(Decanter) - Many winemakers consider S02 essential for consistency and quality in wine, but there have been contentious moves to abandon its use. Are sulfites in wine harmful? And what are the effects on aroma and flavour of cutting back in the cellar? Simon Woolf takes a balanced view...

I have two bottles here in front of me. Both are Sauvignon Blanc 2012s made by Sepp Muster, a biodynamic grower in Austria’s southern Styria region, both sourced from his Opok vineyard. They taste very different: the first is extraordinarily alive, with concentrated citrus fruit and beguiling complexity; the second feels more muted, somehow more lemonade than lemon.

The difference between the two is a mere 10mg of sulfur dioxide (SO2) – or ‘sulphur dioxide’ – added after racking the second bottling. Muster isn’t just trying to prove a point – he’s one of a small but growing niche of winemakers seeking to reduce the intervention and additives used in wine production to close to zero. The spurning of SO2, typically used to prevent oxidation and keep unwanted bacteria at bay, is the final frontier in this quest. It’s regarded as lunacy by most conventional producers, and worshipped like the holy grail in natural wine circles. Why is opinion so polarised around this topic?

Are sulfites in wine harmful?

SO2 definitely has a bad rap when it comes to popular opinion. That could have a lot to do with the terse couplet ‘contains sulfites’, legally required to grace almost all bottles of wine sold in the US since 1988, and within the EU since 2005. Only those with less than 10 parts per million (PPM) are exempted, and here’s the rub – the fermentation process can produce more than that naturally, without any added SO2, meaning that even many ‘no added sulfite’ wines must display the offending words on the label.

Does this mean sulfites in wine are harmful? Probably not, at least not in the minuscule amounts found in modern wines – typically 20-200 PPM. Compare that to a handful of dried fruit, which will have been dosed with anywhere from 500-3,000 PPM. While this amount could theoretically cause an adverse reaction in an asthmatic, it’s extremely rare: sulfite intolerance reportedly affects less than 1% of the population. Sulfites are probably not responsible for your hangover either, as Andrew Waterhouse, professor of enology at UC Davis, asserts: ‘There is no medical research data showing that sulfites cause headaches.’

Given the apparent lack of health risks, why do winemakers like Muster insist on reducing their sulfite usage to a bare minimum, or even to zero? Despite its usefulness in slowing oxidation and knocking out harmful bacteria, some believe SO2 also mutes the delicate nuances that express vintage or vineyard character, as Muster proved to me so definitively in our tasting.

Purity of wine

Fellow southern Styrian winemaker Franz Strohmeier has also moved to zero-added SO2. He explains: ‘When we purchased another vineyard, I found a whole load of old bottles that the previous owners had left in the winery. We tasted them and I loved the complexity, the strangeness of the flavours in these old wines. I feel that when you don’t use sulfites, this character comes through more strongly even in young wines.’

Purity is the ultimate goal for many producers on the no-SO2 path. Alaverdi Monastery, in Georgia’s Kakheti region, simply strives to make its wine ‘good enough for God’. In the eyes of the monks, any additive, SO2 included, would render the wine impure and thus worthless. Belgian Frank Cornelissen, who has made wine on the slopes of Sicily’s Mount Etna since 2000, has the similarly straightforward goal to make ‘wine with nothing added’. His imperative isn’t spiritual, but built on the conviction that fine wine can be a totally additive-free product. Cornelissen believes that the knowledge of how to make wine without sulfites has simply been lost over time: ‘We have to re-learn these skills, which is a slow process.’

Isabelle Legeron MW agrees: ‘Growers are still learning how to make wine with no added sulfur – they only get one go at it every year! Perhaps it’s better if a grower gradually reduces the SO2 each year, rather than immediately trying to make a no-sulfur wine.’