Free sulphur dioxide represents the amount of sulphur dioxide (SO2) not bonded to other molecules.
SO2 usually called "sulphurous" is used in different phases of wine production thanks to its antioxidant and antimicrobial properties. the value of molecular so2 depends greatly on free so2.
Excess free sulphur dioxide may cause unpleasant smells (rotten eggs, garlic, onion).
Determination takes place via cold extraction in an acid environment, oxidation to sulphuric acid by reaction with hydrogen peroxide and quantification with acid-base titration.
This specific analytical method is important in all production phases but it is fundamental in the pre-bottling stage because it returns the true value of so2 present in the wine since the classic interferents of the iodometric method are eliminated (ascorbic acid, polyphenols, colouring etc).

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