Cell count estimation

[Peaty Jones]

Hi,

We all base our cell count on calculators and formulas which is practical but quite a rough estimate. I was just thinking that would it be possible to determine the yeast count much more precisely if you based it on OG, FG and ABV? It would atleast sound reasonable that In a steady enviroment cells reproducing rate would be somehow proportional (linear? Exponential? Logarithmic?) to the sugar content it had used as energy source to reproduce. Ofcourse theres always some alcohol produced also and that should be also take In to account.

So by taking reading of OG and SG you could calculate the sugar spent. ABV couldnt be determines via hydrometer. Measured via vinometer perhaps?

Any microbiologists on this Forum who could do some research on this?

 

[hottpeper13]

Retired millwright here. I think that the growth rate changes with the amount of yeast originally pitched would cause havoc with this conception.

 

[Peaty Jones]

Retired millwright here. I think that the growth rate changes with the amount of yeast originally pitched would cause havoc with this conception.

But isnt it the same with the nowadays method? You pitch a bag of yeast which cell count you assume has approximately this amount of cells.

 

[hottpeper13]

But if you're looking for more then a rough estimate you would first need to do massive amounts of cell counting on different OG's and FG's to determine the growth rate for your predictions to be accurate.
I have a bright field and did this with 3 yeasts and each one was different. It turns out that when I follow the Brewdads calculator and keep the cell growth between 3 & 5 and pitch that amount I get awesome fermentations, and repitching just the right amount keeps me going for 4 generations mostly because I want to use a different yeast.

 

[Peaty Jones]

I agree that calculators do a Great job when doing a 2 or 3 step starters. But what about when you try to propagate from very small vials. Lets say I want to propagate from 0.1g sample of my yeast bank. I need to propagate it multiple times and if each every step has an error of like 30% it then multiplies quickly. In this kind of job you would need to have a better method for cell count approximation.

 

[Gadjobrinus]

I agree that calculators do a Great job when doing a 2 or 3 step starters. But what about when you try to propagate from very small vials. Lets say I want to propagate from 0.1g sample of my yeast bank. I need to propagate it multiple times and if each every step has an error of like 30% it then multiplies quickly. In this kind of job you would need to have a better method for cell count approximation.

If you mean, say, from 10 ml aliquots, that's often what I do, since I maintain several slants. I just step 10-100-500-2500, or even 10-50-250-1000-5000 for most lagers and big ales. And I don't worry about counts, because absent a quality microscope like hotpeper has, it seems like an exercise in futility to me to try various schema to parse it.

 

[hottpeper13]

I mostly do 250 ml overbuild starters and counted them 3 times and average was 30 million cells per ml. I put the date on and when ready to make a starter I input those #'s into the calculator and go from there. The key for me is doing it the same each time so it's repeatable.
Also did some counts on ale, lager and Kolsch yeast cakes and matched those to what the calculator said I'd get for repitching consistency. So I repitch 1/4 of an ale cake , 1/3 of Kolsch ( can go to 1/2 if not repitching) and 1/2 for lagers. This works for me up to ~1.060 SG.
This keeps the growth rate between 3 and 5 for the most viable yeast.

 

[VikeMan]

I agree that calculators do a Great job when doing a 2 or 3 step starters. But what about when you try to propagate from very small vials. Lets say I want to propagate from 0.1g sample of my yeast bank. I need to propagate it multiple times and if each every step has an error of like 30% it then multiplies quickly. In this kind of job you would need to have a better method for cell count approximation.

I think the "errors" aren't as consequential as you are thinking. Starter pitch rates are what I would call "forgiving." What I mean by that is that if, for example, you pitch only half as much yeast into a starter wort as you thought you were, you will get more than half of the originally expected total cell count at the end. And if you pitch double the amount of yeast into a starter as you thought you were, you will get less than double the originally expected total cell count at the end. So it's somewhat self-correcting in terms of cell counts.

The following example uses Kai's stirplate growth rates, but the same phenomenon happens with any of the curves out there.

100B cells into 1 Liter wort @1.036 ---> 234B total cells
50B cells into 1 Liter wort @1.036 ---> 184B total cells (i.e. not 117B)
200B cells into 1 Liter wort @1.036 ---> 289 total cells (i.e. not 468B)

Note that if you're going to add a second step, the "error" going into that step is less (percentage-wise) than the original error. And so on.

 

[hottpeper13]

^^^, that's why I use the 15/150/ 1500 step when I need to step, it makes the most viable yeast.