Fermentation

[Jim L]

can I ferment a 3 gal. batch in a 6.5 fermentor

[tommymorris]

Yes. It will be mostly empty but it will be fine.

[dmtaylor]

Of course you can.

[Robert]

It is much tidier than fermenting a 6.5 gallon batch in a 3 gallon fermenter.     

Seriously, it is advantageous to use a fermenter  considerably larger than batch size; you shouldn't need a blow off.  I ferment 6 gallon batches in a 10 gallon fermenter.

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[Northern_Brewer]

OTOH I once had a leak in a bucket which meant I ended up fermenting one of a 4-way split batch as 1 gallon in a 5 gallon bucket - it was horribly oxidised compared to the other splits fermented in a 1g bucket.

[Robert]

OTOH I once had a leak in a bucket which meant I ended up fermenting one of a 4-way split batch as 1 gallon in a 5 gallon bucket - it was horribly oxidised compared to the other splits fermented in a 1g bucket.

Type of fermenter may be significant.  My oversized fermenter is a closed, stainless pressure vessel (10 gallon corny type tank)  so once fermentation expels the initial oxygen, none is present as there is no gas exchange with the atmosphere.   If there is a possibility of exchange, more gas in the headspace could, I suppose,  be detrimental.

[ynotbrusum]

OTOH I once had a leak in a bucket which meant I ended up fermenting one of a 4-way split batch as 1 gallon in a 5 gallon bucket - it was horribly oxidised compared to the other splits fermented in a 1g bucket.

Type of fermenter may be significant.  My oversized fermenter is a closed, stainless pressure vessel (10 gallon corny type tank)  so once fermentation expels the initial oxygen, none is present as there is no gas exchange with the atmosphere.   If there is a possibility of exchange, more gas in the headspace could, I suppose,  be detrimental.

So, Robert do you ferment without a blowoff and rely on a spunding valve set at a particular pressure?  If so, what pressure level do you ferment at?

[Robert]

OTOH I once had a leak in a bucket which meant I ended up fermenting one of a 4-way split batch as 1 gallon in a 5 gallon bucket - it was horribly oxidised compared to the other splits fermented in a 1g bucket.

Type of fermenter may be significant.  My oversized fermenter is a closed, stainless pressure vessel (10 gallon corny type tank)  so once fermentation expels the initial oxygen, none is present as there is no gas exchange with the atmosphere.   If there is a possibility of exchange, more gas in the headspace could, I suppose,  be detrimental.

So, Robert do you ferment without a blowoff and rely on a spunding valve set at a particular pressure?  If so, what pressure level do you ferment at?

No, this simple airlock arrangement serves during active fermentation.   For cold crashing I remove the "airlock" and apply a few psig before cooling.  I do have a spunding valve, but have never used it.   This seemed a much easier solution.   Maybe someday I'll try a pressure fermentation.

EDIT  If anyone can advise on what would be an appropriate pressure to set the spunding valve to -- strictly for fermentation purposes, not carbonation -- I would appreciate it, and look forward to trying this setup.
 

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[BrewBama]

5-6 PSI seems to be the consensus. http://brulosophy.com/2015/04/27/under-pressure-the-impact-of-higher-psi-fermentations-exbeeriment-results-2/

...or 8   http://brulosophy.com/2015/09/07/under-pressure-pt-2-the-impact-of-pressurized-fermentation-on-saison-xbmt-results/

...or 12. http://brulosophy.com/2016/06/13/under-pressure-pt-3-the-impact-of-pressurized-fermentation-on-lager-exbeeriment-results/

LOL. 

White Labs recommends “under 1.0 bar (14.7 PSI) until final gravity is obtained, generally in one week.” for its WLP925 yeast. https://www.whitelabs.com/yeast-bank/wlp925-high-pressure-lager-yeast

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[Robert]

Thanks.  I'll have to play around with my spunding valve to dial it in (from MoreBeer,  no calibration marks, but I gather the only thing that matters is the gauge.)  I got it for this purpose; as it only goes to 15 psig, it won't do for carbonating at fermentation temperature.   But 5ish sounds perfect as it will not significantly carbonate,  but solves my other problem of getting a CO2 supply to the ferm chamber to draw samples.  This weekend I expect to brew, and I'll try a ~5 psig fermentation.  I'll report in a separate thread.

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[DavieN]

5-6 PSI seems to be the consensus. http://brulosophy.com/2015/04/27/under-pressure-the-impact-of-higher-psi-fermentations-exbeeriment-results-2/

...or 8   http://brulosophy.com/2015/09/07/under-pressure-pt-2-the-impact-of-pressurized-fermentation-on-saison-xbmt-results/

...or 12. http://brulosophy.com/2016/06/13/under-pressure-pt-3-the-impact-of-pressurized-fermentation-on-lager-exbeeriment-results/

LOL. 

White Labs recommends “under 1.0 bar (14.7 PSI) until final gravity is obtained, generally in one week.” for its WLP925 yeast. https://www.whitelabs.com/yeast-bank/wlp925-high-pressure-lager-yeast

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You have to play around with the PRV.....i had to keep an eye on it but levelled out at 12 PSI.....Stayed steady for 3-4 days during fermentation then the pressure dropped to 6 PSI and stopped and has remained steady for 2 days. Am I correct in assuming the beer is ready for transfer to a keg.

[Robert]

5-6 PSI seems to be the consensus. http://brulosophy.com/2015/04/27/under-pressure-the-impact-of-higher-psi-fermentations-exbeeriment-results-2/

...or 8   http://brulosophy.com/2015/09/07/under-pressure-pt-2-the-impact-of-pressurized-fermentation-on-saison-xbmt-results/

...or 12. http://brulosophy.com/2016/06/13/under-pressure-pt-3-the-impact-of-pressurized-fermentation-on-lager-exbeeriment-results/

LOL. 

White Labs recommends “under 1.0 bar (14.7 PSI) until final gravity is obtained, generally in one week.” for its WLP925 yeast. https://www.whitelabs.com/yeast-bank/wlp925-high-pressure-lager-yeast

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You have to play around with the PRV.....i had to keep an eye on it but levelled out at 12 PSI.....Stayed steady for 3-4 days during fermentation then the pressure dropped to 6 PSI and stopped and has remained steady for 2 days. Am I correct in assuming the beer is ready for transfer to a keg.

I'm reporting on my experience with pressure fermentation here
https://www.homebrewersassociation.org/forum/index.php?topic=33013.0

I don't think pressure readings are the guide to progress; like any fermentation you need to track the density.