Since the beer foams up in the pressure cooker during the corned beef cooking process, you might find that the initial force of manually releasing the steam (after the natural release) causes some liquid to spray out of the valve. A little bit of liquid is fine, but if you release the pressure and find that too much liquid is coming out, re-seal the valve, and try releasing the remaining pressure again in another 5 minutes. Or, with a heat-proof glove, release the steam more slowly by turning the valve just until you hear a hissing noise and carefully holding it in that position.