Water kefir vinegar is easy to make by simply keeping your first ferment brewing longer. This typically takes 5-10 days.
Follow your first ferment process and remove the grains after 48 hours, but leave the brew on the counter for 5 days. Taste the ferment, you will know when it has turned to vinegar when the water kefir tastes quite sour. When it suits your taste, pour the liquid into a separate jar and keep the water kefir vinegar in the refrigerator. The water kefir vinegar is full of live probiotics.
Water kefir doesn’t go bad. If it is in a sealed bottle with no chance of cross contamination, the live cultures will slowly continue to eat up the sugars in the drink and eventually the drink will turn to vinegar. The yeast in the fermentation process produces alcohol, and when the ferment is left for a longer amount of time the bacteria is able to consume the alcohol and turn it into acetic acid.