[KCguy]

Pressurized keg with co2. I pull the pressure release valve at the top and I know that exhales CO2 does allow oxygen to go in every time I use that valve?  At this point I do not have the CO2 tank hooked up to the keg it’s merely been filled with new beer and the keg was filled with CO2 before that.

[RC]

In what you describe, you are not allowing O₂ in, but you are also not purging out most of the O₂. A boatload of O₂ is still in there, and it's really just a matter of consuming the beer before the O₂ does damage that you can start tasting. Any O₂ that gets in via the PRV is the least of your concerns.

[MDL]

I fill my kegs fully with water, add sanitizer, and then push sanitizer out with co2. Invert keg and drain last bits of sanitizer out through the prv. Then use CO2 to push beer from the fermenter to the others keg in through the liquid line on the keg. This seems to have eliminated any kegging oxidation.

[Kevin]

The little bit of Starsan left behind from such a purge will not affect your beer. I would be much more concerned that your method will allow microbes from the air into a keg thus undoing all your sanitizing efforts.

[MDL]

The little bit of Starsan left behind from such a purge will not affect your beer. I would be much more concerned that your method will allow microbes from the air into a keg thus undoing all your sanitizing efforts.

The keg is pressurized the entire time. Once it gets filled with sanitizer it never gets depressurized. When it’s inverted to drain the sanitizer it’s under pressure. When it’s being filled it’s under pressure

I keg into 1/2bbl Sankeys with clear beer draught systems installed. There’s about a pint or so of sanitizer left in the bottom of the keg. Inverting and blowing that out the prv is a good idea because there is a lot of oxygen dissolved in that water.

[goose]

Another thing to remember that that there is a good bit of O2 dissolved in the water used to mix up the sanitizer, unless you first boil the sanitizer water water or remove it chemically, it is unavoidable. I try to keep my Saniclean (the non-foaming version of Star San) in a Rubbermaid cooler and when sanitizing kegs use a syphon hose to transfer the sanitizer to the keg through the beer out keg plug to avoid splashing it and introducing additional O2. (I store my clean kegs pressurized with CO2 and sanitize them right before filling them).
The headspace in the keg is then purged with CO2, sanitized, and the sanitizer is pumped out to either a second keg to be sanitized, through the beer out keg plugs, or back to the Rubbermaid cooler.  There will always be a small amount of O2 left in the keg because of Charles' Law and the fact that there is almost always some O2 dissolved in the CO2 that you get from your dealer.  But taking additional steps to minimize any O2 pickup during packaging always helps protect the beer from oxidation.

Just something else to consider

[chinaski]

I gotta say- yes in theory there are lots of ways that small amounts of O2 can enter a keg and in theory decrease the shelf-life of beer.  But jeezum crow- this is homebrewing- do your best and move on.  I would love it if the universe sent me all of the dollars spent on shiny equipment sold to presumably improve homebrewed beer that may not matter.  There is a reason that Charlie P's mantra was Relax, Don't Worry, Have a Homebrew!  Until you test your methods for O2 removal again other, less-cautious, methods- don't assume that it matters that much. 

[BrewBama]

Another thing to remember that that there is a good bit of O2 dissolved in the water used to mix up the sanitizer, …

If I push all the sanitizer out with CO2 does it matter that there was O2 in the sanitizer that isn’t in the keg anymore? 

I figure if I transfer to a keg a few points shy of FG, the yeast will take care of any residual O2, if there is any, and possibly that yeast can carbonate the beer.

…  I would love it if the universe sent me all of the dollars spent on shiny equipment sold to presumably improve homebrewed beer that may not matter.

The only cost for the above is a jumper cable from the fermenter to the keg and a universal quick disconnect post to push the sanitizer out.

There is a reason that Charlie P's mantra was Relax, Don't Worry, Have a Homebrew!

+1. Something so simply as a jumper is so easy it makes sense for me. Now, whether it removes O2 or not….. I don’t test for O2 throughout the brew but this adds so little cost and is so easy to execute I figured why not.

