Development of tools to verify origin and varietal nature of wines
Origin verification of wines relies on the use of parameters that not only reflect the geology and water source of the location where grapes are grown, but which are also not altered during vinification. Building on a recently completed AWRI feasibility study, several additional elemental isotope ratios such as boron, lithium and lead are now being measured as part of the Wine Australia project AWR1505, in order to provide information additional to the strontium isotope ratio, on the crustal composition of source vineyard location.
To supplement this dataset of trace elements and their isotopes, and to achieve true independence of multiple data sources, oxygen-18 will also be analysed as an indication of the vineyard water source. These parameters will be measured in a large number of Australian wines, and wines from North and South America, Europe, and mainland Asia and Africa.
In order to verify that chosen parameters are not affected by variety (as has been highlighted in several recent papers in the literature), laboratory-scale wines will be made to assess numerous varieties grown in the same soil across several different locations. In addition, the temporal variation of these parameters will be assessed through the analysis of several vertical series of wines made from single vineyards over the last ten years. This information will be combined with the continued survey of the parameters determined to be most robust over a five-year period, to provide a series of reliable analytical protocols and metrics for the determination of wine origin.
In the later years of the project, a review of chemical and genetic techniques for the determination of varietal origin of wine will be undertaken, with the aim of targeting appropriate tools for this aspect of wine authentication.
Differentiation of Australian wines
Statistical analysis of data from 60 wines from Australia and overseas was carried out. The discriminating power of trace elements was much lower than that of isotope ratios. Using just isotope ratios of boron, lead, oxygen and strontium, Australian wines were separated from non-Australian wines (Figure 17) and linear discriminant analysis was 98% successful in correctly classifying the wines into the non-Australian wine group or the three regions that make up the Australian group, with just one misclassification.
For these parameters to be considered useful in statistical models, it was important to assess their variability across different vintages and different grape varieties. Vertical series spanning across ten years of three different single-vineyard wines from Margaret River, Hunter Valley and Clare Valley were analysed. Low variability was observed for isotope ratios of lead (maximum 2.4%) and strontium (maximum 0.13%), whereas oxygen-18 showed an increased variability (approximately 30%), as expected, in line with data published in Europe. A similar variability was seen for boron-11. To test the effect of grape variety, two sets of seven varieties grown on a single block, one in the Barossa and one in the Riverland, were harvested and fermented before analysis. The variability of isotope ratios due to variety showed a similar pattern to the vintage variation.