Beergun, CO2 purge

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ol' rummie

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Is it really nessecary to use the purge button on the Beergun?
As the bottle fills with beer, it pushes the oxygen out. The only oxygen that would be in there would come from when you take the gun out of the bottle, and fill the head space (which would happen if it was purged anyway).
 
But, once your beer hits oxygen, you get foam. Foam is carbonation loss. So, hence the purge. If the beer doesn't touch oxygen, you'll have a beer that will last longer.
 
So, does the beer gun actually put pressure in the bottle to reduce foaming from beer entering? or does it only purge with C02?
 
Reverend JC said:
So, does the beer gun actually put pressure in the bottle to reduce foaming from beer entering? or does it only purge with C02?
Click to expand...

it just purges the bottle. I've never noticed the oxygen-contact effect mentioned above but then I've never been looking for it either. Straining to remember my physics class, I don't believe that's accurate though. The foaming should be a result of CO2 released from solution based on pressure drop and temperature shift. The Beer Gun has a very long hose that allows a pressure balance at the outlet to reduce foaming.

The same result can be had with a long length of beer line and a cobra tap with an extension tube to the bottom of the bottle. You can't purge with that setup and it's no where near as elegant or intuitive to use but it works for nearly eliminating pressure induced foaming. Having your bottles the same temp as the beer is also a huge help.

A while back there was almost a fist-fight on our club forum over debating these two methods! I have a Beer Gun and really like it.
 
Derrin said:
it just purges the bottle. I've never noticed the oxygen-contact effect mentioned above but then I've never been looking for it either. Straining to remember my physics class, I don't believe that's accurate though. The foaming should be a result of CO2 released from solution based on pressure drop and temperature shift. The Beer Gun has a very long hose that allows a pressure balance at the outlet to reduce foaming.

The same result can be had with a long length of beer line and a cobra tap with an extension tube to the bottom of the bottle. You can't purge with that setup and it's no where near as elegant or intuitive to use but it works for nearly eliminating pressure induced foaming. Having your bottles the same temp as the beer is also a huge help.

A while back there was almost a fist-fight on our club forum over debating these two methods! I have a Beer Gun and really like it.
Click to expand...

You're right. The beer doesn't foam because of oxygen. I guess that's just my way of explaining that once the pressure drops...ie, hitting oxygen... it starts to foam. It's easier than explaining pressure I suppose. But, I think the point of CPBF's is also to prevent oxygen from getting to your beer. That's why I don't like the hose and picnic tap method. It works...but your beer won't last near as long IMO. Of course, I use a PMBF, so I wanted the cheap way around it also.
 

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