Determining Tritratable Acidity with Sodium Hydroxide

Using Phenolphthalein Indicator Solution

Follow these steps to determine the Titratable Acidity (often just referred to as TA) in your must or wine.

  1. Add a known amount of grape juice to a beaker (usually 10 or 15 milliliters).
  2. Add additional water if the juice is rather dark. The amount of water you add is not critical, adding water does not change total amount of acid in your sample. Do not, however, add more water than 5 times the amount of juice.
  3. Add about 5 drops of phenolphthalein. Phenolphthalein is an indicator that is clear when it is in a solution that is acidic, but will change to a purplish color when that solution becomes neutral to basic.
  4. Add 0.1N NaOH (1/10 Normal Sodium Hydroxide) until the solution starts to turn pinkish and stay pinkish then note the amount of NaOH used for the titration. Make NaOH addition using a pipette graduated in milliliters. A 10 ml pipette works well.
  5. Use the following formula to determine the TA of your wine or must. TA = (Number or milliliters of NaOH / Number of milliliters of juice) X 0.75 The units for the TA in this calculation are: Number of grams of tartaric acid per 100 milliliters of juice.

Using a pH Meter

A pH meter substitutes for the color endpoint. When sodium hydroxide is added to wine, it increases the pH. Standard solution, usually at 0.1 N, is added until the pH meter reads 8.2. Follow these steps to determine the Titratable Acidity (often just referred to as TA) in your must or wine.

  1. Calibrate the pH meter using a two point calibration. The most common buffer solutions used for calibration are pH 7 and pH 4 but pH 10 is also available. Our pH meter has two set screws with one marked pH 7 and the other pH 4 or 10. Fresh pH buffer solutions are important to assure accuracy in the calibration of the meter.
  2. First, calibrate with pH 7 buffer because this is a weaker solution. If the meter does not read pH 7 with the pH 7 buffer, we turn set screw marked pH 7.0 to attain 7.0.
  3. Then calibrate with the pH 4 buffer solution turning the set screw marked pH 4, or whatever method used for your meter.
  4. Add a known amount of grape juice or wine into a beaker (usually 10 milliliters).
    Place the pH meter into the solution. At this point you can take a reading of the pH of the must or wine.
  5. Add 0.1N NaOH (1/10 Normal Sodium Hydroxide) to the solution until the pH meter reads 8.2. In our set-up, we have a stand that supports a 10 ml burette with a stopcock on the bottom of the burette. The burette is calibrated in 0.1 increments. When the stopcock is opened, the solution is allowed to flow into the beaker. Closing the stopcock stops the flow of solution and allows a reading from the burette of how much solution has been dispensed. As the solution pH rises to around a pH of 6.0, changes occur faster so be careful as you pass pH 7.0 on your way to pH 8.2.
  6. Use the following formula to determine the TA of your wine or must. TA = (Number or milliliters of NaOH / Number of milliliters of juice) X 0.75 The units for the TA in this calculation are: Number of grams of tartaric acid per 100 milliliters of juice.