Homemade kombucha, kept at room temperature around 21-27°C, usually ferments and becomes drinkable in 7-14 days. Timing depends on the ambient temperature, the strength of the SCOBY, and how sour you want it.
What happens during fermentation?
The SCOBY consumes the sugar in the sweetened tea, producing carbon dioxide, a small amount of alcohol, and acetic acid. In the early days the tea is still sweet; as the days pass, sugar drops and acidity rises, giving the drink its characteristic tangy taste.
What determines the exact timing?
From day seven onward, tasting a small sip each day is the best way to track progress. If it's still too sweet, let it ferment a few more days; once it reaches the sourness you want, strain and bottle it. In warmer spots, above 25°C, this can shorten to 7 days, while a cooler kitchen, 18-20°C, can stretch it to 14-21 days.
A new, thin SCOBY ferments more slowly; a thicker one that's been used several times can shave a few days off the process. That's why tasting more often in your first few batches is worth it.
How long does the second fermentation (bottling) take?
Once strained and flavoured with fruit or spices, kombucha carbonates in sealed bottles at room temperature over another 2-4 days. Cracking the cap open briefly once a day to release excess pressure during this stage keeps the bottle from bursting.
What happens if it over-ferments?
Fermenting past 3 weeks turns kombucha sharply sour, close to vinegar, at which point it's better used as a salad dressing than a drink. Over-fermented kombucha also tends to be less fizzy and noticeably more acidic.
Can fermentation stall if it's too cold?
Below 18°C the SCOBY's activity slows down considerably and fermentation can nearly stop, so the jar should sit somewhere warm and out of direct light rather than in a cold corner of the kitchen.
What should first-timers watch for?
A thin, whitish new SCOBY layer forming on top and a faint vinegary smell are signs fermentation is progressing normally. Black or green mould spots, a fuzzy texture, or a rotten smell mean the whole batch should be considered unsafe and discarded.