Capturing CO2

[Cherokee6]

After reading several posts and visiting various web sites, I decided to attempt to capture CO2 produced during fermentation. I thought this was also a great opportunity to purge a keg of oxygen so as to limit my beers exposure upon transfer. My process involved connecting a tube from a SS Brew Bucket to a keg full of Star San with a jumper hose running from that keg to an empty keg (with a gas QD connected). The idea was that CO2 produced during fermentation would push the Star San into the empty keg leaving me with an oxygen free primary keg. Here's my problem - after pushing about 4.5 gallons of Star San from the primary keg to the receiving keg, the transfer stopped. Not knowing where the problem resided, I removed the CO2 line running from the fermenter to the primary keg and noticed the release of a large amount of CO2 that had built up in the fermenter. It was clear that the CO2 coming from the fermenter was no longer making it to the primary keg. I have posted three pictures to depict my set-up for the transfer. Anyone have any ideas as to why this might occur?

 

[day_trippr]

Maybe the water pressure in the "catch keg" has built up to where it has caused a leak upstream - like in the lid of purging keg?
I can't believe ~20" of water pressure (~0.7 psi maybe?) could literally stall yeast from making CO2...

Cheers!

 

[DuncB]

If the ferment pressure is not enough to push thru keg one ( now purged ) and then thru the liquid in keg 2 you have a large airlock made.
I would connect keg one to keg two liquid to gas, then liquid keg 2 to a bucket to capture. Once keg 2 empty replumb so keg one gas to keg 2 liquid and put spunding valve on the the gas post of keg 2 and set to the pressure you want.

 

[DuncB]

Maybe the water pressure in the "catch keg" has built up to where it has caused a leak upstream - like in the lid of purging keg?
I can't believe ~20" of water pressure (~0.7 psi maybe?) could literally stall yeast from making CO2...

Cheers!

35 psi never stopped a ferment when I accidentally closed the system.

 

[Cherokee6]

Maybe the water pressure in the "catch keg" has built up to where it has caused a leak upstream - like in the lid of purging keg?
I can't believe ~20" of water pressure (~0.7 psi maybe?) could literally stall yeast from making CO2...

Cheers!

My initial thought was an upstream leak as well, but I was unable to find one. I sprayed all connections and lids with Star San and could not located any obvious leaks. My impression from the release of pressure when I removed the hose from the fermenter was that there was no reason why that CO2 wasn't pushing the remaining Star San out of the first keg.

 

[Cherokee6]

If the ferment pressure is not enough to push thru keg one ( now purged ) and then thru the liquid in keg 2 you have a large airlock made.
I would connect keg one to keg two liquid to gas, then liquid keg 2 to a bucket to capture. Once keg 2 empty replumb so keg one gas to keg 2 liquid and put spunding valve on the the gas post of keg 2 and set to the pressure you want.

Interesting. I truly thought that that the pressure from the fermentation would be enough to push that last 2 quarts out of keg 1. Your suggestion makes sense - push the liquid into keg 2 from in post (gas) on keg 2.

 

[DuncB]

Interesting. I truly thought that that the pressure from the fermentation would be enough to push that last 2 quarts out of keg 1. Your suggestion makes sense - push the liquid into keg 2 from in post (gas) on keg 2.

It works for me, have even done 3 kegs in a row. Not sure what pressure your fermenter can cope with. But once I'm near the end of ferment Krausen dropped at least I normally set the spund pressure to that needed for final carbonation vol. That can be say 30 psi for a kveik ferment at 30 celsius.
This does have a bit more pushing power. But you can easily move the starsan along with a lower pressure earlier during the ferment and get a good flow of CO2 thru the kegs to ensure no oxygen at all. I like to get those kegs up to pressure of my carbonation pressure , so I could have several kegs at say 25 psi.
Once at this pressure I disconnect them and then use the spunding valve on the fermenter ( again at target pressure for the temp current and target vols ).
After cold crashing the fermenting keg is at a lower pressure than the waiting kegs.
When you do closed transfer use gas to gas from the keg to fermenter to boost the pressure in the fermenter. Then liquid to liquid, briefly disconnect one gas to gas connection and pull prv on the keg to get the beer siphoning, then reconnect gas to gas to balance everything. If transfer slows two options spunding valve on keg 2 psi below the target pressure ( that of the fermenter originally ) or use another gas reserve keg to inject gas into the fermenter and push again. Don't reconnect gas to gas until flow slows otherwise you don't keep a difference and flow stops.

