Purging keg with CO2 from fermentation: liquid or gas post?

[DuncB]

So I misunderstood doug293cz's posts I mentioned above and liquid purging results in even less than 0.005 ppm (5 parts per billion) of oxygen?

Most likely yes as less oxygen to flush out, dilution the solution to pollution.
But 5 ppb is super low level and how hard do we need to try?
Purging starsan with ferment gas suits my regime physically and mentally.
I close inject ascorbic acid just before transfer as a final mental crutch.

 

[Spivey24]

First off, I do purge currently just with Star San and a CO2 tank. Mainly due to issues of timing and not having room in my chest freezers for extra kegs.
But when we purge a keg, it is to reduce the amount of oxygen absorbed by or reacting with the beer when filling that keg. So given the low concentrations of oxygen with any method of purging, how much of that oxygen actually comes in contact with the beer and reacts with it or is absorbed by it within the five minutes of filling that keg versus just being pushed out? Just curious how fast that reaction is and does it really matter to get every bit of O2 out.

 

[DuncB]

If you fill the keg to be purged with starsan and push it out with the co2 you will have a sanitized keg and zero oxygen. Works great and zero chance of oxygen in the keg

It does depend on the keg type. Apparently very difficult to 100% fill a corny keg with liquid there is some air space left as per @doug293cz writings on this. Other kegs can be completely filled and you do need to purge once the ferment O2 has been dissipated.

 

[DuncB]

First off, I do purge currently just with Star San and a CO2 tank. Mainly due to issues of timing and not having room in my chest freezers for extra kegs.
But when we purge a keg, it is to reduce the amount of oxygen absorbed by or reacting with the beer when filling that keg. So given the low concentrations of oxygen with any method of purging, how much of that oxygen actually comes in contact with the beer and reacts with it or is absorbed by it within the five minutes of filling that keg versus just being pushed out? Just curious how fast that reaction is and does it really matter to get every bit of O2 out.

I think all of the oxygen will be available to exchange with the beer, especially as oxygen will react with the beer and so keep the gradient going. There won't be a stasis situation as oxygen is being used up in the beer and so will keep coming out of the oxygen reservoir in the headspace.

The reactions start immediately.

 

[Zenmeister]

Like a lot of other people have said previously, I fill the kegs with Starsan, then push that out with the CO2 created during fermentation.

However, in order to eliminate the O2 in that last bit of the keg that is trapped under the lid, I will hook my CO2 tank to the liquid out post, and slowly bubble CO2 into the corny. After about 30 seconds of bubbles (which are CO2 bubbles, with little to no O2) I will put the lid on the top of the keg. There may be some O2 still left, but I believe it is virtually eliminated, especially as I continue to purge my kegs for 4-6 hours after all the Starsan in removed.
It does help that I brew 15 gallons at a time, using a Unitank for fermentation. It typically takes about an 60-90 minutes to purge a corny of all the Starsan when fermentation is active.

 

[brewbama]

I fill the keg with Iodophors and push it out with fermentation CO2. If I get the added benefit of low(er) O2 so be it. …but I do it to conserve CO2. It’s going to be produced anyway, I might as well use it to purge my keg so I don’t have to use bottled CO2 to purge it prior to closed transfer. @doug293cz validated the process.

 

[JRHDBrew]

Like a lot of other people have said previously, I fill the kegs with Starsan, then push that out with the CO2 created during fermentation.

However, in order to eliminate the O2 in that last bit of the keg that is trapped under the lid, I will hook my CO2 tank to the liquid out post, and slowly bubble CO2 into the corny. After about 30 seconds of bubbles (which are CO2 bubbles, with little to no O2) I will put the lid on the top of the keg. There may be some O2 still left, but I believe it is virtually eliminated, especially as I continue to purge my kegs for 4-6 hours after all the Starsan in removed.
It does help that I brew 15 gallons at a time, using a Unitank for fermentation. It typically takes about an 60-90 minutes to purge a corny of all the Starsan when fermentation is active.

I like this idea. Post xfer, I up the pressure to 30 and pull the prv many times. Maybe 10-12. I haven’t had any evidence of oxidization in any brews.

