I have two yeast starters going on my two homemade stir plates. The stir bar or the stir plate for one of them is malfunctioning and I can not increase the speed enough to get a vortex going. It is simply keeping the yeast in suspension.
On the first yeast starter I ever did, I would put an aeration stone in the flask every 5 hours, in addition to the oxygen obtained through the vortex of the stir plate. I believe I read somewhere online that too much oxygen could be a bad thing, and I haven't done it since.
What is the proper way to supplement a yeast starter with oxygen via an aeration stone?