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  • Yeast Propagation System Question

    I've recently been hired part time at a local brewery (10bbl system) to develop and implement a QC/QA program. My background is molecular biology, so the lab side of things are well within my comfort zone.

    However, part of the general plan is to also put together a yeast propagation system. I have no problem slanting, plating, and growing up lab-sized cultures, but I have no experience with industrial-scale microbiology.
    I've done a lot of reading (here and other places) and I think I've put together a general plan for propagation, but I was hoping you guys could provide a bit of feedback.

    Starting from slants, I can easily grow up ~500mL of culture in sterilized wort in the lab within a few days.
    After that, I was planning on pitching this into 50-100 liters of oxygenated wort in a 15bbl conical fermenter.
    From this point, my plan was to double the volume in the fermenter at least once if not twice (each after 24hrs) before pushing the whole thing into a 20bbl batch.


    Unfortunately, we don't have the budget to get a purpose-built propagator, so I was thinking of installing a SS carb stone in the lower port of the fermenter and periodically hitting it with oxygen to mix the culture and maintain a high level of oxygenation.
    As far as this goes, I figured I'd have to play around with frequency and duration of the oxygen pulses to optimize growth rate.


    I have a few lingering questions, though. First off, does this seem reasonable or am I way off base?
    Second, does anyone know of any affordable solutions for automating (at least somewhat) the pulses of oxygen and/or do you have any general guidelines for how frequently it will need to be oxygenated (unfortunately a DO meter is still on the wishlist)?
    Finally, should I be concerned about pushing the 'propagation beer' into a production batch? I suppose I could always crash cool the tank and try to just pull a yeast slurry out instead of pushing the whole batch.

    I definitely appreciate any feedback you guys can provide and I am also very grateful for all of the excellent info I've gleaned from the forum so far.

  • #2
    Once the propagation leaves the lab, brewers (at least smallish ones) tend to treat their propagations like mini fermentations: pitch around 750K - 1M cells/mL/P for most ales, add 8-10 mg/L of oxygen at pitching and give it at least a couple of days before adding more oxygenated wort. Brewery step-ups tend to be 5-10x by volume (i.e. 1.5-3 bbl -> 15 bbl), but you should strive for whatever gets you near your brewers' target pitch rates. If the availability of fermentation tanks becomes an issue, you could add propagation steps between the lab and the brewery by using modified half-barrels or similar vessels. Oxygen is the enemy, so capturing the slurry and dumping the wort would probably be a good idea if you're set on adding intermittent oxygen.

    Joe

    Comment


    • #3
      A few thoughts:

      10x volume increases are my rule of thumb for propagation, if everything seems to be going well. Pure slant -->10 ml-->100 ml-->1L--->10L...you get the idea. It can be pretty rapid.

      I generally upsize when things seem to be rocking and rolling. You can do cell counts to confirm growth rates. I like to 'feed' the yeast when they are at their maximum growth rate. I find this also minimizes the oxidized flavour carryover from wort based propagation medium moving forward into production sized batches.

      For propagation, I generally use filtered air instead of oxygen. Much more difficult to overdo it.

      I also like to propagate in basal medium (glucose based) as long as possible (I find better growth than wort. Have tried it all ways. Just my experiences).

      Yeast love oxygen in their growth phase. It's pretty critical. This is not anaerobic fermentation. This is respiration. Lot's of oxygen-->lot's of energy produced-->lot's of reproduction.

      Yeast ferment wort very well into beer but would rather be elsewhere with more oxygen to breathe.

      I would also remind you to ensure your micronutrient levels (like Zinc) are sufficient.

      Pax.


      Liam
      Liam McKenna
      www.yellowbellybrewery.com

      Comment


      • #4
        Originally posted by liammckenna View Post
        A few thoughts:

        10x volume increases are my rule of thumb for propagation, if everything seems to be going well. Pure slant -->10 ml-->100 ml-->1L--->10L...you get the idea. It can be pretty rapid.

        I generally upsize when things seem to be rocking and rolling. You can do cell counts to confirm growth rates. I like to 'feed' the yeast when they are at their maximum growth rate. I find this also minimizes the oxidized flavour carryover from wort based propagation medium moving forward into production sized batches.

        For propagation, I generally use filtered air instead of oxygen. Much more difficult to overdo it.

