First time on Nitro and having trouble dialing in

[seilenos]

I'm taking a dip into serving on nitro and having some trouble getting a good pour.

Keezer is set to 38 F but beer pours 45 - 50 F depending on where it is in the keezer and if it is a top or bottom draw.
The ESB and Irish Stout pour at 48 - 50 F, both are top draw.
I am aiming for 1.8 vols and am using a 75/25 beergas mix.
Lines are ~42" x 3/16" with Intertap flow control stout taps that are about 6-8" higher than the top of the kegs.
Beer was originally burst carbed at 35 PSI for 24 hours then switched to beergas about 10 days ago.

Up until a few minutes ago I thought the beer would be much closer to the keezer temps so I had the nitro regulator set to 20 PSI, figuring 25% is 5 psi which would get me around 1.8 vols.
Beer would pour but were bigger "co2" bubbles that would rapidly dissipate.

I poured a glass and actually took the serving temp and found it was markedly higher (48 F - 50F).

That would mean that I should be around 32 PSI on the beergas to be at around 1.8 vols.
The goal is to have this dialed in by next Friday (6 days).

Options as I see them:

1) Beergas at 32 PSI and set-and-forget
2) CO2 at 8 PSI until mid-week and then switch to beergas
3) Other?

Any suggestions would be appreciated.

thanks.

 

[day_trippr]

Is the intent to serve both the stout and the esb on beer gas? I've only ever done it with my imperial chocolate stout.
I carbonate only to 1.2-ish volumes - which isn't all that easy considering it's already around .6-.8 volumes at the end of fermentation.
So I carbonate it at fermentation temperature (mid-60s°F) at 5-6 psi for a couple of weeks.
Once chilled I dispense through a MicroMatic stout faucet with 70/30 beer gas at 35 psi, produces a prolonged cascade in the proper glass.
If carbed much higher than ~1.4 the foam became excessive...

Cheers!

 

[seilenos]

Yes, both ESB and stout on beergas.

The ESB is acting "off" and I am not sure if it is just overcarbed ... I followed the same burst carb procedure as I normally do, not considering that it should come in low (7-8 psi instead of 12psi).
I cut the stout burst carb off early and it seems to be pretty much where it needs to be no matter what beergas psi I put it on.

I cut pressure to the ESB and purged. Hopefully it is just a case of being overcarbed for the situation.
Can I get it dialed in on co2 and then just switch to beergas for serving? That is, do I need to give it time on beergas?

In reference to your stout, if you leave it on 70/30 at 35 psi, wouldn't it end up carbed to 10.5 psi?

 

[doug293cz]

You can't do pressure ratio calculations using gauge pressures. You have to work with absolute pressure and partial pressures. Absolute pressure is gauge pressure plus atmospheric pressure (gauge pressure + 14.7 psi at sea level.) The partial pressure of each gas is then the volume % of the gas in the mix times the absolute pressure.

20 psi gauge pressure is 34.7 psi absolute. At 25% CO2 the partial pressure of CO2 is 0.25 * 34.7 psia = 8.675 psia. 8.675 psia is equal to 8.675 psia - 14.7 psia = -6.025 psig. This is a long way from the 5 psig that your incorrect calculation yielded.

Carbonation levels also depend on absolute pressure. We get away with using gauge pressures because we assume that the headspace gas is 100% CO2, and then burying the gauge to absolute pressure adjustment in the chart or calculator (so it is invisible to the user.)

At a beer temp of 38°F and a CO2 partial pressure of 8.675 psia, the equilibrium carb level is 0.83 - 0.84 volumes.

Burst carbing at 35 psig for 24 hours probably gave you a carb level north of 2.5 volumes. Thus you are severely overcarbed to your target.

Your as served beer temp is going to be lower than the in keg temp because of warming passing thru the serving line and tap (unless they are cooled to the keg temp) and warming caused by the glass (again unless the glass was cooled to keg temp.) Carbonation levels are determined by the in keg temp and CO2 partial pressure.

You may also have temperature stratification in your kegerator, unless you have a fan inside circulating air bottom to top. If you don't have a fan you should add one.

@day_trippr 's equilibrium carb levels with 30/70 beer gas will depend on his keg temp. They could be anywhere from 1.49 volumes @ 36°F to 1.26 volumes @ 45°F.

I have attached my carbonation calculator as a .zip file, as HBT doesn't allow attaching .xls or .ods files. This calculator includes calculations for beer gas with variable CO2:N2 ratios. It also explicitly shows gauge and absolute pressures.

Brew on

 

[seilenos]

Didn't expect to be heading back to school on a Saturday! Thanks for the explanation and the files.

I am going to treat it as things are overcarbed and then put back under a lower CO2 pressure for a few days before returning to beergas with a more appropriate pressure.

From your chart, and given that I don't need to push through long lines, it seems like it would make sense to go to a lower nitrogen percentage in the future to lower the pressure I need to run at.

 

[doug293cz]

Didn't expect to be heading back to school on a Saturday! Thanks for the explanation and the files.

I am going to treat it as things are overcarbed and then put back under a lower CO2 pressure for a few days before returning to beergas with a more appropriate pressure.

From your chart, and given that I don't need to push through long lines, it seems like it would make sense to go to a lower nitrogen percentage in the future to lower the pressure I need to run at.

I'm not a expert on nitro dispensing, but I think a lower nitrogen pressure may reduce (or even eliminate) the cascading bubble effect you look for with a nitro pour.

The solubility of N2 in beer is about 100 times lower than CO2 (IIRC - working from memory.) So, higher pressure is needed to get any significant amount of N2 in solution. Because of the lower solubility of N2 you can form stable bubbles that are much smaller than with CO2. So in order to get the tiny bubbles, you need to get a certain amount of N2 in solution. If your N2 partial pressure is too low, this might not happen. I don't know where the threshold is.

Brew on