Molecular sulphur dioxide is the most affective form involved in both the reduction of oxidation reactions and microbial activity in wine.

The recommended level of molecular SO₂ for red wines is 0.5 mg/L (ppm); for white wines is 0.8 mg/L (ppm); and for dessert wines is up to 1.5 mg/L (ppm). You can use this calculator to determine how much Free SO2 is required to protect your wine, based on its pH.  Free SO₂ over 50 mg/L (ppm) can be tasted and detect in nose of the wine.