Have you ever wondered why water forms little droplets or how some bugs seem to walk on water? That’s all thanks to surface tension. Think of it like the "skin" of the liquid. This is very important to render recipients filled with water, like a cup of wine, where you can notice a curve in the upper surface of the liquid, called meniscus.
A meniscus can be convex or concave. It depends on the attraction between the liquid and the container. A glass container filled with mercury produces a convex meniscus, and a glass container filled with water produces a concave meniscus. Most of the time you will deal with concave.
To create this effect, simply create a smooth curve at the top of the liquid. You may need to add more loops for a better control. This subtle change will add more detail to the liquid:
I also recommend checking this VRay article: https://www.aversis.be/tutorials/vray/vray-20-glass-liquid-02.htm
Slightly increase the size of the liquid, so the body of the object goes inside the glass. Make sure that the meniscus touch the inside of the glass.
Doing that will result in a more realistic render. Here is my final model:
