Author Topic: Yeast viability/aging rate  (Read 2487 times)

Offline GigaFemto

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Yeast viability/aging rate
« on: July 31, 2017, 11:50:10 AM »
Sorry if this has been hashed out already, but I couldn't find it on the forum. I have some 4-month old White Labs WLP004 yeast (packaged 3/31/2017, says use by 9/27/2017) that has been refrigerated the whole time. BeerSmith 2.3.12 says the viability is 61%. I usually use the Brewer's Friend Calculator (https://www.brewersfriend.com/yeast-pitch-rate-and-starter-calculator/ ) because it allows you to do two-stage starters. The viability estimated there is 13%. These are wildly different. If I have 13% viability and only do a single-stage starter (I can  do 1.5 liter max) I won't have as many cells as I want. On the other hand, if I do a two-stage starter and the viability is 61%, I will have twice as many cells as I want, and my experience with over-pitching has not been good.

I know that there is no good way to calculate yeast viability accurately, but  the difference between 13% and 61% seems unreasonable. Does anyone have any experience to indicate which of these would be better to use?

--GF

Offline Oginme

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Re: Yeast viability/aging rate
« Reply #1 on: July 31, 2017, 12:31:55 PM »
I cannot comment the the Brewers Friend yeast calculator, but packaged yeast, be it from White Labs or Wyeast or someone else would not put a use by date of September if the viability was only going to be at 13%.  In my experience, many of the calculators out there, including the one that I prefer at Brewunited [gave a 39% viability to your March yeast], tend to underestimate the viability of the yeast packs.  When building a starter using their site (which also supports step starters), I've had far greater viable cell counts from the results of the starter using their recommendations.

Where the truth of the viability rates is, I can't say with any certainty as I have never done cell counts on the packages themselves, just the results of my starters using the packs. 

I know this doesn't help you much right now, but it is the best I can offer.  You may try zipping an e-mail to White Labs to ask them (quote the 13% viability rate and I am sure you will get an answer!).


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Offline GigaFemto

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Re: Yeast viability/aging rate
« Reply #2 on: July 31, 2017, 04:37:50 PM »
Thanks for the information, Oginme. After looking into it a bit more (also known as wasting an afternoon), the difference is whether a linear or exponential decay is used. For fresh yeast there is little difference, but for old yeast the difference is huge. Brewer's Friend uses a linear model, and the viability would be negative by the "Use By" date, so it is definitely not a good choice for old yeast. BeerSmith uses an exponential model but is inconsistent in its aging rates. In the yeast starter calculator it has a default of 21%/month, very close to the BrewUnited value. However, all of the White Labs yeast entries have a 10%/month aging rate specified in the database entries. If you look at Ingredients->Yeast to get the whole list and add a column with aging rate and sort on that you can see that all White Labs have 10% and no other yeasts do. It is hard for me to believe that White Labs has found a fountain of youth that allows their yeast to age at half the rate of the competition. I think this may be an error in the BeerSmith database. In any case, I have more reasonable numbers to work with now.


--GF

Offline GigaFemto

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Re: Yeast viability/aging rate
« Reply #3 on: July 31, 2017, 07:58:39 PM »
Poking around a bit more, I found this BeerSmith blog post from 2010: http://beersmith.com/blog/2010/12/14/yeast-starters-for-home-brewing-beer-part-1/ where Brad says that Chris White says his yeast viability decrease at a rate of about 20%/month. Unless something radical has happened in the last 7 years, I think that the BeerSmith database entries for White Labs yeasts are wrong. I am going to cross-post to the Bugs/Support forum.

--GF

 

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