How Little Sulphur Is Too Little

Sulphur dioxide does two jobs in wine and has done them for centuries. It binds oxygen, which prevents the wine browning and losing its aromatics, and it suppresses the microbes that would otherwise convert it into something else. A few tens of milligrams per litre is enough. The portion still chemically available is called free SO2, and it is the part actually standing guard; the rest has already reacted with something.

Cutting it is the single most consequential decision available in a modern cellar, because everything that makes low-sulphur wine exciting is also what makes it unstable. Removing the protection does not make a wine purer in any straightforward sense. It removes the protection, and whatever happens next happens.

What usually happens first is brettanomyces. It is a yeast that survives conditions ordinary wine yeast does not, and it produces compounds that smell of barnyard, plaster, clove and sticking plaster. At trace levels it divides tasters sharply and both readings are defensible: some people read it as savoury complexity, some as a fault, and neither is being unreasonable. Above a threshold there is no argument at all, and the wine smells of a stable. A cellar running low on sulphur has to be scrupulously clean to keep it out, which is one reason the best low-intervention producers have conspicuously immaculate cellars.

The other characteristic outcome is reduction, which is the mirror image of oxidation: not too much oxygen but too little, producing struck-match, rubber or drain aromas. Low-sulphur cellars meet it constantly, because protecting a wine from oxygen without sulphur generally means excluding oxygen altogether. Mild reduction often blows off in the glass and a number of drinkers actively like it. Severe reduction does not blow off. Telling the two apart in a young wine is genuinely hard, and a good deal of confident tasting-note writing pretends otherwise.

The honest summary is that cutting sulphur raises variance rather than quality. It lifts the ceiling: the best low-sulphur bottles have a directness and lift that protected wine does not quite manage, and anybody who has met one knows why the category has adherents. It also drops the floor a long way, and two bottles from the same cuvée can differ noticeably. Whether that trade is acceptable depends almost entirely on whether the drinker gets to choose their bottle or is simply served one.

Transport is where the theory meets the invoice. A wine with no reserve of protection is entirely dependent on the cold chain, and a week in a hot container can finish it. This is why many low-sulphur producers sell locally and ship reluctantly, and why importers who handle the category properly pay for refrigerated freight. A bottle that was superb in the cellar is not the bottle that arrives if nobody paid for that.

It also explains a conversation that happens regularly and in which nobody is lying. A restaurant returns four bottles of one cuvée as faulty; the grower says all four were sound when they left. Both can be right. Bottle variation is a known feature of unprotected wine, and so is sensitivity to warmth in transit. That is a real cost of the style rather than an accident of it, and it is why the argument about sulphur is finally an argument about who carries the risk: the producer, the importer, the restaurant, or the person who ordered the glass.