Head space when keg priming

[Andy Brosius]

I've started gyle-priming my kegs rather than relying on forced carbonation. I like the idea of having secondary fermentation to scoop up any dissolved oxygen that may have entered the beer while racking to the keg, but I'm a bit concerned about the keg space.

Should I purge the head space with CO2 before allowing the secondary fermentation to commence? Or is that air needed by the residual yeast?

Until now I've purged the head space with good results, but on my latest batch I didn't - and now I'm paranoid that I've oxidized the beer (it's still too early to taste).

Thanks!

 

[IslandLizard]

When you rack into an open, empty (air-filled) keg, I'd say you absorb plenty of O2. But it's an unknown amount, could be too much even. I'd purge that headspace.

For a more controlled amount of air, do a closed or semi-closed transfer by racking into liquid pre-purged keg, through the beer post, leaving the lid on. After filling, just open the lid, add your Speise and close her up. For more air, let her stand open for 5 minutes, then you're sure the headspace is all air, and 1-2 quarts of it.

 

[Vale71]

Refermentation does not require oxygen and any oxygen your beer is exposed to will oxidize it. Yeast offers little to no protection against oxidation once fermentation is complete.

 

[Andy Brosius]

When you rack into an open, empty (air-filled) keg, I'd say you absorb plenty of O2. But it's an unknown amount, could be too much even. I'd purge that headspace.

For a more controlled amount of air, do a closed or semi-closed transfer by racking into liquid pre-purged keg, through the beer post, leaving the lid on. After filling, just open the lid, add your Speise and close her up. For more air, let her stand open for 5 minutes, then you're sure the headspace is all air, and 1-2 quarts of it.

Thanks - I'll need to look into how to do a closed/semi-closed transfer. I do purge the starsan in the keg with CO2 prior to racking; I assume that's what you're referring to as a liquid purged keg? I'm always a bit paranoid about the residual starsan foam that ultimately winds up as a substantial amount of liquid at the bottom of the keg, so I usually pour it out before racking. Perhaps I shouldn't be doing that though.

 

[Andy Brosius]

Refermentation does not require oxygen and any oxygen your beer is exposed to will oxidize it. Yeast offers little to no protection against oxidation once fermentation is complete.

Thanks. I knew it was of dubious value, but common sense would suggest that it's better to not allow the beer to remain exposed to the oxygen indefinitely - right? Or are you saying the damage is done with the first moment of exposure, and additional time has no impact?

 

[Vale71]

Time is certainly a factor and prolonged exposure will only increase the damage.

 

[IslandLizard]

Thanks - I'll need to look into how to do a closed/semi-closed transfer. I do purge the starsan in the keg with CO2 prior to racking; I assume that's what you're referring to as a liquid purged keg? I'm always a bit paranoid about the residual starsan foam that ultimately winds up as a substantial amount of liquid at the bottom of the keg, so I usually pour it out before racking. Perhaps I shouldn't be doing that though.

Indeed, you shouldn't...
If you open the keg after a 100% liquid purge, you defy the whole premise of an oxygen free transfer. The lid should stay on until your next cleaning.

When you fill the keg completely with Starsan then push it out, there's very little foam. Some Starsan will cling to the walls and drip down over time.

After the full Starsan purge, I let the keg sit for 10-15 minutes then blow the rest out at 15 psi or so. That works with full length liquid dip tubes set properly inside the little well in the bottom.

Or you can invert the keg, leaning it toward the gas post, to let it accumulate in the dome, then push the gas poppet. For that you will need to shorten your your gas dip tube so it's flush or recessed within the dome. Which is not a bad thing at all, as it will also reduce the chances of beer backing up into your gas system too if the keg is overfilled or the beer is very foamy.

 

[LittleRiver]

... a bit paranoid about the residual starsan foam that ultimately winds up as a substantial amount of liquid at the bottom of the keg, so I usually pour it out before racking. Perhaps I shouldn't be doing that though.

I sanitize my kegs using about two cups of Starsan, swirling and shaking the keg to make sure all surfaces are wetted. Then I open the top and drain out all of the sanitizer. I use fermentation gas to purge the keg. I find this process to be more efficient and more effective than purging 5gal of Starsan out of a keg with bottled CO2.

Gravity powered closed transfers are easy.

 

[Andy Brosius]

When you fill the keg completely with Starsan then push it out, there's very little foam. Some Starsan will cling to the walls and drip down over time.

After the full Starsan purge, I let the keg sit for 10-15 minutes then blow the rest out at 15 psi or so. That works with full length liquid dip tubes set properly inside the little well in the bottom.

Part of the issue is that I'm not filling the keg completely with starsan - it's a precious commodity here so I try to conserve where possible. I generally fill it up half way.

Still, it's clear I should be purging it after allowing the foam to settle out, and not opening the keg and pouring it out. Thanks

 

[Andy Brosius]

I sanitize my kegs using about two cups of Starsan, swirling and shaking the keg to make sure all surfaces are wetted. Then I open the top and drain out all of the sanitizer. I use fermentation gas to purge the keg. I find this process to be more efficient and more effective than purging 5gal of Starsan out of a keg with bottled CO2.

Gravity powered closed transfers are easy.

Thanks for that link - that's extremely helpful. One quick question about your closed gravity transfer: when you are ready to transfer to the keg, do you use the same line that had previously been used as the CO2 outlet? So just move the line from the top of the fermenter (where the airlock would be) and attach to the fermenter drain instead? Or would you use a fresh line?

