I have been making red wine from grapes for several years. I have been doing the aging in 5 gallon glass carboys with oak sticks. I recently obtained an oak barrel which I am going to use to do some of the aging in. This is where the alternative theory part begins. When wine is stored in oak barrels the wine slowly evaporates through the oak, which results in an air space in the oak barrel. It is recommended that you 'top off' the barrel periodically. Anyone who makes wine (or beer) knows that oxygen is very bad for this process. It is true that a small amount of oxygen is beneficial to the taste of wine (that is why for unblended wines it is good to let them 'breath'). But if you have a bottle of wine that is left out over night (even if the cork is replaced) the flavor degrades. So anyway from what I have read the going theory is that air space in a barrel is not big enough to cause a degregration of the flavor. My alternative theory is that there really isn't any oxygen in the air space of the barrel. I think that as the wine diffuses out through the oak and the air diffuses in through the oak the wine molecules oxidize and consumes the oxygen so that essentially there is only nitrogen that makes into the oak air space. Not sure how to test this since even if oxygen made it into the air space it would be oxidized by the wine in the barrel so there would not be any oxygen in the air space in either case. What do you think? Am I missing something obvious or subtle?