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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)