This test solely measures FREE sulfur dioxide. Total sulfur dioxide present in must and wine is not as useful as a preservative as just free sulfur dioxide, as total SO2 is equal to free + bound. The portion of total SO2 that is bound to other chemical components has reduced effectiveness as a preservative by 30 – 70%, and as such free SO2 is a much more useful figure in winemaking. Also, the degree of binding can change over time, affecting the ability of an adequate dose to continue providing its preservative properties. The effectiveness of sulfur dioxide as a preservative is also pH-dependent, with low pH wines requiring lower levels, and high pH wines requiring significantly greater concentrations to achieve the same effectiveness as in a typical wine with a pH of 3.3 – 3.4.
The Accuvin Free SO2 test kit contains both Low Range (0-40 ppm) and High Range (40-130 ppm) tests. Each test kit contains the 10 tests, tubes with rehydration solution, and samplers. (All kits contain a ratio of 1:4 high range to low range tests.)