Purging

[mancer62]

Can I ask something Im never very clear about. Its about purging the headspace in my filled corny keg. When I give a few blast on my pressure release valve to get rid of the oxygen should the CO2 still be connected and running or turned off?
Also when doing a quick forced carbonation ie (rocking it back and forth on my knee) how long do u recommend for? and what pressure is best for this?
To be honest I'm not interested in the flushing out starsan method etc. I just want to keep it simple and purge the small head space in the keg. Look forward to replies. Thank you.

 

[phildo79]

It should still be connected and flowing into the keg. Oxygen is lighter than CO2 and is therefore pushed out when venting.

I put mine on the floor, set the PSI to 30 and roll back and forth for 5 mins.

You will want to try and remove as much oxygen as possible before transferring to eliminate oxygen contact. Simply filling it and then purging the head space is not best practice. You may notice loss of flavour and aroma in your beers a lot sooner. I used to use the StarSan method but not anymore. Now I seat the lid of an empty keg with 30 PSI and wait until it is full. I then open the vent fully for 10 seconds, close and wait for the keg to re-pressurise. I reckon that should be long enough to get rid of most of the oxygen. I then vent down to 15 PSI and transfer under pressure.

 

[visitor]

When I purge my corny's I do leave the CO2 flowing in. Depending on how much actual space is there I'll purge a bit more or less.

What's most important with the force carb method is temperature. A cooled keg will absorb the CO2 into beer easier. I typically put my pressure up to 20-30 PSI and give the keg roughly 2 minutes of back and forth in an upright position. As long as I hear the gas passing through the regulator you know it's absorbing into the beer. I typically use this just to cut the time to fully carb and then set my desired pressure and let time handle the final carbonation level. If you do the force carb shaking method you can always take a break and pull a bit through the faucet to see how the carb level is coming along. Not carbonated enough, give it another go.

 

[phildo79]

You can also hook the gas up to the liquid post (with the correct disconnect or universal posts), at serving PSI, if you want to use the 'set and forget' method but might want the odd beer now and again. The beer at the bottom will come out carbed. I do this when I make a nitro stout because I am impatient and want delicious homebrewed Beamish ASAFP.

 

[AJA]

It should still be connected and flowing into the keg. Oxygen is lighter than CO2 and is therefore pushed out when venting.

I put mine on the floor, set the PSI to 30 and roll back and forth for 5 mins.

You will want to try and remove as much oxygen as possible before transferring to eliminate oxygen contact. Simply filling it and then purging the head space is not best practice. You may notice loss of flavour and aroma in your beers a lot sooner. I used to use the StarSan method but not anymore. Now I seat the lid of an empty keg with 30 PSI and wait until it is full. I then open the vent fully for 10 seconds, close and wait for the keg to re-pressurise. I reckon that should be long enough to get rid of most of the oxygen. I then vent down to 15 PSI and transfer under pressure.

This won't get rid of all the oxygen, simply due to the 2nd law of thermodynamics. The same reason that the 'co2 is heavier than water' argument doesn't fly. Gases like to mix.
Any reason you ditched the starsan method? This is usually the gold standard (although can be improved by using hot water instead). Top tip, when you are done, invert the keg and pull the PRV to remove the last bit of sanitiser/water.

 

[phildo79]

This won't get rid of all the oxygen, simply due to the 2nd law of thermodynamics. The same reason that the 'co2 is heavier than water' argument doesn't fly. Gases like to mix.
Any reason you ditched the starsan method? This is usually the gold standard (although can be improved by using hot water instead). Top tip, when you are done, invert the keg and pull the PRV to remove the last bit of sanitiser/water.

I ditched it because it is a waste of StarSan. Yes, you can reuse it but how many times? It starts to change colour and just put me off.

There is oxygen in the water that we use to make the beer. You need to boil the water several times to remove the oxygen. This is something I have never even tried. Brew days are long enough without boiling 25L of water 5 times before you even mash.

We do what we can as homebrewers but we can't completely eliminate oxygen. TBF, I haven't noticed any negatives since switching venting methods. Had hoppy beers in the keg for a month and aroma and taste didn't fade.

 

[Agentgonzo]

Oxygen is lighter than CO2 and is therefore pushed out when venting

Unfortunately, it doesn't work like that. Water is heavier (denser) than milk. But try sticking a hose into a bottle of milk and turning it on to "purge" the milk from the bottle. Sure, you'll get rid of a fair amount of milk, but a lot will remain unless you use a huge amount of water.

The density of the fluids doesn't really have any effect when "purging" the headspace.

 

[phildo79]

Unfortunately, it doesn't work like that. Water is heavier (denser) than milk. But try sticking a hose into a bottle of milk and turning it on to "purge" the milk from the bottle. Sure, you'll get rid of a fair amount of milk, but a lot will remain unless you use a huge amount of water.

The density of the fluids doesn't really have any effect when "purging" the headspace.

Never said it did. I was talking about gas.

 

[foxy]

I ditched it because it is a waste of StarSan. Yes, you can reuse it but how many times? It starts to change colour and just put me off.

There is oxygen in the water that we use to make the beer. You need to boil the water several times to remove the oxygen. This is something I have never even tried. Brew days are long enough without boiling 25L of water 5 times before you even mash.

We do what we can as homebrewers but we can't completely eliminate oxygen. TBF, I haven't noticed any negatives since switching venting methods. Had hoppy beers in the keg for a month and aroma and taste didn't fade.

The oxygen is boiled off during the boil, there may be some oxygen left but the yeast will either use it or scrub it from the fermenter, but a pound to a pinch of salt their will still be oxygen in there. Gases do mix no matter what their respective weights.
How long does a keg last? Rarely long enough for oxygen to take effect, providing one is careful to reduce the oxygen during transfer, oxygen will never be eliminated.
My reply to the Starsan method is air is in the foam, better with the none foaming Starsan.

