Speyedr wrote:Agreed, but you get the added benefit of gas exchange, don't you? When you do a starter on the stirplate no one has recommended adding O2. But if you do one in a growler they say shake it up when you walk by...
I believe that it is recommended to add O2 at the beginning of the starter even when using a stirplate.
As far as O2 exchange...while the main purpose of the stir plate is to keep the yeasties up in the wort, the vortex does cause more air exchange.(not that much though) That being said, when water or any other liquid is exposed to open air there is some natural gas exchange AT THE SURFACE TO AIR INTERFACE. When the stir plate creates the vertex it is doing two things to promote air exchange. 1. It increases the surface area of the liquid that is interfacing w/ the air. 2. One can only change so much o2 between liquid and air. What is happening is o2 in the air and the o2 in the liquid are trying to reach equilibrium. Once that reaction gets closer and closer to happening the change of o2 slows down to a stop. The greater the difference in o2 level the faster the exchange wants to go. So, if you constantly stir the liquid you are keeping the difference in o2 levels in the two substances as far apart as possible, therefore keeping the exchange rate as high as possible. A common misconception is that the vertex "sucks" o2 into the starter and I believe this just isn't the case. The vortex just keeps the natural o2 exchange happening as fast as it can, while offering the largest amount surface are to exchange o2 w/ the air.
My question is this. Once the yeast start producing co2, isn’t all the air just pushed right away from the surface of the starter? co2 is heavier than air right? So if this is true then isn’t that another reason to not let your starters ferment out? This is assuming that the yeast do not produce co2 during reproduction. Is that even true?
Anyway, that’s my input
