Co2 fill after kegging

[KimJohansen]

Hi,

I've just started kegging and I have a question. I siphon my beer to my corny kegs and would like to get rid of any oxygen after it's filled. Should I add Co2 through the in or out valve?

Thanks

/Kim

 

[Sammy86]

Through the in valve

 

[doug293cz]

It takes multiple pressurize and vent cycles to really get most of the O2 out of the headspace. Refer to the chart and table below. Values are % of original O2 remaining.





If the purged volume remains constant during all purges, then the "% of original remaining" refers to both total amount and concentration (total amount = concentration * volume.)

If the purged volume changes between purges, for example due to pre-fill and post-fill purges, then the "% of original remaining" refers only to concentration, not total amount. However, since the concentration is the same after a given number of purges, independent of the volume during the purges, the final result will be the same as if all purges were done post-fill, only if no air gets into the keg during the filling process. Any air that gets into the keg during the filling process will reduce the effectiveness of the pre-fill purges on reducing the final O2 content of the headspace.

Brew on

 

[beernutz]

Hi,

I've just started kegging and I have a question. I siphon my beer to my corny kegs and would like to get rid of any oxygen after it's filled. Should I add Co2 through the in or out valve?

Thanks

/Kim

The in valve. You can also pre-purge your keg before the beer goes into it to reduce aeration. Like the chart doug posted recommends, I purge and vent a filled keg 6 or 7 times to get the percentage of air remaining in it down to around 3%.

 

[Dixon9717]

I fill my empty keg with co2 before I fill it with beer. Syphon beer into keg then pressurize with more co2. Wait till carbonated then drink.

 

[thekraken]

It takes multiple pressurize and vent cycles to really get most of the O2 out of the headspace. Refer to the chart and table below. Values are % of original O2 remaining.

View attachment 314068

View attachment 314069

Brew on

This is great, I was looking for something like this a few weeks ago. Source?

 

[doug293cz]

This is great, I was looking for something like this a few weeks ago. Source?

I generated the data using basic gas laws. Posted more details a while ago, but don't know if I can find it again.

Brew on

 

[KimJohansen]

Thanks guys!

 

[MikeSkril]

Logically I would say that even if there is still oxygen in the keg, it should not be in contact with the beer. Wont the oxygen be forced to sit on the very top of the headspace?

 

[Yooper]

Logically I would say that even if there is still oxygen in the keg, it should not be in contact with the beer. Wont the oxygen be forced to sit on the very top of the headspace?

No. While C02 IS heavier than air, gasses don't stratify and they easily mix.

The whole "co2 blanket" some talk about is a myth. Sure, during active fermentation, there is a ton of c02 coming out of the beer (or wine) so it does 'push' out of the airlock and protect the fermenting liquid, but once fermentation slows this is no longer the case.

If gasses did stratify, we'd all die in our sleep from c02 poisoning.

 

[thekraken]

I generated the data using basic gas laws. Posted more details a while ago, but don't know if I can find it again.

Brew on

And it was indeed that math behind that that I was really interested in. Do you remember what gas laws are involved? Maybe I can back into it.

 

[doug293cz]

Logically I would say that even if there is still oxygen in the keg, it should not be in contact with the beer. Wont the oxygen be forced to sit on the very top of the headspace?

No. Gases will homogenize over short periods of time. A "CO2 blanket" is a short lived item. [ame]https://www.youtube.com/watch?v=_oLPBnhOCjM[/ame]

Br2 is a lot heavier then CO2, and even it homogenizes fairly rapidly.

Brew on

 

[MikeSkril]

If gasses did stratify, we'd all die in our sleep from c02 poisoning.

Very good point! I knew there was something wrong with my logic.

 

[doug293cz]

And it was indeed that math behind that that I was really interested in. Do you remember what gas laws are involved? Maybe I can back into it.

Pretty much just this: https://en.wikipedia.org/wiki/Partial_pressure

Brew on

 

[doug293cz]

Just another point: You want to get rid of the air in the headspace so that the CO2 partial pressure is the total pressure (see link in previous post) in order to get proper carbonation. The carbonation charts and calculators assume the CO2 pressure is gauge pressure + 14.7 psi (atmospheric pressure.) The carbonation that you get really depends on CO2 partial pressure, not gauge pressure.

