Wine Analysis

Titratable Acidity Procedure - Variations (advantages/diadvantages)

• Using a pH meter to detect the end point
  
  
• Using a diluted sample and a colour indicator
  
  
• Using a non-diluted sample and colour indicator
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  Using a pH meter to detect the end point
  
  
  Advantages.
  
  
  • The end point is more easily detected and more accurately achieved.
    
    
  • As colour is not involved in end point detection, red wine colour interference is not a problem, and dilutions are not necessary for this reason.
    
    
  • In an appropriate container the pH and titratable acidity can be determined consecutively, using a 10ml of undiluted sample.
    
    Note: an undiluted sample is more likely to give a more accurate titratable acidity determination.
    
    
  Disadvantages
  
  
  • Good quality pH Meters and pH electrodes are relatively expensive.
    
    
  • The pH electrode requires care to provide a long service life.
    
    
  • pH meter operation requires some time and operation knowledge.
    
    
    
  Using a diluted sample and a colour indicator
  
  
  Advantages.
  
  
  • Dilution of the sample with distilled water provides for a larger working volume without increasing the quantity of acid and use of titrant (NaOH solution).
    
    
  • An increase in the working volume -
    
    
    • better accommodates a standard size stirrer bead when using a magnetic stirrer during the titration.
      
    • better accommadates a pH electrode assembly when using a pH meter to detect the end point
      
    • provides a volume that can be stirred manually, using an end point indicator (see diagram).
      
      
  • Red wine sample dilution decreases colour interference with end point detection.
    
    
  • The diluted sample can be degassed by boiling without a significant reduction in volume.
    
    
  • Disadvantages are -
    
    
    • Dilution and the neutralization of the dilutant (distilled water) requires extra steps.
      
      
    • Dilution of sample increases the risk of sample contamination and changes the acidity dynamics.
      
      
    • The pH can not be determined on a diluted sample.
      
      
      
  Using a non-diluted sample and colour indicator
  
  
  • Most acid titration procedures involve a dilution step of the juice or wine sample to increase the working volume. ( see diluted sample).
    
    But it is also possible to increase the sample size to from 10 ml to 20ml or greater without dilution.
    
    Advantages are -
    
    
    • Allows the pH to be measured at the same time.
      
      
    • Non-diluted samples give more accurate results, eliminating the dilution step and the neutralization of the dilutant (distilled water).
      
      
    Disadvantages are -
    
    
    • requires a pH meter to detect the end point when using a red wine sample.
      
      
    • requires larger volumes of the titrant (0.1 M NaOH)
      
      
    • Using a larger than 10ml sample must be allowed for in the calculations.