Keg purging with active fermentation

[DuncB]

I do purge the starsan into a bucket after the fermenting keg has purged it's own headspace. I do this starsan into a spare container.
Yes dilution works but I'm trying to limit the oxygen as much as possible so I have 4 litres of oxygen less to dilute. I suppose the keg being flushed doesn't have to be in the keg ferment ( chest freezer).

 

[doug293cz]

... It seems that the common process is to just connect the kegs at time of pitching yeast...but then all the air in the headspace of the fermenter will be the first to fill the "purged" keg. Then from there you have to rely on some dilution to bring the oxygen levels to an acceptable level.

The analysis in post # 3 assumes that both the fermenter headspace and keg to be purged start out with an air atmosphere. If you start with StarSan in the keg, the final O2 content will be even lower than if you start with air.

And yes, it is all about dilution, since the CO2 flow rate is not enough to safely assume that we get a "sweeping" effect.

Brew on

 

[CascadesBrewer]

And yes, it is all about dilution, since the CO2 flow rate is not enough to safely assume that we get a "sweeping" effect.

I tried to sort through the math and see if it applies to my setup, but could not. I see there was a response earlier saying that fermenting 5 gals was enough to purge out two 5-gal kegs + 1.5 gals of headspace. So I was hoping that my 2.6 gals of 1.053 wort would be enough to purge a 5-gal keg plus the 2.7 gals of headspace.

Any idea if the spunding valve has a positive or negative impact on the mixing of CO2 and air?

Nope. Due to the design of the lid, when liquid comes out of the PRV, there is a 3 fl oz air bubble trapped in the lid. I personally measured this (as have others.)

I wonder if this varies from keg to keg. When I look at my ball-lock kegs, the rim of the lid is higher than the posts. When I fill my kegs with StarSan I do so through the open lid, and I cannot see where there would be any pockets of air. If I filled the keg through the liquid post, I also don't see where there would be any sizeable pockets if liquid was coming out of the PRV on the lid. Maybe if liquid was coming out of the gas post. Or am I not understanding what is being said here.

 

[doug293cz]

I tried to sort through the math and see if it applies to my setup, but could not. I see there was a response earlier saying that fermenting 5 gals was enough to purge out two 5-gal kegs + 1.5 gals of headspace. So I was hoping that my 2.6 gals of 1.053 wort would be enough to purge a 5-gal keg plus the 2.7 gals of headspace.

Any idea if the spunding valve has a positive or negative impact on the mixing of CO2 and air?



I wonder if this varies from keg to keg. When I look at my ball-lock kegs, the rim of the lid is higher than the posts. When I fill my kegs with StarSan I do so through the open lid, and I cannot see where there would be any pockets of air. If I filled the keg through the liquid post, I also don't see where there would be any sizeable pockets if liquid was coming out of the PRV on the lid. Maybe if liquid was coming out of the gas post. Or am I not understanding what is being said here.

Look closely at the lid. If you unscrew the PRV and turn the lid upside down, you can fill the lid cavity with water until it runs out the PRV opening. Dump the water into a measuring cup - it should be about 3 fl oz.

As far as the effect of a spunding valve, I'd have to rerun the analysis at a higher pressure to see what really happens. A lot of what goes on is counter intuitive.

Brew on

 

[DuncB]

I have never looked at corney keg so not sure about them. Sankey I fill to the brim, back fill the dip tube via the post and then put it on it overflows a bit as lid attached. Then purged with the ferment gas. I vent the gas from fermenter and thru the jumper tube for a while before the keg purging.
There is a maths way of working out how much theoretical gas is made for the sugar to alcohol reaction. But friend has a plaato and reckons that a 6 gallon ferment makes about 2000 litres of CO2. This could be right having looked at the bubble rate thru an airlock, assuming each bubble about 1 ml theres a lot of bubbles per hour and for days.

Spunding valve won't have any effect on the gas mixing except in the valve.

 

[doug293cz]

I have never looked at corney keg so not sure about them. Sankey I fill to the brim, back fill the dip tube via the post and then put it on it overflows a bit as lid attached. Then purged with the ferment gas. I vent the gas from fermenter and thru the jumper tube for a while before the keg purging.
There is a maths way of working out how much theoretical gas is made for the sugar to alcohol reaction. But friend has a plaato and reckons that a 6 gallon ferment makes about 2000 litres of CO2. This could be right having looked at the bubble rate thru an airlock, assuming each bubble about 1 ml theres a lot of bubbles per hour and for days.

Spunding valve won't have any effect on the gas mixing except in the valve.

2000 litres is too high by about a factor of 4. In the analysis in post #3 of this thread, I go thru the math on CO2 generation. The net was about 440 litres from a 20 litre ferment.

Brew on

 

[DuncB]

Goes to show that the plaato is perhaps not as good as it looks. I'll stick to the Ispindel.

 

[renstyle]

@doug293cz, I nominate entry #3 of this thread for "sticky" status, or something of similar stature.

Recently I cleaned, then sanitized a serving keg, then used the sanitized water during a brew day (dark mild).

After I seated the lid on the (now empty) serving keg with a burst of initial tank CO2, I used fermentation gas to (more or less) fully purge my serving keg of non-CO2 gases down to the very-low-PPB-I-am-OK-with ranges. The calculations were fantastic especially since they generally low-balled the amount of CO2 produced.

Appreciate the effort. Thanks doug, and everybody who played a part in the conversation.

 

[doug293cz]

@doug293cz, I nominate entry #3 of this thread for "sticky" status, or something of similar stature.

Recently I cleaned, then sanitized a serving keg, then used the sanitized water during a brew day (dark mild).

After I seated the lid on the (now empty) serving keg with a burst of initial tank CO2, I used fermentation gas to (more or less) fully purge my serving keg of non-CO2 gases down to the very-low-PPB-I-am-OK-with ranges. The calculations were fantastic especially since they generally low-balled the amount of CO2 produced.

Appreciate the effort. Thanks doug, and everybody who played a part in the conversation.

Now stickied.

Brew on

 

[Spivey24]

Now stickied.

Brew on

Ha, I was looking at your final calculations, and was convinced this had to be an iterative calculation, and not a power to (^) calculation. I was dead wrong. the software developer in me made me.

I wrote a small program to calculate the decreasing O2 volume and the final O2 concentration and it matched your calculation exactly. I used your assumptions of perfect mixing rather than trying to factor in the diffusion front. I did end up changing the starting parameter to 400L of CO2 produced to be more conservative. But still quite surprised at how low that final concentration is. Thanks for your work.

O2 concentration levels | C# Online Compiler | .NET Fiddle

 

[doug293cz]

Ha, I was looking at your final calculations, and was convinced this had to be an iterative calculation, and not a power to (^) calculation. I was dead wrong. the software developer in me made me.

I wrote a small program to calculate the decreasing O2 volume and the final O2 concentration and it matched your calculation exactly. I used your assumptions of perfect mixing rather than trying to factor in the diffusion front. I did end up changing the starting parameter to 400L of CO2 produced to be more conservative. But still quite surprised at how low that final concentration is. Thanks for your work.

O2 concentration levels | C# Online Compiler | .NET Fiddle

Thanks for checking my math. I don't know if anyone has ever done it before, but no one every pointed out an error.

Brew on

 

[Adam Zerwick]

Here's a spreadsheet I made based on the post by @doug293cz. I decided to explore different purging schemes for my smaller batch sizes as well as using a separate vessel for dry hopping. Calculations are made for the following schemes:

- Purge headspace using only fermentation CO2. Assumes entire headspace is not filled with water/starsan.
- Purge unfilled headspace with fermentation CO2, then purge water/starsan filled headspace with fermentation CO2. Gives you the gravity when to start the water purge given a target O2 ppb
- Purge unfilled/filled headspace using fermentation CO2

Hopefully it helps somebody else. It certainly opened my eyes to potentially how much O2 was left in my kegs using my normal purge process. Also one thing to note, the example in post #59 seems to off by a factor of 1000 based on my math... so please let me know if any of you spot a problem with my spreadsheet!

Keg Purge Final O2

 

[Muddbug]

Here's a spreadsheet I made based on the post by @doug293cz. I decided to explore different purging schemes for my smaller batch sizes as well as using a separate vessel for dry hopping. Calculations are made for the following schemes:

- Purge headspace using only fermentation CO2. Assumes entire headspace is not filled with water/starsan.
- Purge unfilled headspace with fermentation CO2, then purge water/starsan filled headspace with fermentation CO2. Gives you the gravity when to start the water purge given a target O2 ppb
- Purge unfilled/filled headspace using fermentation CO2

Hopefully it helps somebody else. It certainly opened my eyes to potentially how much O2 was left in my kegs using my normal purge process. Also one thing to note, the example in post #59 seems to off by a factor of 1000 based on my math... so please let me know if any of you spot a problem with my spreadsheet!

Keg Purge Final O2

Thanks for the sheet it's great!

When putting in 25 L it's spot on so maybe there isn't enough CO2 for two kegs?

I'm purging a keg using this method right now, the serving keg and the fermenter are both in the fermentation refrigerator

looking forward to a great beer.

 

[Cider Wraith]

Almost certainly meaningless but ... regarding purging as much air as possible - and I'm already accepting of the reality of not being able to achieve laboratory results in a kitchen - but could C02 being heavier than air be used to advantage?

 

[IslandLizard]

Almost certainly meaningless but ... regarding purging as much air as possible - and I'm already accepting of the reality of not being able to achieve laboratory results in a kitchen - but could C02 being heavier than air be used to advantage?

Gasses mix freely. Thus there's no such thing one gas forming a "blanket" on top of another. Especially in more turbulent environments.

 

[doug293cz]

Almost certainly meaningless but ... regarding purging as much air as possible - and I'm already accepting of the reality of not being able to achieve laboratory results in a kitchen - but could C02 being heavier than air be used to advantage?

Not practically. If flow rates are low enough to prevent turbulence, then CO2 and air will mix almost as fast as you can push CO2. In the case of the subject of this thread, there is a minor benefit, as the mixing is not quite as fast as the movement of CO2 into the keg being purged. Thus the actual O2 content after an active fermentation purge is less than that calculated by my analysis (which assumed no benefit of stratification.)

Brew on

 

[Bark0s]

Couldn't say. I only know what was in the presentation.



Interestingly enough, the headspace in both cases is about 6% of the liquid volume. I've measured both, since the question has been asked before.

Commercial bottlers pre-purge with CO2 immediately before filling, and since they are bottling fully carbonated beer, they get significant foam. The foam is full of CO2, and if they cap before the foam subsides, very little O2 gets into the headspace.

Brew on

Thank you for this incredible post! I've signed up to this forum in order to ask some questions, below:

But that foam is in contact with the air? So why can't we fill our corny kegs the same way? Under pressure until the late stages then 'purge the headspace' with the beer's own foam until it escapes through the prv, then close it off?

Also, what is the flux of air (well, oxygen) into beer? If you have an air filled corny keg and you will add 19 litres of beer, then you have a 55cm3 headspace to purge. Does that still take 30 cycles? Has the staling process begun in the minutes whilst the keg is filling? Does the staling persist post headspace purge with co2?

Does ascorbic acid help preserve the beer in corny keg?

 

[DuncB]

That beer foam will still exchange with the air and reach an equilibrium. It won't be CO2 only foam.
The exchange starts immediately the beer comes in contact with oxygen, breweries aim for oxygen in the parts per billion with their processes. A cask ale which starts with virtually no oxygen in it stales within a few days of having been exposed to the air.
Hence the desire to transfer into an oxygen free keg.
Regarding ascorbic acid this thread.
https://www.homebrewtalk.com/threads/vitamin-c-the-game-changer.698328/
also a good read, not sure it's a rescue for oxygenated beer, but I think it helps with the packaging and preservation of well treated beer.

 

[AlexKay]

Has the staling process begun in the minutes whilst the keg is filling? Does the staling persist post headspace purge with co2?

Oxygen dissolves into beer quite slowly — even the pros targeting 100s of ppb total package oxygen have their cans/bottles open to air as they ride the star wheel/conveyer belt from the filler to the seamer/capper. The thing you need to do is keep oxygen out of the headspace in a sealed package. In a bottle on a shelf somewhere, the oxygen will have all the time it needs to dissolve into the beer and react, and which point more will dissolve and react, until it is all gone.

 

[CascadesBrewer]

But that foam is in contact with the air? So why can't we fill our corny kegs the same way? Under pressure until the late stages then 'purge the headspace' with the beer's own foam until it escapes through the prv, then close it off?

