I wouldn't worry about air getting in prior to fermentation. It's the cold crashing just prior to lagering or packaging where I don't particularly want ANY O2 getting in there.
I agree with dstar26 though... a CO2 blanket is an imaginary security blanket. CO2 and O2 don't repel each other, they play nice just like what happens in the atmosphere.
I agree with dstar26 though... a CO2 blanket is an imaginary security blanket. CO2 and O2 don't repel each other, they play nice just like what happens in the atmosphere.