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De-gassing Grape Juice, Must and Wine

• Grape juice, must and wine may contain dissolved carbon dioxide (CO₂) through CO₂ being used as an inert gas cover or from the fermentation process.
  
  
• CO₂ in solution exists as carbonic acid and will be included in titatable acidity or volatile acidity measurements.
  
  
• To prevent this, all samples will have to be de-gassed.
  
  
• This can be achieved -
  
  
  • by the use of a water aspirator (vacuum pump) to apply a vacuum, to a stoppered, thick walled, conical filter flask (see diagram).
    
    Approximately 100 ml of sample can be degassed using this apparatus.
    
    The vacuum should be applied for a few minutes, while swirling the sample, until no further liberation of gas bubbles are apparent.
    
    
    
  • by sparging (bubbling) nitrogen gas (N₂) through the sample for approximately 5 minutes.
    
    Note: this method can cause excessive frothing in some grape juice samples)
    
    
    
  • by measuring the sample quantity required (normally 10ml), and diluting with approximately 100 ml of distilled water that has been adjusted to a pH of 8.35.
    
    This prepartion is brought to the boil and on cooling titrated directly.
    
    Note 1: boiling water cannot retain dissolved gasses.
    
    Note 2: Loss of volume through boiling will not reduce the amount of acid contained in the volume of sample chosen.