        I also like to propagate in basal medium (glucose based) as long as possible (I find better growth than wort. Have tried it all ways. Just my experiences).

        Yeast love oxygen in their growth phase. It's pretty critical. This is not anaerobic fermentation. This is respiration. Lot's of oxygen-->lot's of energy produced-->lot's of reproduction.

        Yeast ferment wort very well into beer but would rather be elsewhere with more oxygen to breathe.

        I would also remind you to ensure your micronutrient levels (like Zinc) are sufficient.

        Pax.


        Liam
        Do you mind sharing your method for creating the medium? Smaller quantities are fairly easy but when I need to go from 20L to 200L it's quite a bit more difficult.

        Comment


        • #5
          Originally posted by liammckenna View Post
          A few thoughts:

          10x volume increases are my rule of thumb for propagation, if everything seems to be going well. Pure slant -->10 ml-->100 ml-->1L--->10L...you get the idea. It can be pretty rapid.

          I generally upsize when things seem to be rocking and rolling. You can do cell counts to confirm growth rates. I like to 'feed' the yeast when they are at their maximum growth rate. I find this also minimizes the oxidized flavour carryover from wort based propagation medium moving forward into production sized batches.

          For propagation, I generally use filtered air instead of oxygen. Much more difficult to overdo it.

          I also like to propagate in basal medium (glucose based) as long as possible (I find better growth than wort. Have tried it all ways. Just my experiences).

          Yeast love oxygen in their growth phase. It's pretty critical. This is not anaerobic fermentation. This is respiration. Lot's of oxygen-->lot's of energy produced-->lot's of reproduction.

          Yeast ferment wort very well into beer but would rather be elsewhere with more oxygen to breathe.

          I would also remind you to ensure your micronutrient levels (like Zinc) are sufficient.

          Pax.


          Liam

          Interesting.

          We're building a propagator (in a 270 liter conical we have).

          * What temperatur would be the optimum for propagation of a regular ale yeast.
          * Would there be any benefit to recirculate the propagation-wort with a pump as well as hitting in periodically with oxygen?
          * I plan to use sterile oxygen, but will not pitch the propagation-beer in the wort - in that case I assume over oxygenation is not an issue?

          -Christian

          Comment


          • #6
            Originally posted by ChristianSA View Post
            Interesting.

            We're building a propagator (in a 270 liter conical we have).

            * What temperatur would be the optimum for propagation of a regular ale yeast.
            * Would there be any benefit to recirculate the propagation-wort with a pump as well as hitting in periodically with oxygen?
            * I plan to use sterile oxygen, but will not pitch the propagation-beer in the wort - in that case I assume over oxygenation is not an issue?

            -Christian
            Temperature depends on strain. Pardon my use of Fahrenheit, 75-77oF works well for most. Agitation is key to rapid and effective propagation so pump recirculation could work. Sanitation is critical at all stages of propagation. Not pitching the propagation medium will eliminate any concern for oxidized wort flavour carryover into production batches from propagation.

            Found this pretty great summary link recently on the subject. Has some good suggestions about media for growth (and much other useful info.)

            Good luck.

            Pax.

            Liam
            Liam McKenna
            www.yellowbellybrewery.com

            Comment


            • #7
              Originally posted by liammckenna View Post
              Temperature depends on strain. Pardon my use of Fahrenheit, 75-77oF works well for most. Agitation is key to rapid and effective propagation so pump recirculation could work. Sanitation is critical at all stages of propagation. Not pitching the propagation medium will eliminate any concern for oxidized wort flavour carryover into production batches from propagation.

              Found this pretty great summary link recently on the subject. Has some good suggestions about media for growth (and much other useful info.)

              Good luck.

              Pax.

              Liam
              Thanks for your feed-back. A few more questions, if you don't mind.

              Won't a propagation temperature of 75-77F make it hard to saturate the wort with O2?

              I plan to hit the conical with glycol when the propagation is done to settle out the yeast. I will keep it around 2-3C in case I do not plan to use it immediately. 1-2 days before brew day I drain off the propagation medium, close off the glycol and let the yeast warm up slowly to just under room temp, while hitting it periodically with oxygen.

              Do you see any problems with that method?

              What would you recommend as pitching rate? When harvesting yeast from a beer I usually pitch 500-1000g per Hl of slurry, but I would assume propagated yeast is much more viable?

              -Christian

              Comment

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