Keep in mind that professional breweries are first purging the bottle with CO2 before filling with beer. Transferring beer into an unpurged keg will introduce some oxygen*. How much?? They also have the benefit of bottling carbonated beer. Unless your beer is pressure fermented and already partially carbonated, it would be hard to get enough foaming action to fill a keg headspace. And I suspect it would be pretty hard to execute correctly with carbonated beer.

Any steps to reduce oxygen while kegging will help. For years I transferred into an open keg (often I would run some CO2 in the liquid post to purge some of the air from the bottom) and would then purge the headspace maybe 8 times after I filled the keg. For a lot of styles of beer and for beer that will be kept cold, that might be "good enough." These days I always do a closed transfer into purged kegs. I have purged kegs with active fermentation (and hope to use that method more often) but usually fill my kegs with Star San solution and purge that with bottled CO2.

*On a related note, I use the "no stinkin beer gun" approach for filling bottles. I have tested bottling IPAs and NEIPAs in CO2 purged vs non-purged bottles, and have not noticed a difference. After several months stored at room temp, I have not noticed any oxidation issues with either method. I am sure to cap those on foam.

 

[Bark0s]

Keep in mind that professional breweries are first purging the bottle with CO2 before filling with beer. Transferring beer into an unpurged keg will introduce some oxygen*. How much?? They also have the benefit of bottling carbonated beer. Unless your beer is pressure fermented and already partially carbonated, it would be hard to get enough foaming action to fill a keg headspace. And I suspect it would be pretty hard to execute correctly with carbonated beer.

Any steps to reduce oxygen while kegging will help. For years I transferred into an open keg (often I would run some CO2 in the liquid post to purge some of the air from the bottom) and would then purge the headspace maybe 8 times after I filled the keg. For a lot of styles of beer and for beer that will be kept cold, that might be "good enough." These days I always do a closed transfer into purged kegs. I have purged kegs with active fermentation (and hope to use that method more often) but usually fill my kegs with Star San solution and purge that with bottled CO2.

*On a related note, I use the "no stinkin beer gun" approach for filling bottles. I have tested bottling IPAs and NEIPAs in CO2 purged vs non-purged bottles, and have not noticed a difference. After several months stored at room temp, I have not noticed any oxidation issues with either method. I am sure to cap those on foam.

I do pressure ferment...well, I ferment in kegmenters and either pressure ferment or add pressure late during ferment...or add pressure post ferment. I have for a couple of years bottled carbonated beer (I got into pressure fermenting because I didn't have temperature control, so I let pressure ride pretty high (26psi) and I would bottle warm at that psi too. I'm not endorsing what I did...it's much easier at 12psi and beer below 4c.

I don't think pro breweries are purging all vessels with co2 first...not in accordance with post #3 from this thread. The cans and bottle arrive open, they travel open into the filler where they may receive a shot or burst of CO2 but it's the beer and its foam that fills and overflows the vessel...then they seal.

I've got a counter pressure bottle filler and although I pressurise the bottle with CO2 before I fill, I surely don't purge out the oxygen. Again, it's the beer that occupies the space...then the foam occupies that last bit. My system, like yours, works well, I room temp store bottled beer and have had neipa's stay vibrant over more than 6 months.

I'm just new to kegging and ultimately, because I have kegmenters, not conical fermenters, I need to transfer my beer off the yeast, as I can't drop yeast in this equipment. So I figure I should hop the empty keg, purge (probably via ferment) and then push the beer onto the hops, sans yeast.

 

[AlexKay]

I don't think pro breweries are purging all vessels with co2 first...not in accordance with post #3 from this thread. The cans and bottle arrive open, they travel open into the filler where they may receive a shot or burst of CO2 but it's the beer and its foam that fills and overflows the vessel...then they seal.

Bottles are evacuated, filled with CO2, evacuated again, and filled again with CO2. Depending on the base vacuum pressure, this will reduce oxygen significantly more than purging and venting (even many times) just with an overpressure of CO2. Cans cannot be evacuated (collapse), so are purged with gas, but then capped and seamed under a flow of CO2. Both cans and bottles are, as you say, capped on foam in order to displace as much remaining air from the container as possible.

