How to effectively purge keg of O2

[gcdowd]

How many times and at what pressure do you burp the keg to purge all the O2? I plan on aging this a little in the keg and just want to clear the oxygen.

 

[E-Mursed]

I go at it with 10 - 12 psi and will purge the keg anywhere from 10 to 12 times over a half hour before pulling it off gas.

I may even shake the keg a few times for no specific reason.

 

[Golddiggie]

I fill the empty keg with CO2, then replease from the lid's relief valve a couple of times. I take the gas feed off of the keg before releasing the pressure in the keg though.

Once the keg has whatever is going into it, I hit it with ~10psi to get the lid seal to seat and then pull the relief again. I do that a few times to ensure only CO2 is over what's in the keg.

No issues to date with this method. Of course, I'm also pushing into the keg via CO2, and using the keg's liquid post to fill from the bottom. Once the keg is sanitized nothing enters it except finished beer (or maybe dry hops, but that's different )...

 

[Sea]

I guess I'm pretty lax. I put the keg on at serving pressure, about 10-12 PSI, then burp it a few times in the first hour. Works for me.

 

[gcdowd]

I've heard so many different methods, I guess it's all about personal preference. Thanks all. This is my first kegging experience so newbie questions abound.

 

[GoodDogShelby]

So what's the best way to burp a keg with an auto pressure relief?

 

[Golddiggie]

So what's the best way to burp a keg with an auto pressure relief?

Either a gas QD without anything on it, a screwdriver to depress the poppet, or something else to press the poppet top to open it up. Personally, I would just get a ball lock lid (with a relief valve you can use) and not worry about it.

 

[Bsquared]

I have a QD connected to my syphon, I like to purge the tubing with CO2 by releasing the pressure from the keg with it before I transfer.

 

[rtrevino]

If you want to be 100% sure it's o2 free, fill the keg to the brim with water. Connect your gas and liquid lines and then push all of the water out with co2. When all the water is out, the keg will be full of co2.

 

[Dan]

Have never had one of my homebrews oxidize in a keg. Here is what works for me.

I cold crash to drop sediment. This usually is done for a week, not because it takes that long but because weekends are when I work on my beer.

1 Rack from fermenter in to clean sanitized keg.
2 Close lid on keg
3 Apply 15 psi to Co2 post for ~10 seconds.
4 Vent a few seconds.
Wait a few more seconds
5 Vent a few seconds.
6 Vent a few seconds.
Wait a few seconds
7 Vent a few seconds.


Repeat 1 & 2 3 or four times.

Force carb with your chosen method.

(Fermenter has been cold crashing for about a week to clear)Works for me. YMMV

 

[LLBeanJ]

Have never had one of my homebrews oxidize in a keg. Here is what works for me.

I cold crash to drop sediment. This is usually done for a week, not because it takes that long but because weekends are when I work on my beer.

1 Rack from fermenter to the bottom of a clean sanitized keg. Do not aerate.
2 Close lid on keg.
3 Apply 15 psi to the Co2 post for ~5 seconds.
4 Vent a few seconds.

Repeat #3 and #4 two or three more times and then force carb with your preferred method

Works for me. YMMV

+1

This is pretty much what I do. I don't make a production out of it. Fill it, vent it, fill it, vent it, fill it, vent it, call it a day. Takes about 60 seconds. Seems to work just fine, as no oxidation issues thus far.

 

[rjwhite41]

I hit the empty keg with 30 psi, wait a few seconds and vent it. I repeat 3-4 times and then I transfer to the keg. Do it another 2-3 times and set it to carb. I used to skip the first part and never had a problem for what that's worth. I've had filled kegs lager for over 9 months and have never had an oxidation problem.

 

[gcdowd]

Have never had one of my homebrews oxidize in a keg. Here is what works for me.

I cold crash to drop sediment. This is usually done for a week, not because it takes that long but because weekends are when I work on my beer.

1 Rack from fermenter to the bottom of a clean sanitized keg. Do not aerate.
2 Close lid on keg.
3 Apply 15 psi to the Co2 post for ~5 seconds.
4 Vent a few seconds.

Repeat #3 and #4 two or three more times and then force carb with your preferred method

Works for me. YMMV

This is the method I used as it seemed the easiest. As long as I don't have oxidation issues, I will continue using this method.

 

[audger]

instead of pulling a method out of thin air, lets look at the science....

the atmosphere is made up of around 21% oxygen, and very close to 15psi at sea level.

so set your regulator to 15psi (which is called "gauge pressure", meaning 15psi over atmospheric pressure; 15psi on the regulator is really about 30psi absoloute). if you have a keg full of air at atmospheric pressure, and then you fill it with 15psi of pure CO2, you will now have a keg that has 50% CO2, and 50% air, right?

now what is 50% of 21%? 11.5%... your keg now has 11.5% oxygen in it. when you purge it, it will remain roughly the same percentage, but the pressure will be reduced.

so now you have a keg at atmospheric pressure with 11.5% O2 in it after 1 purge. each time you fill it and purge it, the oxygen concentration will reduce by half. the reason its dilluted by half is because you are adding 50% partial pressure of CO2 each time. if you used 30psi on your regulator, it would reduce it by 66% (15psi atmospheric to 30psi pure CO2). but that wastes twice as much CO2 to only get only an additional 16% O2 reduction from each purge.

so two purges = 5.75% remaining O2
three purges = 2.9% remaining O2
four purges = 1.4% remaining O2
five purges = 0.7% remaining O2


1% O2 concentration is the threshold that most breweries shoot for. below that doesnt effect the beer very much. so it takes 4-5 purges at 15psi to get there. remember, that is a full 15psi, meaning you completely let the regulator equalize before purging. if you purge while gas is still flowing, you will have to use more than 5 purges.

alternatively, fill the keg to the very top with sanitizer and push it out with CO2, and you will be left with a keg that contains 100% co2 without needing to waste any.