 

[BigDave1303]

I'm just wondering if we are all getting paranoid about removing o2 as close to 100% as possible. I subscribe to many homebrew YouTube channels & also to a couple of small independent breweries. They fill into casks & kegs through a hose just pushed through the hole in the cask/keg. Bottle filling is done in the open air where the beer first fills a reservoir before filling the bottles below. Cans are filled in the open & given a quick shot of co2 just before the lid is manually placed on top. These guys produce some great beer but don't appear to be too concerned about o2.

 

[Nathanologist]

If I connect tubing from the fermenter to a keg to purge it with CO2 from fermentation, what would result in better purging: attaching it to the keg's gas post or liquid post, or does it matter?

Edited: I wrote a descriptive post, because I thought there were only a couple of replies. Then when I sent it- I saw a bunch of replies that made the same points as me.

Here’s the method I’ve arrived at, fwiw.

I use a floating dip tube with screen filter in my fermenting kegs.

Step 1: I fill the serving keg with sanitizer (used for brew day) to the point of overflowing. When I dip the lid into the keg it ends up fully submerged in sanitizer, no air trapped under the lid. Then I close it and put a bit of pressure on it from my co2 tank to seal it. You will not convince me there is any headspace of material concern in that keg.

Step 2: Attach a gas to gas jumper from ferm keg to serving keg. Since serving is slightly pressurized I put a blow tie spunding valve and a check valve in the jumper. Also I attach a liquid to tubing and dip the end into a bucket big enough to hold the 5+ gallons of sanitizer that will be pushed out during fermentation. This becomes its own airlock.

Step 3: Using closed injection technique and tools I add a liquid fining agent to the fermenter keg through the gas post and cold crash.

Step4: After cold crashing I closed inject .3g of PMB. Using closed siphon technique and tools I transfer the clarified beer into the purged serving keg and carb/serve it. My batches have been lasting months on tap with no signs of cold side oxidation.

I don’t see how a liquid purge such as we’ve all described will leave any significant volume of air in the serving keg. Especially if you over fill the keg and seal on liquid overflow. Any residual is scrubbed by the PMB injection prior to closed transfer.

The only downside is that I’ve been unable to find a way to dry hop in the serving keg, so I just do it after fermentation is complete I. The ferm keg using the food grade magnet technique.

 

[Red over White]

I'm just wondering if we are all getting paranoid about removing o2 as close to 100% as possible. I subscribe to many homebrew YouTube channels & also to a couple of small independent breweries. They fill into casks & kegs through a hose just pushed through the hole in the cask/keg. Bottle filling is done in the open air where the beer first fills a reservoir before filling the bottles below. Cans are filled in the open & given a quick shot of co2 just before the lid is manually placed on top. These guys produce some great beer but don't appear to be too concerned about o2.

I think everyone tastes things different. I know 100% that for me low oxygen on the hot and cold side makes my Helles ethereal. Do some beers benefit from oxygen on the hot or cold side, I truly think so and they wouldn't be the same without oxidation.

 

[D-Max]

Question to the mathmeticians on dilution of oxygen in a 19L keg.
At present my pressure fermenter produces approx 0.1 litres per minute at 9 PSI.
I purge my keg from the fermenter to the liquid post of the keg then out of the gas post to my spunding regulator set at 9 PSI relieving pressure.
How many hours will it take to dilute the Oxygen in my 19 L keg to an acceptable ppM level. In other words very little oxygen remaining in my leg.

 

[DuncB]

Question to the mathmeticians on dilution of oxygen in a 19L keg.
At present my pressure fermenter produces approx 0.1 litres per minute at 9 PSI.
I purge my keg from the fermenter to the liquid post of the keg then out of the gas post to my spunding regulator set at 9 PSI relieving pressure.
How many hours will it take to dilute the Oxygen in my 19 L keg to an acceptable ppM level. In other words very little oxygen remaining in my leg.

please have a read of the post linked earlier in this thread about ferment gas and purging. The dilution has been very well explained by @doug293cz

 

[D-Max]

please have a read of the post linked earlier in this thread about ferment gas and purging. The dilution has been very well explained by @doug293cz

Help please.
Yes I read a thread where the dilution was mathmatically calculated but i can not find that link.
I just want confirmation of length of time required to dilute the oxygen content in the 19L keg to an acceptable small amount.
My flow rate from fermenter is approx 0.1L / min.
Cheers.

 

[doug293cz]

please have a read of the post linked earlier in this thread about ferment gas and purging. The dilution has been very well explained by @doug293cz

Why are you worried about the time? Why would you need the keg before fermentation is finished?

