@RM-MN
- The White Labs article you linked to is discussing viability of their 1st generation yeast, benefiting from their FlexCell™ technology and PurePitch® packaging, over the course of 6 months.
- The Woodland Brewing research you linked to is discussing viability of an unknown generation yeast, sourced from washed slurry over the course of 1 month. It's not mentioned in the text, but looking at the picture of the jars of slurries, they look very thoroughly washed. Washing the slurry greatly reduces, if not eliminates, the alcohol content of the slurry.
- The Brew United Calculator provides a list of assumptions at the bottom of the webpage. Ironically enough, the first assumption states, "Liquid yeast is assumed to lose approximately 20% of the total viable cell count per month. This figure comes from a White Labs statement that indicated that you could expect 75%-85% viability after a month; 20% is used as a middling factor." You'll notice the link to the White Labs statement points to a URL for the old FAQ page on the White Labs website. That FAQ was updated when they adopted the FlexCell™ technology and PurePitch® packaging.
Here's a viability comparison of those apples, oranges and limes:
Code:
1 month 2 months 3 months 4 months 5 months 6 months
White Labs
FlexCell™ 99.21% 98.05% 90.26% 84.28% 79.35% 71.59%
PurePitch®
Woodland Brewing
Washed Slurry 99.8%
Brew United
Calculator 77% 61% 49% 39% 31% 25%
Not sure what information we can gleam from that data?
In the Woodland Brewing blog entry, it is mentions the impacts of alcohol to yeast viability, linking to another one of their blog entries:
http://www.woodlandbrew.com/2013/01/abv-effects-on-yeast.html
That entry discusses yeast viability of yeast with slurries of varying alcohol content over the course of 70 days.
Sadly, the Woodland Brewing starter calculator is no longer available for download.
Still, below is a more apples to apples comparison of this blog entry against the Brew United Calculator:
(I'm calling it "more apples to apples" because 4% is typical ABV for a 1.040 starter)
Code:
1 month 2 months 3 months 4 months 5 months 6 months
Woodland Brewing
4% Slurry 78% 63%
Brew United
Calculator 77% 61% 49% 39% 31% 25%
Viability numbers are pretty much in line.
Let's set aside the alcohol content for a moment.
Let's assume my yeast handling skills are so good, they match those at White Labs.
Let's assume that my 5th generation yeast is on par with White Lab's FlexCell™ technology.
Let's assume that my mason jar is on par with White Lab's
PurePitch® packaging.
That would mean that at 2.5 months, my yeast viability is not at ~55%, but matching White Lab's ~94%.
Damn, I'm good.
The net result is that my 1.040 starter would need to be 1.75L, instead of 2.0L.
I've made a 1.75L ale starter in a 2L flask and ended up making a mess all over the stir plate, desk and floor.
Thanks for the homework assignment, but, what's your point?
What do you know that I don't?