Ask The Brewmasters

  • 1.  CO2 Conversion from Vol/Vol in ppm to Wt/Wt in ppb

    Posted 07-25-2023 15:51
    Edited by Walter Heeb 07-26-2023 20:56

    Does anyone know of a conversion to get from ppm values of co2 in vol/vol converted into ppb wt/wt?

    Long story short our bulk CO2 got contaminated with oxygen and when trying to talk to our CO2 reps the translation of how they measure dissolved oxygen is different than what I have used in my brewing career, and it is confusing to them how we could get measurements of O2 in ppb when the gas gets delivered and tested in the ppm range even though we are measuring under different units. Our bulk tank tested at 279 ppm (vol/vol) of dissolved O2 in the liquid CO2 when for beverage grade gas it needs to be under 30 ppm (vol/vol).

    I have found some really good articles on here about how dissolved CO2 levels in CO2 affect DO levels in carbonated beer. We aim to carbonate our beers at 2.65 volumes and at 279 ppm (vol/vol) of O2 that would put our carbonated beer at around 1050 ppb (wt/wt) of O2.

    For example, if the gas is delivered at 30 ppmv of O2 in my CO2 what reading should I expect using a DO meter such as an orbisphere or CboxQC when running the gas through the analyzer from the bulk gas system?



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    Jordan Hunt
    Head Brewer
    Crossbuck Brewing
    Walla Walla, WA
    (503) 516-9569
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  • 2.  RE: CO2 Conversion from Vol/Vol in ppm to Wt/Wt in ppb

    Posted 07-26-2023 15:59
    Edited by Walter Heeb 07-27-2023 12:09

    Hi Jordon,

    1 volume of CO2 is equal to 1.97 g/l.  To convert CO2 in volumes to g/kg, multiply by (1.98 / Beer specific gravity).  Assume your beer specific gravity is 1.008 and you have 2.65 volumes of CO2; 2.65 x 1.97/1.008 = 5.2 g/kg = 5,200 ppm (mg/kg) = 5,200,000 ppb (microgram/kg).

    Is that what you are looking for?

    Cheers,

    Ashton



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    Ashton Lewis
    Manager of Training and Technical Support
    BSG Craftbrewing
    MBAA District Great Plains, Technical Chair
    Springfield, Missouri
    (417) 830-2337
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  • 3.  RE: CO2 Conversion from Vol/Vol in ppm to Wt/Wt in ppb

    Posted 07-26-2023 20:57

    I'm specifically looking for in CO2 so if gas supplier reports that my bulk CO2 is 30 ppmv and I wanted to test it with an orbisphere 3100 which reads it in ppb (wt/wt) what should I expect my reading to be. My chemistry days are failing me because the number I got is way too high.



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    Jordan Hunt
    Head Brewer
    Mt View Brewing
    Redmond OR
    (503) 516-9569
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    Original Message


  • 4.  RE: CO2 Conversion from Vol/Vol in ppm to Wt/Wt in ppb

    Posted 07-27-2023 20:32

    Regarding the Orbisphere 3100: I normally see measurements of gas/CO2 reported as %O2.  Are the ppb units valid for gas-phase measurements, or only for O2 dissolved in liquid?  I'm really not sure, myself.  But I expect other contributors to this thread could answer and explain if this point is relevant to your situation.



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    Cullen Dwyer
    QA Manager
    Wachusett Brewing Co
    Westminster MA
    (978) 874-9965x160
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    Original Message


  • 5.  RE: CO2 Conversion from Vol/Vol in ppm to Wt/Wt in ppb
    Best Answer

    Posted 07-28-2023 14:38

    I can't speak to Orbispheres specifically, but we covered a lot of this same ground back in a 2016 thread on this forum - which includes a spreadsheet that converts between gas measurements in ppb on the liquid setting and true ug/L at ambient pressure:

    https://community.mbaa.com/communities/community-home/digestviewer/viewthread?GroupId=37&MID=1466&CommunityKey=cb7fc054-5008-4b01-87f3-588d3c711e07&tab=digestviewer

    If the link above doesn't work, try searching for 'oxygen meter readings' or just the number 1630.



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    Joe Walts
    Quality Manager and R&D Brewer
    Karben4 Brewing
    Madison WI
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    Original Message


  • 6.  RE: CO2 Conversion from Vol/Vol in ppm to Wt/Wt in ppb

    Posted 07-26-2023 20:57

    vol/vol is a measure of concentration of CO2 dissolved in liquid. For a  given volume of liquid, containing a quantity of dissolved gas, if only the gas was in a separate container at standard conditions, what is the ratio of gas volume to liquid volume.


    Conditions for the liquid are not critical as its volume doesn't vary much with P and T - we can assume 14.7psia, 60F
    Conditions of the vapor must be defined as gas volume varies significantly with T and P. Reference condition is 14.7 psia and 60F

    The easiest way through this is with some numbers – let's look at one cubic foot 
    - at standard conditions we have a mass of 62.4 pounds of water / beer
    - at standard conditions we have a mass of 0.1166 pounds of CO2 gas 

    So at 1.0 vol/vol the mass ratio is 0.1166 / 62.4 = 0.001869 = 1869 ppmW = 1869000 ppb

    more generally
    (vol/vol) x 0.1166 / 62.4 x 1,000,000 = ppmW



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    Thomas Sierra
    Technical Sales Representative
    Pentair Haffmans
    Kalispell MT
    (406) 212-3815
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  • 7.  RE: CO2 Conversion from Vol/Vol in ppm to Wt/Wt in ppb

    Posted 07-27-2023 08:55
    Edited by Walter Heeb 07-28-2023 01:36

    I assume you're trying to figure out equilibrium dissolved O2 given your vol/vol ratio in your bulk tank (this is vol/vol because gasses are being measured so it's most relevant). You need to figure out partial pressure of the oxygen. (Just take tank pressure times ratio of gasses).  Then use Henry's law to figure out dissolved oxygen.  There are constants and unit conversions that you'll have to look up, but that ought to get you there.  That said we're not dealing with pure water and co2 is not an ideal gas in this system so your mileage may vary, but it's an approximation. 



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    Frederick Mattrey
    Brewhouse Manager/R&D Brewer
    Sunken Silo Brew Works
    Lebanon NJ
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  • 8.  RE: CO2 Conversion from Vol/Vol in ppm to Wt/Wt in ppb

    Posted 08-10-2023 12:57
    Edited by Walter Heeb 08-10-2023 15:47

    Don't forget they are reporting ppm vol/vol in liquid and you are measuring ppm or ppb vol/vol in gas.  1L of liquid CO2 = 514L of gas CO2 at 1 atm

    Not accounting for the similar expansion of O2 and no guarantees on my math skills but I get around  279 ppm in liquid would come to 540ppb of O2 in your CO2 at 1 atm

    I love to hear if I'm completely off on that calculation.

    Cheer

    Gary



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    Gary Heil
    Cypress & Grove Brewing Co
    Gainesville FL
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