Sulfur dioxide (SO₂) is widely used today in enology with the aim of preserving and protecting musts and wines. It has 4 main functions:
– Antiseptic action: SO₂ is opposed to the development of microorganisms, more strongly to bacteria than to yeast. The lower the population at the start, its effect is higher. During storage, its antiseptic action makes it possible to prevent the development of spoilage microorganisms, particularly Brettanomyces, responsible for the formation of ethyl phenols, but also to prevent the phenomena of reformation (Lonvaud-Funel et al., 2021).
– Antioxidant action: It binds with dissolved oxygen according to the following reaction in the presence of catalyzers:
SO₂ + 1/2O₂ ⟶ SO₃
In this case, SO₂ protects the wine against chemical oxidation, which is a slow reaction. However, it has no effect on enzymatic oxidations, which are very quick. (Ribéreau-Gayon et al., 2006). In certain red wines, the antioxidant action of SO₂ seems to be weaker than in white wines due to the presence of tannins having a greater reactivity to oxygen. In white wines, its antioxidant activity is important, and it helps protect aromas, prevent or delay wine over-oxidation (Navarre & Langlade, 2016).
– Antioxidaze action: SO₂ makes it possible to prevent the functioning of oxidation enzymes of the laccase or tyrosinase type (Ribéreau-Gayon et al., 2006). It is generally found in harvests presenting a degraded sanitary state, possibly reached by Botrytis Cinerea. In high doses, it can eventually destroy them.
– Impact on the organoleptic qualities: It protects wine aromas and prevents the flat character by binding ethanal and other similar products (Navarre & Langlade, 2016).
It also has a dissolving action. It dissolves grape skins and facilitates the release of their contents. Therefore, increases the extraction of the compounds they contain, in particular anthocyanins. This effect can only be used during the harvest on red grape must (Dallas & Laureano, 1994). Its roles in wine are numerous and quite widely studied. It has a very significant effect on color, initially bleaching pigments, further increasing its stability over time (Blouin, 2014).
References:
Blouin, Jacques. Le SO2 en oenologie. 2014. Dunod.
Dallas, C., and O. Laureano. “Effect of SO2 on the Extraction of Individual Anthocyanins and Colored Matter of Three Portuguese Grape Varieties during Winemaking.” VITIS – Journal of Grapevine Research, vol. 33, no. 1, 1, 1994, pp. 41–41. https://doi.org/10.5073/vitis. 1994.33.41-47.
Lonvaud-Funel, Aline, et al. Microbiologie du vin. 2e édition, 2021.
Navarre, Colette, and Françoise Langlade. L’oenologie. 6e édition, 2016.
Ribéreau-Gayon, P., et al. Handbook of Enology Volume 2: The Chemistry of Wine Stabilization and Treatments. 2006.