Nothing "ferments on it's own." The wild yeast comes from the air. If you overdose something with a starter yeast, then the majority of the yeast will be like the starter. Just sit something on the counter, the yeasts could vary.
I've made vinegar from the starter at this company and it's very good:
Vinegar Starters | Beer and Winemaking Supplies, Northmapton MA
I made kumiss/keifer from this recipe and it was also good: