Defining Regional Sensory Variability of Premium Australian Shiraz Wines

The concept of terroir or the ‘taste of place’ in regards to wine is well understood as a concept but rarely explained with any scientific rigour. It seems to be a concept that is plausible, or even likely, to the ‘wine’ educated. But with all of the possible variables in a viticulture/wine production system, conducting an experiment in a traditional sense where all variables are controlled except one and the differences are measured is not a reasonable endeavour. The logistics, effort, and cost of an experiment like this make it almost impossible to reasonably expect to explain terroir with any sort of scientific rigour. Therefore, a different method must be employed if there are to be some steps forward regarding explaining terroir scientifically. This thesis explores these regional differences in Shiraz wines using various sensory methods, chemical analyses, and climate data, all collected from wines carefully selected to represent the sensory fingerprint of each region. Due to the way the wines were selected from each region – profiling a large amount of commercially available wines from each region, there can be confidence that the sample set is in fact, representative of the place they come from, and therefore the sensory profile, chemical data and climatic indices are valid and appropriate. This novel approach to evaluating regional sensory characters has led to a comprehensive and developed understanding of the regionality of the six Australian Shiraz producing regions profiled herein.
The initial phase of the project was to investigate the new rapid sensory method: Pivot© Profile (PP). It was used as a proof of concept of the project and of the method itself, using it to evaluate ultra-premium, regional Australian Shiraz wines along with some international equivalents, with different sets of judges. These results showed that the method is sensitive enough to properly evaluate wines as it showed that Shiraz wines from different regions exhibited unique sensory characters. It also showed that using sets of judges with different backgrounds gave similar results, highlighting the repeatability of the method. Chapter II explains this part of the project and contains the associated peer-reviewed publication.
Chapter III focused on the regionality of Shiraz from six high profile wine producing regions in Australia. The PP method was used to profile a large number of regional wines, in the regions the wines came from and assessed by winemakers who live and work in the region. These profiles revealed the overall sensory fingerprint of the regions, and through Agglomerative Hierarchical Clustering a small subset of wines was selected from each within-region cluster to represent the sensory variation of the region. That subset of wines was then more rigorously profiled using Descriptive Analysis (DA). Using the PP method to select the subset of wines for the more intricate DA study is a novel approach. This gives an extra level of confidence that the wines that represent the regions are truly indicative of the sensory profile of the wines from the region. This work has resulted in detailed quantitative data on the sensory properties associated with each of the regions, and shown there are distinctive, region-specific sensory characteristics. The peer-reviewed publication relating to this portion of the project is also included here.
Chapter IV builds on the sensory profile of the subset of regional wines from chapter Three and adds more layers of complexity with a comprehensive chemical profile, including wine and oak volatiles, low molecular weight sulfur compounds, colour/tannin data, norisoprenoids and monoterpenes. Climatic data from the vineyard sites for each of the wines was also tabulated. These three data sets were then analysed using partial least-squares regression (PLS-R) in order to examine the relationships between them and evaluate the model produced by the analysis. This work showed that distinctive chemical fingerprints exist for the regions studied, and the climatic profiles were strongly associated with key compounds influencing sensory differences. The final peer-review publication is also included in this chapter.
This project has taken the concept of regional characters in Australian Shiraz wines and put them under the microscope, in a way that has never been undertaken before. This work has shown that Shiraz producing regions in Australia possess unique sensory fingerprints, the result of similarly unique chemical compositions and climatic factors. The results from this project can be used as a template by regional producers to help them exploit characteristics that are prevalent in wines that come from their regions, and can also be used as a blueprint for other Australian wine producing regions as a way to investigate their regional characteristics.