Typically there is only a small amount (0.02-0.05) of naturally fermented alcohol content in the finished drink- the same amount as an overripe piece of fruit. In fermentation, glucose in the sugar is converted by wild yeast to alcohol and CO2. The alcohol level can vary and sometimes it does spike under certain circumstances like long term storage or second fermentation.
The best way to avoid alcohol in your water kefir:
- drink it as fresh as possible with minimal fridge storage. Long term storage, even really cold storage, can slowly increase the alcohol over time.
- in your second ferment, choose fruit that has a low glycemic index. Citrus fruit is best. Avoid cherries, grapes and some other soft fruits which contain more natural sugars and yeasts on the skins. These ferment very quickly and can spike the alcohol content.
If you are concerned about the amount of alcohol in your fermented drink, you can purchase a hydrometer and test it.
Wondering it it is safe for children to drink? Read more about it here.