 

[AlexKay]

Back of the envelope, how much air-filled headspace can you tolerate for a five-gallon batch? Figure a target of 50 ppb (this is much better than professional best-practice total oxygen, and there are enough other sources of oxygen that I don't think it's important to shoot for too much lower than this), so 50 ug of O2 per liter of beer, or 900 ug per 5 gallons. Each ug of O2 takes up about 0.7 uL of space, so you could have ~600 uL of O2-filled headspace, have all the oxygen make its way into the beer, and still hit 50 ppb dissolved O2. Multiply by 5 to get 3 mL of air.

Figure an actual headspace of 300 mL, and your goal is to reduce the O2 concentration to 1% of its original value. That's a pain to do with repeated fill/purge cycles of CO2, but it's not impossible.

If you're filling with StarSan and then purging, better get all of the StarSan out: each ounce contains ~250 ug of dissolved O2.

 

[AlexKay]

Also, for those purging kegs with fermentation gas, is everyone using barrier tubing? Pictures in this thread seem to indicate at least some are using PVC or silicone.

 

[CascadesBrewer]

I'm just new to kegging and ultimately, because I have kegmenters, not conical fermenters, I need to transfer my beer off the yeast, as I can't drop yeast in this equipment. So I figure I should hop the empty keg, purge (probably via ferment) and then push the beer onto the hops, sans yeast.

On the (massively long) "Northeast IPA" thread there are some brewers that do something very similar...add the dry hops to a second fermenter or keg, use fermentation CO2 to purge that vessel, then close transfer the beer into the second vessel. You could serve from the dry hop vessel or transfer into a third purged vessel.

 

[doug293cz]

Back of the envelope, how much air-filled headspace can you tolerate for a five-gallon batch? Figure a target of 50 ppb (this is much better than professional best-practice total oxygen, and there are enough other sources of oxygen that I don't think it's important to shoot for too much lower than this), so 50 ug of O2 per liter of beer, or 900 ug per 5 gallons. Each ug of O2 takes up about 0.7 uL of space, so you could have ~600 uL of O2-filled headspace, have all the oxygen make its way into the beer, and still hit 50 ppb dissolved O2. Multiply by 5 to get 3 mL of air.

Figure an actual headspace of 300 mL, and your goal is to reduce the O2 concentration to 1% of its original value. That's a pain to do with repeated fill/purge cycles of CO2, but it's not impossible.

If you're filling with StarSan and then purging, better get all of the StarSan out: each ounce contains ~250 ug of dissolved O2.

Looks like you might have made the adjustment to 5 gal twice.

Also, a "5" gal keg has an internal volume of about 5.3 - 5.35 gal (I measured.) So, the headspace with 5 gal of beer would be a bit more than a liter.

Brew on

 

[DuncB]

Perhaps purging with late ferment CO2 a completely filled keg of water with Sodium Metabisulphite in would reduce the dissolved oxygen component ( in the liquid not the beer) ?
Would there be 50microgrammes per litre of oxygen in beer at the end of ferment if the system was closed?
Does the calculation take account of the nitrogen percentage in an open ferment system? I realise that the nitrogen is pretty insoluble at atmospheric pressure.

 

[AlexKay]

Looks like you might have made the adjustment to 5 gal twice.

Also, a "5" gal keg has an internal volume of about 5.3 - 5.35 gal (I measured.) So, the headspace with 5 gal of beer would be a bit more than a liter.

Brew on

I thought my first 5 was for gallons, and the second because air is only 20% oxygen. But maybe another 5 snuck in without me realizing.

If one could arrange to brew a little more beer and leave even less headspace, fill-and-release CO2 purging can be for all intents and purposes as good as fermentation gas purging. Maybe that’s another thread, “ways to avoid keg purging by active fermentation.”

 

[doug293cz]

I thought my first 5 was for gallons, and the second because air is only 20% oxygen. But maybe another 5 snuck in without me realizing.

If one could arrange to brew a little more beer and leave even less headspace, fill-and-release CO2 purging can be for all intents and purposes as good as fermentation gas purging. Maybe that’s another thread, “ways to avoid keg purging by active fermentation.”

