SO₂ is used as a preservative to protect grape juice, must or wines from oxidation and microbial spoilage. When SO₂ is added, part of it reacts with different components present in the grape juice/must or wine to bound and become inactive as an antioxidant and antimicrobial agent. What remains is the Free SO₂ and is in two parts "bisulfite" (HSO₃^-) and molecular SO₂. The molecular SO₂ is the active form against microorganisms and unwanted bacteria. SO₂ additions are made at different stages of the wine-making process. The most practical usage of sulfur dioxide addition is by adding liquid SO₂ solution, sodium or potassium metabisulfite.

SO₂ liquid solution can be prepared by bubbling gaseous SO₂ into water. The amount of SO₂ added as a liquid solution depends on the strength of that solution, and can be calculated from its concentration, normally expressed as % weight/volume.