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Free sulphur dioxide (FSO
2
)
FSO
2
(Free sulphur dioxide) is that portion of
sulphur dioxide
(SO
2
) that is not bound to the
sulphur dioxide binding compounds
present in grape juice and wine.
FSO
2
is the active, effective form of
SO
2
(sulphur dioxide) in wine production.
FSO
2
itself exists in
three (3) different forms
in juice and wine. These are
molecular SO
2
and the
bisulphite
and
sulphite
ions.
Both export and domestic legal limits apply to
FSO
2
concentrations in wine.
