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Molecular sulphur dioxide (SO2)
- Molecular sulphur dioxide exists as a gas or as discreet single molecules (see fig. 3)
- This gaseous form can exist dissolved in an aqueous (water) solution (juice/wine).
- Molecular sulphur dioxide is the form that is detected on juice or wine as a pungent smelling gas when in excess.
- Due to the volatile nature of this form, losses from juice or wine to the air is to be expected, especially on agitation.
This results in a reduction in the total sulphur dioxide (TSO2) below that of the amount added to grape juice, must or wine.
- Molecular sulphur dioxide is the most affective form involved in both the reduction of oxidation reactions and microbial activity.
- A decrease in pH results in only a slight increase in molecular SO2.
However, these small increases are very significant considering molecular SO2's effectiveness
- The recommended level of molecular SO2 to inhibit microbial growth is 0.8 ppm. The level of FSO2 required to achieve this is pH dependent (see table or equation for calculations)