[JT]

I submitted the following query on both Lallemand's and Fermentis' websites.  (The wet guys' websites don't seem to offer a way to submit technical questions,  and I'm keen on dry yeast lately anyway.)  I'll post any replies I receive.

"I am a homebrewer switching to a new system, fermenting under 5-6 psig head pressure. What considerations should I be aware of regarding yeast performance? Should I alter fermentation temperature or pitching rate? Are there differences in suitability to these conditions among strains? Thank you in advance."

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Good call.  Interested in the responses.  Great thread topic, btw.

[BrewBama]

They’ll get back with you pretty quickly. I’ve sent questions and received answers right away.


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[Robert]

^^^^
Indeed!  Already got this, from the guy I was in communication with on a previous thread:

Hi Robert,
Thank you for contacting Fermentis. A head pressure of 5-6 psi (head pressure) will not have a big impact in the behavior of the strains. Studies in the past demonstrate for lager strains that over 15psi and mainly over 26 psi you could have a reduction in the esters production but with 5-6 psi is business as usual.
Thank you,
José PIZARRO


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[denny]

^^^^
Indeed!  Already got this, from the guy I was in communication with on a previous thread:

Hi Robert,
Thank you for contacting Fermentis. A head pressure of 5-6 psi (head pressure) will not have a big impact in the behavior of the strains. Studies in the past demonstrate for lager strains that over 15psi and mainly over 26 psi you could have a reduction in the esters production but with 5-6 psi is business as usual.
Thank you,
José PIZARRO


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Just what I was gonna say!

[JT]

Robert, how are you serving the beers you are pressure fermenting?  I'm transferring to a corny, using the Tilt to ballpark SG prior to the transfer.  Are you keeping everything in the 10 gallon corny?

Looking forward to this Best Bitter. 

[Robert]

I'm not currently changing anything but replacing the airlock with the PRV.  Current SOP is to ferment to completion in the fermenter, rack to serving keg (which I just did with this batch,) then a couple of weeks or so lagering at 30°F (fined or not as I see fit,) then into the keezer to carbonate at serving  pressure and temperature before tapping.

BTW planning the next pressure fermented batch right now.  Think I'll do a tweak of a really enjoyable one from a few months ago I want to revisit.   Just pale malt and Invert, and Nottingham.   I'll follow the same mash and fermentation temperatures, since Fermentis says no adjustment  is needed, and see if it gets something like the 76.7% AA it did before.   I'm thinking, regarding this last, slightly underattenuated batch, a) IME S-04 isn't really all that attenuative (manufacturer cites 75% in laboratory conditions) and b) the variation from my reference batch is not all that informative.   Probably enough variables that any effects of pressure can't be teased out of the noise.

(Edited for omitted words.)

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[Robert]

Received this reply from Lallemand:

Hi Robert,
 
All of our brewing strains can effectively bottle condition, which gets to around 30 psi. I don’t expect that you will have any problems fermenting at 5-6 psi. You should be fine using a standard pitch rate between 0.5-1.0g/L for most ale strains. If you are brewing a higher gravity beer than pitch on the higher side.
 
I would appreciate your feedback though, please let me know how it turns out!
 
Cheers,
Eric
 
_________________________________________________________________________________
Eric Abbott, M.Sc. 


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[Robert]

I'm thinking, regarding this last, slightly underattenuated batch, a) IME S-04 isn't really all that attenuative (manufacturer cites 75% in laboratory conditions) and b) the variation from my reference batch is not all that informative.   Probably enough variables that any effects of pressure can't be teased out of the noise.

I've been trying to analyze my records on a  number ( of recent batches using S-04.   Average AA is 69.8%.  Eliminating the high and low it is 69.5%.  4 of the remaining 6 batches are right about on that average.   The highest of that group is 72.2%, the lowest is 66.4%.  The outliers in the 8 are this 64% batch, which is still closer to the average than the other end, 77.7%, a true anomaly.   So I really don't think there is any inference to be drawn from the attenuation of this batch, related to pressure or anything else for that matter.   I also fail to draw any correlation between attenuation and either mash program (which varies very little in my brewery) or mash or wort pH across the whole set.  I must conclude that materials and formulations are surely the most important variables. 