 

[clyne]

I’m curious - what’s the “starsan method”? Putting starsan in the keg, shoogling (Scottish word ) it all around and then purge through a tap with co2? Or have I missed a trick?

 

[Agentgonzo]

Never said it did. I was talking about gas.

Gas is a fluid. Exactly the same principles apply.

 

[MickDundee]

I’m curious - what’s the “starsan method”? Putting starsan in the keg, shoogling (Scottish word ) it all around and then purge through a tap with co2? Or have I missed a trick?

Fill the keg completely with Starsan, and then dispense the whole amount so that you have a keg that’s pretty much all CO2.

 

[Agentgonzo]

I’m curious - what’s the “starsan method”? Putting starsan in the keg, shoogling (Scottish word ) it all around and then purge through a tap with co2? Or have I missed a trick?

Fill the keg to the brim with starsan. This ensures there is no oxygen in it.
Then fill the keg with CO2, pushing the starsan out (either from a CO2 bottle or from a fermenter). Save starsan for future use. You now have a sanitised keg completely filled with co2

 

[gyurmaember]

The oxygen is boiled off during the boil, there may be some oxygen left but the yeast will either use it or scrub it from the fermenter, but a pound to a pinch of salt their will still be oxygen in there. Gases do mix no matter what their respective weights.
How long does a keg last? Rarely long enough for oxygen to take effect, providing one is careful to reduce the oxygen during transfer, oxygen will never be eliminated.
My reply to the Starsan method is air is in the foam, better with the none foaming Starsan.

On the top of that, we didn't pasteurizing or kill the yeast in suspension, therefore it might consume that tiny oxygen left in the keg.
I skipped the whole pressure transfer, purging malarkey at malt forward beers for quite a while(10-15 kegs or so), and didn't experience any negative effect.

 

[phildo79]

Fill the keg to the brim with starsan. This ensures there is no oxygen in it.
Then fill the keg with CO2, pushing the starsan out (either from a CO2 bottle or from a fermenter). Save starsan for future use. You now have a sanitised keg completely filled with co2

Isn't there oxygen in water? Won't that mix with the co2 since gas is a fluid? I'm confused (should have paid more attention in chemistry class)

 

[Agentgonzo]

Isn't there oxygen in water? Won't that mix with the co2 since gas is a fluid? I'm confused (should have paid more attention in chemistry class)

There is oxygen in water in 2 ways.

1. As part of the compound H2O. It's stable and won't mix/react as it has already reacted with the hydrogen and formed a stable molecule. You can ignore this.

2. As dissolved oxygen in the water (ie, a small amount of molecules of oxygen interspersed between the molecules of water. This can come out of the water and mix into the CO2, but the amount dissolved in the water is tiny/negligible compared with the CO2 gas. Using a rough figure for dissolved oxygen at 2ppm gives a total of 60mg of oxygen in 30l of water. 30L of CO2 at room temperature and pressure is roughly 60g, or approximately 1000 times as much.

So yes, a tiny amount of oxygen will come out of the starsan and mix in with the CO2, but it's so tiny you can ignore it

 

[phildo79]

And what about my method for venting the keg for ten seconds at 30 psi? Is there any way to calculate the amount of oxygen that remains?

 

[hoppyscotty]

or instead of using starsan use a sodium metabisulphate solution. Still sanitises and scavenges oxygen. I have used that method before but to be honest using starsan works too, if there is any oxygen in there then its not alot.

If I am purging though I do some initial purging then leave it for 30mins or so for the gasses to settle assuming that the suggestion CO2 is heavier than air is true. I just think that if you purge then you're mixing the gasses in the headspace due to the force the incoming CO2 so not purging air. If it is true that CO2 is heavier than air then in my mind leaving it to settle then purging again would push more air out when you purge again. But this assumes CO2 is heavier than air...which I think it is....in industry when dealing with CO2 you have to be aware of CO2 settling to the bottom of vessels.

 

[Agentgonzo]

And what about my method for venting the keg for ten seconds at 30 psi? Is there any way to calculate the amount of oxygen that remains?

If you pressurise the keg to 30PSI, then you have a keg that is 2 parts CO2 to one part oxygen (normal atmospheric pressure is 15PSI). So each you do a pressurise/vent cycle will reduce the air/oxygen by one third. but that's only if you pressurise, then vent. But as I understand it you're both venting and pressurising at the same time, so it's not that simple.

The maths is complicated as the gases mix as you are venting more CO2 into the keg. We'd need to know the flow rate in and out of the keg, and even then the maths is beyond me and it depends on the vortexes/eddies that form in the keg.

At a very rough guess, I should say you may get down to 5-25% of the original oxygen content, but this is a very wild guess.

 

[Agentgonzo]

If I am purging though I do some initial purging then leave it for 30mins or so for the gasses to settle assuming that the suggestion CO2 is heavier than air is true. I just think that if you purge then you're mixing the gasses in the headspace due to the force the incoming CO2 so not purging air. If it is true that CO2 is heavier than air then in my mind leaving it to settle then purging again would push more air out when you purge again. But this assumes CO2 is heavier than air...which I think it is....in industry when dealing with CO2 you have to be aware of CO2 settling to the bottom of vessels.

You are correct in that CO2 is heavier (more dense) than oxygen, but unfortunately if you leave gases in a vessel, they will mix, not settle out. So when you vent, you are venting the mix of air and CO2, not just the air. Sorry.

(If the gases did settle out, then the same would happen in our atmosphere - all the CO2 in the atmosphere would settle down on the ground and the oxygen would float on top of it. Then we'd all die in a blanket of CO2 that covered the ground)