“Can your Sulfite test strips be used to test acidic foods, such as wine or tomato sauce? How would I use activated charcoal to remove the color from a glass of wine? Is there a mini disposable charcoal filter? Could I reuse the filter, or would I have to use a new one each time? If I use the citric acid method, do I really just hold the test strip in the air above the liquid? Or did I misread the instructions? What is the pH limit that the sulfite test strips can handle?”

Nancy

Hi Nancy,

All great questions. A few of our test strips are a little trickier to use than others. For example, pH test strips tend to be pretty straightforward: dip and compare. However, some test strips require a few more steps, especially if used in ways they weren’t originally intended when developed.

Our Sulfite test strips were developed primarily for use in water. It is used to detect Sulfite ions in water-based solutions. Various types of sulfites can be detected with this strip, including sulfite, bisulfite, and metabisulfite. Our color chart was developed to measure sulfite ions in ppm (from sodium sulfite standards), however, we have checked standards and found that bisulfite and metabisulfite also match the same color chart.

We haven’t ever heard of anyone using the strips for tomato sauce, but we suspect the color and texture would negatively affect the strip performance.

Similarly, the color of red wine tends to make reading colorimetric test strips difficult at the very least. We have tried using activated charcoal, like that used in aquariums found at the local pet store, to reduce the red color. We have found that the charcoal will absorb the color a little while not affecting the ions present in the sample. It’s not a fantastic solution, but it may help.

The activated charcoal is usually available in a small bulk bag. Single use filter cartridges used in a laboratory are likely to be much more expensive, although they would work as well.

sulfite in red wine, sulfite test strips, test for sulfite in red wine, homebrew, test stripsAn alternative to using charcoal would be to dilute the sample with distilled water to reduce the effect of the red color. Just remember, if you do this you’ll need to adjust any result by the dilution factor. For example, if you dilute the sample in half, the result will need to be multiplied by 2.

Yet another alternative test method for detecting sulfites in red wine would be to add 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 sulfite level.

The citric acid will cause sulfites in the wine to convert to sulfur dioxide gas. The gas will react with the test strip. We have tested some sulfite spiked red wine and found that the amount of sulfite added to spike the sample when reacted with acid correlates with the color chart as a measure of the sulfite in the wine sample. Other acids will work as well, but citric acid is probably the least hazardous choice (hydrochloric acid works well but it is not easily handled).

The Sulfite test strips can handle the pH range of most wine. The pH of wine usually falls between 3 and 4. A lower pH tends to have an acidic taste, whereas a higher pH wine will spoil faster. The sulfite strips should work well within the pH range of 2.8 – 4.4. The lower the pH, the more acidic the sample. A pH of 3 is 10 times more acidic than a pH of 4. The pH scale is a logarithmic scale, like the Richter scale for earthquakes, only in the case of pH, lower numbers are stronger (a negative logarithmic scale).

To sum it up, there are ways to make the Sulfite strips work when testing red wine, but you’ll probably have to try a few of our tricks.