Bottle Transparency.

[micheus]

Ravyn, I make a similar bottle here and the result was the same. You just will not see it if you are using One Light on View menu.
It seems to be an OpenGL issue.

When you use too objects very close (touching each other) - like the liquid inside the bottle - you can get that issue in some renders. Bellow is an image where the liquid was scaled a few less than glass repository in order to avoid that black artifacts (you see in left side of picture):

it was rendered with POV-Ray.