To answer your question with any accuracy, we need to know the fermenter headspace volume, the volume of all plumbing connecting the fermenter to the keg, and how the rate of gas evolution varies with time (it's not constant.) Also, what do you consider an acceptable O2 ppm level?

Brew on

 

[D-Max]

Ok I will just assume 0.1L / minute on average for 50 Hrs during rapid fermentation should be sufficient to purge my 19L keg.
I do not connect my keg for purging until the 2nd day of rapid fermentation to allow for the head space in my fermenter King to itself be purged.
I try to have an efficient brew area that is not cluttered with hoses and kegs. I store all my kegs after sanitation in my kegerator.
Thanks for the input.
Cheers

 

[doug293cz]

Ok I will just assume 0.1L / minute on average for 50 Hrs during rapid fermentation should be sufficient to purge my 19L keg.
I do not connect my keg for purging until the 2nd day of rapid fermentation to allow for the head space in my fermenter King to itself be purged.
I try to have an efficient brew area that is not cluttered with hoses and kegs. I store all my kegs after sanitation in my kegerator.
Thanks for the input.
Cheers

The original analysis assumes everything starts as air atmosphere (fermenter headspace, keg, plumbing), and is connected at the the time of pitch. There is no need to wait for the fermenter headspace to be purged of O2 before hooking up the keg for purging. In fact, doing so may actually reduce the effectiveness of the overall process. Why bother?

Brew on

 

[CyberFox]

I'm just wondering if we are all getting paranoid about removing o2 as close to 100% as possible. I subscribe to many homebrew YouTube channels & also to a couple of small independent breweries. They fill into casks & kegs through a hose just pushed through the hole in the cask/keg. Bottle filling is done in the open air where the beer first fills a reservoir before filling the bottles below. Cans are filled in the open & given a quick shot of co2 just before the lid is manually placed on top. These guys produce some great beer but don't appear to be too concerned about o2.

I've wondered that myself, but I doubt breweries are spending so much money and effort to mitigate oxygen just for the fun of it. I think it's especially important for shelf life and for styles like NEIPAs since they are so prone to oxidation.

I remember hearing how The Alchemist brewery (Heady Topper) makes sure their beer has final oxygen levels of less than 1 part per billion, which is crazy low. The founder, Kimmich, said that he was very meticulous about preventing oxygen and that they "gently" transfer the beer with CO2. Heady Topper was pretty much the precursor to NEIPAs and Kimmich seemed to have already known how important it is to mitigate oxygen in that style.

 

[day_trippr]

Given Kimmich is the Big Daddy of New England IPAs (note: not "Northeast IPAs") I wouldn't call Heady the "precursor".
I would call it the prototype...and the beginning of things to come.

And, yeah, cold side oxygen is the Kryptonite of NEIPAs...

Cheers!

 

[CyberFox]

Given Kimmich is the Big Daddy of New England IPAs (note: not "Northeast IPAs") I wouldn't call Heady the "precursor".
I would call it the prototype...and the beginning of things to come.

And, yeah, cold side oxygen is the Kryptonite of NEIPAs...

Cheers!

Precursor, prototype, forerunner, predecessor...same difference.

If we're getting that specific, we can say that Kimmich is actually the Big Daddy of the Vermont Style IPA, which is the precursor/prototype of the New England IPA, which is the precursor/prototype of the Northeast IPA.

 

[day_trippr]

There is no "Northeast IPA".

 

[CyberFox]

There is no "Northeast IPA".

My bad. New England IPA and Northeast IPA are used pretty interchangeably, but New England IPA was the first official name.

 

[day_trippr]

I think it is/was simply folks seeing "NE" and going with the less educated choice...

Cheers!

 

[doug293cz]

That's a good way to do it, but I'm planning to use the crazy amount of CO2 from fermentation to purge the keg. I've heard that it does a better job of purging than pushing out sanitizer, but I can't remember the numbers. I also just make up one gallon of sanitizer per batch and it only takes me a few seconds to sanitize the inside of a keg, so I'm good there.

No it doesn't,
@doug293cz has done the maths and in a thread on purging kegs with ferment gas.
Pushing out starsan is even less oxygen provided you start purge after fermenter oxygen used up or purged.
Some keg types can also be completely filled with starsan.
Other option is starsan sanitise then fill keg with water and sod met and purge that with ferment gas.
Leftover liquid in keg may deactivate any further oxygen as sod met antioxidant. I have no numbers re the sod met concentrations.

