Caution: Sodium Hydroxide is caustic, and can burn skin. Use with proper safety procedures.
Testing Acid in Musts or Wine with Sodium Hydroxide:
White– Measure 15mL of juice or white wine into the beaker. Add 4 to 5 drops of phenolphthalein. Fill the syringe with 10ml of sodium hydroxide. Add sodium hydroxide drop by drop to the sample. With each drop, you will see a fleeting pink zone which will vanish when the sample is swirled. Keep adding until the pink flush remains, but not until it turns a bright red. This is your endpoint. Record the number of mL of sodium hydroxide used.
Red– The test for reds is the same, but due to their color, the endpoint is very difficult to see. Work with a brightly lit background. As you add the sodium hydroxide, the red color will gradually disappear and turn a gray to green shade. The endpoint is reached when the reddish tinge reappears.
Testing Acid with a pH Meter:
Calibrate your pH meter. Measure 15ml of must or wine into beaker. Fill the syringe with 10ml of sodium hydroxide. Hold the pH probe in the sample and slowly add sodium hydroxide drop by drop, stopping to swirl sample. Once the pH meter reading reaches 8.2, stop and record the number of mL of sodium hydroxide used.
The number of mL of sodium hydroxide used is the g/L of Titrable Acidity (TA) of your sample.
Typical TA for RED: 5.0g/L to 6.5g/L Typical TA for WHITE: 5.5g/L to 8.0g/L