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Thread: unusual changes in viability

  1. #1
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    unusual changes in viability

    I have been brewing professionally for 6 years now and have practiced the same yeast handling practices throughout that I was taught from the first big brewer that I worked for. Dumping off the bottom portion of yeast from the cone, harvesting a healthy pitch of dense slurry from the tank, zero-no storage time prior to use, doing cell counts and viability each harvest. I have recently started at a new brewery and have found that my standard practices aren't always applicable. Where I used to be able to take yeast out to 10-15 generations, now I am seeing only 2-6 generations before viability in the tank drops to about 50%. Fermentations have proceeded well, often attenuating in 4-7 days (with WLP090) with additional time added for D-rest and QC tests to pass. But at harvest time, even with a tank that received a pitch of 90% viability prior, I am seeing massive die off of yeast under the scope, often down to 50% viability. My conicals and equipment are standard, I ferment at 68 F, I crash to 35 F prior to harvesting non dry hopped beers or to 60 F for dry hopped beers. Any insight that you folks have would be greatly appreciated. Thanks.

  2. #2
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    Feb 2014
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    west coast
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    Tank size/geometry/cooling on cone?

  3. #3
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    Sep 2015
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    San Francisco, CA
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    Can you elaborate on wort oxygenation practices? And have you investigated any differences in raw materials, specifically protein/nitrogen content, that might be solved by using YeastEx or similar yeast nutrient?

  4. #4
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    I use yeast nutrient in every batch. My KO time is 1 hour due to cooling contraints so I aerate with pure O2 at 4-5 liter per min. In general, I get active fermentations without blow off. My Conicals are cone cooled. They are about 14 ft high, 15 bbl fermenters, with about a 60 degree cone. I routinely dump off cold break and trub after first few days of fermentation. If I am doing a double batch, I will do them over 2 days, only oxygenating the first batch. I pitch enough yeast by cell count to ferment a single being under the assumption that the cell count will double overnight. The yeast will typically ferment well through the first double batch like this from the lab, show 90% viability at harvest, work through the second double batch, but show up at harvest time after the second double batch with about 50% viability.

  5. #5
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    Oct 2012
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    Palatine, IL
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    Try harvesting when the beer reaches terminal, prior to d-rest. We found that our yeast was quickly losing viability while the tank/cone were warm between d-rest and crashing. BSI recommends this method, I know it's scary to remove yeast from a diacetyl positive tank but it doesn't take many cells to reduce diacetyl and those in the cone aren't doing any work anyways.

    You'll probably see a decrease in cell density, but that's just a trade off you'll have to work with for getting decent viability. We still harvest our lagers and other low flocculating strains post d-rest as their flocculation and fermentation temps don't cause the massive cell death in the cone.

  6. #6
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    Quote Originally Posted by AT-JeffT View Post
    Try harvesting when the beer reaches terminal, prior to d-rest. We found that our yeast was quickly losing viability while the tank/cone were warm between d-rest and crashing. BSI recommends this method, I know it's scary to remove yeast from a diacetyl positive tank but it doesn't take many cells to reduce diacetyl and those in the cone aren't doing any work anyways.

    You'll probably see a decrease in cell density, but that's just a trade off you'll have to work with for getting decent viability. We still harvest our lagers and other low flocculating strains post d-rest as their flocculation and fermentation temps don't cause the massive cell death in the cone.
    Thank you so much for this info. I have been doing this with some positive results (92% viability) and the theory makes sense, however, I have used this yeast strain (WLP090) for a long time now and never had this problem before. I will have to warm harvest most of my beer, I guess, carrying on, but it just makes logistics that much tougher since different beers finish at different times and yeast storage after harvesting is no longer recommended. I will just have to be ready to go with the next batch on the fly. I have been hearing of other brewers (bigger ones) harvesting this way, but the conventional wisdom has always been 10-14 days on yeast, cold crash, and harvest. I am just confused why this doesn't work for me anymore. Anyway, thanks for the input.

  7. #7
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    Sep 2005
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    Louisville, KY
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    Is it occuring on all your recipes? Any different additions, PH, High Grav?
    Joel Halbleib
    COO / Zymurgist
    Goodwood Brewing Co
    636 East Main St
    Louisville, KY
    goodwood.beer

  8. #8
    Join Date
    Oct 2012
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    Palatine, IL
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    Quote Originally Posted by OtherBrother View Post
    Thank you so much for this info. I have been doing this with some positive results (92% viability) and the theory makes sense, however, I have used this yeast strain (WLP090) for a long time now and never had this problem before. I will have to warm harvest most of my beer, I guess, carrying on, but it just makes logistics that much tougher since different beers finish at different times and yeast storage after harvesting is no longer recommended. I will just have to be ready to go with the next batch on the fly. I have been hearing of other brewers (bigger ones) harvesting this way, but the conventional wisdom has always been 10-14 days on yeast, cold crash, and harvest. I am just confused why this doesn't work for me anymore. Anyway, thanks for the input.
    No problem. Once the yeast is harvested in a brink and kept cold, you should be able to store it for about a week, without too much trouble. I can't really comment on why your previous method isn't working, but if I had to guess I'd say it probably has something to do with tank geometry or tank cooling, possibly tank volume.
    Last edited by AT-JeffT; 09-10-2018 at 12:09 PM.

  9. #9
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    Chesterfield, UK
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    I believe you are simply overworking your yeast. If you have only started double batching at this brewery, then I suggest that there is insufficient yeast (mainly) of suitable viability by the time you come to add your second batch of wort. Either increase the pitching rate to cope with 1.5 to 2 times the initial wort volume, and aerate / oxygenate properly, but don't aerate the second batch, or continue with current pitching rates but aerate both batches of wort equally. Don't worry about diacetyl being generated from this source, it is far too early in fermentation to leave any as a result of the second aerated wort.

    Don't be surprise though if the best results are from yeast pitching rate suitable for both brew volumes, added to the first brew only, with first wort fully aerated, and second wort at 50 to 100 % of full aeration rate.

    And don't forget that just because you add so much oxygen, it all dissolves. Simply stating a flow rate is completely meaningless if virtually none of it dissolves.

    Agree with the comment about cropping whilst warm, but then cooling the yeast slurry to 3 deg C, 36 to 37 deg F for storage

    The longer the yeast is left in FV, even with cone cooling, the more it deteriorates. One brewery discovered temperatures of 49 deg C in the centre of the yeast cones, even with cone cooling on. There is no circulation in the yeast, and the layers in contact with the cooling panels simply insulate the bulk of the yeast from the panels, and allow autolysis.
    dick

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