This was actually the post I intended to write a few weeks ago, but then I realised there are many poorly-understood aspects of sulphites, and decided first to embark on a mini-series of posts on the subject – clearing up a few points, maximum and typical concentrations and headaches.
Health-effects aside, most people seem to regard the primary function of sulphites to be the prevention of spoilage. It kills off bacteria and yeasts that can create nasty off-flavours, and works against oxidation, allowing the supposedly unsullied essential wine characteristics to shine through. And many people who object to the use of sulphites think and argue in the same arena, saying that the off-flavours add interest and character. However, it is true that some also praise the clarity and brightness of fruit flavours in natural wine. Terroir is mustered by both pro- and anti-sulphite factions to serve their separate causes: either saying the faults resulting from insufficient sulphur mask terroir, or that those qualities are actually a reflection of terroir, because the microorganisms that cause them are an essential component of it.
What is often common to both sides of the argument is a general failure, beyond the mere existence or absence of faults, to recognise the far-reaching consequences of sulphites on the organoleptic properties of wine. This point was clearly made in a recent SevenFifty Daily article, How Sulfites Affect a Wine’s Chemistry, which I make no apology for summarising below. I encourage you to read the whole article for further details and references.
There is a lot we still don’t know about how sulphites impact on wine chemistry, but research is starting to show that they affect a large number of chemical components in wine, and its organoleptic properties. Notably, sulphites act with oxygen and acetaldehyde to affect colour and mouthfeel, and aromatic compounds are also altered significantly. For example, a Sauvignon Blanc made reductively with sulphites in stainless steel tanks has a very different aromatic profile to one made in barrels with no sulphite additions. The effects are not only wide-ranging, but long-lasting. Research with Chardonnay shows that differing amounts of sulphite cause differences in the finished wine, even after several years of bottle age
Sulphite additions early in the winemaking process are particularly important. You either allow oxidative processes at that stage by not using sulphites, or must commit to fighting oxidation with sulphites throughout the winemaking process. Counterintuitively, winemaker experiments in vinifying with and without sulphites have shown that the “without” wines tend to have better long-term resistance to oxygen. They also tend to taste older when young, but show freshness of fruit as they get older, also exhibiting softer tannins, lighter colour, and more floral notes. On the other hand, reductive notes (not necessarily a bad thing) and cassis are more likely to be associated with sulphite additions.
The author of the SevenFifty Daily article seems to argue for the pragmatic approach of letting science decide how sulphites are to be used, with the goal of creating a stable wine that has the organoleptic properties intended by the winemaker. I certainly have some sympathy with that view, but on the other hand I also fully appreciate the ideological stance that added sulphites simply do not belong in wines. Should we use them simply because they are perceived by some to be beneficial? And if so, what other additions should be permitted on the same basis?
Irrespective of what we think, the presence or absence of sulphites in wine is an undeniably important issue – it affects stability in complex ways, and sulphites are a dangerous allergen for some – but also, as is becoming increasingly clear, its effect on flavour and mouthfeel can be profound, and cannot be ignored.