Keg purging with active fermentation

[mac_1103]

At some point all your hoses and connections become the weak point. One should consider diffusion rate into tubing if going to that extreme.

EVABarrier is good enough for months in the kegerator so I figure it should be good enough for a couple of weeks in the fermenter.

 

[Bassman2003]

I little active yeast would be the best insurance. Just transfer with like a gravity point remaining. Sort of like a mild bottle conditioning that will consume and extra O2 that makes it through.

 

[joshbuhl]

I little active yeast would be the best insurance. Just transfer with like a gravity point remaining. Sort of like a mild bottle conditioning that will consume and extra O2 that makes it through.

Yeast oxygen scavenging in the bottle is better than nothing, but unfortunately DO has done it's damage and is already bound up within 20 minutes (which is why you have to measure DO immediately fter packaging and can't take a bottle to a friedly brewery with a DO meter) and I haven't yeat read anything that yeast is quicker in scavenging.

 

[Bassman2003]

That is why I said insurance. To eat up the little bit that comes in from transfers, seals etc...

 

[mashdar]

EVABarrier is good enough for months in the kegerator so I figure it should be good enough for a couple of weeks in the fermenter.

Oh, yeah, I just mean you hit a point where theory and practice diverge. Luckily it appears to be well below an acceptable level.

Here's another one: Every time you attach a quick disconnect, there may be ~1ml of air above the gasket between the mating QD parts. That 1ml of 21% O2 into a 21L keg would yield 10ppm O2. Yet another massive source of O2 compared to the ppb discussed above. Luckily, you'll displace most of that with beer, and the remainder will give <10ppb in the beer because the density is so different.

(I've yet to find a non-crazy way to purge the QD interface...)

 

[DuncB]

If the keg has some pressure greater than the tube and QD connect and then vent the tube would that help?
Or have far end of tube QD open as you connect to a positive pressure fermenter or keg.

 

[Bassman2003]

If the keg has some pressure greater than the tube and QD connect and then vent the tube would that help?
Or have far end of tube QD open as you connect to a positive pressure fermenter or keg.

Sadly, no. It seems gas laws and movement is kind of a black box. Oxygen and CO2 and other gasses can coexist and move freely outside of pressure.

Now physical movement of the space can deter *some* gas from coming in but it is a challenge no doubt. (think disturbing a mud bottom in a pond and trying to direct the sediment in a certain direction). If one has the choice of lifting a PRV or having 6 feet of EVA barrier connected to a gas post with positive gas coming out and bleeding off at the end of the tubing, the tubing will be a better approach as it is farther away from the source.

 

[tracer bullet]

I finally started using the fermentation gasses to purge my kegs, after following this thread. This will be my 3rd brew doing so, the last 2 seem to have worked wonderfully.

@Bobby_M (BrewHardware) made the tubing. He welded some 1/2" SS tubing to Female Flare adapters in such a way that the nut still moves, to let me align things before I tighten them to the quick-disconnects. I later made the cut to one of the tubes to add a push-connect tube fitting (from McMaster) to help the assembly process, but in retrospect I really didn't need it. It still works but if anyone pursues something similar, FYI that this was not needed. Also, I originally had a different setup in mind with a host of adapters but he was kind enough to email me to ask what I was up to and offered a much better solution.

If it isn't obvious, it goes: Fermenter to keg, keg to Ball jar suck-back preventer, and then finally to some star san / iodophor combo.

(The fan is an aquarium cooler I use to do my chilling, but that's a different topic).

 

[Bassman2003]

Sweet. Yes Bobby is a big help.

 

[hooper]

I do similar, but I go fermenter to black (output) thinking CO2 is heavier than air.

 

[doug293cz]

I do similar, but I go fermenter to black (output) thinking CO2 is heavier than air.

Feeding the CO2 from the fermenter into the liquid out post (and "filling" with CO2 from the bottom of the keg) provides better removal of O2 from the keg. You have concurrent pushing of O2 up and out along with O2 mixing back into the lower part of the keg by diffusion. Feeding CO2 in thru the gas post will cause faster mixing of CO2 and O2 as the CO2 falls to the bottom of the keg before completely mixing with the gas already in the keg.

Brew on

 

[Bassman2003]

I do similar, but I go fermenter to black (output) thinking CO2 is heavier than air.

Yes, @tracer bullet, I did not notice before but it is better to run the gas into the liquid post and out of the gas post.

 

[tracer bullet]

Yes, @tracer bullet, I did not notice before but it is better to run the gas into the liquid post and out of the gas post.

I wondered about that, but then there's the whole "there's no such thing as a CXO2 blanket, it all mixes" which I believe in, and so I leaned towards it not mattering. Especially when we are talking a trickle of incoming CO2 taking several full days, at least. I feel like any existing O2 and incoming CO2 are going to constantly mix and it wont' really matter. I could of course be wrong.

 

[doug293cz]

I wondered about that, but then there's the whole "there's no such thing as a CXO2 blanket, it all mixes" which I believe in, and so I leaned towards it not mattering. Especially when we are talking a trickle of incoming CO2 taking several full days, at least. I feel like any existing O2 and incoming CO2 are going to constantly mix and it wont' really matter. I could of course be wrong.

Yes a persistent CO2 blanket is a myth, due to how gases spontaneously homogenize over time (a matter of minutes.)

It's the time factor that makes a difference, If you go back to post #3, I show that the rate of flow upwards thru the keg being purged is about equal to the speed of O2 diffusing into the CO2 at the bottom of the keg. This means that mixing will NOT be complete, and you will have at least a partial CO2 blanket while CO2 is being actively pushed into the keg. Once CO2 is no longer entering the keg, the gas inside will homogenize in about a half hour or so.

Because the dynamic flow effects are too complicated to deal with, when I did the calculations, I did it for the worst case of complete mixing of the CO2 with the existing gas in the keg. And the results showed that even with complete mixing, fermentation gas purging is highly effective. The fact that you don't have complete mixing if feeding CO2 into the bottom of the keg means that the purging is even more effective than the calculation predicts. If you feed the CO2 to the top of the keg, you will get more mixing, and the results will be acceptable, but not as good as they could be.

Brew on

 

[tracer bullet]

@doug293cz that makes sense, the time factor, and that reversing my setup could be better. I was thinking things were quicker, but perhaps not.

I'll go switch it.

 

[doug293cz]

@doug293cz that makes sense, the time factor, and that reversing my setup could be better. I was thinking things were quicker, but perhaps not.

I'll go switch it.

I wouldn't switch mid fermentation, but rather wait for my next batch.

Brew on

 

[Bassman2003]

I also think there is just a physical attribute as well. Bringing in the CO2 from the bottom means any force is pushing on all of the contents upward with the only escape being the small opening at the top. If the incoming gas is brough in from the top, any force will be pushing downward into the keg and the only escape will be through a tube at the bottom. So there is a chance some gas might not get pushed out because it stayed generally up the corner etc... New gas might go directly downward at straight out where we want the gases to mix and eventually clear the entire space and be replaced with only CO2 over time.