Determination of Total Sulfur Dioxide (SO₂) in wine/ must and vinegar

Sulfur dioxide (SO₂) is used in oenology mainly as preservative, but also for other purposes (for example for antiseptic, antioxidant, antioxidasic, solubilizing, combining and clarifying functions). Part of the SO₂ that is added as potassium metabisulfite to musts and wines undergoes a series of reactions. Therefore, after a short period of time, most of the sulfur dioxide reacts with some of the substances present, binds with them and forms addition compounds (combined sulfur dioxide) that are unable to express the typical properties of unbound molecules. Therefore, only the part that does not combine (free sulfur dioxide) plays an important role in preserving wine from oxidizing alterations and from some micro-organisms.

This test can be used to determine the total content of SO₂ in wine, which is the sum of the free and combined sulfur dioxide fractions.