Yeast in Storage: Viability and Vitality

Discussion in 'Homebrewing' started by LeeryLeprechaun, Feb 1, 2014.

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  1. LeeryLeprechaun

    LeeryLeprechaun Savant (1,094) Jan 30, 2011 Colorado
    Trader

    Hello everyone!

    Starting Monday I plan to shed some light on the question about how long yeast can be kept cold in your fridge. I currently have a starter of 1056 growing. I will then split it into 14 different portions. For the next two months I will open a bottle once a week and test both its Viability and Vitality.

    I will be able to report not only how many yeast cells are still alive but also how "healthy" they are.

    Viability will be tested using a hemocytometer and methylene blue.
    http://microbebrewer.blogspot.com/2014/01/yeast-cell-counting-and-viabilty.html

    Vitality will be tested using an Acidification Power Test which gives you an idea of how well the yeast will be able to ferment a simple sugar.

    I will post the results here every week. After the first two months of weekly sampling the frequency will drop to only once every two weeks or once a month, not sure yet.

    After I have done this preliminary test I will repeat the test with several other yeast strains.
     
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  2. JackHorzempa

    JackHorzempa Grand Pooh-Bah (3,181) Dec 15, 2005 Pennsylvania
    Pooh-Bah Society

    I really, really want to thank you for conducting this study. The topic of an appropriate yeast die off rate for packages of liquid yeast (Wyeast smack-pack and White Labs tubes) is of great interest to me.

    I am not a scientist by profession so I do not have a lot of experience is setting up experiments. Hopefully others (e.g., @mattbk and @phattysbox ) will chime in with their thoughts/ideas.

    I took note of: “I currently have a starter of 1056 growing. I will then split it into 14 different portions. For the next two months I will open a bottle once a week and test both its Viability and Vitality.” My read is that you intend to bottle starters, is that correct? Does a difference in packaging (i.e., smack-pack, tube, bottled starter) have an effect on yeast die off rate? In other words, will the same percentage of yeast die off in a factory sealed smack pack as would occur in a bottled starter?

    In prior discussions with mattbk he made mention that the accuracy of yeast counting: “but an experienced technician with good tools and an adequate dilution scheme should have a measurement uncertainty of around 5-15%”

    Cheers!

    Jack
     
  3. psnydez86

    psnydez86 Initiate (0) Jan 4, 2012 Pennsylvania

    Thank you @LeeryLeprechaun !!! I'm very excited to see what the results are!

    God speed.
     
  4. FATC1TY

    FATC1TY Pooh-Bah (2,502) Feb 12, 2012 Georgia
    Pooh-Bah

    Damn.. Very big thank you for doing so..

    Looking forward to seeing what you find out.
     
  5. wspscott

    wspscott Pooh-Bah (1,934) May 25, 2006 Kentucky
    Pooh-Bah Society

    So you will use 8 samples in the first 2 months, can you stretch out the remainder so you have at least one sample at 6 months? I sometimes find yeast in the back of my fridge that are 6-9 months old. It seems to be a coin flip on whether or not I can bring them back to life at that point. I would definitely appreciate a more scientific approach.
     
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  6. LeeryLeprechaun

    LeeryLeprechaun Savant (1,094) Jan 30, 2011 Colorado
    Trader

    I will see how quickly the values are dropping and adjust my sampling plan based on that. This is just a "proof of concept" that I will most likely repeat once I have a better idea of what to expect.
     
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  7. LeeryLeprechaun

    LeeryLeprechaun Savant (1,094) Jan 30, 2011 Colorado
    Trader

    I placed the samples into PET bottles. I did not want to risk contaminating a sample by opening and closing it multiple times. I would like to test Wyeast and White Lab samples of varying dates but as you can imagine that would get expensive very quickly. To avoid this expense I grew up my own starter.
     
  8. JackHorzempa

    JackHorzempa Grand Pooh-Bah (3,181) Dec 15, 2005 Pennsylvania
    Pooh-Bah Society

    “I would like to test Wyeast and White Lab samples of varying dates but as you can imagine that would get expensive very quickly. To avoid this expense I grew up my own starter.” I understand and appreciate that.

