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What are Sulfites?

Sulfites are compounds both added to and found naturally in wine. The common forms of sulfites found in wine are potassium metabisulfite and sodium metabisulfite. These compounds act as antioxidants, inhibiting the oxidation of other molecules, thanks to the sulfur dioxide (SO2) found in their molecules. This attribute make them a critical factor in the preservation of wine, especially wine with aging potential.

Effect on Wine

Sulfur Dioxide exists in both free and bound forms in wine. The bound form exist due to bisulfites having a property of binding to molecules that contain carbonyl groups. Running SO2 tests on wine can give you accurate values for their free, bound, and total (free + bound) SO2 levels. Achieving the proper level of SO2 in wine is a complicated balancing act with the target being the active SO2 level which is expressed as molecular SO2. The molecular SO2 is calculated using the Free SO2 and pH (acidity) of a wine.

Calculating Molecular SO2

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