I personally think there are two things going on here:
- CG technical. There is a noisy reflection of the ground-plane. That can be improved by Denoising, and the other considerations for reducing noise. You might also consider discriminating between rays: sampling at different levels according to the Light Paths the renderer is evaluating, if you find you are having to push the overall sampling rate too high.
- Perceptual. I think this is more important, actually, here. This all depends on what kind of shot you want: an idealized product or pack-shot, or the glass in a more fully-realized scene. At the moment, in the absence of context, the eye interprets the reflection of the floor, noisy or not, as a feature of the surface of the glass, rather than a reflection of its environment.
For a product-shot, you could, for example, make a full soft box, (an emissive rounded cube containing the scene) you can subdivide its faces, delete some, color some, whatever you like, and it can be visible in lighting, refractions, and reflections without being visible to the camera. Your best references probably come from real-world commercial photography. Other devices available to you are depth-of-field, to soften reflections from a distance and emphasise the scale of your object, flags / gobos for detailed shadows.. reflective or emissive 'cards' to punch up the glow in the liquid ... the list is endless.
At its crudest, the more fully realised scene is less work: put the glass and the floor into an HDRI environment. This is no great shakes, but it took no time.