Using keg as long term secondary - co2 and airlock

[doug293cz]

Hey Doug,

I did about four or five brews where I filled the keg with starsan then removed via CO2 thus leaving a keg full of C02. I ferment in kegs so I can do closed system transfers. When I transfer I either need to leave the PRV open or sit there releasing it a number of times. I thought I read somewhere that diffusion happens quickly so that if I leave the PRV open the C02 in the receiving keg gets diffused with air. Because of this incomplete knowledge I stopped doing the water transfer. Could you provide any advice on whether it is worthwhile going back to water purging?

Thanks.

Opening the PRV just as you start transfer, and leaving it open only for as long as the transfer takes, will not allow significant ingress of O2. The smaller the opening the less diffusion takes place, but more importantly during the transfer, there will be a flow of CO2 out of the PRV which is fast enough to overwhelm any diffusion in the opposite direction. As noted in previous posts, you may still want to do a few purge cycles to get rid of residual O2 from the unfillable headspace.

Edit: Here's some more comforting info:

Industrial and laboratory fume hoods are designed with minimum face velocities that will prevent diffusion of vapors within the hood enclosure back into the room. The specifications call for face velocities of 60 - 100 ft/min (ref: http://www.escoglobal.com/resources/pdf/guide-fumehoods.pdf.) The PRV has an opening diameter of 0.235" and an area of 0.0434 sq. in. A gallon is equal to 231 cu. in. So, if it takes 10 minutes to fill a keg (0.5 gal/min), the flow rate out of the PRV is:

231 * 0.5 / 0.0434 = 2663 in/min => 222 ft/min​

More than 2X what's needed to prevent diffusion of O2 into the keg during filling. But remember, once the beer flow stops, O2 can start diffusing back into the keg as long as the PRV is open.

Brew on

 

[Iseneye]

Thanks Doug. It takes some time for the transfer - haven't timed it but probably in the 5-10 minute range. Looks like I'm going back to water purging. I purge head space either way.

 

[TAK]

I can't say how nice it is to hear someone else mention the deadspace in lid as a shortcoming of the typical liquid purge method. It seems like it's easily overlooked. I've mentioned it a few times, but it tends to get sluffed off. It's not a huge deal, of course, but it is something.

The first time I heard of purging with liquid, I thought to myself, duh, why didn't I already think of that. I did it, and shook the keg a bit. To my surprise, I heard sloshing. If it was 100% full, I shouldn't hear a thing. Then it occurred to me, the deadspace in the lid was causing it.

Doug - It's cool to see some numbers behind it too. Thanks for sharing!

This is my method of attack against this:

I keep a keg of StarSan at all times, as well as a bucket. I fill the keg most of the way from a bucket, then push the rest of the StarSan in with CO2 pressure. I fill with StarSan until it begins to come out the release valve. Then I tilt the keg upside down, so that pocket of air is at the bottom of the keg. Then I slowly tilt the keg back upright at about a 45 degree angle, with the gas-in tube at the uppermost point. So, the air bubble is there. Then, with just a bit of pressure, I continue to push StarSan in the liquid-out tube while I unscrew the gas-in post. Once off, the last little bubble of air will be pushed out and StarSan will flow out; I put the post back on to stop the flow.

At this point, if you shake the keg, all you hear is silence. There's no air at all in there. At that point, I push all the StarSan out with CO2, and push beer back in with CO2.

As for filling back with beer under CO2 pressure, instead of opening the pressure release valve, I put a liquid post on with a tube going into a container tiny bit of StarSan. That's essentially an airlock/blow-off. The added benefit of this is, if and when beer starts to flow out the gas tub, I'm collecting the excess in a growler or bottle.

 

[Iseneye]

As for filling back with beer under CO2 pressure, instead of opening the pressure release valve, I put a liquid post on with a tube going into a container tiny bit of StarSan. That's essentially an airlock/blow-off. The added benefit of this is, if and when beer starts to flow out the gas tub, I'm collecting the excess in a growler or bottle.

That's a good idea that I think I'll use.

Your method of complete filling of the keg with star-san is too much work for me so I will just fill up with star san and purge the small amount of headspace with CO2 four or five times.

 

[makisupapolice14]

Nothing OCD about it I reckon. Just makes sense to eliminate O2 or the possibility of O2. It's not hard and requires minimal kit.

I fill it till beer comes out the PRV.

Zero headspace.

Hook the keg to the gas and draw off beer till it's below the CO2 post and leave it alone at 34F and the desired CO2 pressure to force carbonate.

No additional purging needed. Simple.

Total newb kegging question but when you say to hook the keg to the gas and draw off beer till its below the co2 post how do you accomplish this and how do you know that the beer is actually below the co2 post? Do you just have the liquid and gas qds attached and open the tap handle?

 

[Gavin C]

Do you just have the liquid and gas qds attached and open the tap handle?

No worries at all mate


Yes. Exactly that.

If the beer is above the CO2 post you will hear gurgling as the CO2 flows in

Once it gets below the CO2 post the gurgling stops.

It's very easy to hear both the gurgling and its cessation.

 

[makisupapolice14]

Awesome thanks going to do this right the first time wish me luck haha!

 

[makisupapolice14]

Well all went off as seemingly planned. No beer came out of the prv though so I was just under the full keg and didn't need to pour below the dip tube. One thing I noticed vs my test run with sanitizer is that the beer flowed a good deal slower from the fermenter into the qd than the starsan did from my bottling bucket. Same tubing and liquid qd were used. Maybe the much smaller opening at the top of my spiedel fermenter vs the opened bottling bucket cause a
Pressure differential slowing the flow? Anyway excited for my first kegged and first all grain beer. Purged/vented 13 times at 30 psi also and set psi to 30. My liquid temp of the crashed beer was 38f. Plan to leave this for 24 hours and then reduce to serving pressure (12psi). Any thoughts and thanks!

 

[doug293cz]

Well all went off as seemingly planned. No beer came out of the prv though so I was just under the full keg and didn't need to pour below the dip tube. One thing I noticed vs my test run with sanitizer is that the beer flowed a good deal slower from the fermenter into the qd than the starsan did from my bottling bucket. Same tubing and liquid qd were used. Maybe the much smaller opening at the top of my spiedel fermenter vs the opened bottling bucket cause a
Pressure differential slowing the flow? Anyway excited for my first kegged and first all grain beer. Purged/vented 13 times at 30 psi also and set psi to 30. My liquid temp of the crashed beer was 38f. Plan to leave this for 24 hours and then reduce to serving pressure (12psi). Any thoughts and thanks!

Sounds like you have everything under control.

Brew on