Sulphur Dioxide
Sulphur Dioxide (SO2) is a common substance used in winemaking that prevents the wine from reacting with oxygen which can cause browning and off-odors (oxidation), and it inhibits the growth of bacteria and undesirable wild yeasts in the grape juice and wine. Recognised by both Codex Alimentarius and the OIV, Sulphur dioxide is permitted for use in grape wine in over 70 countries worldwide.
Sulphur dioxide is a colorless, non-flammable gas with a sharp, suffocating odor. It is stored and transported in liquid form in hardened steel tanks. These solutions are not stable and should not contain less than 50 g/l SO2. At a temperature of 20 °C, it is liquid under a pressure of 3.36 kg per square centimeter, or 3.30 bars. Under standard pressure, its boiling point is -10 °C. Its density is ?20 = 1.383. This product falls under the category of antiseptic and antioxidant preservatives. Its content level in wine is subject to the regulatory limits in force concerning quantities.
Sulphur dioxide has a strong, characteristic odor. Sulphur dioxide blackens a filter paper which is impregnated with mercury (I) nitrate. Sulphur dioxide turns a filter paper impregnated with potassium iodine and starch solution blue. Then, the blue color disappears because of reduction of the iodine initially released. For further substance information, please see the International Oenological Codex.
Synonyms: Sulfur Dioxide, Sulphurous Anhydride, Sulphur (IV) Oxide
CAS Number: 7446-09-5
E Number: 220
INS Number: 220
International Organisations
Codex Alimentarius
-Approved for use in winemaking by CXS 192-115, General Standard for Food Additives Food Category (GFSA Online)
-14.2.3 Grape wines Functional Class (GFSA Online) Antioxidant Preservative Recommended Usage (GFSA Online) 14.2.3: 350 mg/kg As residual SO2 Except for use in special white wines at 400 mg/kg
International Organisation of Vine and Wine (OIV)
-Food Category Wine (grape) Functional Class Antioxidant Sulphur dioxide additive Recommended Usage (International Code of Oenological Practices – Annex: Maximum Acceptable Limits) Sulphur dioxide (total): 150 mg/l for red wines containing at the most 4 g/l of reducing substances 200 mg/l for white wines and rosés containing at the most 4 g/l reducing substances 300 mg/l: red wines, rosés, and whites containing more than 4 g/l of reducing substances 400 mg/l: exceptionally in certain sweet white wines
FIVS
Classification Category 2 – Naturally occurring in grapes and treatment residual in wine
Recommended Usage
Please refer to the Joint FAO/WHO Expert Committee on Food Additives’ (JECFA) “acceptable daily intake” (ADI) for recommended usage.
As outlined in Section 3.2 of the Preamble of the CODEX Alimentarius General Standard for Food Additives, Sulphur Dioxide is used:
To enhance the keeping quality or stability of a food or to improve its organoleptic properties, provided that this does not change the nature, substance or quality of the food so as to deceive the consumer.
As outlined in the OIV’s International Code of Oenological Practices, Sulphur Dioxide is used:
To obtain the microbiological stabilisation of wine by limiting and/or preventing the growth of yeast and technologically unwanted bacteria To use its reducing and antioxidant properties To combine certain molecules that give undesirable odours To inhibit possible oxidasic activities.
Usage in Winemaking:
Sulphur dioxide serves as an antibiotic and antioxidant, protecting wine from spoilage by bacteria and oxidation. Its antimicrobial action also helps to minimise volatile acidity. Sulphur dioxide exists in wine in free and bound forms, and the combinations are referred to as total SO2. Binding, for instance to the carbonyl group of acetaldehyde, varies with the wine in question.
The free form exists in equilibrium between molecular SO2 (as a dissolved gas) and bisulphite ion, which is in turn in equilibrium with sulphite ion. These equilibria depend on the pH of the wine. Lower pH shifts the equilibrium towards molecular (gaseous) SO2, which is the active form, while at higher pH more SO2 is found in the inactive sulfite and bisulphite forms. The molecular SO2 is active as an antimicrobial and antioxidant, and this is also the form which may be perceived as a pungent odour at high levels.
See FIVS technical papers for more information - click here.
