How do I measure sulfur dioxide?

Free and total sulfur dioxide (SO2) are commonly measured via Ripper Method (titration) or Aeration Oxidation Titration (aspiration).

The Ripper Method Titration

This method utilizes a redox (reduction-oxidation) reaction between iodine and sulfur dioxide to titrate for sulfur dioxide (SO2). This method requires very little sample preparation, making the analysis quick and easy. However, this method can have interference from substances such as vitamin C.

To run a wine sample in compliance with the Ripper Method for free sulfur dioxide:

1. Aliquot, (measure) 50 mL of wine into a clean beaker.
2. Add 5 - 7 mL of 25% sulfuric acid to the beaker.
3. Add one packet of potassium iodide (KI) to the beaker.
4. Titrate immediately.

To titrate a sample of wine via the Ripper Method for total sulfur dioxide:

1. Aliquot, (measure) 50 mL of wine into a clean beaker.
2. Add 5 mL of 5M sodium hydroxide in excess. This liberates any sulfites bound to other substances such as sugars and proteins. The wine will need to react with the sodium hydroxide for approximately 20 minutes.
3. Add 10 mL of 25% sulfuric acid to adjust the pH of the sample.
4. Add one packet of potassium iodide (KI) to the beaker.
5. Titrate immediately.

Aeration Oxidation Titration

While this titration still measures sulfur dioxide, it utilizes an acid/base titration instead of a redox titration. The sample preparation for this method requires more equipment and time (it's a bit complicated). However, this method is not subject to interferences.

1. Set up the necessary laboratory equipment including the aspiration apparatus.
2. Add hydrogen peroxide to the bubble trap.
3. Add your acidified wine sample to the round bottom flask.
4. Run the apparatus and aspirate the sample through.
5. Take the resulting sample and titrate it with a sodium hydroxide titrant (this an acid-base titration).

 Download A Free SO2 in Wine eBook HERE!