Purging the oxygen out of the keg?

Will it affect your beer if you don’t purge the oxygen out when you first keg?

It could. Especially if you shake it or roll it to quick carb it.

If you put it on gas right away and just let it sit it’s less likely to cause an issue. The CO2 is heavier and will naturally drop down over the beer and protect it from the O2.

I wouldn’t sweat it too much. We’ve all done it at one time or another. If it tastes a bit oxidized just dry hop the crap out of it and serve it at a party.

I may get a little carried away with keeping my beer away from oxygen, so keep that in mind as you read this.

I fill the keg with star san from another keg until star san flows out the pressure release and the CO2 in valve. Then I pressurize the keg and blow all the star san out. I connect a hose with a liquid disconnect to the spigot at the bottom of the fermenter and let a bit of beer flow into the hose by pressing the pin in the center of the disconnect, Release the pressure from the keg, attach the disconnect to the keg and open the fermenter spigot. Release the pressure that builds up in the keg as it fills (I use a CO2 disconnect with a couple of feet of hose on it). You could probably figure out a way to do something similar with a siphon.

once cleaning the keg with starsan i do flush it out with co2 and ready to keg my kegs i do use are heineken and do close them up again carbonate its a pain once closed its done only empty i do open them again

After cleaning my keg, and ready to put brew in it, I would loosen the top, blast it for 30 seconds with CO2, then sneak yer racking tube into the keg, all the way to the bottom and transfer. You can alway blast it whilst you rack quietly…. I’m currently working/playing with fermenting in the keg, so far, so good… Sneezles61

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All I have ever done is to rack the beer into the keg, seal the top, connect the CO2 then pull the pressure release for a couple of seconds. If you have pin lock kegs and there is no pressure release, just hook up the CO2, pressurize the keg, disconnect and press the poppet valve with a small screwdriver. The O2 will be on top and vent out first.

Try not to splash the beer when filling the keg and it will be fine.


One reason I’m so extreme in purging my kegs is because I thought I remembered from some class in the far-distant past that gasses of different densities would mix in spite of different densities.

I did a little searching on Wikipedia and found:
"…gases of different nature, when brought into contact, do not arrange themselves according to their density, the heaviest undermost, and the lighter uppermost, but they spontaneously diffuse, mutually and equally, through each other, and so remain in the intimate state of mixture for any length of time.”

You are correct. Oxygen and co2 are not oil and water - they will readily mix. Otherwise we would all be dead with a layer of co2 at ground level, and all the nitrogen and oxygen at high elevations.

I thought that’s why I have to carry my son around!!! :wink:

As @old_dawg and @porkchop mention they will mix. However I don’t know if you need to go to absolute extremes to avoid any O2 pickup. Remember, this is a hobby and should be fun, not a second FT OG trying to avoid O2.

I agree. I don’t mind a little reading and research but there is a limit for me. Once I get the general idea then I try it. If it comes out good beer, I’m done with the research. That is not to say you guys that are really scientific about it are doing it wrong. Homebrewing is whatever you want to get out of it.

When I first started kegging I didn’t even purge the air out after filling the kegs. Can’t remember any problems with that. Just purging the headspace is easy so I do that just in case.

So I’ll say, sometimes I do forgot to blast my keg with CO2, and then It happens… some old swamp dog rolled around in my brew! :dizzy_face: I am more diligent to blast it with CO2 now more than ever… I will try old_dawg’ trick tho, why? Because I can and will see, ifn its something I will incorporate into my method, Trial and error… This exactly why I enjoy this forum, someone else did the extra reading and passes on the info, or has a tried and proven method that works for them, and Ifn it makes sense to me, I should give it a try. My quest is not the holy grail of brews, rather brew beers consistently, little to no flaws… Sneezles61

Just playing devil’s advocate…If the gases mix then it makes no difference either way purging the keg empty or after fill. Maybe it’s safer purging after the fill because there’s less O2 to mix with the CO2?

I’d estimate that I purge prior to fill about 50% of the time. Lately my MO has been after cleaning the keg i put a quart or so of starsan in, swish it around then push it out with CO2 prior to filling the keg or storing it for later.

If you enjoy your brewing process and the beer you produce, you’re doing it right!


basic gas law what i do use everyday at work filling nitrox tanks for diving

I THINK this is what happens when you repeatedly pressurize a keg with CO2 at 30 psi then depressurize. The upper set of numbers is in gallons. The bottom set is in percentages. I’ve ignored the CO2 and trace gasses in the atmosphere because they disappear into insignificance very quickly.

I usually hit it 2 or 3 times. Your saying 6? I usually go through a keg before there is a problem but maybe my lagers need a few more shots. What about beer that has been tapped for awhile ? Sometimes I pull them off line to make room , they may sit for awhile any benefit to repurging

I don’t provide a money-back guarantee on that spreadsheet, IF my arithmetic is right, three fills/releases will get you down to one pint of O2 which is 2.5%. Six times might be overkill. Or, if you subscribe to the low dissolved O2 school of German brewing it might not be sufficient.

I fill my kegs with Star San till it comes out the CO2-in port and the pressure release, then blow it all out with CO2. That’s extreme, but it only uses up one keg of CO2. The fill-and-release x ? seems to eat up 1/2 a keg with each repetition. I’m a cheapskate, so I go with one Star San fill followed by the CO2 fill.

It just occurred to me that if you have known sterile water, such as a chlorinated public water supply, you could sanitize the keg, then fill with water and force it out with CO2. Would the amount of chlorine in 2 - 4 oz of city water cause problems?

Old_dawg, your spreadsheet looks right to me.

CO2 is pretty expensive where I live, so I try not to waste any more than necessary, while balancing that the more critical goal of protecting the beer from oxidation. And I one time did forget to purge a keg and could notice the difference. What I’ve found works well is to siphon the beer into the empty keg, then purge 3-4 times. With a gentle racking into the keg, the air inside is displaced without significant mixing to the beer. And the headspace to be purged after that is only a quart or less, meaning at most using up a gallon of CO2.