I have analyzed pressurize and vent O2 purging and posted the results on HBT numerous times. The math doesn't care what the headspace volume is, but the larger the headspace, the more CO2 is required for whatever level of residual O2 you target. The results are summarized in the chart and table below:

Brew on

 

[AlexKay]

I have analyzed pressurize and vent O2 purging and posted the results on HBT numerous times. The math doesn't care what the headspace volume is, but the larger the headspace, the more CO2 is required for whatever level of residual O2 you target. The results are summarized in the chart and table below:

View attachment 784372View attachment 784373

Brew on

The pressure in the headspace is independent of the headspace size. But the total amount of oxygen in the headspace depends on the volume, n=PV/RT. While DO is proportional to pressure (headspace volume doesn’t matter) I’m working under the assumption that any dissolved oxygen will react, and (LeChatelier) the entire quantity in the headspace will eventually stale the beer. (headspace volume matters)

What I calculated was that if you could swing an admittedly impractical 3 mL of headspace, you could leave it full of air. More headspace requires fill and vent cycles, but if you can keep the headspace small, not that many of them.

Purging the keg before a closed transfer lets you avoid pickup or DO during filling. This is why cans are flushed (fill and vent!) in pro setups. I don’t know how to calculate the speed of O2 solubilization, but I think it’s safe to assume the process is pretty slow if you can keep surface area of the liquid down.

 

[Bark0s]

What I'm proposing is purging my sanitised corny keg...with beer.

I transfer the beer in under pressure with a spunding valve, then when full (flowing out the prv or spunding) I disconnect the spunding valve. I attach the gas to the liquid post, then I vent foam out the prv...job done, all oxygen purged?

Or maybe I stop risking $70 worth of beer over 1 dollar's worth of CO2 (and I buy a second CO2 bottle so I don't run out).

It's just a matter of the maths...I will not purge a keg 30 times to get the oxygen down to low enough ppb...so what's the point in doing initial purging at all if it's insufficient?

 

[doug293cz]

What I'm proposing is purging my sanitised corny keg...with beer.

I transfer the beer in under pressure with a spunding valve, then when full (flowing out the prv or spunding) I disconnect the spunding valve. I attach the gas to the liquid post, then I vent foam out the prv...job done, all oxygen purged?

Or maybe I stop risking $70 worth of beer over 1 dollar's worth of CO2 (and I buy a second CO2 bottle so I don't run out).

It's just a matter of the maths...I will not purge a keg 30 times to get the oxygen down to low enough ppb...so what's the point in doing initial purging at all if it's insufficient?

A corny keg lid has an air pocket with a volume of 3 fl oz (90 mL) trapped when fluid flows out of the PRV (it's been measured by me and others here at HBT.) You can shorten the gas dip tube such that it doesn't reach into the vessel proper, and then tilt to get all of the trapped air out if you want to go to the trouble. 3 mL of air contains enough O2 to degrade a hoppy beer.

Brew on

 

[AlexKay]

The situation is about a thousand times less dire than it seems.

When beer professionals give a target of 50 ppb (and I don't think it's common to get this low), that's 50 parts of oxygen by weight to a billion parts of water, or 50 ug per kg. What @doug293cz is showing in his table a few posts back is ppm oxygen in the headspace gas by number (or volume, or mole fraction, though not by mass). Because beer is roughly 1000 times denser than air, this means that even if you started with 5 gallons of pure O2 gas (1,000,000 ppm by volume), and forced it all into 5 gallons of beer, Henry's Law be damned, you'd only be looking at ~1000 ppm of O2 (still a lot, but still.)

If you can manage a 10:1 ratio of liquid to headspace, that's ~100 ppm, down to ~20 ppm when you consider that air is only partly oxygen. Now, 20 ppm is still too much for beer to have much of a shelf life, and reasonably speaking you need a 100-1000x improvement. Displacing air with beer gives you a better liquid:headspace ratio -- that's what @Bark0s is proposing, and it works to an extent. You could shoot for 100:1, say (~0.05 gallons headspace, or 6 ounces), and then you need a 10-100x improvement, which could come from replacing air in the headspace by CO2. That's ~5 purges at 10 psi. Not so bad.

 

[DuncB]

It is a dynamic situation, a basically oxygen free beer at the start of transfer being exposed to a keg full of air will immediately start to seek equilibrium of the oxygen gradient. It's not a simple solution either because the oxygen that gets into the beer will then react with all kinds of ingredients which will lower the amount of oxygen in the beer and hence promote more oxygen entry.

 

[Bark0s]

A corny keg lid has an air pocket with a volume of 3 fl oz (90 mL) trapped when fluid flows out of the PRV (it's been measured by me and others here at HBT.) You can shorten the gas dip tube such that it doesn't reach into the vessel proper, and then tilt to get all of the trapped air out if you want to go to the trouble. 3 mL of air contains enough O2 to degrade a hoppy beer.

