Measure sulfite levels in red wine with Indigo® test strips. Learn how tannins and color compounds affect SO2 readings and how to manage sulfites in small-batch winemaking.
Red wine naturally contains more phenolic compounds such as tannins, anthocyanins, and pigments that interact with sulfites during fermentation and aging. These compounds can bind SO2, reduce measurable free sulfite levels, and slightly complicate color-based test methods. Our sulfite test strips work well with most red wines when a simple dilution step is used to reduce color interference and reveal the free sulfite reading clearly.
Check sulfite levels in your red wine quickly and reliably using easy-to-read Indigo® sulfite test strips. Perfect for home winemakers, educators, and anyone evaluating low-sulfite claims.
Phenolic compounds bind SO2 more strongly in red wine, reducing measurable free sulfite.
Test free SO2 levels in a red wine sample; compare with a white wine control.
Reinforces how wine chemistry affects sulfite availability and sensory impact.
Color Interference & Measurement Workaround
Anthocyanins and tannins in red wine mask colorimetric pads, so direct-contact strip tests are unreliable.
Acidify a small aliquot (e.g., 25 mL wine + citric acid crystals), suspend a lightly moistened sulfite strip pad above the solution for ~5 min to absorb evolved SO2 gas, then compare to the chart. (Do not use simple dilution as a substitute.)
Demonstrates matrix effects; teaches a standard, safe enology workaround and provides a direct comparison with white wine testing.
SO2 Management in Red Wine
Aging, oxygen exposure, and tannin levels all influence sulfite retention.
Measure SO2 at different stages: young wine, after racking, and after aging.
Teaches how SO2 protects wine over time and when adjustments are needed.
Comparing Wine “Purifier” Claims
Some devices claim to remove sulfites but do not measure actual levels.
Test SO2 before and after using a purifier product to evaluate actual effect.
Encourages evidence-based evaluation of consumer wine gadgets.
How Red Wine Chemistry Affects Sulfite Testing
Red wine contains a high concentration of phenolics that readily bind with SO2. This increases the proportion of bound sulfites, which are chemically stable and do not contribute to antimicrobial protection or sensitivity reactions. Strip tests primarily measure the free sulfite fraction.
Because red wine pigments can mask the test pad, a simple 1:1 dilution with water improves accuracy without affecting the reading scale. This keeps free-sulfite values meaningful for home winemakers and small wineries.
Sulfite Levels in Organic Red Wine
Organic certification typically limits added sulfites to:
Maximum 100 mg/L total sulfites
Up to 35 mg/L free SO2 at bottling
Indigo®: sulfite test strips detect up to ~100 ppm, making them suitable for verifying that red wine stays within recommended ranges.
Correct Method for Testing Red Wine Sulfites
Sulfite cannot be measured directly in red wine due to color interference.
Add 5ml (1 teaspoon) of citric acid crystals to 25ml (1 ounce) of red wine.
Wet the pad of a sulfite test strip with water
Hold strip above wine-acid solution for ~5 minutes.
Compare test strip to color chart
Citric acid converts sulfites to sulfur dioxide gas which can be absorbed by a wetted test strip pad. The resulting color change, when compared to the color chart, gives a fairly accurate measure of the sulfite concentration.
You can buy citric acid crystals in baking supply stores. Or, use hydrochloric acid (HCl, aka muriatic acid) in place of citric acid. Small quantities can be bought in aquarium supply stores. Muriatic acid, used to clean brick work, etc. can be bought in some hardware stores. Wear gloves & googles when handling HCl as it is highly corrosive.
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?