Hi. I hate to beat a dead horse, as I've seen and read numerous posts here on the subject of carbonating nitro stouts. I'm just hoping that somebody can shake a bit of confusion out of me.

I been trying to fine tune the carbonation on my nitro stout for a few batches. This latest batch I think hits it spot on. It pours beautifully with the cascade of bubbles and ends up with just the right amount of head. But there is some math about it that doesn't make sense to me. And as a brewer, I fancy myself a bit of a science nerd, so it really bugs me when math doesn't make sense to me.

As one probably should, I have tried to model my stout carbonation and presentation after Guinness, and I've gathered the most consistent data that I could find about serving/equilibrium pressure for Guinness. ~32 psi @ 38°F up to ~38 psi @ 42°F are the numbers I've been working with. With Henry's law in mind, I carbonated with just CO2 my stout at 38° up to 8 psi (25% of 32 psi as Guinness gas is 25% CO2). And voila, it has been pouring beautifully. I couldn't be happier.

But here's the kicker. By every carbonation chart that I have referenced, My beer is up in the area of 2 to 2.2 volumes CO2. Yet I hear regularly that Guinness itself is carbonated to something like 1.2 volumes. I downloaded the McDantim EasyBlend app and when I plug in the gas mixture, temperature, and pressure, it spits out 1.25 volumes as the carbonation level at which it would find equilibrium. So that makes sense with Guinness' supposed 1.2 volume carbonation level. So, what variable am I missing? 1.25 to 2.2 volumes is a huge error gap. I want this to make sense.

I been trying to fine tune the carbonation on my nitro stout for a few batches. This latest batch I think hits it spot on. It pours beautifully with the cascade of bubbles and ends up with just the right amount of head. But there is some math about it that doesn't make sense to me. And as a brewer, I fancy myself a bit of a science nerd, so it really bugs me when math doesn't make sense to me.

As one probably should, I have tried to model my stout carbonation and presentation after Guinness, and I've gathered the most consistent data that I could find about serving/equilibrium pressure for Guinness. ~32 psi @ 38°F up to ~38 psi @ 42°F are the numbers I've been working with. With Henry's law in mind, I carbonated with just CO2 my stout at 38° up to 8 psi (25% of 32 psi as Guinness gas is 25% CO2). And voila, it has been pouring beautifully. I couldn't be happier.

But here's the kicker. By every carbonation chart that I have referenced, My beer is up in the area of 2 to 2.2 volumes CO2. Yet I hear regularly that Guinness itself is carbonated to something like 1.2 volumes. I downloaded the McDantim EasyBlend app and when I plug in the gas mixture, temperature, and pressure, it spits out 1.25 volumes as the carbonation level at which it would find equilibrium. So that makes sense with Guinness' supposed 1.2 volume carbonation level. So, what variable am I missing? 1.25 to 2.2 volumes is a huge error gap. I want this to make sense.

## Comment