How are you adding the coffee? 2 oz of regular brewed coffee will add little to the keg. 2 oz of espresso could be a minor, subtle coffee-like note, but even then, I would probably add 8 or more oz. Adding 2 oz of grounds or whole beans makes some sense (assuming you take it out after a day or two to avoid over-extraction), but my experience would tell me your best bet would be adding filtered, concentrated cold brewed coffee to the keg - it is much more stable than hot-brewed coffee. I use a 2-cup french press and add double the amount of coffee I would use for regular coffee. then add room temperature water and give it 12 hours. Then I press the coffee and pour it through a coffee filter before adding it to the keg. I tell myself the acidity of the coffee protects against infection, but I'm not really sure.