I recently bought a 6 1/2 gallon carboy where I buy my 6 gallon pails of wine juice. Don't ask me why he sells 6 1/2 gallon carboys or why I bought it. However, after realizing this is not going to work with a 6 gallon pail of juice I returned it. The vendor had two of the larger carboys on display from his 6 gallon pails. The head space was about 6-8 inches from the top. The wine was obviously less than 6 gallons after racking. He said it's fine like that and was going to leave it like that for for 6 weeks and then bottle it. I have always topped off my carboys. So is a limited amount of exposure to oxygen acceptable? Why do we have to be so cautious about oxygen and headspace? I should note that this juice is pasteurized - I don't think that makes a difference.