There seems to be risk of some confusion being propagated here, which is why I asked for some genuine benefits for fermenting ale yeast under pressure. It's not something commercial brewers do. If anything, they're challenged to do the opposite or at least manage things to reduce pressure during peak fermentation. Hydrostatic pressure in tall commercial vessels is one thing, partial CO2 pressure building up in the fermentation vessel is another. The main issue is the impact of CO2 pressure on yeast growth therefore fermentation performance. Yeast stop budding at a CO2 pressure of about 40 psi. It's not an abrupt change, it starts at lower CO2 pressures and gets worse as CO2 pressure increases. Commercial brewers generally repitch yeast for at least several generations, which is key to business and the heart of any brewery. Therefore professional brewers are very conscious about taking very good care of the yeast, especially to promote sufficient biomass for maintaining fermentation performance and subsequent repitchings. Of course, as home brewers, we can do whatever we want, but fermenting ale yeast under pressure seems to be making compromises without any clear benefits specific to fermenting under pressure. I still think it's just a case of some doing it just because they can. Those opting for fermenting ales under pressure probably should increase pitching rate by quite a lot, but if they do that, they might find, quite ironically, that fermentation finishes sooner without any head pressure and that the final beer has a more balanced quality generally. And the same great results can be achieved in a non pressure-rated FV too.
