Originally Posted by SumnerH
Carbonation doesn't really matter. It's easy to see that yourself: You can let the Bass and/or Guinness go completely flat and it doesn't affect how hard it is to pour a black and tan. It's all about the density (ie specific gravity).
I don't know that I agree with you on this. I know specific gravity is the major contributing force behind it, but we had many problems over the years, mostly with long draw systems that wern't balanced properly. We worked pretty closely with Guinness to on these issues (in the days prior to Deagio). Once we replaced lines for proper resistance, or adjusted psi output on the regulators, the problems went away. I estimate 30 - 40 accounts with similar problems over the years that Guinness was consulted on, and I trust those guys new what they were talking about.
Are you talking about pouring from a bottle or can? There is a lot less force when pouring a beer from bottle or can rather than dispensing from a keg. I have never seen a keg of Bass or Guinness go flat while pressurized by a dispensing system so I have no comparison there.
I don't dispute the fact that different gravities will layer regardless of carbonation, but I do know from experience that it is harder to keep them from "mixing" if there is not enough upward pressure from the bottom layer, specifically when poured from a pressurized system through a creamer faucet which, when set up correctly, does come out at a considerable force. The spoon can only disperse so much of the force.