At what level ABV in a wine kills bacteria?

[Bocochoco]

Title say it all.
Like if I had a 15% wine I wanted to add watermelon juice unpastuerized in to it without worry

 

[ShadesManna]

It likely will not ever be high enough. Check out this article about beer and wine's alcohol content, and bacteria:

Beer & Wine vs. Bacteria

 

[bernardsmith]

There are always going to be some bacteria that will thrive in wine - Think MLF. But if you are adding juice to a wine and the wine has been fermented without stress and you have a large viable yeast culture then that yeast is likely to have created an environment that suits it and which very strongly inhibits the growth of competing fungi and bacteria.
That said, if you are anxious why not pitch yeast into the juice and allow the juice to ferment and then whack it with K-meta and only then blend the two wines... (I would suggest that you whack the juice with K-meta prior to pitching the yeast (or even adding the juice to the wine but watermelon juice is notorious for spoilage if you are not introducing a very large and active yeast culture almost as soon as you have juiced the melon.