I propose that the suspected underattenuation of this batch cannot be confirmed by the data, and that my first pressure fermentation is consistent with confirming the yeast manufacturers' assertions that this level of pressure has no effect on fermentation.   I will of course continue to report results on the next few batches, and hope that anyone else trying this will also contribute their data in this thread.

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[brewinhard]

Beware (from what I understand) that fermenting under pressure can result in underattenuation and increased diacetyl/acetaldehyde production. Harvesting yeast from this and repitching can also lead to issues over time.

[Robert]

Beware (from what I understand) that fermenting under pressure can result in underattenuation and increased diacetyl/acetaldehyde production. Harvesting yeast from this and repitching can also lead to issues over time.

Do you have any references for this?   I'd appreciate any information.   

[denny]

Beware (from what I understand) that fermenting under pressure can result in underattenuation and increased diacetyl/acetaldehyde production. Harvesting yeast from this and repitching can also lead to issues over time.

Do you have any references for this?   I'd appreciate any information.

The chart Chris had that I'm trying to get a hold of.  Temp, pressure,  and yeast strain all played parts in the tests White Labs did.   That's why I wasn't too surprised at your results at that pressure.

[Robert]

Beware (from what I understand) that fermenting under pressure can result in underattenuation and increased diacetyl/acetaldehyde production. Harvesting yeast from this and repitching can also lead to issues over time.

Do you have any references for this?   I'd appreciate any information.

The chart Chris had that I'm trying to get a hold of.  Temp, pressure,  and yeast strain all played parts in the tests White Labs did.   That's why I wasn't too surprised at your results at that pressure.

Did some more reading, don't know how I missed this before.

Briggs, Boulton et al. (p. 482) refer to trials under "moderate" top pressure leading to suppressed yeast growth as well as yeast damage, higher than normal pH, reduced head retention and other effects suggestive of autolysis and effects of increased dissolved CO2.   It should be noted that what they call "moderate" pressurization is 1.2-2 Bar, and the trial conditions also included increased temperature.   Nonetheless, they make an important distinction:

Brulosoohy (always taken with a grain of salt) suggested that 5-6 psig top pressure is merely equivalent to the hydrostatic pressure yeast experience in commercial fermentation.   I wondered about this, whether it was apples and oranges.  Briggs, et al. clearly state that the effects of hydrostatic pressure are quite distinct from those of top pressure, primarily, I gather, because a sealed (top pressurized) vessel does not allow the escape of deleterious substances.

Since I may ( I know I tried to dismiss it yesterday) have experienced three of the key effects mentioned in Briggs -- suppressed yeast growth indicated by or the slow start and low attenuation,  a higher than normal pH,  and possibly reduced foam capacity (can't confirm this yet, but samples may have suggested it) -- I'm now having serious second thoughts about continuing with this procedure even at 5-6 psig.

Thoughts welcome.

[denny]

Beware (from what I understand) that fermenting under pressure can result in underattenuation and increased diacetyl/acetaldehyde production. Harvesting yeast from this and repitching can also lead to issues over time.

Do you have any references for this?   I'd appreciate any information.

The chart Chris had that I'm trying to get a hold of.  Temp, pressure,  and yeast strain all played parts in the tests White Labs did.   That's why I wasn't too surprised at your results at that pressure.

Did some more reading, don't know how I missed this before.

