To make sure it’s acidic enough, measure the pH (optional). It should be below 4. 6 pH. If not, keep adding starter tea, vinegar, or citric acid (not Vitamin C; that’s too weak) until the desired pH is reached.
The culture will sink or float or do something in between. It is better that the mushroom floats on top to block aspergillus contamination. The best way to pull a sample is with a straw. Don’t drink directly from the straw, as backwash may contaminate the tea. Also, do not dip the test strip into the brewing vessel. Instead, dip the straw about halfway into the tea, cover the end with your finger, pull the straw out, and drink the liquid inside or put that liquid on the test strip. If the kombucha tastes very sweet, it probably needs more time for the culture to consume the sugar. A pH of 3 tells you that the brewing cycle is complete and the tea is at the correct point to drink. Of course this can vary a bit to suit your needs and taste. If this final pH is too high, then either the tea will need a few more days to complete the brewing cycle, or it should be chucked.
You may use each layer of culture to make a new batch of tea; some recommend using the new layer of culture and discarding the old one. It is not necessary to put both layers of culture back into a single new batch; one will suffice. Every fermentation cycle creates a new child from the mother. So once you have fermented your first batch you will now have two mothers, one from the original mother, and one from the new child. This multiplication will occur for every subsequent fermentation.
