Is sulfur in wine evil? Dangerous for human health? Should it be avoided altogether? For a rather common antioxidant and sterilizing agent, sulfites sure generate an incredible amount of attention and worries.
In the last few years, sulfite-related health concerns in the public have even helped spur a whole sub-category of sulfur-free wines made through a variety of enological techniques meant to help stabilize the wine without using the “demonized element,” as natural wine writer Alice Feiring put it in a recent article. Although sulfite-related health concerns are often overstated–sulfites’ responsibility for “wine headaches” is greatly disputed, for instance, and drinking a full bottle per day of most wines would still have you well below the recommended maximum daily intake–market demand has grown. This has led to the creation of higher-volume brands of no-sulfur wines like Naturae by Gérard Bertrand, in Southern France, or even the production of special lines of no-sulfur wines aimed at supermarket chains.
The sulfite spectrum
We’re seeing these product lines appear in the general market because the use of sulfites in wine has been one of the most hotly debated subjects in the world of wine over the last 10 to 15 years. With the growth of the natural wine movement, in particular, a small segment of the wine world has been decrying the use of sulfur as something almost purely negative. In turn, others have replied that sulfite-free wines can only be bacterial and problematic, and attacked the natural wine movement as promoting faulty wines.
The truth is, as most often, somewhere in the middle. Clean and delicious wines can be made without sulfite additions, but it is a tricky business that demands well-thought-out oxygen management in the cellar, as shown notably in an article by the Nomacorc enology team published in the Revue des oenologues. At the other end of the spectrum, wines can also be marred by excessive use of sulfur, which can affect and mask fruity aromas, among other things.
In the world of natural wine, most producers will point out that the quality of the viticulture is a much more important part of the process than the question of sulfite additions per se, and a lot of natural winemakers will use moderate amounts of sulfur just before bottling to ensure stability in the wines as they are shipped to far away markets. Bigger producers have also been looking to fine tune–and generally reduce–sulfite additions to encourage better aromatic expression and to avoid reductive issues. And whatever the style of wine made, sulfites are used pretty much everywhere as a cleaning and sterilizing agent for winemaking equipment, tanks, barrels, and bottles–and they also occur naturally in wine as a byproduct of fermentation. In other words, there is certainly a consensus in the winemaking community that sulfites can play a useful role in wine–or at least in the cellar.
However, that doesn’t mean that sulfur is just a stabilizer and sterilizer or that it just acts as a barrier against oxygen. Its impact on a wine’s chemical composition is much deeper than preventing the formation of bacteria–or things like matchstick aromas, when higher amounts make it directly perceptible. During vinification, it is anything but neutral, on that front.
Adding sulfites in the early stages of winemaking, in particular, can have a whole range of effects on the must and wine. In his book Wine Science: Principles and Applications, Ronald S. Jackson points out things like their effects on the potential browning of wine (by affecting the oxidation of caftaric acid), the extraction of phenolics from oak or grape skins into the wine, or the color of red wine (through a bleaching effect when sulfites combine with phenolics or through its interaction with acetaldehyde or hydrogen peroxide). Sulfur dioxide also breaks down thiamine or inhibits (or destroys) oxidation enzymes, which affects processes during fermentation and aging, and it reduces the presence of volatile acidity (because acetic bacteria need oxygen to prolifer).
In a series of papers on oxygen and sulfite additions to Sauvignon Blanc, South African researcher Carien Coetzee noted a number of effects of SO2 additions on the composition of this white wine, especially as sulfite additions have a protective effect on volatile thiols that provide the variety’s signature aromas. The levels of “higher alcohols,” glutathione, esters, and fatty acids were also affected in a variety of ways, depending on whether SO2 additions took place in combination with higher or lower exposure to oxygen. Research by Vicente Ferreira, of the University of Zaragoza, has also shown that sulfite levels are closely related to the formation and presence of precursors of oxidation (notably certain aldehydes) in wines.
Such changes in wine composition are also very durable. Effects on phenolic components and aromatic components last for years and years, meaning that the bouquet, mouthfeel, and color of the wines can differ for the short, medium, and long term. As mentioned in a recent article on this blog, a metabolomics study by Régis Gougeon and his team showed that “memories” of sulfur additions persist after years of bottle aging.
Is the resulting wine better or worse, when you’re adding sulfites at various stages of vinification? That’s a difficult question to answer, and much of it is a matter of taste. It could be said, however, that if you’re looking to express the intrinsic qualities of the grapes and the terroir, significant sulfur additions will alter that expression. And it is clear that, from a chemical standpoint, different regimes of sulfite additions will result in different wines, even if using the same grapes.
Whatever your opinion about natural wines, their proponents do have a point: Sulfur does change the expression of the grapes. Sometimes, philosophy can go hand in hand with chemistry.
Photo credits: FreeImages.com/EmmaPayne and Wine Turtle.