Briggs, Boulton et al. (p. 482) refer to trials under "moderate" top pressure leading to suppressed yeast growth as well as yeast damage, higher than normal pH, reduced head retention and other effects suggestive of autolysis and effects of increased dissolved CO2.   It should be noted that what they call "moderate" pressurization is 1.2-2 Bar, and the trial conditions also included increased temperature.   Nonetheless, they make an important distinction:

Brulosoohy (always taken with a grain of salt) suggested that 5-6 psig top pressure is merely equivalent to the hydrostatic pressure yeast experience in commercial fermentation.   I wondered about this, whether it was apples and oranges.  Briggs, et al. clearly state that the effects of hydrostatic pressure are quite distinct from those of top pressure, primarily, I gather, because a sealed (top pressurized) vessel does not allow the escape of deleterious substances.

Since I may ( I know I tried to dismiss it yesterday) have experienced three of the key effects mentioned in Briggs -- suppressed yeast growth indicated by or the slow start and low attenuation,  a higher than normal pH,  and possibly reduced foam capacity (can't confirm this yet, but samples may have suggested it) -- I'm now having serious second thoughts about continuing with this procedure even at 5-6 psig.

Thoughts welcome.

Chris was pretty specific about 1 bar being the required pressure.  I was thinking about trtying this, but after doing some more research it looks like it's too finicky and has variable results.  Can't really see an advantage to it.

[Robert]

Beware (from what I understand) that fermenting under pressure can result in underattenuation and increased diacetyl/acetaldehyde production. Harvesting yeast from this and repitching can also lead to issues over time.

Do you have any references for this?   I'd appreciate any information.

The chart Chris had that I'm trying to get a hold of.  Temp, pressure,  and yeast strain all played parts in the tests White Labs did.   That's why I wasn't too surprised at your results at that pressure.

Did some more reading, don't know how I missed this before.

Briggs, Boulton et al. (p. 482) refer to trials under "moderate" top pressure leading to suppressed yeast growth as well as yeast damage, higher than normal pH, reduced head retention and other effects suggestive of autolysis and effects of increased dissolved CO2.   It should be noted that what they call "moderate" pressurization is 1.2-2 Bar, and the trial conditions also included increased temperature.   Nonetheless, they make an important distinction:

Brulosoohy (always taken with a grain of salt) suggested that 5-6 psig top pressure is merely equivalent to the hydrostatic pressure yeast experience in commercial fermentation.   I wondered about this, whether it was apples and oranges.  Briggs, et al. clearly state that the effects of hydrostatic pressure are quite distinct from those of top pressure, primarily, I gather, because a sealed (top pressurized) vessel does not allow the escape of deleterious substances.

Since I may ( I know I tried to dismiss it yesterday) have experienced three of the key effects mentioned in Briggs -- suppressed yeast growth indicated by or the slow start and low attenuation,  a higher than normal pH,  and possibly reduced foam capacity (can't confirm this yet, but samples may have suggested it) -- I'm now having serious second thoughts about continuing with this procedure even at 5-6 psig.

Thoughts welcome.

Chris was pretty specific about 1 bar being the required pressure.  I was thinking about trtying this, but after doing some more research it looks like it's too finicky and has variable results.  Can't really see an advantage to it.

That's where I am.  I may come back to try it again, but until at least after I've tapped this first batch and really seen the results,  I don't feel like blindly risking any more batches.   The big advantage for me was a built in supply of CO2 for sampling, but that's not worth potentially damaging yeast and beer.  I wonder if the effects are not only strain specific, but scale in unexpected ways.  Maybe for some reason, 6 psig does to 6 gallons what 2 Bar does to 100 bbl.

Hey Denny, at least I'm rediscovering my experimental impulses! 

[denny]

That's where I am.  I may come back to try it again, but until at least after I've tapped this first batch and really seen the results,  I don't feel like blindly risking any more batches.   The big advantage for me was a built in supply of CO2 for sampling, but that's not worth potentially damaging yeast and beer.  I wonder if the effects are not only strain specific, but scale in unexpected ways.  Maybe for some reason, 6 psig does to 6 gallons what 2 Bar does to 100 bbl.

Hey Denny, at least I'm rediscovering my experimental impulses! 

Then it's not a total loss!  Where did you come up with 6 psi, though?