So I misunderstood doug293cz's posts I mentioned above and liquid purging results in even less than 0.005 ppm (5 parts per billion) of oxygen?

Whether or not pushing sanitizer out with CO2 results in lower O2 depends on whether you use bottled CO2 or fermentation CO2 to push.

Bottled CO2 is less pure (has higher O2 contamination) than fermentation produced CO2. Bottled CO2 is only guaranteed to have less than 30ppm of O2, but is usually much less (more like 50ppb [0.05ppm].) When purging with bottled CO2, the O2 level cannot be driven lower than the O2 content of the CO2 doing the purging. Therefore, if you purge with bottled CO2, you can’t get lower final O2 than 50ppb, or more.

If you push sanitizer out with fermentation CO2, then you will end up with even lower O2 than if you start with an air filled keg. But since even an air filled keg gets below 5ppb (the analysis was pessimistic, and measured results are even better than predicted) there is no need to worry about it. It won’t hurt anything to fill the keg with sanitizer first, but the improvement will be insignificant.

Brew on

 

[doug293cz]

Yes it does matter.
Without a doubt, connect to the liquid post. That has the long diptube going all the way to the bottom, resulting in better mixing and purging the air.

Yes, when purging an “empty“ keg, you want to connect the fermenter outlet to the liquid post of the keg, and connect the gas post to some kind of airlock, but not for the reason stated in the quoted post.

Pushing CO2 into the bottom of the keg will actually minimize mixing of the CO2 and air, which will enhance to the CO2’s ability to push air (and O2) out of the keg.

CO2 is more dense than O2 or N2, so will tend to fall to the bottom of the keg if fed from the top, and stay pooled in the bottom if fed from the bottom. Falling from the top will encourage mixing, thus reducing any stratification. Any stratification is only temporary however, as over time (a matter of minutes) gas mixtures homogenize completely due to diffusion.

In my original analysis I estimated how fast CO2 would be pushed into a keg vs. how fast the CO2 would mix with the gas already in the keg (assuming mixing only due to diffusion, no convection currents, or turbulent flow to speed mixing.). Turns out the rates are similar which means that some of the gas in the keg gets pushed out before it mixes completely with the incoming CO2. To the extent the existing headspace gas gets pushed out before mixing, more of the preexisting O2 will be pushed out, than for the case of complete mixing.

The actual case of partial mixing in the keg being purged was too difficult to analyze, so instead I did a worst case analysis. For purging, the worst case is when the incoming CO2 completely mixes with the preexisting headspace gas, before any of the existing headspace gas is displaced from the keg. The worst case analysis came out at 5 ppb residual O2, which means the actual should be even less. The worst case analysis showed the fermentation gas purging method was more than adequate to purge O2 to insignificant levels.

Brew on

 

[CyberFox]

Yes, when purging an “empty“ keg, you want to connect the fermenter outlet to the liquid post of the keg, and connect the gas post to some kind of airlock, but not for the reason stated in the quoted post.

Pushing CO2 into the bottom of the keg will actually minimize mixing of the CO2 and air, which will enhance to the CO2’s ability to push air (and O2) out of the keg.

CO2 is more dense than O2 or N2, so will tend to fall to the bottom of the keg if fed from the top, and stay pooled in the bottom if fed from the bottom. Falling from the top will encourage mixing, thus reducing any stratification. Any stratification is only temporary however, as over time (a matter of minutes) gas mixtures homogenize completely due to diffusion.

In my original analysis I estimated how fast CO2 would be pushed into a keg vs. how fast the CO2 would mix with the gas already in the keg (assuming mixing only due to diffusion, no convection currents, or turbulent flow to speed mixing.). Turns out the rates are similar which means that some of the gas in the keg gets pushed out before it mixes completely with the incoming CO2. To the extent the existing headspace gas gets pushed out before mixing, more of the preexisting O2 will be pushed out, than for the case of complete mixing.

The actual case of partial mixing in the keg being purged was too difficult to analyze, so instead I did a worst case analysis. For purging, the worst case is when the incoming CO2 completely mixes with the preexisting headspace gas, before any of the existing headspace gas is displaced from the keg. The worst case analysis came out at 5 ppb residual O2, which means the actual should be even less. The worst case analysis showed the fermentation gas purging method was more than adequate to purge O2 to insignificant levels.

