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Malic Acid

• Malic acid is found in many fruits, including grapes and is the main acid of apples (malum, Latin for apple).
  
  
• The concentration of malic acid expected in grapes at maturity is 0-4.0 g/L measured as tartaric acid.
  
  
• Malic acid, within the grape berry, is biologically unstable and can be converted to carbohydrates, hence reducing the grape's total acidity.
  
  This metabolism of malic acid occurs during the ripening period and increases with temperature and time.
  
  Hence grapes grown in cool climates retain a higher concentration of acid.
  
  
• Malic acid can also be converted to lactic acid through a process called Malo-Lactic Fermentation (MLF).
  
  
• Malic acid is a weaker acid than tartaric acid and hence not the choice for addition to reduce grape juice and wine pH values.
  
  
• Malic acid, as indicated above, is subject to microbial attack by MLF (Malo-Lactic Fermentation) and hence not the choice for acid additions.
  
  
• Malic acid, as Tartaric acid, is a diprotic acid (see diag.) and also requires two molecules of NaOH to react with one molecule of malic acid (see equivalent equation).