Author Topic: Re-using CO2 from a spent keg?  (Read 400 times)

Offline Joe_Beer

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Re-using CO2 from a spent keg?
« on: October 29, 2021, 05:29:32 pm »
cheapskate question for the week: Anyone ever use the co2 from a spent keg to purge starsan out of a "new" one in order to prep for a closed transfer? I've done it a few times now because reusing the CO2 from a spent keg just seems like an easy cheat. Not sure what I could be screwing up though so kinda curious if others have tried this.

Offline allenhuerta

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Re: Re-using CO2 from a spent keg?
« Reply #1 on: October 29, 2021, 05:38:11 pm »
Interesting.. I never thought of this lol the only think I can think of is maybe some gunk might get kicked up from the old keg.. but it's a sanitary environment and wouldn't expect enough, if any, issues from that with the new beer. I think you're onto something...

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Offline Richard

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Re: Re-using CO2 from a spent keg?
« Reply #2 on: October 29, 2021, 05:40:09 pm »
I have never tried this, but I don't see anything wrong with it offhand. I stopped doing the keg purge with StarSan because I found it was a waste of CO2 and of StarSan. I don't have any need for more than a gallon of StarSan at any time. Now I sanitize my kegs with a few cups of StarSan that I recover, then I purge them with fermentation gas. I am using the same CO2 cylinder I started in April, so I don't feel a need to be any stingier with it.
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Offline Joe_Beer

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Re: Re-using CO2 from a spent keg?
« Reply #3 on: October 29, 2021, 06:17:03 pm »
I purge them with fermentation gas. I am using the same CO2 cylinder I started in April, so I don't feel a need to be any stingier with it.

So true. I'll sometimes spend $10 trying to save $5 before I realize what I'm doing. The last time I got my tanks filled though, the guy at the counter said they were starting to have some concern regarding supply. I'm not really sure if he was speaking about actual gas or shipping issues (like everything else right now).

Harvesting fermentation Co2 is a cool idea too. I used a big garbage bag taped to a hose last year to capture it but I hadn't quite perfected the method of squeezing the bag afterward to purge a new keg. It was bit of a comedy trying to get all the gas out of the bag.

Offline Bob357

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Re: Re-using CO2 from a spent keg?
« Reply #4 on: October 30, 2021, 06:13:30 am »
I don't see any difference between using CO2 from fermentation or a spent keg for purging. Been using CO2 from my pressurized fermenter since I got it. Between that, and my beer being mostly carbonated when it goes into a keg, a cylinder of CO2 now lasts me more than twice as long.
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Offline ynotbrusum

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Re: Re-using CO2 from a spent keg?
« Reply #5 on: November 01, 2021, 03:26:59 pm »
I don't see any difference between using CO2 from fermentation or a spent keg for purging. Been using CO2 from my pressurized fermenter since I got it. Between that, and my beer being mostly carbonated when it goes into a keg, a cylinder of CO2 now lasts me more than twice as long.

This is true - since I started using pressure fermentation, I can purge as many kegs as I can line up for the process.  Plus the final purged keg stays on through a cold crash.  My CO2 supplier is losing a lot of money on my account.  If only I could figure out a way to go from pressure ferment to capturing CO2 in a CO2 bottle....
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Offline Richard

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Re: Re-using CO2 from a spent keg?
« Reply #6 on: November 01, 2021, 04:48:43 pm »
I don't see any difference between using CO2 from fermentation or a spent keg for purging. Been using CO2 from my pressurized fermenter since I got it. Between that, and my beer being mostly carbonated when it goes into a keg, a cylinder of CO2 now lasts me more than twice as long.

This is true - since I started using pressure fermentation, I can purge as many kegs as I can line up for the process.  Plus the final purged keg stays on through a cold crash.  My CO2 supplier is losing a lot of money on my account.  If only I could figure out a way to go from pressure ferment to capturing CO2 in a CO2 bottle....

There's an easy way to do it, but you need to pressure ferment at 500 psi!!
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Offline Andy Farke

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Re: Re-using CO2 from a spent keg?
« Reply #7 on: November 07, 2021, 09:31:11 am »
I reuse my CO2 from spent kegs all the time! I started doing this in earnest during the start of the pandemic, when CO2 supplies were dodgy and I was avoiding unnecessary trips out. In fact, I recently submitted a post to the Zymurgy gadget issue with my (incredibly simple and cheap) CO2 transfer setup.

I've found that one empty and used five gallon keg of CO2 is a perfect amount for purging a Starsan-filled keg, with just a tiny bit of gas to spare.

Here is a blog post I did awhile back on this: https://andybrews.com/2020/04/05/conserving-co2-while-purging-kegs/

I have not noticed any ill effects from this -- I assume that as long as you are avoiding liquid transfer (which would only be an issue if you turn the keg on its side or plug into the wrong port), you should be OK.
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Online BrewBama

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Re: Re-using CO2 from a spent keg?
« Reply #8 on: November 07, 2021, 11:47:01 am »
I used CO2 from a spent keg to push sanitizer out of another keg once.  I don’t do it regularly.



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Offline kramerog

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Re: Re-using CO2 from a spent keg?
« Reply #9 on: November 15, 2021, 09:31:46 pm »
Yes, I reuse CO2 routinely.