The Australian Wine Research Institute

Rotundone and its role in defining terroir in iconic Australian cool climate ‘peppery’ Shiraz

Project summary

Rotundone is the potent, grape-derived compound responsible for ‘black pepper’ aroma in wine. Previous research demonstrated that the Grampians and Pyrenees regions in Victoria can produce wines with substantially higher levels of rotundone than other Shiraz-producing regions such as Barossa and McLaren Vale. Patterns of rotundone variation appear to be stable within an individual vineyard across different growing seasons. A collaborative project with CSIRO focused on premium cool-climate Shiraz, with the aim of defining features at the within-vineyard scale that contribute to rotundone formation. The research explored if genetic features in grapevine planting material (which may be transferable through propagation and between vineyards) or environmental features (which are site-specific and might be influenced by management practices) contribute to distinctive aroma attributes. This project was completed during the year, with a Final Report available from Wine Australia’s website.

Latest information

Summary of overall project findings
This project has found that development of the sought-after ‘peppery’ aroma from rotundone in Shiraz grapes appears to depend on site characteristics and environmental factors that regulate sesquiterpene biosynthesis, rather than genetic determinants of planted vines. Overall, it has provided science-based evidence supporting the concept of terroir, demonstrating how the interplay of site, viticultural management, climatic and environmental/biological effectors (which are yet to be identified) shape distinct sensory attributes in Shiraz wine. From a practical management perspective, a very late harvest date was demonstrated as being key to achieving elevated grape rotundone concentrations. This is because extensive formation of the immediate rotundone precursor α-guaiene, and subsequently rotundone itself, typically only commences well after veraison. The importance of harvest date provides an explanation as to why higher grape rotundone, and consequently ‘peppery’ aromas in wine, are typically found in very high premium Shiraz from cool-climate regions where such late harvest is commercially viable. Further research and insights into the environmental regulation of sesquiterpene biosynthesis in Shiraz are required to retain the desirable, but elusive, ‘peppery’ flavours in existing cool-climate vineyards by preserving the responsible environmental and/or biological triggers. In addition, such knowledge could potentially allow Shiraz grapes with ‘cool-climate-like’ flavour attributes to be grown in warmer/hotter regions. Ultimately, the findings of this project represent an important step towards mitigating risks from climate change, biodiversity loss or viticultural management decisions, which might otherwise lead to unintended flavour consequences in Shiraz.