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  • Questions About Media Growth

    I've been seeing some growth on WLD plates for canned beers, and I am interested in finding out what they are. Unfortunately, besides endpoint PCR, we have no way to determine what exactly is growing, but I've got my own guesses on some of them.

    Does anyone have any experience interpreting these plates and what grows, or does anyone know of a good resource that I could use to compare pictures?

    Thanks!

  • #2
    WLD is a selective media variation of WLN (non-selecive) that includes cycloheximide which acts as a growth inhibitor of Saccaromyces among other eukaryotes. Knowing this you are likely looking at bacteria or wild yeast such as Brettanomyces. You could streak from your WLD plates onto something like WLC+ media plates. If you see growth there is a good chance you are looking at Brettanomyces. If you see no growth you are probably dealing with something bacterial. Before that I would take a look under the microscope at a slide of each different type of colony you are seeing on your WLD plates. Should be able to tell pretty quickly if you are looking at wild yeast or bacteria...then proceed from there. Cheers!
    Last edited by fermentedlife; 01-08-2018, 10:37 PM.

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    • #3
      If you've got a good microscope and the ability to do stainings, you could get one of the colonies, stain it and go through a morphological identification. Haven't looked it up yet, but its very common in the medical field, there are books and books on what different bacteria, yeast, etc. look like under magnification. For bacteria, usually a gram stain and then checking them out under a scope can easily identify what it is.

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      • #4
        Jebzter and fermentedlife have great suggestions. Microscope to identify yeast or bacteria, then gram stain or media. If you have suspicions of certain contaminants, I would suggest you streak the plate on media that is specific to those concerns:

        LMDA - Lee's Multi-Differential Agar for acid producing bacteria. Add cycloheximide to suppress brewers yeast growth.
        HLP - Hsu's Lacto/Pedio Media for Lactobacillus and Pediococcus
        LCSM - Lin's Cupric Sulfate Media for Non-Saccharomyces Wild Yeast
        LWYM - Lin's Wild Yeast Media for Saccharomyces Wild Yeast

        Easiest would be to ship a sample (can) to a lab for testing either by plating or PCR. If you need to know exactly what it is, go the PCR route, but if you just want ideas of the organisms behavior, then go cheaper with plating. If you have time and equipment, run through as many media as possible to cross reference results. White Labs & Brewing and Distilling Analytical Services offer some great micro lab packages.

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