Accurate Indigo® 10–500 ppm sulfite test strips for food, wine, cider, seafood, potatoes, textiles and more. Fast results, low cost, and easy screening for free sulfite.
Sulfites are widely used preservatives that control browning, inhibit microbial growth, stabilize color, and prevent oxidation in foods, beverages, and industrial processes. Indigo® sulfite test strips measure free sulfite in the 10-500 ppm range, giving producers, educators, and hobbyists a simple way to check whether levels fall within recommended limits for safety, flavor, and regulatory compliance.
Ensure accurate, fast sulfite monitoring across all your food, beverage, and textile processes. Order Indigo® sulfite test strips today and start testing within seconds.
Monitor nucleophilic reaction with oxidized keratin
Qualitative
Checks residual process chemicals
Free sulfite is a reducing agent. The test strip pad contains an oxidizing dye system that changes color when sulfite transfers electrons to it. The degree of color change correlates with the concentration of free sulfite in the sample. Because the reaction is direct and does not require pH adjustment or reagents, the strips can be applied to:
liquids (wine, cider, brines)
wet surfaces (shrimp, potatoes, dried fruit)
acid-released SO2 atmospheres (citric-acid method for red wine)
This makes the strip a versatile field tool for qualitative or semi-quantitative sulfite testing. For those who are VERY interested in the chemistry of how these strips work, please refer to this pdf which explains the theory of how free sulfite is detected.
Survey of Sulfite Forms
Sulfite preservatives appear in several chemical forms, each of which interconverts rapidly in water and contributes to measurable free sulfite:
Sulfite ion (SO32-): trigonal pyramidal; the primary reactive species.
Bisulfite (HSO3-): protonated form, common in mildly acidic foods.
Metabisulfite (S2O52-): Na/K salts used in winemaking & food processing; hydrolyzes to bisulfite.
Sulfur dioxide (SO2): dissolved gas in wine/cider that equilibrates with sulfite/bisulfite.
All four forms can be illustrated using molecular models which can help understand the nature of free sulfite as detected by Indigo® test strips.
Health Related Issues
Various heath organizations have set 10ppm as the lower limit for people with asthma & other health concerns. If the test strip does not change color, you can assume that the sulfite level is low enough to be considered safe for consumption. Read more in our blog on what the 10ppm level really means.
The presence of sulfites may be listed on food labels as: sulfur dioxide, potassium bisulfite, potassium metabisulfite, sodium bisulfite, sodium metabisulfite, or sodium sulfite.
Related information or images
Potatoes
Cider Preservative
Dried Fruit
Red Wine
White Wine
Seafood
Specifications
This Indigo® test strip indicates the presence of sulfite ion in increments of 10, 50, 100, 250, and 500ppm after 15 seconds.
The number of strips (100) vial is approximate.
Vial has a built in desiccant and if kept tightly closed, strips can be effective up to 5 years.
Strips test for: sulfite, bisulfite and metabisulfite
Documentation
Test Strip Documentation
Stability Statement
Certificate of Analysis
SDS
Reviews (2)
2023-10-27
Test strips worked as described, including the red wine citric acid method. I first did some comparisons using sulfites in water. Dipping the strips and the citric acid method gave the same result, albeit a little lower than expected. Solution was mixed to 100 ppm and both strips showed about 75. Used a similar technique on red wine, although dipping does not work. Wine with no sulfites showed zero. Added and got similar readings to the water results. Thanks for the great product and the citric acid trick.
2021-01-22
Great place for a hard to find product. Excellent price! Quick shipping.
Thanks for letting us know. This might interest you since you are in quality control: Can 10ppm of Sulfite & Quat Really Mean Zero?