Lindsey Greene, by email, asks: Why don’t producers put sulphur dioxide levels on wine labels? I’d be interested in a winemaker’s perspective.
Nigel Greening, owner of Felton Road Wines in Central Otago, New Zealand, replies: SO2 (sulphites, as it is referred to on labels) is present in all wine naturally, and added to most to act as an antimicrobial and antioxidant. It works by binding to the offending item – be it microbial or oxide – effectively removing the offensive presence of the problem. When each molecule of SO2 does so, it becomes ‘bound’ and is no longer able to attach to anything else. So there are two different kinds of sulphites in wine: bound SO2 and free SO2. The bound SO2 has done its job, the free is available to prevent any further deterioration in the wine. Both together are referred to as total SO2.
While the total SO2 is fairly stable, the free SO2 – the active part – constantly changes, so the free SO2 at bottling will not be the same, or even similar to, the free SO2 when you open the bottle. Because of that continuous change, regulations measure the more stable total SO2.
Permitted levels have been reduced considerably over time and organic wines have lower legal limits than conventional ones.
As Rupert Joy observes in his feature on no added sulphites wines, ‘making wines with no added SO2 is fraught with challenges. No sulphites added wines are more liable to wine faults, bottle variation and premature ageing.’
Red wines are limited to lower SO2 levels than white wines. The UK and EU currently apply the following limits for all wines sold there: reds up to 150mg/L (100mg/L organic), and still dry whites to 200mg/L (150mg/L organic).
White wines need higher levels of SO2 to protect them as they don’t have the tannins and phenolics of red wines – these compounds are also antioxidant in nature so they help protect red wines. There are separate, higher limits for sparkling and sweet wines.
But it is probably the active, free sulphur that will react with people sensitive to it. And because that continually changes, even from one bottle to another, it can’t be measured.
Hence the lack of what would otherwise be a useful ingredient labelling: frustrating for producers as well as customers.
This was first published in the July 2021 issue of Decanter magazine.