When making a yeast starter from a slurry how do I know what my initial cell count will be?

[mgillard1976]

Title says it all. Do you typically assume a certain number of cells per ml?

 

[Qhrumphf]

Option one, you can estimate it. Some calculators (Mr Malty for example) can get an approximate viable cell count based on slurry density, non-yeast solids, and harvest date. Problem is then you're using someone else's math (for example many say Mr. Malty is overly conservative with both growth and viability loss over time, the defense of that being that a conservative figure is safer as an overpitch is more forgiving than an underpitch). If I recall though, you may have to use multiple calculators for that, since the ones with repitching from slurry calculations don't also also custom input for starters initial cell counts. Then again been a LONG time since I've used one of the calculators so that could have changed.

Option two is use a microscope, hemocytometer, and some methylene blue and count em yourself and then there's zero question about count and viability. https://www.whitelabs.com/beer/cell-counting-viability-testing

 

[LLBeanJ]

Title says it all. Do you typically assume a certain number of cells per ml?

I don't have the counting equipment, so I estimate. I go with 1-1.5B cells per ml. If the batch is more hop heavy, I'll use the low end, otherwise I use the high end. You will be pretty safe using those values.

 

[rodwha]

I’ve never concerned myself. It seems most people talk about an over/under pitch doesn’t make a big deal until you get on some larger commercial scale.

I typically make a 5.25 or 5.5 gal batch. I use yeast that’s no older than 3 months. I make a 1.5 qt starter using 6 oz of DME using 2/3 for the beer and saving the other 1/3 placing that date on the jar.

Granted most of the time the yeast has been within 2 months, but I’ve not had an issue and I’d guess I’ve brewed somewhere around 60 beers or so.