Factoring Starter Into Yeast Viability

[chieftain]

Sorry if this was covered before, but I was curious how to factor in a starter to my yeast viability calculations. Basically, I had a 3 month old yeast slurry, which I dumped into a 2L starter, yielding 400+ml of new slurry - do I consider that a "new" batch of yeast, for purposes of Mr. Malty or other calculators? Does the starter essentially reset the yeast "born by" date? The difference is significant in terms of calculating how much slurry I need for a 1.065 IPL I plan to brew tomorrow.

TIA

 

[flars]

I consider the term "slurry" as the volume harvested from the fermentor. This volume will have a varying count of yeast cells per milliliter depending upon how much non yeast there is. The fresh yeast cells propagated with a starter have the current born on date.

You would need to estimate how many cells were contained in the harvested slurry and then use a good pitch rate/starter calculator to estimate the viability. I find these two calculators are more clear for doing this than mrmalty.
http://www.brewunited.com/yeast_calculator.php
https://www.brewersfriend.com/yeast-pitch-rate-and-starter-calculator/

This thread will help estimate how many yeast cells you had harvested.
https://www.homebrewtalk.com/showthread.php?t=579350

A conservative estimate is 1 billion cells per milliliter. You could have up to 4 billion cells per milliliter if there is no visible non yeast matter in the slurry.

 

[chieftain]

I consider the term "slurry" as the volume harvested from the fermentor. This volume will have a varying count of yeast cells per milliliter depending upon how much non yeast there is. The fresh yeast cells propagated with a starter have the current born on date.

You would need to estimate how many cells were contained in the harvested slurry and then use a good pitch rate/starter calculator to estimate the viability. I find these two calculators are more clear for doing this than mrmalty.
http://www.brewunited.com/yeast_calculator.php
https://www.brewersfriend.com/yeast-pitch-rate-and-starter-calculator/

This thread will help estimate how many yeast cells you had harvested.
https://www.homebrewtalk.com/showthread.php?t=579350

A conservative estimate is 1 billion cells per milliliter. You could have up to 4 billion cells per milliliter if there is no visible non yeast matter in the slurry.

I should have clarified that I rinsed the slurry I originally harvested 3 months ago. That harvested yeast is what I pitched into the 2L starter, which yielded 400+ ml of new yeast last Friday. Thanks for your answer re: born on date. Since it's pretty clean yeast, I figure I probably have at least 800 billion cells...