Yeast density in sedment vs. dry yeast

[joshbuhl]

Just starting to go down the yeast rabbit hole…

I‘ve read up on the calculations, etc. that‘s all fine. I‘m just wondering what I‘m missing about understanding the pitching rates using fresh harvested vs. dry yeast.

Tl;DR
====
Why do you need about 200-300ml of slurry with 50% yeast solids to pitch into 20l of wort, whereas you only need an 11g sachet of dry yeast for the same amount? What does yeast sediment primarily consist of if it‘s not yeast cells?

Calculations
=========

A standard pitching rate often quoted is 10^6 cells/°P/ml. So about 2.4*10^11 Cells for 20l of 12°P (1.048) wort.

A slurry that settles out with about 50% solids will have about 1.2billion cells/ml in the mixed up slurry (cf. white labs, or byo.) So you‘d need about 200ml of the slurry for the 20l of 12°P wort.

Verdant IPA yeast, for example, is cited as having 5*10^9 CFU per gram, so 5.5*10^10 CFU in an 11g sachet and is supposed to be about the right amount for 20l of wort. Assuming a viable cell is a CFU, then this is only 1/5th the amount calculated above…or do you need 5 cells on average to have a colony forming unit?

 

[bailey mountain brewer]

My guess would be proteins and maybe some hop matter that the yeasts drag down with them when they floc out. But I imagine someone will respond with a more accurate answer. Oh, and possibly some dead yeast cells in there as well, though if fresh I'd expect minimal.

 

[Halfakneecap]

Just starting to go down the yeast rabbit hole…

I‘ve read up on the calculations, etc. that‘s all fine. I‘m just wondering what I‘m missing about understanding the pitching rates using fresh harvested vs. dry yeast.

Tl;DR
====
Why do you need about 200-300ml of slurry with 50% yeast solids to pitch into 20l of wort, whereas you only need an 11g sachet of dry yeast for the same amount? What does yeast sediment primarily consist of if it‘s not yeast cells?

Calculations
=========

A standard pitching rate often quoted is 10^6 cells/°P/ml. So about 2.4*10^11 Cells for 20l of 12°P (1.048) wort.

A slurry that settles out with about 50% solids will have about 1.2billion cells/ml in the mixed up slurry (cf. white labs, or byo.) So you‘d need about 200ml of the slurry for the 20l of 12°P wort.

Verdant IPA yeast, for example, is cited as having 5*10^9 CFU per gram, so 5.5*10^10 CFU in an 11g sachet and is supposed to be about the right amount for 20l of wort. Assuming a viable cell is a CFU, then this is only 1/5th the amount calculated above…or do you need 5 cells on average to have a colony forming unit?

Overthinking it. Fresh yeast slurry is super healthy and active, and, its free ( kind of ). You don't need much, but the effort of calculating exactly how much isn't really worth it when you can just pick a set amount ( 200ml, 300ml whatever you decide ) and relax knowing there's a tonne of healthy yeast in your beer.


Unless you really like maths, then feel free to play around working out an equivalent amount etc

 

[corncob]

Isn't it the water that's missing from dry yeast?

Seems like back in the before times when e rehydrated the stuff before pitching, I used to end up with about half as much (or close to the same) volume as I usually pitch when using 2 week old top cropped slurry.