I've been researching the limitations of yeast starters. In particular, why a starter, innoculated with a given amount of yeast cells, has an upper limit to it's size. Thus, the whole step-up thang.
So, it appears that yeast health suffers when you pitch a small innoculation into a large starter. Apparently, yeasts create a low pH during fermentation as part of the process to ensure cell wall permeability. If the initial pH is high, they have to work hard to do this. If the initial wort is strongly buffered at a high value, they have to work really hard to do this. So, when you underpitch a starter, so few cells are acidifying the wort that the pH never really gets down to where it needs to be and the cells wear out and the tires fall off of that jelopy.
Now, boiled worts have a pH around 5.0-5.3 or so. And finished beer has a pH 4.1-4.5 or so. Suppose you know that with a given specific gravity of a given DME boiled starter wort you get a pH of, say, 5.1. And suppose, by trial, you establish that a given strain of yeast lower that pH to, say, 4.4 during fermentation. So, here's my question: why not take the boiled starter wort and acidify with phosphoric acid to pH=4.4 to begin with? That's what the yeast want to do immediately anyway. Why not save them the energy expenditure? With this obstacle removed, wouldn't any size starter from any size innoculation be possible?
So, it appears that yeast health suffers when you pitch a small innoculation into a large starter. Apparently, yeasts create a low pH during fermentation as part of the process to ensure cell wall permeability. If the initial pH is high, they have to work hard to do this. If the initial wort is strongly buffered at a high value, they have to work really hard to do this. So, when you underpitch a starter, so few cells are acidifying the wort that the pH never really gets down to where it needs to be and the cells wear out and the tires fall off of that jelopy.
Now, boiled worts have a pH around 5.0-5.3 or so. And finished beer has a pH 4.1-4.5 or so. Suppose you know that with a given specific gravity of a given DME boiled starter wort you get a pH of, say, 5.1. And suppose, by trial, you establish that a given strain of yeast lower that pH to, say, 4.4 during fermentation. So, here's my question: why not take the boiled starter wort and acidify with phosphoric acid to pH=4.4 to begin with? That's what the yeast want to do immediately anyway. Why not save them the energy expenditure? With this obstacle removed, wouldn't any size starter from any size innoculation be possible?