Why did my cherry juice turn directly into vinegar while never being wine? These canned, additive-free cherries are packed in their own juice, watered down.  I previously left this juice in a plastic water bottle while drinking it, for only three days, and it became pleasantly bubbly - carbonated juice.  A honey and water mix used for eye medicine turned into a strong alcohol over just 1-2 weeks (it was only one ounce of mixture).  This time, I used the extra, way-too-high amount of yeast to put in the juice, but after two months, it is still just sour juice, and no tasteable bubbles.  So I added a very small piece of kombucha SCOBY - maybe it will become kombucha-like or become fizzy juice.  One week later, it tastes exactly the same.  Two weeks after that, it is vinegar.  It was never wine and it was never kombucha.  Why?
It's difficult to answer why fermentation did not complete without further information.

It's quite possible the sugar content was too high and pH to low for whatever yeast was added to survive and begin fermentation.

Vinegar however is created when bacteria that produce acetic acid are present in an environment with a sugar source and oxygen. They will thrive off of the sugar just like brewer's yeast, but will also produce acetic acid as a byproduct of their life processes.

If you wish to make cherry wine, I would suggest diluting the juice down to somewhere in the range of a sugar concentration of 10 percent, measuring with a hydrometer or refractometer, and using a yeast, possibly a dry wine yeast, that can withstand alcohol in ranges of 10-14 percent abv.