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Enzymes -

• Enzymes are organic catalysts found in living systems.
  
  
• There are many different enzymes, each specific for a particular reaction.
  
  
• Grape berries contain oxidative enzymes (tyrosinase).
  
  
• Once the grape berry cells are ruptured, oxidative enzymes, juice and oxygen come into intimate contact, allowing oxidation to occur.
  
  
• Oxidative enzymes found in grapes are not very soluble and remain predominantly bound to grape particles and hence their concentration can be reduced through juice clarification.
  
  
• The grape berry's oxidative enzyme (tyrosinase) does not persist through to the wine and is inhibited/denatured by sulphur dioxide.
  
  
• Oxidative enzymes, introduced through botrytis infection of the grape berry, exist in solution and therefore can not be removed by juice clarification and can persist through to wine.
  
  
• Also see unreactivity of oxygen