The primary source for oxygenating the beer in the receiving keg, if not purged, is due to splashing of the wort in the receiving keg, along with beer surface exposure to air. That is why when transferring via auto-siphon you place the the hose end at the bottom of the keg - so that it is quickly buried under the level of beer so as to reduce splashing.
I rarely do it, but especially in certain circumstances purging the keg prior to racking into it is recommended, such as by Vinnie Cilurzo when racking Pliny the Elder into kegs and wanting to minimize oxegenation of the beer. He explains it in:
My SOP is to pressurize the keg to 20 psig (30 psia) and push the sanitizer out to get the dip tube, beer line, and faucet sanitized, then blow down using the PRV and repeat the pressurize/blowdown process twice more. That should reduce the O2 from 21% to <1%. Attach the auto-siphon to the liquid post, open the PRV to start the flow, finish racking the beer, and then pressurize/blowdown three more times to purge the headspace. Once you actually play around with a DO meter, it’s shocking how much purging is necessary.
5 Star’s CMC, in case anyone was wondering. Awesome stuff.
How would you attach the auto-siphon to the liquid post? What if I don’t use an auto-siphon anymore and simply fill the keg with a silicone tube from my ball valve on the fermenter.
Gave this a try yesterday and even after purging the empty keg with the PRV multiple times, gunk kept squirting out of the keg randomly. Did I do something wrong? Figured something was off so I never bothered trying to transfer beer this way.
I’m guessing you can’t do a closed transfer without using two kegs. In my case I’m using a keg and a fermenter.
Just to clarify, I ran a silicone tube from my fermenter into the out post of the keg as others mentioned above. Prior to hooking up the tube, I noticed that there was dark green sediment that would periodically spray out of the keg. This is after bleeding off all pressure, perhaps there was more in there as the lid wasn’t opened yet.
Whoops, guess I should’ve specified…this is the same keg that I’m using to just dump a new batch of beer into an existing empty keg without cleaning. “Lazy Kegging” post…
I figured as much. Still not sure I understand what’s happening though. Beer is coming out of the PRV when you vent it? Or leaking from somewhere else?
You wouldn’t need to purge a “dirty” keg, by the way. It’s already full of CO2.
I typically gravity feed my beer into the keg through the open lid via silicone tubing from the fermenter.
This time I tried to do the same thing, but instead of letting the beer flow through the lid, I was going to try and let if low through the “Out” post on the keg (assuming this was a closed transfer).
I assumed I needed to bleed off pressure or else the beer wouldn’t be able to gravity flow into the keg. Once I got the post on (prior to attaching tubing), it started to squirt some of the trub out even after I continued to bleed CO2.
After spraying this trub various times, I said &%$& it and transferred like I normally do.
That doesn’t sound like a great practice anyway. The tubing would be full of air prior to starting the transfer. What I do is start the siphon with the end of the tubing in a bucket of sanitizer, then attach the QD to the tubing under the level of the sanitizer once beer has filled the tubing.
Regardless, it’s really weird to have anything coming out of the liquid post with no pressure on the keg. Are you sure the PRV was locked open?