What does the geometry for the foam look like? Just trying to get an idea of what the bubble geometry in KS is doing to it.
Clay Render?
You want all of my secrets!? Haha, ok, so yes, there's a lot going on in this render. But there are only 4 parts (aside from the backdrop, the physical lights, and the ground).
The mug is a solid part, the liquid beer is a solid part (nested into the glass walls), the foam overflow is one object, and there are 'large' bubbles that are manually modeled and placed into the foam. They also cut into and remove the geometry of the foam overflow mass.
This was done in the modeling phase. The foam overflow (outside the glass) is a liquid shader with a LOT of bubble geometry via Keyshot.
Since the liquid shader has an IOR outside of 1 (air) the bubbles get treated as they would in reality (in reality, bubbles are just air trapped inside of liquid). The beer inside the glass is using a similar treatment, however I wanted to vary the density of the bubbles mapped inside the solid, which is where the .vdb comes into play.