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Well-Known Member
Jun 23, 2011
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Need y'all to reaffirm or poke holes in this for me.....

I ferment in corny kegs and have been thinking about ways to save on some CO2. I'm not looking to replace my tanks or anything but since so much CO2 is produced during fermentation I was thinking why not capture and use it for stuff like transfers and purging. What I am wondering is given enough head space so I don't have blow back, can I create a gas to gas jumper and have the CO2 from the fermenting keg transfer into the a clean sanitized keg?

Initial thoughts on problems to over come:

1. Getting pure CO2 not an O2, DMS, CO2 mix. Possibly over come this one by spunding the first 24 hours of fermentation to purge a bit and then add the jumper (not a scientist)?

2. Making the CO2 go into the keg you want it to (the empty one). I am looking at building a blowtie spunding valve and and essentially would put a ballock on the end of the blow off going into the keg I want to have capture the CO2. This would do two things 1) make sure the PSI is under control and 2) from what I can tell is the blowtie is directional so it would make sure the gas flow is going the right direction.

Please tear this apart or offer solutions. I have time to experiment with this these days :).
It totally works. Just hook up a tube from the fermenter keg's gas IN post to either post on the serving keg to vent the CO2 and purge the serving keg. Hook up a blow-off tube to the other post on the serving keg, terminated in a jar of Star-San.

When fermentation is finished, you can transfer into the serving keg under complete cover of CO2.

If you have a spunding valve, you have several more options. You can ferment under pressure (spunding valve replaces the blow-off on the serving keg during the entire process), then transfer into the serving keg. This allows you to use gravity for transferring rather than pressure from an external CO2 tank, since both kegs are already pressurized.

Or, you can ferment normally with a blow-off until the point of spunding, then transfer into the serving keg with a few gravity points remaining, and proceed to spund.

Here's an example of doing this with another kind of fermenter. You can see the blow-off jar at the lower left, under the stool. Right now it's about 32 hours into fermentation, and I'm waiting for the right time to transfer and spund.

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