Premature Oxidation

Sometime in the late 1990s, people who had been buying white Burgundy for decades began opening bottles that were wrong. Not corked: corked is unmistakable and smells of wet cardboard. These were deep gold instead of pale, and instead of citrus and stone they smelled of bruised apple, honey and something faintly sherried. The fruit was gone. The wines were six or seven years old, which for a premier cru Meursault ought to be adolescence.

It happened across producers, across price levels, and across a run of vintages from about 1995 onwards. It hit the most expensive white wines on earth. And it was maddeningly random: two bottles from the same case, stored side by side, could differ completely. The trade named it premature oxidation, then shortened it to premox, and spent fifteen years failing to find a single cause.

Several changes had happened at once, which is the worst possible situation for diagnosis.

Cork was the first suspect and remains the leading one. The period coincided with rapid growth in demand, changes in cork processing (including washing methods introduced to reduce taint) and, by broad agreement, a decline in average cork quality. Cork's job is to admit a very small, very consistent amount of oxygen over decades. A cork that admits more will oxidise the wine early, and a batch of corks with varying porosity will produce exactly the bottle-to-bottle randomness that was observed. That randomness points at the closure more strongly than at anything else, because everything upstream is shared by the whole cuvée.

But other things had changed too. Free sulphur dioxide levels at bottling had fallen, as part of a general movement towards lighter handling; sulphur is the wine's principal defence against oxygen. Presses had become gentler, extracting fewer phenolic compounds, which also act as antioxidants. Lees stirring had become more aggressive in pursuit of richness, and lees consume oxygen and reducing capacity. Harvests were riper. Any of these could reduce a wine's resistance; together they could leave a wine with no margin, so that a slightly porous cork finished it.

The response was empirical rather than scientific: change everything plausible. Producers raised sulphur at bottling, changed cork suppliers, pressed more gently, reduced or abandoned bâtonnage, and a substantial number moved to DIAM. A technical closure made from cork granules cleaned with supercritical carbon dioxide and bound into a plug with specified, measurable oxygen transmission. Some went further, to wax seals or glass stoppers. Recent vintages are widely held to be far more reliable, and the bottles from the worst years are now mostly drunk or written off.

But it was mitigated, not solved. No controlled study ever isolated the cause, and buyers of white Burgundy still approach older bottles with an anxiety that no other fine wine requires. That residue of doubt is itself part of the damage.

The episode is worth sitting with because of what it says about ageing. A grand cru vineyard, immaculate farming, forty-year-old vines and a careful cellar can all be undone by a piece of bark that cost a few cents. Ageing is a property of an entire system (fruit chemistry, sulphur management, oxygen ingress, storage temperature, the closure) and the romance of terroir tends to obscure the plumbing. Premox was an expensive, decade-long demonstration that the plumbing decides.