There's a serious error in the interpretation of the Coor's England experiment.
Coors England developed an amazing method that is perfect for homebrewers to steal. Take a stir plate and make a starter. Add yeast and 10˚P [1.040 SG]. Aerate for 4 hours. At the end of 4 hours pitch into the wort. Do not aerate the batch. This maximizes “vitality.” Vitality is the most difficult to measure and important parameter in yeast. A standard starter is fermented out and then re-pitched. This [a vitality starter] uses continuous air and only allows the starter to spin for 4 hours. No alcohol is produced. The yeast respires but does not enter fermentation until after it’s pitched into the wort.
A batch grown starter never respires in the truest sense unless the glucose level is held below the Crabtree threshold of 0.3% glucose weight by volume. This phenomenon is due to something known as carbon catabolite repression (some researchers believe that is it due to respirative metabolic pathway saturation). Whether or not there was an appreciable amount of ethanol produced during the 4 hours that the culture was spinning is up for debate. However, all reproduction is fermentative in wort that has a glucose level that is above the Crabtree threshold. What happens is that O
2 and a small amount of carbon are shunted to the respirative metabolic pathway for the production of ergosterol and unsaturated fatty acids (UFAs).
With that said, I have preached yeast vitality (i.e., health) over cell count for a while now. That's why I preach pitching at high krausen over allowing a starter to ferment out. High krausen occurs when the cell count reaches maximum density for the medium into which it was pitched. Allowing a culture to proceed beyond this point results in reduced vigor upon pitching unless dissolved O
2 is increased due to lower ergosterol and UFA reserves. Pitching at high krausen is a part of the perceived magic in my method. It reaps the rewards of batch propagation while only paying a partial price with respect to vigor. Initial O
2 demands are lower because the ergosterol and UFA reserves are not as depleted as they would be if the fermentation was allowed to proceed to quiescence.
Topic: Yeast Pitch Rate - Pt. 2: Viable Cell Count vs. Vitality | exBEERiment Results! (Read 4222 times)
