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Thread: Co2 Stratification in BBT?!

  1. #1
    Join Date
    Jan 2014
    The Great White North

    Co2 Stratification in BBT?!

    We're having a recurring issue, where our co2 levels fluctuate significantly (+/- .5 vol) when the BBT is tested throughout a packaging run.
    Some folks here insist that the co2 is stratifying in the BBT, with higher vols at the bottom of the tank due to hydrostatic pressure.
    Can anyone prove or disprove this?

  2. #2
    Join Date
    Oct 2002
    Chesterfield, UK
    I have never experienced major stratification like this, even with 1500 hl vertical BBTs (say 15 metres high). We used to get a certain amount of decarbonation near the top if left for a few days before packaging if either there was virtually no pressure, or we used nitrogen, and a certain degree of higher carbonation right at the top after a couple of days if the top pressure was way over the equilibrium pressure.

    It sounds as though you simply are not mixing effectively during filling / carbonation.

  3. #3
    Join Date
    Jul 2008
    As DM says, significant CO2 stratification is unusual when a full tank is held, unless there are headspace gas or pressure conditions to force it. On the large verticals we tended to find this only affected the top 5% or less of the contents.

    Could the cause be related instead to how the tank is being emptied as it runs to the filler? Eg:

    - How are you maintaining top pressure?
    - Are the measurements from the tank itself or from packaged beer ex-filler?
    - What gas is backfilling the tank during emptying?

  4. #4
    Join Date
    Oct 2013
    Cincinnati, OH
    I would suggest it is a fact that there will be a difference in the actual amount of dissolved gas between the top and bottom due to the hydrostatic pressure you mention, however it will be very minimal (and most likely un-measureable) in most every common instance.

    You mention fluctuation, but you do not specify if it happens between beginning and end of your run (top and bottom of tank), or if it happens to fluctuate back and forth. Also you do not mention your method of measurement (Zahm, Anton Parr CBox, ect). Test your packaged product if possible to see if the variation holds true after BBT and into package. This will help narrow down a filling issue or a carbing issue.

    I would think this is more likely to be a skewed reading over an actual .5 volume variation in stratification. It is possible that your BBT jackets do not cover all of the beer, and warmer beer in the top (5% or so mentioned) could be seeing a difference.

    I have seen stratification in carb (zahm test during transfers), but it was only in tanks that were mostly spunded with some top pressure applied. Also it only appeared in my "tall and skinny" tanks above 100BBL. After transferring to brite, the beer was evenly mixed and the "issue" was not present.

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