You could up the absorption value, and/or throw in a volume scatter node (coffee often isn’t perfectly clear - it has dissolved solids in it).
Make sure you up the number of volumetric bounces in the render panel if you do use volumetric scatter - you’ll probably need at least 2.
Also - I noticed your coffee object is slightly undersized for the cup. Make it a bit bigger to ensure that the coffee object overlaps with the cup.
