What's the best way to estimate yeast count w/o a microscope

[DownHillonWater]

I make 3 L yeast starters on a stir plate with 300 g DME and 1 g yeast nutrient. I let the starter go 3-4 days and then cold crash for 2 days I use half the yeast immediately and store half of the resulting yeast cake in the frig in a pint Mason jar. After settling more than a week I usually have 60-70 mL of very compact yeast under an equal amount of supernatant. There seems to be a consensus that such a yeast cake is ~4 billion cells per mL or about 240-280 billion cells.

Do the yeast experts out there see this as a reasonable way to estimate yeast count for those of us who don't have a microscope?

 

[Queequeg]

You have a few options, first simply weigh the Surry then use a pitch rate estimator like brewers friend. Or you can count the yeast, either by serial dilutions and plate count or by serial dilution, staining and counting using a microscope and hectocytrometer.

In most instances an estimate will be sufficient, only if you can making batch after batch and you want repeatability do you need to count.

 

[Queequeg]

To clarify by plate count I mean subculturing onto selective agar.

 

[PoppinCaps]

Unfortunately the size and compaction of different strains varies so widely, volume of slurry is vague at best. As well as final cell count in a starter, they each like to propagate to slightly different densities. Slurry from cake off of a beer is even worse with hops and break material mixed in. Without a scope or agar plates, your best bet is to create a protocol that works for you (X liter starter plus settling time/temp), and repeat that.

 

[Queequeg]

even doing a plate will only give you colony forming units and not viable cells. A cfu can be anywhere between 1-1000 viable cells, assuming you are within the countable range of the plate where you don't competitive inhibition of colonies.

The only real why to count, is to err count them. You can estimate with a photo spectrometer as well, not that helps OP.

 

[DownHillonWater]

@Queequeg @PoppinCaps Thanks for all the helpful feedback.

Question: Are there any good references out there on strain specific growth and compaction? Happy to dig into scientific literature if that's what it takes. I'm becoming a little fascinated by this aspect of brewing....

 

[bierhaus15]

Dunno if this helps or not, but I found that a smack-pack or WL vial in a 1000 ml stirred starter of 10-11P oxygenated wort usually netted around 5-600 million cells per ml. For 5.5 gallons of 12 P wort pitched with 0.5 m/cells/ml per degree plato... you'd need around 250 ml of slurry. This is based on a dozen or so starter measurements.

Thick cake slurry (minus trub/hops) has often been about a billion cells per ml, or more.

Typically, I won't pitch less than 0.750 m/cells/ml/plato and lager fermentations are about double that.

 

[Queequeg]

@Queequeg @PoppinCaps Thanks for all the helpful feedback.

Question: Are there any good references out there on strain specific growth and compaction? Happy to dig into scientific literature if that's what it takes. I'm becoming a little fascinated by this aspect of brewing....

I doubt it, if you find anything please remember to share your findings