How to use the group node:

First of all you must made your shape with the cut or branch cut oriented to the local Z axis and the origin in the center of the geometry as this:

Once finished the geometry you must create a new material and, in the node editor, add a pricipled BDFS shader if nedeed, add a new  Group->foam and connect as the image.

Set the colors of the liquid and foam and play with the other parameters as you want. Done!

Parameters:

liquid color: The color of the liquid

foam color: The color of the foam

foam density: The foam transparency of the not bubbles area

foam bubble height: The height of the foam bubbles

foam bubble scale: The size of the foam bubbles

foam noise height: The height of the foam noise, more height make the foam more rugged

foam micro scale: The size of the micro foam bubbles

foam height: The height of the separation between foam and liquid

liquid bubbles scale: The size of the first set liquid bubbles

liquid bubbles scale 2: The size of the second set liquid bubbles

liquid bubbles density: The quantity of the liquid bubbles

liquid roughness: The roughness of the liquid