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  • how / when to test DO

    Starting a 1.5-bbl nano and have an inline oxygenation stone unit which we put inline after a plate chiller. I have a waste-water / fisheries DO meter (made by Hanna) and am wondering how and when to test DO to see whether we are oxygenating enough or too much. I assumed boiled wort is close to zero ppm as the oxygen has boiled out? Can I just grab a sample from my conical shortly after the batch is all chilled and oxygenated, and test that? Or what is the procedure most people use?

    thanks,
    Red

  • #2
    I'm assuming your meter has the sensor on the end of a long cable, as most water-type DO2 meters do; in that case your best bet would be to lower the sensor into the oxygenated wort to take a reading. If you have already pitched your yeast, then take the reading as quickly as possible, as the yeast will start to use it, lowering the apparent reading.

    Taking a sample in a bottle, etc. is fraught with difficulty as it's way too easy to gain or lose dissolved oxygen, making any resulting measurement close to meaningless.

    The ideal would be to have a sample tap around 20 feet downstream of your stone. This should give a reasonable time after oxygenation to get close to dissolution, then measure through some form of flow-chamber direct onto the sensor. This is why most portable DO2 meters have a sealed flow chamber or flow path, so samples can be taken direct from mains, tanks or package without risking compromising measurement accuracy.

    Hope that helps!

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    • #3
      Originally posted by TL Services View Post
      I
      Taking a sample in a bottle, etc. is fraught with difficulty as it's way too easy to gain or lose dissolved oxygen, making any resulting measurement close to meaningless.
      Hope that helps!
      Sampling the DO directly from the tank is difficult if it is a conical or otherwise closed as well as risky from a hygiene stand point.

      I have just received my DO meter and plan to take my sample from the sampling valve into a flask that I have purged with Co2 to avoid oxygen pickup when filling the flask. Does that make sense or have I overlooked something (I am not to worried about the Co2 scrubbing the oxygen out, but I could be wrong)

      -Christian

      Comment


      • #4
        ChristianSA - in over 30 years of being closely involved in dissolved gases measurement (starting as a lab tech back in early 1980's) I can't recall any hygiene issues resulting from direct-from-tank measurement. If this was a real concern, then you could always spray the sample tap & meter inlet connector with IMS or similar before use.

        Taking a sample into a flask then measuring DO2 is possible, but I would have concerns about how accurate the measurement would be:

        - How do you plan to connect the flask to the tank?
        - How do you ensure there is no oxygen in the bottle (other than measuring the effectiveness of the purge)?
        - Can you be sure there is no oxygen ingress between tank & flask?
        - If the flask is genuinely 100% CO2-filled, you would lose O2 into the flask during filling
        - How do you plan to get the sample from the flask to the meter without risking DO2 pick-up?
        - Why is attaching a flask to the sample point any more hygienic than a meter?

        I'm not being negative here, just that my experiences tell me there is (a) negligible hygiene risk and (b) better measurement accuracy, from attaching the meter direct to the tank's sample point.

        Hope that helps!
        Tim Lawrence EngTech MInstMC
        TL Services

        Comment


        • #5
          Originally posted by TL Services View Post
          ChristianSA - in over 30 years of being closely involved in dissolved gases measurement (starting as a lab tech back in early 1980's) I can't recall any hygiene issues resulting from direct-from-tank measurement. If this was a real concern, then you could always spray the sample tap & meter inlet connector with IMS or similar before use.

          Taking a sample into a flask then measuring DO2 is possible, but I would have concerns about how accurate the measurement would be:

          - How do you plan to connect the flask to the tank?
          - How do you ensure there is no oxygen in the bottle (other than measuring the effectiveness of the purge)?
          - Can you be sure there is no oxygen ingress between tank & flask?
          - If the flask is genuinely 100% CO2-filled, you would lose O2 into the flask during filling
          - How do you plan to get the sample from the flask to the meter without risking DO2 pick-up?
          - Why is attaching a flask to the sample point any more hygienic than a meter?

          I'm not being negative here, just that my experiences tell me there is (a) negligible hygiene risk and (b) better measurement accuracy, from attaching the meter direct to the tank's sample point.

          Hope that helps!
          Tim Lawrence EngTech MInstMC
          TL Services
          No negativity perceived; on the contrary: I appreciate your input.

          I think I misunderstood what you meant. I had the impression that you would open the top of the tank and put in a proper. I agree with you that the risk of compromising the hygiene of the wort is probably negligible. However, sampling into the tank is still not really possible with a conical unless you crawl up on a ladder to many and lower the proper into the wort.

          I will do some trials to see if there is any difference between samples taken directly from the wort and samples taken from the sampling valve and post them here.

          -Christian

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