Growing Huge Starter

[wingnutbrew]

I understand, for the most part, about the process of making a large starter from a small amount of yeast. My question is that if in the stage where the yeast are multiplying they are not fermenting the sugars out of the wort then why does the wort have to be discarded and new wort be added to begin the cycle again?

Or maybe another way to ask it would be what are the yeast taking out of the wort during the initial stage before fermentation?

 

[brewmeister13]

If I'm remembering this correctly, before fermentation is the growth phase. Yeast are taking all of the oxygen they can get and using glycogen reserves. They then begin to take up nutrients and sugars (they take sugars in a specific order) from the wort. One thing I remember reading was that yeast aren't moving from one phase to the next all together in a nice neat set of organized steps. I think I remember that at any given moment all phases are occurring until oxygen is depleted and fermentation is complete. I could be wrong about that last part though, too many books to look back through to double check my memory though.

 

[duboman]

The purpose of a starter of any size is to reproduce cells up to proper pitch rate. Most importantly is doing this so you are growing the healthiest yeast possible.

During the first phase the yeast consume the o2 and then begin to consume the sugars in the wort and thus, your starter becomes a very low gravity beer.

Not sure where you heard that the yeast don't consume the sugar of the starter wort as they do as part of the process so yes, you then ideally crash and decant to only pitch the yeast