PurePitch viability and starting cell count equations updated

Discussion in 'Feature Requests' started by PNW Ale Project, Jun 13, 2019 at 2:35 AM.

  1. PNW Ale Project

    PNW Ale Project New Member

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    Hey guys,
    Currently, when calculating my starting cell count for Whitelabs Purepitch yeast, I go to the QC website here:
    https://www.yeastman.com/Login/Public/Report/PublicLabQCResult.aspx

    I punch in the lot # and change the dropdown menu to homebrew purepitch, and that gives me an initial cell count in the packet.

    The next place I go is the viability website here:
    https://www.whitelabs.com/news/purepitch-shelf-life

    From here I can work out a percentage based on the percentages given and the time the yeast was manufactured. I know it isn't perfect but it is a lot more accurate than the current Whitelabs equation used in the software.

    For instance, I have a packet of WLP001 that was manufactured on 1/7/2019. The lot number is 1067653. In the current calculator, I have essentially no usable yeast.
    Using the above method, I see I have 2.23 billion cells/mL. It is a 40 mL packet so on 1/7/2019, I started with 89.2 billion cells. Using the viability percentage, I now have about 79% viability so I am actually starting with 70.468 billion cells.

    You can see the large disparity between the two numbers. Even just updating the percentages to better reflect the purepitch packet would be better than the current calculator allows.

    Just my two cents.
    Love the program and everything you do!
    Sean O
     
  2. Yooper

    Yooper Administrator
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    I'm trying to picture how this could work. It would involve only one manufacturer and only one set of yeast strains so I'm not sure how we could integrate it into the entire yeast library/pitching calculator.
     
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  3. PNW Ale Project

    PNW Ale Project New Member

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    The easiest way to make it work is assume each Purepitch has a starting cell count of 2.4 billion cells per mL. 40mL packet means each packet starts with an average of 96 billion cells. The next thing you could do, is as best as possible, use the viability page to develop some averages over time. It isn't exactly linear but at least it will be more accurate than the current calculator. Just put those under another drop down option for purepitch.

    The initial cell count isn't even that great of a deal, it is more the viability that would benefit people the most. It shouldn't be to hard to develop the equations for that.
    Again, just a suggestion.

    Thanks Yooper!
     
  4. Nosybear

    Nosybear Well-Known Member

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    What does White Labs say about pure pitch viability? I scanned the site briefly and didn't find anything other than a 4-month recommended shelf life.
     
  5. PNW Ale Project

    PNW Ale Project New Member

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    All I'm saying is the viability percentages used are from 7 years ago and the pure pitch viability is much much greater than the vials used to be.
    Per Whitelabs website:
    Average viability of PurePitch® pure liquid yeast over a period of six months:

    1 month - 99.21%

    2 month - 98.05%

    3 month - 90.26%

    4 months - 84.28%

    5 months - 79.35%

    6 months - 71.59%


    The current BrewersFriend calculator viability percentages are as follows:
    • Liquid yeast viability drops 21% each month, or 0.7% each day, from the date of manufacture. The assumption is the yeast viability drops in a linear fashion. In 4.75 months or 143 days, this calculator assumes the yeast is 100% dead (100 / 0.7 = ~143).
    • From the White Labs FAQ 11/2012: What is the shelf life of White Labs Yeast? Quick Answer: 4 Months. Long Answer: .... After 30 days in the vial, the viability of our yeast is 75-85%,...
     
  6. Yooper

    Yooper Administrator
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    We'll definitely think about this, and ways it could be implemented. We're open to ideas from others, as well!
     
  7. Nosybear

    Nosybear Well-Known Member

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    PNW: What's the source of your numbers? I was poking around on White Labs' site last night and couldn't find them. Anyway, I punched them into Excel and got the following chart:

    upload_2019-6-14_13-44-18.png

    Assuming 100% viability at packaging, you can model the yeast's viability using the equation shown. Note "X" is months! So you'd have to use "Days" divided by the average month length to use this equation to model the decrease in viability. And note the R-squared is very high so this would definitely be close enough for homebrew.

    I did find that White Labs lists the shelf life of their yeast at 4 months so they want to keep the viability at around 85% or greater. Again, in the "close enough for homebrew" range, the error of assuming 100% viability (I've been known to miss this step in the calculator), your error in pitch rate is 15%. I'd bet we'd be hard-pressed to detect the difference in yeast made with yeast at 100% viability and yeast made with 85%.
     
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