de-carbing for nitro? keg already carbed to 12psi

[odie]

I have an RIS that has been conditioning since march. The keg has been sitting on CO2 at about 10-12 PSI for a while because it was gonna be served on CO2.

I just scored single tap home kegerator that I would like to set up as a dedicated nitro unit. I'm assuming I will have to bleed all the CO2 off the keg to get to 1-1.5 vol before I hit it with the nitro mix.

Can I just drop the CO2 regulator to the desired pre-nitro pressure and let the excess carbonation bleed off down to 1-1.5 vol? Or does a CO2 reg not work that way?

Or am I just gonna have to vent the keg and let it go flat and then re-carb to a low PSI?

 

[yowzers]

You should be good. Nitro is really a blend of CO2 and N2 so you are right where you want to be. You'll just switch it over to the higher pressure beer gas.

 

[day_trippr]

The question I have is at what temperature has that keg been sitting at 10-12 psi.

At "room" temperature (~68°F) that would eventually reach equilibrium at ~1.4-1.5 volumes
At "cellar" temperature (~55°F) -> ~1.7-1.9 volumes
At "fridge" temperature (~40°F) -> ~2.3-2.5 volumes.

fwiw, I've kept a chocolate imperial stout on tap for years now, driving it with 75/25 beer gas at 35 psi through a stout faucet. Anything above 1.4 volumes and the CO2 breakout volume is excessive, so I carb to 1.2 volumes (at ~60°F and 5 psi) then put the keg on the beer gas when its slot opens up...

Cheers!

 

[Jag75]

Yup I agree . You wanna get those volumes down then put on gas blend .

 

[odie]

My “cellars” are temp controlled freezers... one for lagers and one for ales. it’s been held at 55’ for a while

 

[odie]

Can I reduce the regulator to 5 and bleed it out?

 

[Jag75]

I dont know how long it would take get your carb level down . I think I would degas it then release the pressure every day for a few days then hook up to your gas blend and try it . If it's still to much take it off again and check it daily . I wouldn't think it take too long .

 

[Qhrumphf]

You absolutely have to degas that unless your lines are REALLY long (and then you don't have nitro but a long draw draft system). Otherwise you'll pour nothing but head.

You can't just lower the regulator. They don't work that way. If you're at fridge temps already, your equilibrium pressure for the CO2 you want is next to nothing.

I would completely unhook from gas, and bleed almost all pressure off the keg daily until it's holding steady at next to no pressure. Then hook it up to your beer gas at 30 PSI, and shake the bejeezus out of it. In my experience getting a good nitro pour from head pressure alone takes FOREVER since nitrogen doesn't dissolve nearly as easily as CO2.

Alternatively, a carb stone and pure nitrogen will do the job in minutes, *then* put it on beer gas to serve.

 

[Qhrumphf]

You could also switch posts around and use CO2 to decarb fast by using large CO2 bubbles to knock CO2 out of solution. Depressurize your keg to near nothing. Blow CO2 through the *beer* side in fairly high pressure short bursts (20-30 PSI for a few seconds each time). After a few bursts, let it sit for 5-10 minutes to stabilize. Bleed of the pressure down to near nothing, and repeat. Do this til it's decarbed.

It's not good for the beer (you'll drive off aromatics), but it's very fast.

 

[odie]

Sounds like I need to just pull the relief valve a bunch over several days or weeks. Or just crack it a little and leave it to bleed off until flat and then start over