It doesn't matter at all. As long as the stir bar is moving and the yeast and wort are mixing, it's fast enough. Contrary to the myth, a bigger vortex gains you nothing.
Quote from: denny on January 12, 2015, 01:02:04 pmIt doesn't matter at all. As long as the stir bar is moving and the yeast and wort are mixing, it's fast enough. Contrary to the myth, a bigger vortex gains you nothing.So it's not so much the aeration as it is the mixing that gets you the good yeast growth of a stir plate vs. intermittent shaking, etc.?
The vortex makes no difference as mentioned, as for the aquarium pump idea, not sure. While o2 is beneficial for the starter I'm not sure if it wouldn't be detrimental pumping into the starter for the 48-72 hours it would take to ferment out. Maybe someone else has a thought on that?
JT, you were given bad information. Adding oxygen after fermentation is complete causes yeast cells to enter diauxic shift where they consume ethanol as their carbon source. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3133784/"The preferred source of carbon and energy for yeast cells is glucose. When yeast cells are grown in liquid cultures, they metabolize glucose predominantly by glycolysis, releasing ethanol in the medium. When glucose becomes limiting, the cells enter diauxic shift characterized by decreased growth rate and by switching metabolism from glycolysis to aerobic utilization of ethanol. " In the absence of post-fermentation dissolved oxygen, yeast cells enter a quiescent state after storing glycogen. The cells also undergo morphological changes where their walls thicken in preparation for quiescence, which is why one does not want to allow a starter to ferment out before pitching it.
i presume everything you say is factual. but the question that lingers, is that if making a starter and pitching or even attempting to significantly slow fermentation by cold crashing is the preferred or optimal way to do it, how can it be explained that good results are obtained by letting a starter finish, cold crashing, decanting and then pitching? seems like a lot of us have done it this way over the years and for me personally, I cant say its caused any issues. just curious I guess.