Brew on

 

[thekraken]

I generated the data using basic gas laws. Posted more details a while ago, but don't know if I can find it again.

Brew on

Found it: https://www.homebrewtalk.com/showthread.php?t=537407&page=2

My googlefu is strong today

 

[day_trippr]

While the chart is kinda interesting, doesn't it depend on a rather stupid paradigm: filling just the head space with CO2 pressure with the keg sealed, then popping the PRV, then repeating?

I mean, seriously. Latch the PRV open, turn on the gas, let it run for 10 seconds or so...

Cheers!

 

[Yooper]

While the chart is kinda interesting, doesn't it depend on a rather stupid paradigm: filling just the head space with CO2 pressure with the keg sealed, then popping the PRV, then repeating?

I mean, seriously. Latch the PRV open, turn on the gas, let it run for 10 seconds or so...

Cheers!

What's the difference?

 

[doug293cz]

While the chart is kinda interesting, doesn't it depend on a rather stupid paradigm: filling just the head space with CO2 pressure with the keg sealed, then popping the PRV, then repeating?

I mean, seriously. Latch the PRV open, turn on the gas, let it run for 10 seconds or so...

Cheers!

Leaving the valve open will use more CO2 to get the same level of residual O2. Also, the residual O2 concentration is not determinable.

If you study the table, you can figure out that more purges at lower pressure will use less CO2 to get the same residual O2 content. A purge at 10 psi uses half the CO2 as a purge at 20 psi, and likewise a purge at 15 psi uses half the CO2 as a purge at 30 psi.

Brew on

 

[Rev2010]

I pretty much always force carb at 30psi for about 36 hours then set to my serving psi and wait another 5 days, because why not? As a result I purge the headspace 3x, so far zero issues. Looking at the chart that leaves 5% or less O2 in the headspace. Good enough for me. I also fill the keg with CO2 once, purge, and fill once more before filling. So far I've seen no need to do more, just seems like a waste of gas for me. For me getting refills is a pain since I don't drive and need to get a family member to drive me to the gases place.


Rev.

 

[doug293cz]

I pretty much always force carb at 30psi for about 36 hours then set to my serving psi and wait another 5 days, because why not? As a result I purge the headspace 3x, so far zero issues. Looking at the chart that leaves 5% or less O2 in the headspace. Good enough for me. I also fill the keg with CO2 once, purge, and fill once more before filling. So far I've seen no need to do more, just seems like a waste of gas for me. For me getting refills is a pain since I don't drive and need to get a family member to drive me to the gases place.


Rev.

Since air is about 21% O2, and 3x purges @ 30 psi leaves about 5% of the original O2, the actual residual O2 is a little over 1%. Also, since you are purging the keg before filling, your residual O2 is probably somewhat lower.

However, air will mix into the CO2 during the filling process, unless you are using a sealed transfer process. And the pre-fill purge is much less effective than you think it is. Because of this, you would use less CO2 and get lower residual O2 by skipping the CO2 purge prior to filling, and just purging 5x after filling.

Brew on

 

[day_trippr]

What's the difference?

Honestly, I have no idea

I can't really metricize the original proposition, but intuitively, if I blast CO2 through a really small head space (I tune my recipes to end up with 5.25 gallons in my kegs - had to shorten the gas dip tubes but it totally maximizes the space) for a solid 10 seconds at a high enough pressure that it literally sounds like a blast - it's going to flush the head space clear enough that I'm not going to give a crap about what's left.

Maybe it's not the most efficient use of CO2, but I don't care.

Otoh, charging and popping a dozen times while eyeballing a table seems like part of a short lifetime wasted...

Cheers!

[edit] And in any case, this whole thing doesn't matter. I fill my kegs with a standard Star San mix, push that out with CO2, then CO2-push my carboy contents to the keg. There isn't any "air" left to contend with. If you want to go totally O/C, there's your game plan

 

[Rev2010]

Thanks for the info Doug, very enlightening! Can I ask, do you do a pre-fill CO2 purge? I'm not adamant about it, I just do it for good measure but when I was bottling I never had a single care about the fact that there's O2 in the bottles, never seemed to make a difference yet I see some posters here concerned about it at times. I plan to keep doing a CO2 purge pre-fill but am definitely interested to hear your opinion on it. Thanks again!


