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Few Generations from Yeast

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  • Few Generations from Yeast

    Hello! In our brewery we have been used yeast from previous fermentations with good fermentations and with out off flavors. Time weeks we decided to start with a fresh yeast pack (500 grams of SafAle S-04, and once rehydrated, used in a 500 liters fermenter) because in our laboratory we detected low viability of the yeast cells.
    The "fresh" yeast and their following generations started with good performance and very well attenuation, better than previous culture yeasts. However, at the generation number 5, we detected low cell counting and low viability of the yeast, so we could not continue to re-use them because there were not guarantees for their good quality to be reused. We don't understand what could have happened to cause that they can not achieve the enough nor viability or counting cells throught the sucesive generations. (We are working without changes in our CIP and sanitizations procedures, as we have be usually worked without issues).


    Regards,
    SERGIO
    Argentina

  • #2
    A load of possible reasons, but the most common ones are low wort oxygenation, lack of yeast nutrient, most typically zinc, and yeast treatment / storage conditions once the primary fermentation has finished.

    Trawl through this discussion base and you will find lots of suggestions / comments, but my comments for a starter -

    Oxygen - dissolved oxygen for say 5 % ABV beers - circa 10 ppm

    Yeast nutrient - zinc addition as zinc sulphate or chloride - 0.15 to 0.25 ppm zinc at start of fermentation

    Yeast - remove as soon as fermentation finished and store at 3 deg C until required for use. Don't stir / oxygenate / aerate until required for use and you need to ensure a consistent slurry. Then stir, don't use oxygen or air.
    dick

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    • #3
      Thanks! Yes... We've measured week ago our O2 concentration wort and it was OK, about 9-10 ppm. Also, we used fermentation nutrients.
      I will check case by case the time we had since fermentation was finished (related to FG values) till fermenented beer was cooled... may be there was an unnecessary elapsed time...
      Thanks again!

      SERGIO

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      • #4
        Having said that most yeasts seem to work OK at about 10 ppm oxygen, some do require more, especially if you are brewing at higher gravities. One of the local major breweries used to use 27 ppm for about 7.5 % beer, and some breweries yeasts presumably require more, because they collect wort with circa 10 ppm, but then have to rouse during fermentation, adding an unknown amount each time they rouse.

        So it might be worth trying more oxygen / rousing with air / recirculation through a fishtail early in fermentation only, as an experiment - but don't go overboard, and watch out for flavour changes, particularly ester reduction.
        dick

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