“You’re choosing either to create a pool of antioxidants in the wine or to have wines where the oxidative processes have already taken place. “The choices made on this front, especially at the start of the process, will lead to a completely different molecular fingerprint in the wine, and to very different trajectories for the wine’s evolution in bottle,” says Gougeon. The differences in chemical composition linked to sulfite additions persisted even as the wines evolved in bottle. A study published in Analytical Chemistry in July 2015 by Gougeon and his colleagues showed that “memories” of sulfur additions persisted in Chardonnays that had undergone three different levels of sulfite additions-even after several years of bottle aging. Not only are the effects of sulfite-related decisions wide ranging but they are long lasting: Using the same grapes to make different wines with different sulfite regimens will cause the bouquet, mouthfeel, and color of each wine to differ in the short term and the long term. The way sulfur is present in the wine-whether bound in those various compounds or available as free SO2-also affects the way chemical reactions will develop during and after vinification. Sulfur-related reactions will affect the formation and prevalence of many other compounds, like aldehydes, which are linked to the appearance of oxidative character amino acids, which are involved in the development of various polyphenols and aromatic compounds peptides and fusel alcohols and things like hydrogen sulfide (H2S), which can produce reductive off-flavors like rotten egg, and various polysulfides. Winemaking and barrel aging with little or no sulfur added, on the other hand, will sharply reduce the presence of these thiols, leading to a set of aromas that will trend more toward mineral, citrusy, or tropical notes. For instance, in Sauvignon Blanc, greater sulfite additions will favor the presence of thiols, sulfur-based compounds that provide aromas like grapefruit and passion fruit, especially if the wines are vinified using a reductive approach-such as in stainless steel tanks, with very limited contact with oxygen. The type and prevalence of aromatic components like esters and thiols are also affected. Notably, SO2 acts in combination with oxygen and/or acetaldehyde to affect color and mouthfeel. Phenolic compounds like tannins and anthocyanins-and the way they combine at the molecular level-are modified by the sulfite levels in fermenting or aging wine in a variety of ways that are still not fully understood. Using or eschewing SO2 at various stages of winemaking has effects on an array of chemical compounds in wine. “What research is increasingly showing,” says Régis Gougeon, a professor of enology at the University of Burgundy in Dijon, France, who has been studying the subject for well over a decade, “is that changing sulfite additions-or eliminating them-means modifying the organoleptic characteristics of the wine and its whole chemical profile.” Scientists and winemakers are becoming ever more aware of the multifaceted effects of sulfur in wine chemistry. Indeed, sulfur, the “S” in SO2, is a highly reactive element because it has six valence electrons that enable it to chemically bond to other compounds in many different ways, contributing to the formation of a broad range of molecules. While SO2 is effective in that manner, it also does quite a lot more, especially in the early stages of vinification, when it becomes part of numerous reactions and transformations. Traditionally, sulfur dioxide (also known as SO2 or sulfite) has been thought of as a relatively innocuous preservative agent, acting mainly as a barrier against oxidation and undesirable bacteria. Chemistry may be more useful than ideology for resolving those disputes, and on that front, scientific research is increasingly showing that sulfites have a very wide set of effects on wine’s aromas, mouthfeel, structure, and development in both the cellar and the bottle. The emergence of natural wine and the strong viewpoints that sometimes come with it-or against it-have generated endless arguments about sulfite additions and their effects on wine.
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