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Investigation of the minimum level of sulphur dioxide required for optimum red wine quality

The research project studied the influence of sulphur dioxide on colour development, microbial stability and overall quality, as defined by the sensory properties, in red wine production. In model wine solutions detailed studies were done to determine how sulphur dioxide affects chemical polymerization reactions between coloured pigments (anthocyanins) and chemically similar non-coloured compounds, responsible for colour changes during red wine maturation. Factors such as pH and acetaldehyde concentrations and sulphur dioxide concentrations affected polymerization and gave further information about the mechanism. Additional studies in wines determined the effects of pH, alcohol, storage temperature and sulphur dioxide and showed that sulphur dioxide influenced the vinification as well as the maturation during storage.

Microbiological investigations showed that the minimum inhibitory concentration (MIC) of sulphur dioxide to prevent growth of yeasts in media was 115 mg/L at pH 3.4 and 75 mg/L at pH 3.2 for yeasts and < 50 mg/L for lactic acid bacteria. Investigation of the effect of different wine fractions demonstrated that the highest molecular weight fraction, containing polymeric phenolic compounds, was the most inhibitory to yeasts and lactic acid bacteria. Sensory differences between the wines mainly related to colour attributes, indicating that when wines are made using modern hygienic techniques, sulphur dioxide has a negligible effect on aroma and flavour attributes.