Shiraz wines have chemical ‘fingerprints’ that are specific to their region – despite variations in the natural condition of vineyards and human interventions in the winery – new research confirms.
‘Put simply, our study provided evidence for the concept of terroir – wines of the same grape variety grown and vinified in different regions have underlying patterns in their chemical compositions that are characteristic of the region’, said Dr Sijing Li from Charles Sturt University and the National Wine and Grape Industry Centre.
Until now, determining the key influences on terroir has presented a challenging conundrum for the Australian wine sector, requiring the collective input of experts in spatial and climate science, wine production, sensory, analytical and data sciences.
In this ongoing research project, supported by Wine Australia, Shiraz wines from various regions were classified according to their volatile composition, and a small number of compounds characteristic of particular regions were identified.
Wines from six Australian regions covering a range of climatic conditions – including Barossa, Canberra, Heathcote, Hunter Valley, McLaren Vale and Yarra Valley – were selected for the project.
‘In each region, an expert panel was convened to choose 3 to 4 wines that were representative of the regional style from an initial line-up of 22 to 26 wines. In total, 22 wines, from either 2015 or 2016 vintage, were selected’, Dr Li explained.
The research team found concentrations of some compounds showed large within region variations, which may indicate the effect of different viticultural and oenological practices adopted by individual producers.
Key findings included:
- All six regions could be separated from each other based on their volatile profiles.
- Hunter Valley wines selected for this project showed larger in-region variations than wines from the other regions.
- Compounds that were identified as important to the discrimination between regions included esters (diethyl methylsuccinate, ethyl 2-hydroxyisovalerate and ethyl furan-2-carboxylate), higher alcohols (1-octanol, 1-octen-3-ol) and aldehydes and ketones (furfural and acetovanillone).
- It appears that the whole wine production chain contributes to the regional typicality of wine, including grape composition, fermentation and use of oak.
Co-leader of the study, Charles Sturt PhD candidate and senior scientist from the Australian Wine Research Institute, Wes Pearson, summarised key findings of the study as an invited speaker at the Australian Wine Industry Technical Conference, held in Adelaide in July last year. His summary included the sensory properties expected from each of the regions and found:
- Wines from Canberra were rated highly for their floral attributes and were found to be high in monoterpene compounds citronellol, trans-geraniol, linalool and terpinolene
- Yarra Valley wines were higher in two cinnamate compounds, which are related to stalky attributes, and a ‘cooked vegetable’ aroma.
- Barossa Valley wines were distinct from wines from the other regions with higher concentrations of C-13 norisoprenoids, phenyl ethyl acetate and ‘dark fruit’ attributes. There was also a correlation with lactones and oak aroma.
- McLaren Vale wines were found to be high in colour density, pigmented tannin and the esters ethyl 2-methylbutyrate, ethyl isovalerate, ethyl propanoate and ethyl isobutyrate.
Dr Sijing Li's study found that Shiraz wines have chemical 'fingerprints' that are specific to their region.
Dr Li said results from the untargeted analysis could be used as a pointer to more specific studies in the future, which in turn could lead to a more comprehensive answer to the Australian terroir question.
‘We hope that by defining objective measures of terroir and provenance it will lead to an improved understanding of the interplay of climate, geography and people in the production of Australian Shiraz wines in the future’, said Dr Li.
The Final Report from this project is available here.