Beer Forum

Is it necessary to purge oxygen from a keg before filling the keg with beer?

I have been filling from the bottom, without pre-purging, and then purging once the keg is full. It seems that the beer would only be in contact with oxygen for a short period of time, but maybe it would be worth pre-purging.

Thoughts?

Necessary? No, but the only reason I see for not doing it that you use more CO2 than you would if you don't pre-purge. For me it depends on the beer I'm filling the keg with. If it's going to be drank real soon, then I'm less worried about O2 exposure, but if it's something I want to age I'll be more careful.

Personally, it doesn't take much CO2 and I like having that extra security in case it does splash around during transfer.

TheDarkSide wrote:Personally, it doesn't take much CO2 and I like having that extra security in case it does splash around during transfer.

How do you do it? I usually use CO2 to push out the starsan I used to sanitize the keg. I always feel a little like I'm wasting CO2 since that's basically one less keg-worth of beer I'll be able to dispense with that tank of CO2. Maybe I'm using more than I need?

Travisty wrote:How do you do it? I usually use CO2 to push out the starsan I used to sanitize the keg. I always feel a little like I'm wasting CO2 since that's basically one less keg-worth of beer I'll be able to dispense with that tank of CO2. Maybe I'm using more than I need?

I only run a small amount of star san out and then leave some in the line. Then I dump the rest ( I'm only putting about a gallon or so in the keg and shaking it). Then I run the CO2 for a few seconds and then fill from the bottom. Since the CO2 is heavier, I assume it's falling to the bottom and pushing the O2 up. I know some attach the CO2 to the liquid posts so it fills the CO2 from the bottom, but I go a disconnect stuck doing that once so I don't so it anymore.

By scrupulous purging of air I am able to keep beers "fresh" for over 2 years. These kegs sit in a cooler at between 34 and 38°F and never get moved and that helps too. I'm using Sankey kegs which I sterilize with steam which I replace with CO2 as it condenses. I don't see how you could do that with Cornies but I've seen guys describe a process in which the sanitized keg is filled completely with water (which I suppose must contain a no-rinse sanitizer or have been boiled) which is then pushed out with CO2. That ought to work.

Thanks for the responses guys. I guess the bottom line is: pre-purging is best practice unless you know that the beer will be consumed quickly. Then again, CO2 is cheap enough (relative to producing a 5 gallon batch anyway) that I ought to always pre-purge just in case.

I keep a keg of Star San in the brewery all the time. It's really handy to be able to use a picnic tap to dispense small amounts of sanitizer when needed. When I go to keg a beer I just use CO2 to push the Star San to a different keg and then use the just emptied keg for my beer. This way I always have a freshly sanitized purged keg for use. I have kept beers for 3+ years in the keg with no oxidation problems this way.

Wayne