Sulfites in wine and almost anything else are present in both free and complexed or “bound” forms. This strip is designed to test free sulfites (Sulfur Dioxide) but with some adjustments can test both forms. The FDA requires labeling of food as “containing sulfites” if the level exceeds 10 ppm. FDA is referring to total sulfite (free and combined).
The Bartovation Free Sulfite Test Strip can be utilized for testing total sulfites, but special preparation of your solution is required. Before we go into detail on this, we believe it is important for you to understand how this test actually tests your solution.
The sulfite test pad contains buffer salts that when moistened will soak up sulfur dioxide (what they mean by sulfites in wine) and convert it to sulfite that then reacts with the indicator. The buffer agents on the test pad convert the free sulfur dioxide to sulfite ions which then react with the dye indicator. This leads to the development of color proportional to the amount of free sulfur dioxide (sulfite) present. This is highly effective for testing free sulfites in any solution. If the solution is not highly alkaline, it will not detect complexed sulfites.
This is why when you test a wine, which is acidic and usually has a pH between 2.8 and 4.4 you get such a small reaction. When testing Chardonnay white wine for example, you have a total sulfite level around 150 PPM, but free sulfite is around 15 PPM. A common ratio of free sulfite to bound sulfite in wines is usually around 1 to 10. As a result you will see a very small reaction if any, even if the item is labeled as “contains sulfites”. With the strip alone, the other 135 PPM of bound sulfite would not be detectable.
As a result, the sulfite bound to the other components must be disintegrated to become free sulfites before the strip will detect them. We would recommend the following procedure:
1. Adjust the wine sample to pH 12 with sodium hydroxide solution (confirm the pH with pH test strips).
2. Dip test strip, following the instructions on the label and after about 30 seconds compare with color chart.
The concentrated sodium hydroxide or any other very alkaline material should be handled similar to concentrated bleach with the appropriate safety precautions.
In addition to these steps that must be taken to test total sulfur dioxide, steps must be taken to test red wine for free or total sulfites. One of the most common issues users have when using our strips to test a red wine is the pigments of the red wine get affixed to the test pad and distort the reading, making it very difficult to determine the pH. An alternative method for testing red wine involves liberating the free sulfite present by adding approximately 1 teaspoon of citric acid to a 1 ounce sample of red wine in a small cup. Holding the Sulfite test strip above the solution for 5 minutes will result in the test strip reading the free sulfite level. The citric acid will cause free sulfites in the wine to convert to sulfur dioxide gas. The gas will react with the test strip. That will test for free sulfites only in the wine sample. This would have to be done after the pH is adjusted as per the instructions above in order to test red wine for free sulfites.