Estimating Yeast Cell Counts in Fresh Starter

[WoodlandBrew]

Great thread. I have a question about Woodlands latest blog post. Hope you don't mind me tacking it on here. Woodland discussed an equation showing the number of cells produced as a function of sg and fg. Seeing as most people pull their starters after 24 hours, are we not getting the optimal number of cells out of our starters? I assumed most reproduction occurred during the lag phase, but the numbers seem to indicate that reproduction chugs along until you hit fg.

Also, I've never really measured the sg of my starters. Do most starters hit fg after 24 hours?

It would be good to hear what others think about this as well.
(here is a direct link to the post for anyone interested: http://woodlandbrew.blogspot.com/2013/02/cell-growth-as-function-of.html )

This is something I have been investigating and am working on some posts that might help illuminate some of this. In short, it's dependent on a number of factors, but given some constraints you can get a pretty good estimate. For a starter propagated at room temperature with an inoculation rate of about 50 million healthy cells per ml and a gravity of about 10°P (1.040) It takes about 4-6 hours for propagation to begin. In the first 24 hours half of the cells are generated. By 48 hours nearly all of the cells have been generated.

Feel free to comment on the blog with questions directly related to it. I'm normally pretty quick about replying.

 

[diegobonatto]

Seeing as most people pull their starters after 24 hours, are we not getting the optimal number of cells out of our starters?

This is very yeast strain-dependent and also yeast age-dependent. Some strains grow fastest that others; and the aging of culture also influence the generation of new cells in a short time (older cells = more time in starter)

I assumed most reproduction occurred during the lag phase, but the numbers seem to indicate that reproduction chugs along until you hit fg.

Yeast division occurs during exponential phase and not during lag, which is an adaptation phase to new culture conditions. Long lag phases indicate that the yeast initial culture is too old or that starter conditions are not adequate (too much high/low temperatures, too much high/low SG of wort, etc...)

 

[CryoEng]

It would be great if this entire thread were rewritten with everyone using the same order of magnitude definitions. Preferably based on base 10 and exponentials as defined a few thousand years ago.

(10^6 as a "million," 10^9 as a "billion," etc, etc....)


Cheers!

 

[HomebrewPadawan]

Visually by volume is probably the best for most homebrewers. 1 billion per ml of slurry from a beer and 2 billion per ml for yeast from a starter. (after refrigerating for a day or so)

Good stuff! I came here looking for a simple answer, and after reading all 7 pages of discussion, I now understand that there is no simple answer! The question I had was roughly; "How many billion cells are in 1 ml of cold crashed yeast at the bottom of a starter?"

WoodlandBrew seemed to answer my question in the quote provided, and nobody seemed to contradict that statement as far as I could tell; diegobonatto stated 1-3 billion.

I guess I will start estimating visually with the assumption that a fresh starter, that has been crashed for a few days, has approximately 2 billion cells for every 1 ml of yeast.

 

[bowler]

Sorry for reviving such an old thread.

However, if we consider the stationary phase of growth for the major yeast strains, all yeast strains reach the maximum concentration of 1-3x10^8 cellls/mL of culture medium (wort, YEPD, or other rich medium that are plenty of complex nutrients). It is possible to achieve high cell numbers (above 3x10^8 cells/mL) by using special equipments (e.g., bioreactors), where the physico-chemical parameters are better controlled (pH, O2 concentration, nutrient levels, etc...).

WoodlandBrew seemed to answer my question in the quote provided, and nobody seemed to contradict that statement as far as I could tell; diegobonatto stated 1-3 billion.

It seems to me that you're calling 'slurry' the compacted yeast at the bottom of a crashed starter, and while that seems to be the case for Woodlandbrew's estimate, it seems no to be for diegobonatto's. The latter seems to be the maximum cell density in the total starter volume. Also, diego estimates 100-300 million per ml of total starter volume, not billion per ml of compacted yeast (if you decanted 90% of a 1L starter, you'd have 1-3 billion, but no mention was made of how much you decant).

There's a bit of looseness in the term 'slurry' which I think leads to this confusion - for some, slurry is very dense and has a toothpaste-like consistency, for others it's like cream; the difference in cell density between these extremes has to be huge. Because of that, I think we could, in this context, read slurry to mean 'the entire volume of the starter', as that's how these cell counts have been estimated. Once you have an estimate of cell count, it doesn't matter how much liquid you decant, as that only affects concentration, not count.

Anyway, thanks for the insight into yeast growth, it's super handy!