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So I am into making kombucha at home: I made a SCOBY, grew it, and I have successful kombuchas. My normal recipe makes a "ginger kombucha", pretty much kombucha with sugar and ginger. It disappears after around a week.

However, I decided to make a plain batch: kombucha and just kombucha. It's been in the fridge since the first of February, getting drunk every now and then. I tasted it today (~45 days) and it smells / tastes slightly reminiscent of wine. However, I can't tell whether it is alcoholic or not.

If it was alcoholic, some searching around told me that people making drinks like beer can use a brewer's hydrometer; you measure its specific gravity before and after to find the % alcohol by volume. Would this work for kombucha becoming alcoholic, and if so, do I measure as the kombucha goes into the bottle (as OG) and use other measurements throughout as its FG?

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The problem is that the hydrometer is used the amount of sugar in the solution, not the amount of alcohol. So you can measure the original gravity (OG), and the final gravity (FG), but in kombucha the alcohol produced by the fermentation is transformed into acetic and other acids. So you can not measure if there really is alcohol in the kombucha.

The only way to know for sure would be to heat the solution for a long time to more than 80°C, but less than the boiling point for water, and then check what the weight is after the heating. Since the boiling point for acetic acid is around 118°C, if there is a reasonable difference, you would be reasonably sure that there is more alcohol in the solution.

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  • Thank you. I was thinking about possibly using distillation to try to "distill" alcohol from it (to see if there was actually any alcohol), but thought it would be easier to use specific gravity. This is easier than actually trying to distill it!
    – Ethan Slota
    Commented Mar 21, 2020 at 23:53
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Kombucha contains a variety of micro-organisms, the most important ones of which are brewing yeast (Saccharomyces Cerevisae) and Acetobacter. The S. Cereviseae converts sugar into alcohol, after which the Acetobacter combines the alcohol with oxygen into acetic acid (vinegar).

If both are in good shape and present in the proper quantities, and your Kombucha is sufficiently oxygenated, these two should work in a balanced fashion and the amount of residual alcohol should be minimal. And, of course, the amount of fermentable sugars you start with should not be excessive which, in most Kombucha recipes, should give you less than a percent or so of alcohol to begin with.

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