Hello my dear friend:
I believe that the problem of your bottom of bottle could be due to certain problems that I could enumerate.
1.-transmission of light rays between the glass material and the material that simulates the liquid.
2.-the increase in the factor or simulation of caustics generated by both the glass and the wine material and both materials vary their IOR levels or refraction values
3.-Apparently you are using an enviroment that is not helping you much, which reflects in that glass below your bottle and makes it look darker. bottle.
4.-If you want a better finish for your wine bottle, you should propose a lighting flow that is based on main lights and support lights (three points) as a lighting studio. Or failing that, create backlights to generate those effects in the glass of the bottle that would give it that depth you are looking for and that would give that feeling that you are looking for in the final part of your bottle.
greetings my dear friend