Edit: already carbonated keg meaning force carbed with CO2 or primed with sugar in the keg.

- Thread starter Izzie1701
- Start date

Edit: already carbonated keg meaning force carbed with CO2 or primed with sugar in the keg.

Brew on

- Joined
- Mar 9, 2015

- Messages
- 90

- Reaction score
- 22

CO2 is absorbed or desorbed based on the

Also, my brain was already slowing for the evening when I posted my original reply. I forgot to add in the effect of atmospheric pressure. 25 psi gauge pressure (psig) of beer gas will give a total pressure of about 40 psi (39.7 actually, but can't do the math in my head with that.) So, the partial pressure of the CO2 would be 0.25 * 40 = 10 psi. 10 psi total pressure is equivalent to -4.7 psi gauge pressure. At 38°F, -4.7 psig gives an equilibrium carbonation level of about 1.0 volume. Much lower than my previous, incorrect estimate.

Brew on

- Joined
- Mar 9, 2015

- Messages
- 90

- Reaction score
- 22

- Thread Starter
- #6

Ok so then is there an issue using beer gas? I think I have gathered it would go flatter then I wanted even if it was pre carbed and a standard faucet would work? Or would I require 2 stout faucets? Im thinking I would still get a bit of head on a standard faucet and a lower carbonation then I wanted. If I remember correct when we toured Smithwicks they used a 50/50 mix on a standard tap and had some carbonation and a creamy head. Not as creamy as Guinness but close. It was a flow control standard faucet.

If you put beer gas on a fresh keg that is fully carbonated, the CO2 partial pressure will be a little higher than optimal due to the CO2 already in the headspace, but as you serve, and the headspace increases, the CO2 partial pressure will drop. So, as the keg goes down the carb level will drop. If you finish a keg in a week, you might not notice it. If it takes a couple of months, you will definitely notice.

Pre-mixed beer gas at more than 25/75 can get problematic. With 25/75 and a cylinder pressure of 3000 psi, you only have 750 psi CO2 partial pressure, and the CO2 stays as a gas above 60°F. A 50/50 mix would only be able to have a cylinder pressure of 1500 psi to keep the CO2 as gas above 60°F, cutting the total amount of gas in a fresh cylinder in half. If the CO2 partial pressure is too high in the cylinder, then some of the CO2 will condense to liquid, upsetting the CO2/N2 ratio. Smithwicks probably has an on-demand gas mixing system to get around this issue.

I'm not a faucet expert, so won't comment on standard vs. stout taps.

Brew on