 

[FlyDoctor]

Once this has been accomplished, do you keep the keg covered while racking to prevent air entry?

 

[jro238]

instead of pulling a method out of thin air, lets look at the science....

the atmosphere is made up of around 21% oxygen, and very close to 15psi at sea level.

so set your regulator to 15psi (which is called "gauge pressure", meaning 15psi over atmospheric pressure; 15psi on the regulator is really about 30psi absoloute). if you have a keg full of air at atmospheric pressure, and then you fill it with 15psi of pure CO2, you will now have a keg that has 50% CO2, and 50% air, right?

now what is 50% of 21%? 11.5%... your keg now has 11.5% oxygen in it. when you purge it, it will remain roughly the same percentage, but the pressure will be reduced.

so now you have a keg at atmospheric pressure with 11.5% O2 in it after 1 purge. each time you fill it and purge it, the oxygen concentration will reduce by half. the reason its dilluted by half is because you are adding 50% partial pressure of CO2 each time. if you used 30psi on your regulator, it would reduce it by 66% (15psi atmospheric to 30psi pure CO2). but that wastes twice as much CO2 to only get only an additional 16% O2 reduction from each purge.

so two purges = 5.75% remaining O2
three purges = 2.9% remaining O2
four purges = 1.4% remaining O2
five purges = 0.7% remaining O2


1% O2 concentration is the threshold that most breweries shoot for. below that doesnt effect the beer very much. so it takes 4-5 purges at 15psi to get there. remember, that is a full 15psi, meaning you completely let the regulator equalize before purging. if you purge while gas is still flowing, you will have to use more than 5 purges.

alternatively, fill the keg to the very top with sanitizer and push it out with CO2, and you will be left with a keg that contains 100% co2 without needing to waste any.

While I love the approach, you are leaving out one important variable--gas' molecular weight. CO2 has a MW of 44 while oxygen's MW is 32 and 'air' is around 29. While this doesnt really matter much if you are filling and purging your tank immediatly, if you let it sit for a minute the 'air' will tend to rise to the top of the tank and thus you will be venting a greater % of air vs CO2.
(Will this actually have any effect whatsoever on the method of purging you keg? Probably not :cross.

Cheers!

EDIT: Realized I wasn't really clear about this in my last post...clearly given some time all of the CO2 and O2 will completely mix together but in the short term the two will stratify.

 

[Landshark67]

CO2 / O2 stratification is why I don't worry much about purging the keg. I simply pump CO2 into the open keg for 20-30 seconds and then let settle for 5 minutes. The beer flows into the bottom of the keg and pushes the CO2 up until the keg is full. My theory is that the "bed of CO2" rises uniformly. No oxidation issues to date.

 

[phoenixs4r]

Wow.

There so little air in the keg I really don't think it matters.

None of my lids seal unless I hit them with 30 psi, so I do that, purge, hit it one another shot to keep it sealed. Throw it into the closet

 

[D_Nyholm]

Just racking into a keg remove the oxygen and replace it with beer? I usually have about 2" of headspace in my full keg and I purge it at 12 psi about 3-5 times. Never had a problem yet! Or if I did, I couldn't taste it!

 

[audger]

While I love the approach, you are leaving out one important variable--gas' molecular weight. CO2 has a MW of 44 while oxygen's MW is 32 and 'air' is around 29. While this doesnt really matter much if you are filling and purging your tank immediatly, if you let it sit for a minute the 'air' will tend to rise to the top of the tank and thus you will be venting a greater % of air vs CO2.
(Will this actually have any effect whatsoever on the method of purging you keg? Probably not :cross.

Cheers!

EDIT: Realized I wasn't really clear about this in my last post...clearly given some time all of the CO2 and O2 will completely mix together but in the short term the two will stratify.

in theory, yes, CO2 is heavier than air/oxygen, but in reality they behave much more like an ideal gas (and almost completely mix) rather than stratify by any appreciable amount. the only isntance i know of where CO2 being heavier has any real effect is in fermentation- the CO2 produced that emerges from the liquid surface is very effective at pushing the oxygen in the headspace up and out. but that is a very slow trickle of CO2 emerging from the surface over a wide and complete area. if you move the carboy at all you will instanly mix the gasses again.

people usually think about CO2 and oxygen as oil and water. its really a closer analogy to water and alcohol. yes they will stratify a decent amount under very ideal conditions, but in practice they almost never do at all.

think about the nitrogen and oxygen in the air. if you are sitting in a closed room with very little air movement, does the nitrogen stratify twoards the ceiling and oxygen to the ground? maybe a very small amount, but nothing noticable (and probably not even measurable).