Enology: Oxygen and Oak

March 9th, 2006

Given that the topping regimes are beginning with the ‘05, I want to revisit the topic of oxygen and oak (previous entry). It is taken for granted that aging wine in oak not only imparts yummy complementing flavors to the wine, but also is an excellent way to slowly expose the wine to O2. Now, I do not doubt that the wine in oak is exposed to more O2 than the wine in a sealed stainless tank, but is it really true that the O2 is coming into contact with the wine through the staves? Before answering let me say that this issue is beyond taken for granted, what I am about to do is commit enological heresey. For most this discussion is useless because it is already settled. Not only that but in their minds there was nothing to ’settle’, it just is, a fact, a priori. Back to my answer: no.

When barrels are topped and tightly bunged a vacuum is typically created as the wine moves into the staves via capillary action. The existence of the vacuum (heard each time you remove the bung) is the strongest evidence that air is not moving into the barrel (whether through the staves or bung hole). If air was moving in it would fill the space created by the wine moving outward, negating formation of a vacuum. The strength of the argument for oxygen passing through the staves is based on diffusion and/or permeability theory using Fick’s or Darcy’s law respectively. The problem is that the stave is not a uniform ‘membrane’ for air to pass through making the calculation of gas flows almost impossible to estimate due to the variation in the size and number of channels.

So am I saying that no oxygen moves into barrels during aging? No. O2 most certainly does move into the barrel, just not through the staves. Most of the O2 that moves in is going to occur each time we top the wine and in a case where the bung is loose thus allowing air to fill the headspace. Additionally, the amount of O2 entering each time we top is probably negligible compared to a racking. Of course this begs the question, do we need to top as frequently as we do if very little air is moving into the barrel. Well, in theory, no. If the bungs are very tight and a vacuum typically forms, then it means your headspace is not filled with O2, so why top it. I’m not sure its a risk I want to take until I can “tight bung and roll” (which I won’t get into now).

Leave a Reply

You must be logged in to post a comment.