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Citric Acid

• Citric acid is the acid found in citrus fruits
  
  
• Only very small quantities of citric acid exist in grapes.
  
  
• While small quantities of citric acid are also produced during fermentation, the presence of large quantities are due to winemaker additions.
  
  
• Citric acid is often added for acidification as it is claimed to taste fruitier and is a cheaper alternative to tartaric acid.
  
  
• Citric acid however, is not biologically stable and subject to microbial attack, especially by lactic acid bacteria (LAB), producing unpleasant flavour compounds.
  
  Hence, citric acid should not be added until after malo-lactic fermentation (MLF) is completed and stabilised against microbial attack by additions of sulphur dioxide (SO₂).
  
  
• Citric acid is a triprotic acid (see diag.) and requires three molecules of NaOH to react with one molecule of citric acid (see equation).
  
  
• Expected levels of citric acid found in wine are 0.0-0.5 g/L.