    The discussion point I wanted to make was that yeast die off rates can be influenced by the media in which they are stored. For example, I do not know how to classify the storage media of a Wyeast smack pack (I do know they have packs which include yeast nutrient and wort in the enclosed packs). I also don’t know exactly what the media is within a White Labs tube. I am wondering whether the yeast die off rates in the Wyeast media, the White Labs media and your starter wort in a bottle will have a common yeast die off rate.

    Please conduct your experiment and report back your results. As I stated in my prior post I am thankful you are willing to conduct this study.

    Cheers to you sir!
     
  9. LeeryLeprechaun

    LeeryLeprechaun Savant (1,094) Jan 30, 2011 Colorado
    Trader

    2/3/2014
    Culture Age: 3 Days
    Viability: 98%
    Vitality: Very High
    Total Cells: 9.00 E7 CFU/mL
     
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  10. LeeryLeprechaun

    LeeryLeprechaun Savant (1,094) Jan 30, 2011 Colorado
    Trader

    2/10/2014
    Culture Age: 10 Days
    Viability: 97.75 %
    Vitality: Very High

    Still looking good! I am surprised that there was almost no change since the first sample.
     
  11. LeeryLeprechaun

    LeeryLeprechaun Savant (1,094) Jan 30, 2011 Colorado
    Trader

    2/19/2014
    Culture Age: 19 Days
    Viability: 96.6 %
    Vitality: Ran out of time at work to test

    The culture still looks great. I would still use this yeast to start a fermentation without any hesitation.
     
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  12. mattbk

    mattbk Savant (1,099) Dec 12, 2011 New York

    For those keeping track: the viability would be 85% using a typical online calculator. (note that those models assume yeast stored in packs/vials, not a starter - you may argue amongst yourselves whether this is represents a best or worst-case scenario - either way - this is killer data.)
     
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  13. FeDUBBELFIST

    FeDUBBELFIST Pooh-Bah (1,703) Oct 31, 2009 Pennsylvania
    Pooh-Bah Society

    Would someone mind explaining to me the difference between viability and vitality in practical terms?
     
  14. ssam

    ssam Pundit (973) Dec 2, 2008 California

    Viability is how many yeast are alive and vitality is how healthy they are/how well they can handle fermentation.
     
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  15. barfdiggs

    barfdiggs Initiate (0) Mar 22, 2011 California
    Deactivated

    Just curious , did you ensue that the 1056 starter was finished with fermentation before aliquot ing into your storage bottles ? If not, you could be grossly over estimating yeast health as they would have a sugar source for propagation during cold storage.
     
  16. LeeryLeprechaun

    LeeryLeprechaun Savant (1,094) Jan 30, 2011 Colorado
    Trader

    I tested glucose remaining in the culture. They'd was no glucose left. I do not have a way to test for maltose but am fairly certain the fermentation was over as I had also let all the yeast flock out before putting them in the fridge.
     
  17. Hanglow

    Hanglow Pooh-Bah (1,977) Feb 18, 2012 Scotland
    Pooh-Bah

    This is good stuff

    Would you get similar numbers from rinsed yeast from a previous batch?
     
  18. GUNSLINGER

    GUNSLINGER Initiate (0) Nov 18, 2013 Colorado

    Thanks for doing this. Great info/resource. Looking forward to seeing more data as the process continues.
     
  19. LeeryLeprechaun

    LeeryLeprechaun Savant (1,094) Jan 30, 2011 Colorado
    Trader

    3/3/2014
    31 Days Old
    Viability 81%

    As you can see after 1 month the viability has dropped. The next time I run this experiment I will take more sample between this one and the previous to try and catch the drop. I did not test the vitality as it would have been low due to a lack of viable cells. At this point I would not use this culture to start a fermentation but would step up a starter from it. Even though 81% of the cells are alive you have to think that those that are still living are getting close to kicking the bucket themselves.
     
  20. utahbeerdude

    utahbeerdude Maven (1,374) May 2, 2006 Utah

    Just caught this thread. Great experiment!
     
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