[Richard]

Another thing to remember that that there is a good bit of O2 dissolved in the water used to mix up the sanitizer, …

If I push all the sanitizer out with CO2 does it matter that there was O2 in the sanitizer that isn’t in the keg anymore? 

I figure if I transfer to a keg a few points shy of FG, the yeast will take care of any residual O2, if there is any, and possibly that yeast can carbonate the beer.

…  I would love it if the universe sent me all of the dollars spent on shiny equipment sold to presumably improve homebrewed beer that may not matter.

The only cost for the above is a jumper cable from the fermenter to the keg and a universal quick disconnect post to push the sanitizer out.

There is a reason that Charlie P's mantra was Relax, Don't Worry, Have a Homebrew!

+1. Something so simply as a jumper is so easy it makes sense for me. Now, whether it removes O2 or not….. I don’t test for O2 throughout the brew but this adds so little cost and is so easy to execute I figured why not.

Yeast that are dormant can't take up any oxygen. Unless you warm up your beer to a temperature where yeast are active they are not important, and I think you are better off keeping your beer cold.

After doing the sanitizer purge a few times I have given up on it. Now I sanitize kegs a few days before brew day, empty them out and let them sit closed up. Then on brew day I hook them up so the fermentation gas flows through the kegs and purges them, then goes into a blowoff jar. It is easier than pushing sanitizer out with CO2 and it works as well or better. I also have a tee in the line to the keg to fill up a mylar balloon to eliminate suckback during cold crash. No residual sanitizer, no use of bottled CO2 for purging, no suckback. Simple, easy, clean and cheap.

[ynotbrusum]

Another thing to remember that that there is a good bit of O2 dissolved in the water used to mix up the sanitizer, …

If I push all the sanitizer out with CO2 does it matter that there was O2 in the sanitizer that isn’t in the keg anymore? 

I figure if I transfer to a keg a few points shy of FG, the yeast will take care of any residual O2, if there is any, and possibly that yeast can carbonate the beer.

…  I would love it if the universe sent me all of the dollars spent on shiny equipment sold to presumably improve homebrewed beer that may not matter.

The only cost for the above is a jumper cable from the fermenter to the keg and a universal quick disconnect post to push the sanitizer out.

There is a reason that Charlie P's mantra was Relax, Don't Worry, Have a Homebrew!

+1. Something so simply as a jumper is so easy it makes sense for me. Now, whether it removes O2 or not….. I don’t test for O2 throughout the brew but this adds so little cost and is so easy to execute I figured why not.

Yeast that are dormant can't take up any oxygen. Unless you warm up your beer to a temperature where yeast are active they are not important, and I think you are better off keeping your beer cold.

After doing the sanitizer purge a few times I have given up on it. Now I sanitize kegs a few days before brew day, empty them out and let them sit closed up. Then on brew day I hook them up so the fermentation gas flows through the kegs and purges them, then goes into a blowoff jar. It is easier than pushing sanitizer out with CO2 and it works as well or better. I also have a tee in the line to the keg to fill up a mylar balloon to eliminate suckback during cold crash. No residual sanitizer, no use of bottled CO2 for purging, no suckback. Simple, easy, clean and cheap.

If fermenting under pressure, you could put an inline spunding valve (think "Blowtie" from Kegland) and then connect to the keg's gas in post.  I prefer to blow out sanitizer with the fermenter produced CO2 and skip the early transfer and final spund in keg.  I can let my carbonated, finished beer clear up in the primary fermenter and transfer (using a floating dip tube) after a few days to the serving keg.  Cold crash is done under pressure, as well, adding CO2 in that process from the bottle.  If necessary, I will push it from the fermenter to the keg with a little extra CO2 from the bottle at that point.  I also have a spunding valve on the recipient keg set at a few psi lower than the primary fermenter.  It sounds like a lot of effort, but it really is not. 

Ultimately, the trade off is CO2 from the bottle (with its level of O2) versus catching the spund at the right point to make sure the O2 is fully scavenged.  Of course the Tilts make it easier to catch the spund timing.

Good discussion; I might try your way on the next batch.