Rev.

 

[doug293cz]

Thanks for the info Doug, very enlightening! Can I ask, do you do a pre-fill CO2 purge? I'm not adamant about it, I just do it for good measure but when I was bottling I never had a single care about the fact that there's O2 in the bottles, never seemed to make a difference yet I see some posters here concerned about it at times. I plan to keep doing a CO2 purge pre-fill but am definitely interested to hear your opinion on it. Thanks again!


Rev.

I don't purge the keg prior to filling. I shouldn't get any more O2 exposure than racking to a bottling bucket, since I keg from primary. If you are really OCD about avoiding O2 exposure, do something like @day_trippr, and fill the keg with water or starsan, push it all out with CO2, and then pressure fill thru the beer out post.

Brew on

 

[kevink]

I don't purge the keg prior to filling. I shouldn't get any more O2 exposure than racking to a bottling bucket, since I keg from primary.

As if that's the acceptable amount? The whole point of purging is to minimize the amount of oxygenation. Racking to a bottling bucket causes way too much.

 

[doug293cz]

As if that's the acceptable amount? The whole point of purging is to minimize the amount of oxygenation. Racking to a bottling bucket causes way too much.

Yet people do it all the time. If you're not doing a totally sealed transfer, then you are just fooling yourself about how much O2 exposure you are actually getting. Purging the keg, and filling thru the open lid let's in quite a bit of O2.

Look at the video above. Br2 has a molecular weight of 160 vs. CO2 at 44. Air will mix into your open keg several times faster than that Br2 in the video mixes with the air.

Brew on

 

[IslandLizard]

Curiously enough, using @Doug's graphs, the break-even point of the amount of CO2 needed between pre-purging a whole 5 gallon keg and only purging the headspace after filling* lays at around 4 gallons of beer. That means that break-even point is already reached at 80% fill level!

So if you have 4 gallons or less beer to fill a keg, you're better off pre-purging.

*This is to achieve a residual O2 level of around 1-2% (5-10% air) in the post-filling purge. The O2 (air) level in a pre-purged keg is almost nil.

Pre-purging:
Pre-purging is done by filling the keg all the way to the very top with Starsan (~5.5 gallons), then closing it up, followed by pushing as much Starsan out as possible using CO2.

To fill the now pre-purged keg with beer, do not remove the lid, but instead remove the gas post and the (short) dip tube. Feed a 1/4" OD hose through the threaded stub all the way to the bottom leaving a few inches to a foot sticking out. Fill the racking/siphon hose with beer before attaching to the 1/4" tubing. As the keg fills with beer, the CO2 will escape between the inside of the threaded stub and the 1/4" hose.

 

[kevink]

Yet people do it all the time. If you're not doing a totally sealed transfer, then you are just fooling yourself about how much O2 exposure you are actually getting. Purging the keg, and filling thru the open lid let's in quite a bit of O2.

Then don't fill it through an opened lid.

There is still way less oxygenation happening when you fill a purged keg through an opened lid than an unpurged bottling bucket. Come on...

 

[Rev2010]

@IslandLizard - After reading that, I think I'll just stick to my usual pre-fill purge then 3x post fill headspace purge.

Not saying there isn't merit to it!, just that I think we're getting to extremes these days for home brewing and going to tiring lengths for possibly little to no benefit. For me, what I've been doing kegging, and previously bottling, all led to excellent beers, many of which I can honestly say were on par with commercial quality. So I'm OK with my current process.


Rev.

 

[iijakii]

^^^ After reading that, I think I'll just stick to my usually pre-fill purge then 3x post fill headspace purge.

Not saying there isn't merit to it!, just that I think we're getting to extremes these days for home brewing and going to tiring lengths for possibly little to no benefit. For me, what I've been doing kegging, and previously bottling, all led to excellent beers, many of which I can honestly say were on par with commercial quality. So I'm OK with my current process.


Rev.

Right. Unless you're brewing under pressure with a spundling valve I just don't see the point in getting too intense. Youre getting oxygen in when you pull a sample, throw in dry hops, rack, etc. Definitely try to minimize, but there's a certain reality you have to accept unless it's completed closed-system.