Fermenter volume vs. batch size

[ilan]

Hi everyone,
I'm just about to run my very first batch and while everything seems pretty much in order on paper, I am wondering what is the impact of a largely overdimensioned fermenter on a much smaller batch size: 25 liters vs. 5-6 liters targeted batch. Is that too much air that would oxidize the batch? or will the carbon dioxide produced during fermentation form a protective layer between the batch and the air in the bucket?
Thanks

[twhitaker]

Should be fine, they used to ferment in open vessels back in the old days.  Generally you want more volume than that though, but I find allowing 8 inches of headspace at least makes blow off requirements no longer necessary. Just dont plan to leave it in there for too long . Once it has completed its activity and cleared up  bottle or keg it.  Then it can age with appropriate seal and minimal airspace.