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  • Expired citric acid?

    Hi, I just found someone who has a sealed 25kg bag of anhydrous citric acid. They told me it was 2 years old but I just got the bag and it was manufactured in 2012. I can't read the expiry date on it. It still feels like a powder. Would this still be good to use for passivating some stainless steel tanks? Any way I can check it's efficacy?



    Last edited by frank.cazabon; 02-09-2021, 05:08 PM.

  • #2
    Don’t worry too much about age. Anhydrous should be a dry crystalline powder. If it’s exposed to air, it will become monohydrate as opposed to anhydrous. Means it will have a water molecule attached. Not a problem when you’re looking to dissolve in water anyways.

    Test the solution by pH or Total Acidity titration.

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    • #3


      Originally posted by UnFermentable View Post
      Don’t worry too much about age. Anhydrous should be a dry crystalline powder. If it’s exposed to air, it will become monohydrate as opposed to anhydrous. Means it will have a water molecule attached. Not a problem when you’re looking to dissolve in water anyways.

      Test the solution by pH or Total Acidity titration.
      Thanks. What should the pH be of a 4% (1lb per gallon) solution?

      Sent from my Moto G (5) Plus using Tapatalk

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      • #4
        What I am saying is, mix an aqueous solution to the proper pH or Total Acidity for your application. The Citric Acid (C6H8O7) is a pure substance. You mix it with water for passivation, and you need to achieve an ideal pH (~2 for austenitic) for optimum passivation.

        It is possible to chemically calculate the pH but that is quite complicated and I’ve already had a couple beers. The molar mass is 192.124 g/mol

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        • #5
          Ok, thanks very much.

          Sent from my Moto G (5) Plus using Tapatalk

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          • #6
            As long as the citric acid did not get contaminated it is fine. Especially during passivation it is not such a big issue, since you still have to do a CIP afterwards.
            Keep in mind citric acid is very good chelating agent and prepares a stainless steel surface for passivation (same is phosphoric acid). Citric acid has hardly any oxidative power so the chromium of the stainless steel needs to rely on the oxygen from the air to form chromium oxide. Just for your information a 1,000 bbl fermenter takes about two weeks to passivate if you "use" the oxygen of the air. In addition you need to heavily vent the tank with a big blower for the period of time.
            Zee Loeffler
            888-484-6248 (US & Canada only)
            www.loefflerchemical.com
            Oliver.meinhold@vincitgroup.com

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            • #7
              Thanks Oliver. This is a 3 bbl brewery. Hopefully I'll be okay with just air drying.

              This is the process I understand I need to follow:

              Heat water to 60C (140F)
              Add the relevant amount of citric acid (1lb per US gallon)
              Leave for 60 minutes
              Drain (I believe I can use the same solution in another vessel afterwards, right?)
              Rinse
              Let air dry for a few days.
              When I'm ready to use the vessel clean (and sanitise if a fermenter)

              Does that sound right?

              Sent from my Moto G (5) Plus using Tapatalk

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