I've read a bunch about comparisons done with starters where they either just sat, were swirled on occasion, or used a stir plate. The advantage of a stir plate and swirling is, from what I read, keeping the yeast in suspension and mixing in more oxygen. I have also seen the many posts by people stating that they use a loose foil cover so that oxygen can get in. This is where I have a question - how does the oxygen get in? CO2 is heavier than O2 and I would think it would keep the O2 away from the wort. People that have open fermenters or that knock an airlock off for a moment say that that the CO2 being heavier than air is what keeps a protective layer over the wort. Also, the continuous production of CO2 by the starter is constantly displacing gas nearest the opening - out flow with no room for in flow.
Has anyone done any or read about any studies on the amount of oxygen that is flowing into starters by swirling or using a stir plate? I am starting to wonder if the oxygenation we are giving starters is all coming from the initial blast we give it at the beginning (by injection or shaking) and that the benefit gained from stiring/mixing during fermentation of the starter is strictly from the yeast staying in solution and not being allowed to flocculate.
Kegged: Barrel Aged Imperial Sweet Stout, Rye Ale, Old Ale
Secondary: Barrel Aged Imperial Sweet Stout On Cherries
Primary: Fruitcake Old Ale, RIS
Next Up: White IPA
Projects: Brutus Strut-stand (Done), Freezer Conversion (Done), HERMS (Done), Lager Fermentation Mini-fridge Extension (Done)
Drinking: Great Lakes Edmund Fitzgerald, Fuller's 1845, Founder's Dirty Bastard, New Glarus Moon Man, Fat Head's Hop Juju