 

[IslandLizard]

Part of the issue is that I'm not filling the keg completely with starsan - it's a precious commodity here so I try to conserve where possible. I generally fill it up half way.

Still, it's clear I should be purging it after allowing the foam to settle out, and not opening the keg and pouring it out. Thanks

I understand that wherever you live Starsan may be expensive or difficult to obtain. But Starsan can be recovered, stored and reused, almost indefinitely.
A Starsan working solution really doesn't go bad, even after a year (or 2). There are a few precautions though, when storing it... Let me know if interested in more details.

If you're already filling half the keg, you may as well go all the way and fill the whole keg.
Reclaim the purged Starsan in another keg, and top up to the brim. Don't leave (much) air in it!

Alternatively, you could use clean drinking water to purge. If your water isn't quite "kosher," after all water has been pushed out, resanitize by adding some Starsan working solution (pint, quart) through the liquid or gas post. Swirl, shake, roll, whatever you fancy, then push that out, and reclaim. Done!

The essence is, after purging, the lid remains on at all times until you clean it.

 

[IslandLizard]

I should be purging it after allowing the foam to settle out,

You cannot purge a half filled keg from air (oxygen) content to any standard, without wasting inordinate amounts of CO2.

When you fill the keg to the brim, there simply is no foam. Both problems solved!

 

[balrog]

I highly recommend the purge with fermentation gasses method.

 

[Andy Brosius]

You cannot purge a half filled keg from air (oxygen) content to any standard, without wasting inordinate amounts of CO2.

When you fill the keg to the brim, there simply is no foam. Both problems solved!

Perhaps I'm missing something here. Wouldn't it require the same amount of CO2, whether the keg was half full or completely full to begin with? Ultimately the keg will still be filled with the same volume of CO2... right?

 

[IslandLizard]

I highly recommend the purge with fermentation gasses method.

Agreed! But he still needs to start out with fully filled kegs, right?

And as long as the fermenter doesn't leak (gas) and can generate enough pressure to purge the keg(s), yes?

 

[Andy Brosius]

A Starsan working solution really doesn't go bad, even after a year (or 2). There are a few precautions though, when storing it... Let me know if interested in more details.

Absolutely - please share! I do keep a few spray bottles around that go weeks/months without changing, but for really sensitive items like kegs and fermenters I've always erred on the side of caution and created a fresh batch.

Reclaim the purged Starsan in another keg, and top up to the brim. Don't leave (much) air in it!

Thanks - I'll try this next time.

 

[IslandLizard]

Perhaps I'm missing something here. Wouldn't it require the same amount of CO2, whether the keg was half full or completely full to begin with? Ultimately the keg will still be filled with the same volume of CO2... right?

Sorry, that's not the case.

Purging a partially filled keg you end up with a mixture of air (containing ~21% O2) and CO2. You can decrease the amount of O2 with additional purges, but never get rid of it.

 

[Andy Brosius]

Sorry, that's not the case.

Purging a partially filled keg you end up with a mixture of air (containing ~21% O2) and CO2. You can decrease the amount of O2 with additional purges, but never get rid of it.

I had not thought of that. Good point.

 

[LittleRiver]

... closed gravity transfer: when you are ready to transfer to the keg, do you use the same line that had previously been used as the CO2 outlet?...

I just take off the black "beer" quick disconnect fitting and put on a grey "gas" fitting. I have a little pinch clamp on the hose near the fitting, so I can retain the fermentation gas in the hose while the fitting is changed.

I use bottled CO2 to purge the fermenter drain hose before I attach it to the fermenter. I want to eliminate this use of bottled CO2. My plan is to join the drain hose to the fermenter blow-off hose during fermentation, with some in-line quick disconnects. That way fermentation gas will purge both hoses, and I can easily take them apart when it comes time to transfer.

 

[balrog]

Agreed! But he still needs to start out with fully filled kegs, right?

And as long as the fermenter doesn't leak (gas) and can generate enough pressure to purge the keg(s), yes?

Reading @doug293cz 's master treatise on the subject, here, says start empty with air, purge with fermentation gas of standard 5g batch, will purge O2 from keg.

 

[doug293cz]

Reading @doug293cz 's master treatise on the subject, here, says start empty with air, purge with fermentation gas of standard 5g batch, will purge O2 from keg.

Correct. But at some point there will be too much headspace, or trying to purge too many air filled kegs will not give adequate results (i.e. residual O2 higher than acceptable.) You shouldn't ever have to worry about headspace volume equal to beer volume, or purging up to two kegs. Can, you purge 5 or 10 kegs? This analysis gets complicated, and the original analysis is likely not completely applicable.

Brew on

 

[balrog]

I am a one batch, one keg, at a time, kinda guy. Still working out the purging of lines and learning the joys of push in tubing connectors.

 

[Andy Brosius]

I just take off the black "beer" quick disconnect fitting and put on a grey "gas" fitting. I have a little pinch clamp on the hose near the fitting, so I can retain the fermentation gas in the hose while the fitting is changed.

I use bottled CO2 to purge the fermenter drain hose before I attach it to the fermenter. I want to eliminate this use of bottled CO2. My plan is to join the drain hose to the fermenter blow-off hose during fermentation, with some in-line quick disconnects. That way fermentation gas will purge both hoses, and I can easily take them apart when it comes time to transfer.

Thanks! One step at a time for me...