is not carbonating runs the causes in order of likelihood.
• Something grew on top. Usually a new pellicle, sometimes yeast, rarely mold — and the three look nothing alike once you know what to look for. Mold versus SCOBY is the page to read before you throw a batch away.

What is genuinely a safety question

Most kombucha worry is misplaced, and a couple of things are worth taking seriously. Acidity is the real defense, which is why pH testing earns its place. Fuzzy mold on the surface means the batch and the culture both go, with no exceptions. And every fermented drink produces a trace of alcohol, which matters for some households and not for others — kombucha alcohol content covers what is actually known.

We are not a medical source and we do not offer health advice. What this site can do is be exact about process and materials, cite what makers publish, and say plainly when something is not published. Home fermentation safety keeps to that line.