Chapter 18

Sulfur Dioxide Use in Winemaking

Measurement of Sulfur Dioxide in Wine

In winery settings, the free sulfur dioxide concentration is likely to be determined routinely (on a weekly or monthly basis) as a quality control measure. The analysis of sulfur dioxide in wine remains one of the most frequently conducted winery lab analyses. There are two generally accepted methods for the determination of total sulfur dioxide - performing titrations manually or using an automatic titrator.

Manual Titration

In a manual titration an apparatus called a burette is used to slowly add the titrant to the sample. An indicator solution will usually produce a color change signifying the end point of the reaction.

Ripper Method

Most small wineries use the Ripper method to measure sulfur dioxide in their wines. The Ripper method produces quick results, it is simple to use, and it is inexpensive. In this method, standardized iodine is used to titrate free sulfur dioxide. The iodine reacts with the sulfur dioxide and the amount of sulfur dioxide present is calculated from the amount of iodine used.winemaker will have target a specific free sulfur dioxide level to ensure there is enough molecular sulfur dioxide. To complicate matters, as mentioned, the amount of molecular sulfur dioxide will depend on the pH of the must or wine.

Aeration-Oxidation Method

The aeration-oxidation method involves heating an acidified sample of wine to liberate the sulfur dioxide in the molecular form. A stream of air is then used to carry the liberated sulfur dioxide to a reservoir of hydrogen peroxide where it is oxidized to form sulfuric acid.

Automatic Titration

Automatic titration is done with instrumentation that delivers the titrant, determines the endpoint and calculates the concentration of the wine sample automatically. Automatic titrators offer increased accuracy and repeatability for two reasons

Sample Handling and Management

Sulfur dioxide is a relatively volatile compound, which means that sample handling and management are critical to ensure accurate and precise results. Samples should be opened prior to analysis, not before, to avoid loss of sulfur dioxide through volatility or oxidation.

Click on the following topics for more information on sulfur dioxide use in winemaking.