 

[Bilsch]

After reading several posts and visiting various web sites, I decided to attempt to capture CO2 produced during fermentation. I thought this was also a great opportunity to purge a keg of oxygen so as to limit my beers exposure upon transfer.

It's not necessary to push a liquid to create an oxygen free receiving keg. There is enough CO2 produced from a ferment to purge the serving keg many times over of the oxygen in contains. You simply need to connect from the fermenter to a cleaned, sanitized and dry serving keg then through a fermentation lock. This had been verified by several people who have the proper measuring equipment. Besides you don't want all that residual sanitizer in your beer if you can help it.

 

[DuncB]

Invert the keg after purging the liquid out and ensure it's disconnected. Briefly pull the PRV and any remaining sanitiser will come out of the prv.
I tend to flush liquid out then ongoing CO2 purge to be on the safe side and build up reserve CO2.
Agree with Bilsch though that a lot of CO2 is made by beer and more than enough to purge and pressurise several kegs.

 

[Cherokee6]

It's not necessary to push a liquid to create an oxygen free receiving keg. There is enough CO2 produced from a ferment to purge the serving keg many times over of the oxygen in contains. You simply need to connect from the fermenter to a cleaned, sanitized and dry serving keg then through a fermentation lock. This had been verified by several people who have the proper measuring equipment. Besides you don't want all that residual sanitizer in your beer if you can help it.

Pushing out the Star-San seemed like a better way for a guy like me who does not have the fancy equipment to ensure that the keg was oxygen free. I am not a chemical engineer (if that's the right job description), but I have read enough on various homebrew sites that talk about the mixing of gases to stay away from this topic as much as I can. However, maybe I can do a little more research....

As for the residual Star San, I can get most of it out - maybe a thimble remains? Seems that this is in the realm of reasonable for my homebrewing purposes.

 

[Cherokee6]

Invert the keg after purging the liquid out and ensure it's disconnected. Briefly pull the PRV and any remaining sanitiser will come out of the prv.
I tend to flush liquid out then ongoing CO2 purge to be on the safe side and build up reserve CO2.
Agree with Bilsch though that a lot of CO2 is made by beer and more than enough to purge and pressurise several kegs.

I too tend to flush the keg with CO2. Maybe overkill, but it works for me.

 

[doug293cz]

Invert the keg after purging the liquid out and ensure it's disconnected. Briefly pull the PRV and any remaining sanitiser will come out of the prv.
I tend to flush liquid out then ongoing CO2 purge to be on the safe side and build up reserve CO2.
Agree with Bilsch though that a lot of CO2 is made by beer and more than enough to purge and pressurise several kegs.

If you remove the PRV from the keg lid, turn the lid upside down, fill it with water, and let the water drain out thru the PRV opening, you will find the lid still holds ~3 fl oz of water. You get less remaining StarSan in the keg just pushing out thru a standard length dip tube.

If you really want to get all the StarSan out of a closed keg, then trim the gas tube so that it doesn't stick down past the fitting into the keg, and then tilt the keg so the lowest point is the gas disconnect fitting.

Brew on

 

[Bilsch]

Pushing out the Star-San seemed like a better way for a guy like me who does not have the fancy equipment to ensure that the keg was oxygen free. I am not a chemical engineer (if that's the right job description), but I have read enough on various homebrew sites that talk about the mixing of gases to stay away from this topic as much as I can. However, maybe I can do a little more research....

I understand your hesitation and would have probably done the same thing if it weren't for the information on such things I have access to.

The theoretical calculations, which were initially done by doug293cz on HBT, showed there is more then enough CO2 produced by the ferment to get the job done. Furthermore this was put to the test several times by three different brewers on a different forum and the actual numbers are quite a bit better than the theoretical ones. It takes slightly less than a day of ferment gas purging to bring the receiving keg to zero DO.

Trust us.. the liquid push is just not necessary.

 

[Cherokee6]

I understand your hesitation and would have probably done the same thing if it weren't for the information on such things I have access to.

The theoretical calculations, which were initially done by doug293cz on HBT, showed there is more then enough CO2 produced by the ferment to get the job done. Furthermore this was put to the test several times by three different brewers on a different forum and the actual numbers are quite a bit better than the theoretical ones. It takes slightly less than a day of ferment gas purging to bring the receiving keg to zero DO.

