The determination of total SO2 in grape juice. A comparison among five methods.

The EC official method of total SO2 analysis in grape juice was modified in 1990. The main improvements concerned the amount and concentration of H3PO4 used during the distillation to recover the combined SO2 and the standardization of the distillation time at 15 min. This comparative study evaluated the total SO2 level of 12 grape juices determined by five methods, including distillation, iodimetric and enzymatic-based methods. Attention was focused on the total SO2 legal limit of 10 mg/l fixed in Europe for grape juice. Analysis of variance disclosed a significant difference among the total SO2 content in grape juices determined by five methods. Each analytical method showed limits in relation of their ability to release the combined SO2. In particular, the SO2 bonded to phenolic compounds is partially released at low pH in the acidified juice leading to higher results.