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You are here: Home --> Forum Home --> Brewing Forum --> Brewing Discussion --> a couple of new stupid kegging questions

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Stonehands
Charter Member
Birmingham, AL
59 Posts


Yeah, if the gasses didn't mix, we'd all be dead. 



Posted 34 days ago.

testingapril
Charter Member
Atlanta, GA
595 Posts


Carl, I totally agree about post transfer purging being more important if you didn't start with a closed transfer.

Personally, I closed transfer except the receiving keg has the purge open, but exiting co2 should prevent the vast majority of o2 from entering.

Now I'm kind of thinking about giving the filled keg a purge or two just to make sure it's all co2 and no o2 snuck in.

Necro, what Carl said. The whole co2 blanket thing is basically a myth. I think someone on milkthefunk did the math and found that the 'blanket' is diffused in about 5 seconds.





Posted 34 days ago.

flapjackcarl
Houston, TX
595 Posts


I'd be willing to bet you're safe with the purge being open, but it's so easy to do, it can't hurt. I'm going to clean up the spreadsheet I just made with purge calculations, I can send it out or post some info if people are actually interested. 



Posted 34 days ago.

homebrewdad
Charter Member
Birmingham, AL
2480 Posts


We love data and in depth stuff. Please do share.





Posted 34 days ago.

Necropaw
Charter Member
Central WI
608 Posts


Thats interesting to hear, though i wonder if the temperature difference does anything?

I guess ive put CO2 in a keg before and could 'see it' in the keg. Maybe its just temp difference, but does that influence the mixing of gasses?

Also, still curious about how that works with a container thats 95% closed off to the outside world (maybe more? I dont feel like doing math on the surface area of a keg right now)

Yes, gasses mix, but whats the effect when theres so little surface area connecting the 'pure' gas and the atmosphere?




Posted 34 days ago.

Necropaw
Charter Member
Central WI
608 Posts


Oh yeah, for the record...

Picnic taps dont handle 25~30 PSI.

Threw some pressure in my keg to grab a gravity sample through my picnic tap. Picnic tap didnt like that very much. :P




Posted 34 days ago.

flapjackcarl
Houston, TX
608 Posts


Necro: I see what you're saying, and I'll say a couple of things in response. First off, on seeing CO2. CO2 is a colorless gas. My suspicion is that you keep your CO2 in your keezer. So you have cold CO2, which gets colder when you break down the pressure across the regulator (most gases auto-refrigerate when you decrease their pressure. CO2 in your tank is at something like 600 psig, so it will actually cool quite substantially). So now you have very cold CO2, mixing in a keg that was probably just rinsed with hot water. When this happens, you'll condense water vapor in the air, forming a bit of a cloud. At least thats my guess.

On the surface area  front, the issue isnt one of surface area. When you add CO2 into the keg, the velocity is decently high. This high velocity promotes mixing of the air and CO2 in the keg. When you purge the keg in this way, most of what's coming out is going to be CO2 and Nitrogen. As a result, once you stop purging, you end up with residual oxygen still in the keg. Basically what I'm saying is: the CO2 velocity is high enough that surface area doesn't matter and you end up with a well mixed vapor very quickly because of the turbulence. 

If you were going to try and clear a keg of O2 prior to filling your best bet would be the method testing april mentioned: Fill the keg completely with water, and then pressure it out with CO2. This should get you to a very low O2 concentration (the keg is likely never 100% liquid full, so you'll end up with trace amounts of O2 present, but probably very little).




Posted 34 days ago.

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