How much residual sugar is left in Kombucha?

I know this is a ‘how long is a piece of string’ question. I’ve been making the stuff on and off for years but it’s the only ‘brewing’ I’ve done. Is there a simple way of testing how much sugar is left - I’m thinking this is probably what wine makers do?

i suppose a refractometer would give you some idea, but the amounts of alcohol (and maybe other compounds) present would skew the results a little. probably a small enough amount that you’d get a decent snapshot, though.

when it’s been fermenting for a while, most winemakers would use a hydrometer (which gives amount of alcohol based on density), since at higher alcohol levels you need more math/correction for a refractometer.

Thank you Greg. That gave me some useful leads. From what i gather, the sugar gets converted to alcohol by the yeast. The alcohol is then turned into acetic acid by the bacteria. Unlike cider or wine making, this is an incomplete process. There are also many other by products - the cellulose mat. I went down the rabbit hole and found a pretty comprehensive report from 2014. A Review on Kombucha Tea—Microbiology, Composition, Fermentation, Beneficial Effects, Toxicity, and Tea Fungus.  “ Investigations showed that 34.06% of sucrose stays unfermented after 7 d, and after 21 d this value is 19.28%” - I typically leave mine for 14 days so there’s still roughly 25-30% sugar left. My brew is 100g / litre, leaving 25 to 30g of sugar per litre. That’s way more than I would like.

you can certainly  go longer, but i imagine you’re stopping it when you do because you like the taste there. all that residual sugar is keeping it from tasting much more sour.