*SO2 is used as a preservative to protect juice, must or wines from oxidation and microbial spoilage. When SO2 is added some of it immediately becomes bound. 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 liquid solution can be prepared by bubbling gaseous S02 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.

The potassium metabisulfite (K2S2O5 or KMBS) is a white crystalline salt, which may be dissolved in water before addition. The proportion of SO2 in the KMBS is 57 % w/w.

Hydrogen Peroxide (H₂O₂) is a powerful oxidizer and can be used to reduce SO₂ .The H₂O₂ should be added slowly to the wine in a dilute form to avoid oxidation. After the H₂O₂ addition,wine should be allowed to equilibrate for several hours before any confirmation analysis of the concentration of remaining SO₂ in the wine.

To avoid over adjustment and oxidation, lab trial should be performed.

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

SO₂ liquid solution can be prepared by bubbling gaseous SO₂ into water. The concentration of SO₂ solution can be calculated from its specific gravity. You can use this table to determine the concentration of SO₂ solution based on its specific gravity at different temperature.