Yeast propagation

I am trying to gain a practical understanding of yeast propagation, as it relates to starters. I keep seeing something that I just can't make any sense of.

White Labs says that a single stage starter will create a 4-5 times increase in cell count, and Wyeast says it's more like 6 times, almost entirely regardless of the volume of the starter (ignoring the lower end, because obviously the yeast cannot continue once they have fully attenuated). This is for starters that are aerated and agitated.

This means that if you put 100 yeast cells into a 1.040 starter that is 100 gallons in volume, you will end up with between 400 and 600 yeast cells, and then they will just stop reproducing. Obviously, at such a ridiculously low cell count to volume ratio, the properties of the wort would be almost perfectly unchanged, and yet the yeast just stop reproducing. So here you have a 1.039999 wort with almost exactly as much oxygen in it as before you started, and for some reason the yeast in it won't do anything anymore. If you decant off the beer and repitch the yeast into a nearly identical but different 100 gallons of wort, they'll then reproduce up to 1600 - 3600 cells, and then again stop.

Does anyone understand what's going on here? Can you explain it it me?

The volume of the starter has a large effect on the final cell count. I'd assume that when White Labs/Wyeast say you get 4-6 times the number of yeast, they're probably assuming you make a 'standard' 1L starter using a stir plate or something like that.

You can see some example yeast cell count versus starter volume curves here: http://www.yeastcalc.com/growthcharts.html

I think the problem is that the scale is not linear at the very low range of yeast numbers. I read through Chris White's yeast book, and I believe if I am remembering right, was that if you pitch a large amount of yeast into a starter, you will not get as much cell division compared to pitching 1/4 the amount of yeast. I guess sort of a terminal yeast population. A volume of wort of a given OG will give you X yeast, whether you pitch .1X yeast, or .5X yeast (the time to get there will be different though) Pitching for a starter is different than for beer production. You want lots of cell division in the starter, but much less in beer fermentation

I believe this article will clear most of your questions:
http://www.maltosefalcons.com/tech/yeast-propagation-and-maintenance-principles-and-practices

diS said:

I believe this article will clear most of your questions:
http://www.maltosefalcons.com/tech/yeast-propagation-and-maintenance-principles-and-practices

Click to expand...

Thank you! ! I just happened across this thread and that article was the most easily understandable explanation of yeast handling I have read. I now know how to get more from my yeast. Thanks again and I'll have a pint in your honor. Cheers Kev