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?
This piece originally appeared on Decanter.com.
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 percent 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."
Challenges of no-sulfite wine
There are challenges. When sulfite inputs are forsworn, the risk of bacterial or microbial infection is vastly increased. Obsessive hygiene has to take their place—Cornelissen uses ionised air to clean his cellar. A more "laissez faire" attitude is required when it comes to speed of fermentation, and the yeasts that will be involved. Conventionally, SO2 would be used to see off any wild yeasts on the bloom of the grapes, so that the winemaker can inoculate with his or her choice of laboratory yeast.
Adverse effects vary in their seriousness—wines made without SO2 can have slightly wild, "funky" aromas, which prompt the same love/hate reaction as a ripe/stinky cheese. "Mousiness" is another matter—the curse of the "no-SO" winemaker, this characteristic, feral finish is undetectable on the nose, but hangs around on the palate and can easily render a wine undrinkable. Once confused with brettanomyces, it’s now recognised as a completely separate problem.
How and why mousiness develops is still only loosely understood, as wine scientist Geoff Taylor of food and drink research company Campden BRI explains: "To the best of my knowledge, very little work has been done matching the taint with the compound." He clarifies: "The (lactic) bacteria can remain dormant for years and when conditions permit (sufficiently low free SO2, warmth), they will grow. And growth is slow." The risk is increased by poor hygiene in the winery or damaged grapes. As Taylor implies, this can cause severe bottle variation—another tricky factor to explain to wine drinkers used to more consistent, industrially made wines.
Producers working in this extreme fashion tend to be small, artisanal, and loosely allied under the "natural wine" banner. There are exceptions—Stellar winery in South Africa’s Western Cape is a large-scale producer that very successfully introduced a no-SO2 range of wines to the UK’s supermarkets in 2008. No-SO winemaking has been around a lot longer—Jules Chauvet and Jacques Néauport, widely hailed as the godfathers of the natural wine movement, started experimenting in Beaujolais in the 1980s.
There’s little doubt that making wine without adding any sulfites is a high-wire act. Producers who succeed tend to be those with considerable experience. The results can be stunning in their clarity and character, but for most winemakers, the unpredictability and risks of spoilage or instability are simply too great. Keep a keen eye on those pushing the boundaries though—their wines might just surprise you.