Quantification of time trends in vintage scores and their variability for major wine regions of Australia

This paper quantifies time-trends of vintage scores and their variability in 24 wine regions of Australia. Our working hypotheses are that, owing to improved crop husbandry and winemaking techniques, (1) vintage scores had increased with time, and (2) variability in vintage scores had decreased with time, whereas (3) interactions between improved technologies and climate should be reflected in temperature-related time trends of vintage score and its variability. Published data were used to calculate rates of change in vintage score and its variability for the period 1980-2005. Rates were calculated as the slopes of regressions between two dependent variables, i.e. 3-year running average of vintage score (10-point scale) and 3-year running coefficient of variation of vintage score (%), and year of vintage as independent variable. The statistical agreement (r = 0.86, P < 0.05) between rates of change in vintage score derived from two independent sources indicated the vintage scores used in this analysis were fairly robust. Our analysis supported the hypotheses of improvement in vintage score and reduction in variability. More importantly, we provide a quantitative assessment of these trends: the rate of change in vintage scores averaged 0.09 per year, ranged from -0.07 to 0.20 per year, was dominantly positive (35 out of 48 cases), and significant (P < 0.05) in 29 cases, whereas the rate of change in variability of vintage scores averaged -0.52%/year, ranged from -2.1 to 0.8%/year, was dominantly negative (37 out of 48 cases), and significant (P< 0.05) in 19 cases. Consistent with hypothesis 3, the rate of change in vintage score for red wine and the rate of change in variability of vintage score for white wine, were inversely related to temperature (long-term daily mean during the month prior to harvest in each of the regions). By contrast, the rate of change in vintage score for white wine and the rate of change in variability of vintage score for red wine were unrelated to daily mean regional temperature. Owing to the intricate correlations between climate variables, however, the associations between change in vintage scores and temperature cannot be interpreted in terms of cause and effect.