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Procedure to Determine the Titratable Acidity of Grape Juice, Must or Wine

Using a pH meter to determine the end point.

(see advantages and disadvantage of various methods)

Procedure

1. - Secure an adequate, representative sample of grape juice, must or wine.

2. - Prepare sample -


• Allow to settle to obtain a clear sample.
  
  
• Degas the sample.
  
  
3. - Set up a 25 ml or 50 ml burette on a retort stand, as per diagram, and fill with your standardized 0.1 M sodium hydroxide (NaOH) solution.

4. - Zero or note the level of the 0.1 M NaOH solution in the burette and record.

5. - Set up and calibrate your pH meter.

6. - If you choose to dilute a 10ml sample to obtain a larger working volume, follow the neutralization procedure and proceed to step 8.

7. - Pipette accurately, 10 ml or a larger volume of prepared sample into the 50 ml beaker or conical flask or a special container

8. - Titrate the sample solution until a pH close to 8.2 is reached.

Note: at the early stages of titration the pH will increase slowly, but then rapidly increasing past a pH of 6.0 and requiring only a few drops after pH 7.0.

Do not worry if one drop causes the pH to over shoot the end point pH of 8.2 as plus or minus one drop is well within the accuracy required.

9. - Record the new burette level and calculate the titratable acidity.


Using a 10 ml sample and exactly 0.100 M NaOH solution -



Titratable Acidity (g/L)

=

titre (ml)

*

0.75

.

.

(10 ml sample, 0.100 M NaOH)