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acceptable number of bacteria in sample?

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  • acceptable number of bacteria in sample?

    I pulled a yeast slurry from recent batch of IIPA for cell count/viability. However, in the 100ml dilution I counted a total of 10 cells of what appear to be brettanomyces. This count was from all 25 center squares on my slide. Would this be considered too many to re-pitch? Is there a standard count for wild yeast and bacteria that is being used as to determine a safe re-pitch qty? Thanks for any help.

    mark taylor
    cerveceria dos aves

  • #2
    Sorry to hear that you may be dealing with a possible infection in your yeast slurry. The first point to make is that unless you have a lot of experience looking through a microscope and differentiating brewing yeast and wild yeast, it's hard to get a positive ID by how the cell looks. Reliably, most operators would only be able to tell that it's not their brewing strain. To get more of an ID you'll need to plate it out on wild yeast media or send it off for PCR. Now to the main part of your question of whether there is an acceptable amount of contaminants in slurry or beer and the answer to that is not really no. Ideally you'd have no contaminants and to be able to make a decision, most folks in the QC world would argue that you would need to know what the contaminant is to determine the risk. If you have 10 cells in the counting area then you could have as many as 100,000 cells per mL and honestly more depending on your dilution factor, of that potential wild yeast which is a huge deal. Wild yeast are a big deal because they like the same conditions as your brewing yeast and are competing for the same resources. I'm not saying that you should destroy the yeast based on microscopy alone though, if you're worried then have the sample screened for contaminants and then make a decision.

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    • #3
      Thanks for the info.
      These odd cells are small and they appear to make a back and forth motion to move, almost as if hinged near one end. Doesn't look like pedio or lacto or acedobactor. Very strange

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      • #4
        Originally posted by mbirdlane View Post
        I pulled a yeast slurry from recent batch of IIPA for cell count/viability. However, in the 100ml dilution I counted a total of 10 cells of what appear to be brettanomyces. This count was from all 25 center squares on my slide. Would this be considered too many to re-pitch? Is there a standard count for wild yeast and bacteria that is being used as to determine a safe re-pitch qty? Thanks for any help.

        mark taylor
        cerveceria dos aves
        To follow up what R.Cockerell said, you also have to consider that if it is wild yeast/bacteria, it will propagate up in that next batch, and more and more in subsequent batches. By the time you're at later Gens it will have increased in quantity by a significant amount. From a quality guy's opinion, better to search for a better route and get a fresh pitch rather than continue this yeast lineage...

        Good luck!

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        • #5
          Hey,

          I would just like to add to this question as I am in somewhat of a similar dilemma. I am also a quality guy and lately I have been presented with positive results for bacteria and for the first time ever some days ago what seems to be a wild yeast positive. We are using media tubes for bacteria and plating for wild yeasts, so basically for bacteria we know we have a positive if we see a change in the media color or an increase in turbidity and for wild yeast we evaluate that by the presence of colonies.

          I would agree 100% with stopping a lineage as this would otherwise mean that you are propagating your infection as you guys mentioned. However, when dealing with a tank that I, for example know that won't be used for repitching another tank or from which we will not be harvesting from, would not one be able to talk about a minimum risk threshold? What about having 5 CFU/ml in a beer? ... what about 10? what about 100 CFU / ml? surely there must be a difference. We are counting this by plating an exact volume and then counting the colonies after incubation time.

          I have a feeling that it would all depend on what the organism is and how much it can thrive in the media (beer) but I would also like to know what other people are doing out there as I tend to believe that yes, any amount of wild yeast would have an impact and would potentially, slowly but surely turn a beer into a potential beer bomb or foamy mess... Of course no one wants a contaminated beer, but I mean 1 - 3 CFU / ml in a beer of a wild yeast... would that really become an issue in a packaged beer? Would a wild yeast be able to grow if at all? What are you guys doing out there? What does theory say?

          I am incubating my wild yeast plates aerobically so that also affects what I see. Are any of you guys incubating anaerobically and if so what are you using?

          Cheers and thanks in advance!

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