Simple Sulfite Wine Chemistry

There is no denying: sulfur dioxide (SO2) can be a source of headaches for winemakers — even without drinking any wine. Why does SO2 continue to be such a perplexing and confusing topic? All too often I am asked to help out with problems that seem completely unrelated to sulfite additions, though these are at the root of many problems when not used correctly or at the wrong time in winemaking. Much has been written about the role of SO2 as an antioxidative and antimicrobial agent in wine. Here, we will take a fresh look at the chemistry of SO2 and sulfites but with a focus on interactions between SO2 and other wine compounds and microorganisms, why and how they happen, and how you can use that information in your cellar. SO2 refresher SO2 in solution can exist in three forms as shown in the following equilibrium equation (hydrogen ions (H+) have been omitted for the sake of simplicity). Molecular SO2 is usually shown as SO2•H2O to distinguish the aqueous form from its gas form, but we will use SO2