Brew on

Seriously good info. Thanks a lot!

 

[TheMadKing]

Only if your fermenter can hold pressure, otherwise the CO2 will escape through gaps in the fermenter (e.g., lid connection) and not purge your keg.

Set it to a lowish threshold pressure, perhaps around 3-10 psi. It will even carbonate your beer somewhat too.

So this is the exact problem I've always had with this method... Corny kegs don't seal unless they are pressurize. So how do y'all make sure that they stay sealed while you are purging with fermentation CO2? Or do you pressurize it a little bit with a CO2 tank first and then use a spunding valve to keep the pressure at like 3PSI?

If that's the case, it seems like that would have a profound effect on your ability to control fermentation ester production since it is suppressed by even 2PSI of head pressure. If you never make english ales thats no problem, but I like me some esters sometimes!

For these reasons I've completely given up on purging with fermentation CO2 and just do a standard liquid purge with a CO2 tank.

On the dry hop discussion, I just dump them in quickly through the top 1.5" port in my Spike CF5. The residual CO2 in solution foams out on contact with the hops and has a purging effect, and then I hit it with 10PSI from my CO2 tank and vent it a few times. I've had NEIPA's stay juice and not brown for month and months like this

 

[day_trippr]

Corny kegs don't seal unless they are pressurize.

I have sixteen 5 gallon ball lock kegs - all bought well used - and only one has difficulty holding a water tight seal with no pressure.
I've been fermentation-purging my kegs for a few years now - a pair at a time as I do 10 gallon batches with pairs of 6.5 gallon carboys. The end of the daisy chain is from the gas post and I submerge it a few inches deep in a gallon bucket. If the kegs leaked there wouldn't be the profound bubbling

Cheers!

 

[CyberFox]

So this is the exact problem I've always had with this method... Corny kegs don't seal unless they are pressurize. So how do y'all make sure that they stay sealed while you are purging with fermentation CO2? Or do you pressurize it a little bit with a CO2 tank first and then use a spunding valve to keep the pressure at like 3PSI?

If that's the case, it seems like that would have a profound effect on your ability to control fermentation ester production since it is suppressed by even 2PSI of head pressure. If you never make english ales thats no problem, but I like me some esters sometimes!

For these reasons I've completely given up on purging with fermentation CO2 and just do a standard liquid purge with a CO2 tank.

The only reasons I can think of that would cause keg sealing problems are worn out o-rings and the o-ring material.

I've heard that Buna-N o-rings are the least compressible (worst sealing), but have lower oxygen permeability and silicone is the most compressible (best sealing), but has higher oxygen permeability. EPDM o-rings are kind of a middleground since they have low oxygen permeability like Buna-N and are more compressible like silicone.

My kegs have silicone o-rings and I haven't noticed any leaks without pressure.

 

[TheMadKing]

I have sixteen 5 gallon ball lock kegs - all bought well used - and only one has difficulty holding a water tight seal with no pressure.
I've been fermentation-purging my kegs for a few years now - a pair at a time as I do 10 gallon batches with pairs of 6.5 gallon carboys. The end of the daisy chain is from the gas post and I submerge it a few inches deep in a gallon bucket. If the kegs leaked there wouldn't be the profound bubbling

Cheers!

Well my experience has been the opposite. I have 11 pin lock kegs and 10 of them requires a burst of about 20psi to get the lids to seal. One will seal with about 10psi

I have replaced the O rings and used keg lube on all of them and replaced the entire lid on 2 of them.

If i put 5psi in them it just leaks out the lids almost immediately and they don't hold liquid or gas at all.

So if I hit them with a sudden hard burst they will seal and then I can back the pressure back down. They will stay sealed at that point until the pressure is almost gone.

just because you see bubbles coming out the hose doesn't mean you have a complete gas seal around the lid. It just means the rate of loss from any lid leaks is lower than the hydrostatic pressure of the water on the end if your hose. So that really doesn't prove you aren't getting air ingress via the lids.

Without positive pressure sealing mine, I just don't trust that air isn't getting in

 

[day_trippr]

Trust me, these kegs are truly gas tight. I was going light on your proposition...

Cheers!