Short Note #65 on the distillation of wine describes a novel procedure for the determination of Total SO2 contents in wine. The most important advance stems from a calibration by means of a stabilized SO2 standard containing acetaldehyde simulating a wine matrix. A calibration equation is derived from a linear correlation of a series of SO2 determinations with SO2 standards and the calibration equation is applied in order to adjust measured SO2 results in samples. Total SO2 contents in a series of 11 wines were evaluated and results compared to the OIV SO2 Method.
The OIV SO2 Method is based on the entrainment of SO2 from the wine sample into a titration vessel by means of a nitrogen stream.
Simple steam distillation, as a possible alternative, does not produce results comparable to the OIV SO2 Method without further optimization and adaption.
The most important improvements stem from acidification of the sample with an acid mixture of methanol, water and ortho-phosphoric acid and a calibration by means of a stabilized SO2 standard solution containing acetaldehyde simulating a wine matrix. The calibration reveals an excellent linear relationship between the determined SO2 amounts and the corresponding known amounts of standard solution. The linear equation is applied in the calculations to correct for Total SO2.
The distillation unit should preferably be equipped with an acid resistant pump as available in the BUCHI K-355 (picture above) and the K-360.
The sample is acidified with the acid mixture and steam distilled into the specially designed BUCHI SO2 absorption vessel in which the SO2 reacts with a defined volume of iodine standard solution. Subsequently the distillate is back-titrated with Na-thiosulfate standard solution using a titrator suitable to carry out redox titrations.