How to measure yeast?

[bd2xu]

Newbie yeast ranching question. I saved the yeast from the cake in secondary from a saison, it's wy3724. I have it in a small mason jar in the fridge, when it separates I will decant. How do you know approx how many cells you have to pitch? Say I brew a batch, and use yeastcalc to say I need 250 billion cells. How do I know how many I'm starting with so I know how big to make the starter, etc. I can't figure out how I would measure cell count of saved yeast.

 

[psnydez86]

If you use jamils mrmalty.com yeast calculator he has a pitch from slurry option that will give you a ballpark idea of what you have.

 

[guldalian]

I agree with OP. For instance, brewers friend yeast calc has an option for slurry density. Default is 1 bill. Cells per ml, but how do you know if that's correct? If its more like .5 or 1.5, your calculation will be substantially off.

 

[barmyarmy]

Mr. Malty is a great tool for estimation. In my opinion viability is much more important than cell count. That's why I wash yeast and make a starter.

 

[guldalian]

Ok, I also wash and make starters. I also freeze yeast sometimes. But how do you know either cell density OR viability in your washed/frozen slurry?

 

[Polboy]

Sometimes i use this picture as a reference (often i use the same 50ml tubes to keep my yeast) if i keep it in the jar i add about a cup of slurry per 5gal and i still think its over pitching

 

[theredben]

Just for clarity in the above picture, the "2.5 E8" means 2.5x10^8 cells in the 50 ml tube, and the 10% is the rough estimate of sediment volume.

 

[winvarin]

Just for clarity in the above picture, the "2.5 E8" means 2.5x10^8 cells in the 50 ml tube, and the 10% is the rough estimate of sediment volume.

I'd be interested in learning more about this as well. If I read the pics properly, the percentages represent how much of the 50 ml volume is occupied by yeast. I spot checked the first 2, and the 40% vial. If my math is correct, each of those work out to right at .5 billion cells per milliliter

 

[winvarin]

Another thing. Using .5 billion cells would probably be a low, but likely fair estimate. Speaking for myself only, I try to be as diligent and thorough a I can with harvesting, sanitation, transfer, etc. but let's face it. I am not a biologist, and i don't have anywhere near a lab grade setup

Between the accuracy of non scientific equipment and simple potential mistakes like letting some of my yeast go down the drain because I don't use a centrifuge to separate solids from liquids, I am likely leaving a lot of potentially good yeast behind at various steps in my process.

All other things being equal, if I have a clean harvest, .5 billion cells/ ml is a number I can work with

 

[el_caro]

I store in graduated vials which makes estimating quantity of compacted yeast very easy. I use 3bn cells per ml of compacted yeast. So if I have around 33ml of yeast sitting in bottom of vial then I would say that is my 100bn cells.
I would then use Yeastcalc and the date of harvesting to determine how many viable cells there are in the 100bn cells. That will let me calculate the size of starter needed to hit the number required for the task at hand.