Purging with CO2

[daryl]

At last week's judging, Lee Paulson mentioned purging kegs, fermenters, etc. with CO2, helps prevent exposure of the beer to oxygen and the slows/prevents oxidation (and the off flavors that comes with that).

Is this as easy as releasing some CO2 into these vessels?

I am guessing, that as long as there is a blanket of CO2 on top of the beer, that is sufficient...rather than trying to purge all of the air out of the vessel.

Thoughts?

[Matt F]

I just hit my kegs with CO2 for a few seconds with the lid off through the beverage out tube so it fills from the bottom. No set guidelines I use other than get some CO2 in there. Unless I am naturally carbonating, then I let the yeast take care of the O2 for me. Purging with CO2 is a big deal, especially for hoppy beers. You should also be careful when racking and such. Once the beer is fermented, you should avoid O2 as much as possible.

[Matt F]

Important when bottling from a keg too. That is why they say cap on foam. Foam should be mostly CO2 and leave less room for O2. I use a counter pressure filler which is a little more complicated than the popular beer gun but it allows me to fill the bottle with CO2 and fill under pressure, minimizing the interaction with O2. Seemed to work well for the Bock I made. That was bottled from a keg a few months ago.

[DrPaulsen]

Purging via pressurizing the keg & releasing it several times works well, but the best method I've found includes filling the keg with water and emptying it with CO2.

[DrPaulsen]

Also, I would argue that minimizing O2 pickup post-fermentation is every bit as important as purging kegs. I've found that blanketing the bucket/carboy/conical with CO2 during cold-crashing is very effective. In my way of thinking, this is because as the temp drops, the gas in the headspace shrinks and pulls in air. At the same time, the gas solubility of the beer is going up, causing its Dissolved Oxygen (DO) levels to rise. This DO enables staling reactions that make beer taste flat. It's most obvious in hoppy beers with darker crystal malts (think of an old can of 2 Hearted or Dale's Pale Ale), but it even shows up in lagers.