How Much Yeast In Starter Supernatant

[SilverZero]

Does anybody have a lead on any literature regarding how much yeast is left in suspension after cold crashing a yeast starter? It's always bugged me especially when trying to design a step-starter where I really need to decant between steps.

I want to have a reliable calculation when I need to make a starter for a 12-gallon batch and I want to overbuild by 100b cells to store for the next go-around, but I want to do it in steps so I can observe good inoculation rates and also not pitch a gallon of spent starter wort.

Thanks!

 

[IslandLizard]

A qualitative approach.

Hard to tell without doing a count. With less flocculent yeasts there will be more cells in suspension longer. But take a yeast like WY1968, it flocculates like egg drop soup, even while on a stir plate or shaker.

24 hours of cold crash is recommended before decanting. But in low flocculent yeasts, I look for clarity and after 2-3 days at 38F they get decanted then pitched or ramped up. Relatively, there can't be that many cells left floating around.

 

[SilverZero]

I'm thinking about trying to do a cell count somehow. It just always bugged me that we talk about crashing a starter to get the yeast to settle out, then we turn around and say we can cold-crash a brew and there's plenty of yeast left for natural carbonation (which there totally is, based on my experience). How much are we actually throwing out?

(Also - am I "off topic" or was that in regards to your own answer?)

 

[IslandLizard]

I'm thinking about trying to do a cell count somehow. It just always bugged me that we talk about crashing a starter to get the yeast to settle out, then we turn around and say we can cold-crash a brew and there's plenty of yeast left for natural carbonation (which there totally is, based on my experience). How much are we actually throwing out?

(Also - am I "off topic" or was that in regards to your own answer?)

Although there are plenty of yeast cells left for carbonation, the total amount is quite small compared to the cake on the bottom. You can see how little this is, when crashing just the slightly cloudy starter beer liquid for a few weeks, after decanting it off the settled slurry.

Now those cells that remain suspended are the stragglers, belonging to the least flocculent population. But they are also responsible for finishing out and conditioning the beer, dropping those last few points, after the majority has gone dormant on the bottom.

I raised the "off topic" flag since I'm uttering only qualitative analysis and very little "science" in this otherwise technical forum. I don't have any research data or quoted literature. All I said is based on observations over the years. The poured-off starter beers, cold crashed for several weeks yielded very thin layers of yeast in each case. Sheer moving the vessel would start clouding the beer quickly. Again, I'm guessing, those precipitations were no more than 2-5% of the total slurry, if that much.

 

[55x11]

Although there are plenty of yeast cells left for carbonation, the total amount is quite small compared to the cake on the bottom. You can see how little this is, when crashing just the slightly cloudy starter beer liquid for a few weeks, after decanting off the settled slurry.

Now those cells that remain suspended are the stragglers, belonging to the the least flocculent population. But they are also responsible for finishing out and conditioning the beer, dropping those last few points, after the majority has gone dormant on the bottom.

I raised the "off topic" flag since I'm uttering only qualitative analysis and very little "science" in this otherwise technical forum. I don't have any research data or quoted literature. All I said is based on observations over the years. The poured off starter beers, cold crashed for several weeks yielded very thin layers of yeast in each case. Sheer moving the vessel would start clouding the beer quickly. Again, I'm guessing, those precipitations were no more than 2-5% of the total slurry, if that much.

I agree with that sentiment, and I was going to post something along the same lines, but I felt like it's just a guess-timate / wild guess, not backed up by any quantitative methods. Depends on yeast flocculation, but based on qualitative optical transparency of the wort, I would have also guessed that yeast cake of properly cold-crashed, flocculated yeast contains ~> 90% of yeast cells.

 

[SilverZero]

Thanks everyone, I'll go with that. If I can find a good microscope I'll do some cell counts of my own.