The growth phase of the yeast produces esters which add to the characteristic ale flavor. Overpitching will reduce those.
Or, as I often point out, according to Dr. Clayton Cone of Danstar/Lallemand, yeast growth will reduce esters. That's been my experience with slurries.
Thanks for the link Denny.
My take on it . . . this is an important sentence. "Ester and other flavor component production or synthesis is a complex subject because there are so many variables taking place at the same time"
It's very complex, and because of that I am not convinced that the effects he mentions can be entirely put into growth+/growth- bins.
I think this is important too: "I am also sure that there are beer makers that have experienced the very opposite with each of the variables." Several of the conditions that he says "inhibits or slows down yeast growth" I call "stressing your yeast", for example "low nutrient, low O2", and we both agree that it will increase ester production.
There is plenty of evidence that ester formation increases with temperature, but I don't know that those studies differentiated between high start vs high finish temperatures so I'm not going to comment on that.
I think the problem I'm having with his statement is that we know that ester production comes after glycolysis, but we also know that glycolysis is an important part of amino acid synthesis, for example valine and leucine. Those are required for all protein synthesis. You can supply them to the yeast, which explains why nutrients reduce ester formation. So inhibiting amino acid production reduces ester formation, however, that doesn't mean that growth
is inhibiting ester formation. One could just as easily argue the other side of the coin: since growth requires proteins, and protein synthesis requires amino acids, and amino acid synthesis produces esters, growth produces esters.
I think the reality is that "growth" is too macro of a level to discuss ester formation.
I refer you back to his first sentence: "Ester and other flavor component production or synthesis is a complex subject because there are so many variables taking place at the same time"