Brew on

Hi @doug293cz , those are some simple terms I can get my head around. Thanks.

I was aiming to fill that 90ml of air with 90ml of foam. SO rather than 'cap on foam' I'm shutting the prv on foam.

@AlexKay thanks for the different and calming science.

@DuncB - seeing as most people only do a single purge, according to Doug's chart we go from 210k down to 70k (69k really). So we're 1/3 as reactive but still reactive. Also (and this isn't science at all) but if we are filling from the bottom...isn't it only the top layer of head of the beer that'll be in contact with air? So it won't be a swirling solution?

I am open to being convinced, I'm not here to be stubborn. It seems I'll need to do a brulosophy style direct compare of two corny kegs (mixed, to eliminate other variation). Or just use some SMB.

 

[doug293cz]

Hi @doug293cz , those are some simple terms I can get my head around. Thanks.

I was aiming to fill that 90ml of air with 90ml of foam. SO rather than 'cap on foam' I'm shutting the prv on foam.

I'm not sure how well the foam will displace air in a pocket above the exhaust port (PRV valve opening.)

Anyway, I went ahead and did the math for TPO (Total Packaged Oxygen) that 90 mL of air would contribute to 5 gal (19 L) of beer. Air is 21% O2, so 90 mL of air contains 90 * 0.21 = 18.9 mL of O2. At freezing temps (assuming cold crashed beer) and atmospheric pressure, a mole of (any) gas occupies 22.4 L, so 18.9 mL is 0.0189 / 22.4 = 0.000844 mole of O2. The molecular weight of O2 is 32 g/mole, so we have 32 * 0.000844 = 0.027 g or 27 mg of O2. 1 mg / kg is 1 ppm (by mass), and since 19 L of 1.010 beer weighs 19.2 kg, we have 27 mg / 19.2 kg = 1.4 ppm TPO from 90 mL (3 fl oz) of air in 5 gal of beer. Commercial brewers target less than 0.2 ppm TPO to get good self life.

This gets to the point that @AlexKay was making about headspace O2 concentration not being the whole story for TPO

Brew on

 

[AlexKay]

Also in your favor is that you’re (hopefully) going to put that keg right in the freezer. The pros (at least those without their own refrigerated truck fleet) are considering less-than-ideal handling when they’re trying to figure out what’s needed for good shelf life. Homebrewers can cool the beer immediately and keep it cold, which is pretty much the best-case scenario.

Don’t get me wrong, if I’m kegging an NEIPA I made with $40 worth of hops in it, I’m going to get rid of all the oxygen I possibly can.

 

[dave_1]

Not sure why you are concerned about the possibility of some yeast in the CO2 that would then get into your keg. What do you think is going to happen that won't when you put beer with yeast in it into your keg? If you really want to filter out the yeast, use one of the Norcal Krausen Catchers with one of these between the catcher and the keg. (Coincidentally, my Krausen Catchers arrived in the mail today.)

Brew on

Hi My experience of fermenting under pressure, 7.5 PSI or a head of about 5 metres, results in no Krausen reaching the top of the fermenting vessel. I leave a head space of about 160 mm or 6 inches between the Wort and the top of the fermenter. I'm using a see through fermenter so can observe very closely the goings on inside. . I have now changed to using the CO2 generated by the fermentation very successfully to purge the small amount of residual Starsan and then basically replace the air in the keg with CO2. I also pressure transfer to my keg thus saving heaps of tank CO2.
Really appreciate these forums, thanks.

 

[murphyslaw]

Sorry if this has been asked before, but how long can you safely wait after pitching to hook up the serving keg and still feel confident that you have enough co2 to purge it? Really I just want to be wait until there’s no blowoff.

 

[doug293cz]

Sorry if this has been asked before, but how long can you safely wait after pitching to hook up the serving keg and still feel confident that you have enough co2 to purge it? Really I just want to be wait until there’s no blowoff.

It's not a matter of time, but rather a matter of current SG and FG. These will determine how much CO2 will be generated by the end of fermentation. You'd have to do the calcs for your specific configuration's beer volume and purge volume (fermenter headspace, plumbing volume, and keg volume.)

Brew on