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Thread: Carbonating for Guinness Gas

  1. #1
    Join Date
    Jun 2010
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    Cedar Rapids, IA
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    Carbonating for Guinness Gas

    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.

  2. #2
    Join Date
    Jun 2017
    Location
    Mississauga, ON. Canada
    Posts
    39

    Nitro stout

    I'm interested to learn more about this as well. Guinness, please.
    Any Irish/English brewers out there who could shed some light on the subject?

    Quote Originally Posted by ChrisEllis View Post
    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.

  3. #3
    Join Date
    Oct 2002
    Location
    Chesterfield, UK
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    1,787
    Guinness will be carbonated and nitrogenated in-line. I don't think I ever knew heard what the Guinness CO2 level was, but I understand the nitrogen dissolved prior to BBT is measure in a few tens of ppm, nitrogen being very insoluble compared to CO2. The calculator you are looking at is purely for dispense purposes, to keep both the CO2 and a few ppm of nitrogen already in the beer in solution. The brewery will inject minute amounts of nitrogen in line, separately from the CO2 injection, calculating injection flows, and subsequently measuring both, using one of the many commercially available dissolve gas instruments for CO2 and N2.

    Not sure if this helps answer your query.
    dick

  4. #4
    Join Date
    Jun 2010
    Location
    Cedar Rapids, IA
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    Not sure that answers my question

    I deliberately left Nitrogen out of my query because, as you said, it has such poor solubility that it appears that it would be a non-factor in the equation. Maybe I'm wrong there.

    I realize that the McDantim calculator that I used is for dispense purposes. But equilibrium is equilibrium. At a given temperature, the dispense pressure that maintains the solution of CO2 in the beer is the same pressure at which I should eventually reach that level of CO2 in solution while carbonating.

    So are you thinking that the small amount of nitrogen in solution in Guinness is taking the place in solution of that extra volume of CO2? The Mcdantim calculator isn't even considering the variable of whether or not the beer is Nitrogenated, so I'm guessing not. Let's look at the question from another angle and say that I'm not even talking about a nitro beer. Am I wrong about the application of equilibrium pressure in dispense vs. carbonation? Can a pressure that can carbonate a beer up to 2.2 volumes only maintain carbonation at 1.25 volumes in the context of dispensing? Or am I misunderstanding Henry's law? Does 38 psi of a 25% CO2 / 75% nitrogen blend not behave like 8 psi CO2?

    I just feel like there is some obvious variable that I'm missing that is going to make my want to hit myself in the head with a 2x4 when I finally get it.

    Quote Originally Posted by dick murton View Post
    Guinness will be carbonated and nitrogenated in-line. I don't think I ever knew heard what the Guinness CO2 level was, but I understand the nitrogen dissolved prior to BBT is measure in a few tens of ppm, nitrogen being very insoluble compared to CO2. The calculator you are looking at is purely for dispense purposes, to keep both the CO2 and a few ppm of nitrogen already in the beer in solution. The brewery will inject minute amounts of nitrogen in line, separately from the CO2 injection, calculating injection flows, and subsequently measuring both, using one of the many commercially available dissolve gas instruments for CO2 and N2.

    Not sure if this helps answer your query.

  5. #5
    Join Date
    Oct 2002
    Location
    Chesterfield, UK
    Posts
    1,787
    Nitrogen makes a huge difference. At 3.33 C (38 F), at 1.25 g / litre CO2, and zero nitrogen, the equilibrium pressure is minus 0.6 bar. Add in 35 ppm nitrogen and the equilibrium pressure is plus 0.68 bar according to one calculator I have.
    dick

  6. #6
    Join Date
    May 2004
    Location
    St. John's, Newfoundland, Canada
    Posts
    817
    You are correct in thinking that most nitro stouts are in the 1.2-1.5 vol CO2 range. Generally nitrogenated to saturation (about 40 ppm). Nitrogen is very difficult to get into solution. high pressures and low temperatures increase chances of success. There are purpose built machines to 'drive' nitrogen into solution at high pressures using multistage centrifugal pumps and there are also contactor membranes that can saturate beer with nitrogen at low pressures. Head presentation and texture of nitro beers requires a fine balance.

    Our process: we spund at the tail end of primary to maintain some natural carbonation. Usually in the 1.5 range at this point. Tank is crashed to .5oC. It is then transferred into secondary, at -1oC. Before the transfer begins (by gravity), the source and destination tanks are raised to 2 bar with N2 and connected head to head with a balance line. During the transfer, we nitrogenate inline taking care not to foam the beer as it moves into secondary.

    After a week in Secondary, it gets filtered. Brite tank and conditioning tank are pressurized and balanced as above with nitrogen. The inline nitrogenation process is repeated (as above) during the filtration process (post filter on the way into brite).

    After the stout moves into secondary and nitrogen is in solution, measuring CO2 accurately is difficult. I train filter operators to evaluate the stout organoleptically for mouthfeel prior to filtration. If the CO2 is too high, the resultant stout will pour 'high' (giving bartenders nightmares). If it is too low, the head will be flat and/or very short lived. A trained operator can make slight corrections to the CO2 balance during filtration.

    Works well 29 times out of 30. Ha!

    Pax.

    Liam
    Liam McKenna
    www.yellowbellybrewery.com

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