When I make starters lately they are usually 1.5 liters minimum up to 3.2 liters. My concern is gas exchange (which I understand is a huge key in growing healthy yeasts during a starter) is not occurring as well in my larger starters. I used to get a visible whirlpool/vortex thing on the top level of the wort in the smaller starters on my stir plate which I would assume pulls air in. However, now that I have larger starters and the same stir bar I don't get that visible vortex anymore. Does this mean air isn't being pulled in and thus rendering my stirplate useless? Would a larger stir bar remedy this issue?