Trust us.. the liquid push is just not necessary.

BIlsch - anyway you can make that information available? I would love to read up on the process. Seems easier than the current process I am using. I am always looking to "up my game" and make my brew day easier, and what you are suggesting seems to meet both of these criteria!

 

[Bilsch]

BIlsch - anyway you can make that information available? I would love to read up on the process. Seems easier than the current process I am using. I am always looking to "up my game" and make my brew day easier, and what you are suggesting seems to meet both of these criteria!

I wish the circumstances were different and I could, but alas it is two different brewing forums and for what ever reason both prefer to keep separate from one another. Certainly their are members who belong to both and therefore some information will invariably migrate. Posting actual data however would probably cross a line and so I feel it's best to refrain from doing that.
Nothing stopping you from going and finding it though.

 

[Cherokee6]

Not a problem. I am sure that my friend Google can point in me in the right direction. Thanks for the information!

 

[doug293cz]

I understand your hesitation and would have probably done the same thing if it weren't for the information on such things I have access to.

The theoretical calculations, which were initially done by doug293cz on HBT, showed there is more then enough CO2 produced by the ferment to get the job done. Furthermore this was put to the test several times by three different brewers on a different forum and the actual numbers are quite a bit better than the theoretical ones. It takes slightly less than a day of ferment gas purging to bring the receiving keg to zero DO.

Trust us.. the liquid push is just not necessary.

Nice to see the confirmation on my theoretical calculations. As noted in my post, because of the similarity between CO2 flow rates and O2 diffusion rates, my only choice was to do a worst case analysis. So, it's not surprising that the actual data comes in better than the theoretical. Even the worst case analysis gave much lower residual O2 than I expected before I did the calculations. From a practical perspective, the pessimistic estimate of residual O2 is very useful, as it tells you that you don't have to worry about what's in your keg after the purge.

Brew on

 

[Bilsch]

Nice to see the confirmation on my theoretical calculations. As noted in my post, because of the similarity between CO2 flow rates and O2 diffusion rates, my only choice was to do a worst case analysis. So, it's not surprising that the actual data comes in better than the theoretical. Even the worst case analysis gave much lower residual O2 than I expected before I did the calculations. From a practical perspective, the pessimistic estimate of residual O2 is very useful, as it tells you that you don't have to worry about what's in your keg after the purge.

Indeed a great job especially considering some assumptions needed to be made where their were holes in the data available when you did the work. Glad we could help confirm. Perhaps this is the seeds of glasnost between our two countries?

 

[DuncB]

Sorry I don't use Corny kegs, so I don't have that gas dip tube issue discussed above leaving a cupful or whatever in the keg.
Of course could open the rabbit hole of using sod met solution as the flush out liquid instead of starsan and then any residual Sod met is an antioxidant / oxygen scavenger anyway!

 

[day_trippr]

Don't you have to make sure there's only enough SMB introduced to do the job as excess will confer a sulfur character?

Cheers!

 

[DuncB]

Don't you have to make sure there's only enough SMB introduced to do the job as excess will confer a sulfur character?

Cheers!

It's a very grey area and I'm not going there, just mentioned it. Obviously it's used in winemaking finishing for some kits and there's an allowable amount.
I suppose any sulphur character would be okay if you were making a burton ale.
I have seen it suggested to reduce oxidation of NEIPA, I'm not advocating it just putting it out there. Someone did reply in one thread about this and had some data to back it up as well as the use of ascorbic acid.
Maybe sterilise with starsan and then flush out a weak sod met solution. I'm happy with starsan and a lot of CO2 from the beer ferment.

 

[Bilsch]

Don't you have to make sure there's only enough SMB introduced to do the job as excess will confer a sulfur character?

Excess meta in the ferment sometimes causes sulfury notes but luckily you can remove it with extra oxygenation before the pitch. It's actually quite elegant the way the process works. Sulfites can also be added after the yeast are finished for stability but generally that isn't necessary if your process is solid.

 

[day_trippr]

The discussion was on using SMB for racking to kegs...

Cheers!

 

[Bilsch]

The discussion was on using SMB for racking to kegs...
Cheers!

So it was, sorry to miss that. Just assumed the mash as that is where the yeast can create some offensive sulfur compounds from the sulfites if they are not expended. I'm not aware that this same thing can happen after the ferment is complete.