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Mixed gas dispense

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  • Mixed gas dispense

    We had a nitrogen generator installed yesterday in order to have a nitro stout on tap. The mix for the stout tap is 75/25, the stout was carbonated to 1.7 volumes of CO2, it is all working as advertised. The other blend available out of the box is 70% CO2/30% nitrogen. My question is this; since all other beers on tap were carbonated to 2.4-2.5 volumes for straight CO2 dispense, will they pour correctly with the second available blend of gas? They currently pour fine with straight CO2, but would like to utilize the 70/30 blend.
    The installer wasn’t sure, neither was I, so he just got the nitro tap up and running while I did more homework. Most of the references I’ve seen concerning the latter blend are about long draw systems, we’re right out of the cooler to the tapwall.
    Any practical experience and/or advice appreciated.

    Location Six Brewing

  • #2
    Hey Craig, if it's a through wall system you don't really have any need for the 70/30 blend. It will pour fine at first, but if the keg sits for too long equilibrium will happen and your dissolved volumes of CO2 will start to drop. With 70/30 it may not even be noticeable (especially if you're moving through kegs fairly quickly), but theoretically it will happen. I highly recommend the McDantim Easy Blend app for a quick reference point.



    • #3
      I second the easy blend app. However, as long as you have the right restriction to pour at a proper speed (2 oz a sec) with the proper pressure of co2 within the blend to hold your vol carb, It will be fine. So with a 30% nitrogen blend If the carb level and temperature dictates a 10psi equilibrium, you would be at 13psi push.

      But yes, most direct draw setups don’t require mixed gas as the lines aren’t long enough to have enough restriction to need the extra push.

      Try it, if you run flow control faucets it’s easy to dial in restriction to get perfect speed even if you don’t need the blend. Worst case scenario you have the stout blend you need, and you replumb your push to straight co2 that you already have at the blender. A couple tees, some tubing, and some oetiker crimps. Boom your done.

      Sent from my iPhone using Tapatalk


      • #4
        Craig, The trick is to control the partial pressure of CO2. By that, you have to pick the right total pressure to push the beer out of the keg, but not have too much CO2 partial pressure (=CO2% in gas * total push pressure). It can be quite a frustrating experience that you can finally arrive at by a trial and error (because the effect won't be immediately apparent because CO2 will get into the beer slowly as you continue tapping it). Since you already have a Nitrogen generator and CO2 supply available, why not use the NitroBrew Infusion module? It is just plug-and-play and you don't even need blended gases anymore. Just fill a keg after fermentation (no need to even force carbonate), hook it up to NitroBrew and dispense. A light CO2 pressure can be maintained on the keg to prevent air pick up and oxidation while maintaining the proper amount of carbonation needed for the nitro style in the glass. Check out:

        Mechanical Engineer, QuantiPerm


        • #5
          Like other have said, you don't need it for a short run, and you'll actually be wasting nitrogen if you use it and get the restrictions balanced. That blend is for longer runs, where the restriction is too much for just straight CO2 pressure.
          Linus Hall
          Yazoo Brewing
          Nashville, TN