Repitching Yeast Cell Count

[dmaxweb]

Assuming the 16 oz jar is the slurry and the bottom 8 oz layer (50%) is yeast solids, using the Wyeast formula below, I get an estimate of 284 billion yeast cells.
8oz = 237ml
237ml yeast solids x 1.2 billion = 284 billion cells (at harvest date)
Using Homebrew Dad's Yeast Starter Calculator there are 220 billion viable yeast cells (78%) 30 days post harvest.
For someone with experience, does this appear at all reasonable?
https://wyeastlab.com/resource/professional-yeast-harvesting-repitching/Estimates of cell counts can be made using percent yeast solids of the slurry. Percentage of yeast solids per volume of slurry can be estimated by allowing a sample to sediment under refrigeration and estimating the percent solids. Generally 40-60% yeast solids will correlate to 1.2 billion cells per mL. This will vary with the yeast strain. By using this method with every brew, a brewer can achieve consistent pitch rates batch to batch resulting in a more consistent product.

 

[McMullan]

Pure guesstimates generally. Kind of ‘how long is a piece of string’ questions, when the string runs underground from point A to B and we have no idea if it runs in a straight line or zigzags all over the place. I’d test some in a smaller starter then step up.

 

[day_trippr]

This is why I stick to over-built starters. It's much easier to use a good yeast calculator to track what gets stashed in the fridge for the next starter and make adjustments if required...

Cheers!

 

[IslandLizard]

30-day old saved out slurry containing ~220 billion viable cells? I'd pitch the whole thing after decanting the liquid on top and passing the smell test.
That is if your new brew needs 220 billion cells and the slight darkness of the yeast won't taint your new brew.

If you want to make a fresh starter from it:
1. Decant the beer on top. You can save it to add some of it back, later.
2. Homogenize the slurry with a good stirring, and scoop out 2 oz (4 Tbsp) ~44 billion cells,* and make a fresh starter with that.

* It looks like you have closer to 10 oz of slurry, so each oz will contain around 22 billion viable cells.
I don't see any stratification (layers), but I'd homogenize it for all security.

 

[dmaxweb]

Planned Beer:
Bier de Garde
11.25 gallons
OG 1.072
SRM 12.45

Due to some unforseen personal circumstances, the yeast will be 66 days old when I make the starter.
Using a modifed version of dads yeast starter, the required cell count is 746 billion cells. Considering the age of the harvested yeast, the viable cell count at the date of the starter will be 337 billion cells. A conservative estimate of using both jars of slurry is 16 oz. A 3.5 liter starter yields 858 billion cells.

Comments welcome.
Thanks

Target Pitch Rate (millions/(mL × °P)	Batch Volume	Volume Units	Original Gravity (SG)	Overbuild Cell Count (billions)	Yeast Cells Required (billions)
1.00	11.25	Gallons	1.072	0	746
Yeast Details
Intial Cell Count (billions) at 66 Days	Harvest or Production Date (mm/dd/yyyy)	Viability	Viable Cell Count (billions)		Package Yeast Initial Cell Count (billons)	Harvested Yeast Solids (ounces)
568	12/2/2023	59%	337		100	16
Starter Details
Flask Size (litres)	Gravity (SG)	Pre-Boil Water Factor (liters)
6.00	1.039	1.20
1st Starter Step
Method of Aeration	Starter Volume (litres)	Dry Malt Extract Required (grams)	Inoculation Rate (millions/mL)	New Cells Created (billions)	Total Cells (billions)	Growth Factor
Stir Plate	3.50	372	49	521	858	1.55
Pre-Boil RO Water	4.20

 

[rizziot]

I second to just make a new starter from it.