evelopment of beautiful “Bottle Bouquet” is a primary goal of long term wine cellaring. It’s well established that bottle bouquet requires the absence of oxygen to develop. Wine would die early and fail to age properly in bottle (being unable to develop bottle bouquet) if corks were to breathe air, so it’s a good thing they don’t. Although sound wine corks don’t breathe, I admit they have a confusing way of showing it. Just imagine: corks never inhale, and they exhale only once (right after bottling). The exhale is slow, lasts a few weeks and is only a partial one. To understand this, look at the cork structure.

Corks are cut from the thick, non-living bark of cork oak trees, Quercus Suber, which grow naturally on land around the Mediterranean Sea. The bark of cork differs from that of other trees in that most tree bark contains fibers running lengthwise like the wires in a cable. Cork bark does not. Rather, cork bark is made up completely of myriads of tiny cells, each imprisoning within its walls a microscopic bit of air. Those bits of air are natural, having been imprisoned there as the bark cells grew on the tree. There are about 200 million minute cells in a one inch cube of natural cork, the cells averaging 1/1000 inch in diameter. Each cell is separated from its neighbors by a thin, thread-like but extremely strong membrane of resinous materials which binds the cork cells together. Just over 50 percent of the volume of a piece of cork is this captive air within the tiny cells.

Remarkably, each cork cell is tetrakaidecahedral (14 sided). The math majors among us realize that it takes 14 sided bodies to exactly fill a space with uniform bodies of minimal surface dimensions and without interstices. The cells snug together perfectly to fill the whole space without leaving any voids at all. A piece of cork is completely cellular with no “empty” spaces between the cells. This seems to me a major reason why corks don’t transmit air: the path through a cork is just too tortuous for significant numbers of gas molecules to work their way through, even if pressure is applied to one end of the cork.

Champagne Proof Positive

Champagne people have known since Dom Perignon that carbon dioxide gas doesn’t escape from a bottle of bubbly during many years’ storage even though the pressure inside a bottle of Champagne or Sparkling Wine is as much as 5 atmospheres (75 psi.) If CO₂ gas can’t get through a cork and out of a bottle with 75 psi of pressure pushing on it, how could O₂ get into a bottle with only a few ounces of outside pressure pushing it? CO₂ molecules are physically larger than O₂ molecules - but only a little larger, and that factor doesn’t explain it. If cork contained longitudinal gaps, voids or fibers, the escape route for gases would be easier. But that only happens with damaged corks (read: cheap) which might contain cracks. Since cracks in corks are usually obvious, proper inspection and grading eliminates defective corks prior to their shipment to a winery.

Let’s suppose a newly bottled wine contains a trace of air or oxygen (O₂). Fortunately, wine contains a few parts per million (ppm) of SO₂, which protects wine from oxidation by the O₂. The SO₂ and O₂ destroy each other as the two react whenever they make contact. The chemical reaction between them in wine is complex but this simplification doesn’t change the gist of the story. Winemakers have long noticed that the free SO₂ content of newly bottled table wine diminishes by 5 or 6 ppm within the first month after bottling, then by only 1 ppm or less in the months after that. The accepted explanation is that this initial loss of SO₂ is due to the pickup of O₂ by the wine as it passes through pumps and hoses while moving from the bottling tank through the bottling operation. The SO₂ is lost from the wine by reacting with, and removing, any O₂ that gets in.

What if the wine was oxygen-free at the time of bottling? There should be no loss of SO₂ since there was no O₂ to remove. At Beaulieu Vineyard, I ran into a stone wall that was hard to believe at first: wine lost this SO₂ following bottling even when we carefully excluded air from pumps, hoses and equipment. That is, virtually no air had entered the wine prior to bottling, yet we still had that same loss of SO₂ in the first month after bottling. Somehow oxygen was entering the wine in the first weeks after bottling to the extent that 5-6 ppm of SO₂ was used up in getting rid of that O₂. Where the !@&# did that O₂ come from?

Another mystery: many wines containing traces of H₂S (“rotten egg” smell) tend to lose the H₂S immediately after bottling with corks but not with screw caps. Obviously, O₂ enters the bottle and oxidizes the H₂S, getting rid of it. But where did the O₂ come from? How could O