Spunding pressure and temperature

[TheMadKing]

So I was listening to a podcast with Chris White where he was discussing fermentation under pressure to reduce esters. I know this is well understood but some of his data got me thinking about spunding.

He stated that pressure exceeding 15psi will reduce yeast health and start killing yeast, so you shouldn't exceed this pressure when warm fermenting a lager. It would make sense that this same principle applies to spunding toward the end of a fermentation.

However in order to get a beer carbonated to 2.4 volumes at ale yeast temp (65F) we need 27psi.

So if we are transferring before primary fermentation is finished and spunding for full carbonation, are we damaging our beer? Possibly under attenuating? I've just recently started spunding and don't have enough experience to know yet.

Thoughts on this?

 

[hopjuice_71]

Hmmm, thats interesting. Intuitively one might expect that at some point pressure would have some kind of negative influence on yeast, including the effects of increased CO2 in solution. The idea of them (significantly) pooping out and dying at pressures common to brewing, particularly homebrewing, however, seems counter to experience.. ..well, mine at least. I started fermenting in kegs a couple of years ago, partly so I could spund. Must have at least 50 batches done in kegs. Not only did my beer improve but I have had no evidence of impaired attenuation. This being said, around 90%-ish of the fermentation is done without pressure, then the keg is capped with the spunding valve until the pressure increases to 20-30 psi (fermentation temperature and desired CO2 volumes depending). The yeast seems to perform just fine. I also repitch the yeast from these batches and still get healthy fermentations. I even had one batch where the blowoff clogged at peak fermentation, I didn't notice it, and the pressure skyrocketed for a couple of days. Once I fixed the problem (along with the ensuing horrible mess) the fermentation finished off just fine. Again, I'll note that spunding really improved my beer - if any damage has been caused by pressure it gets completely overwhelmed by the positive influences, which I largely attribute to O2 mitigation.

Cheers

 

[TheMadKing]

Hmmm, thats interesting. Intuitively one might expect that at some point pressure would have some kind of negative influence on yeast, including the effects of increased CO2 in solution. The idea of them (significantly) pooping out and dying at pressures common to brewing, particularly homebrewing, however, seems counter to experience.. ..well, mine at least. I started fermenting in kegs a couple of years ago, partly so I could spund. Must have at least 50 batches done in kegs. Not only did my beer improve but I have had no evidence of impaired attenuation. This being said, around 90%-ish of the fermentation is done without pressure, then the keg is capped with the spunding valve until the pressure increases to 20-30 psi (fermentation temperature and desired CO2 volumes depending). The yeast seems to perform just fine. I also repitch the yeast from these batches and still get healthy fermentations. I even had one batch where the blowoff clogged at peak fermentation, I didn't notice it, and the pressure skyrocketed for a couple of days. Once I fixed the problem (along with the ensuing horrible mess) the fermentation finished off just fine. Again, I'll note that spunding really improved my beer - if any damage has been caused by pressure it gets completely overwhelmed by the positive influences, which I largely attribute to O2 mitigation.

Cheers

Great feedback thank you! That makes me less worried about it.

One other thought I just had, and maybe an expert in fluid dynamics can answer this:

Fluid in not compressible, so how does that affect how the yeast would experience the pressure?

does that mean that there would be a pressure gradient throughout the liquid with the surface experiencing the most pressure from the compressed gas above, and it would decrease toward the bottom of the keg? Or maybe a sweet spot in the middle?