Findings from the long-term Shiraz terroir project are set to help producers better understand and market the ‘effect of place’ on their wines.
The recently completed project described and compared compositional and sensory properties of Shiraz wines across the Barossa Valley, McLaren Vale, Heathcote, Yarra Valley, Canberra District and Hunter Valley wine regions. The properties of the wines were then compared to a range of climate indices calculated specifically for the vineyards where the grapes were sourced.
“This allowed us to interpret how some aspects of climate and winemaking practises in each region can affect wine composition. Some of these factors can then be tasted in the wine,” explained chief investigator, Dr John Blackman, from Charles Sturt University.
A sensory technique called Pivot© Profile, validated by the Australian Wine Research Institute and the National Wine and Grape Industry Centre, was used in the Wine Australia-funded project.
Pivot profiling is a rapid data collection method that asks people not to assess and describe each wine in isolation but to compare it to a control wine (the pivot).
“Not only does that change the dynamic of the process, it also changes the type of judges who are best suited for the method,” said Dr Blackman.
The Pivot© Profile method demonstrated that it produced consistent results with similar outcomes to that of the gold standard technique routinely used for sensory analysis, sensory descriptive analysis.
The Pivot Profile technique was 'road tested' with sommeliers as part of the Somms of the World program in 2017
Subsequent use of the Pivot© Profile method in regional tastings confirmed it to be a suitable alternative in sensory studies in situations where time and cost preclude the use of descriptive analysis.
A snapshot of the Shiraz terroir project
Sets of wines (22 to 28 wines) from six Australian Shiraz producing regions were evaluated by groups of local winemakers using the Pivot© Profile method to obtain maps of their sensory characteristics. Three or four wines from each region were then selected using cluster analysis and 22 wines were evaluated using sensory descriptive analysis.
The regional Pivot© Profile assessments provided a ‘sensory fingerprint’ of the variability of each of the regions studied and identified sensory characteristics that typified the largest groups of wines of each region. The descriptive analysis highlighted sensory characteristics that distinguished the wines from the different regions.
The same 22 wines were then analysed for 70 chemical markers and 17 site and season-specific climate indices.
The team found the wines were well grouped by region of origin: distinctive chemical fingerprints existed for the regions studied, and the climatic profiles were strongly associated with key compounds influencing sensory differences.
“Wines with stalky/cooked vegetal sensory properties had higher cinnamate esters and dimethylsulfide, relating to later bud break and harvest date. Wines with higher monoterpenes were associated with floral aroma,” Dr Blackman said.
High radiation measures were linked to higher tannin, colour density, norisoprenoid compounds and phenylethyl acetate and stronger dark fruit/dried fruit and tannin/colour attributes. High rainfall indices were related to generally low intensity of most sensory attributes and most compositional measures.
Findings on esters
The project discovered some interesting findings on esters, which are volatile compounds that give fruity aromas.
“In our profiling of volatile composition of Shiraz wines, we found that a large proportion of compounds that showed regional differences were fermentation-derived esters,” Dr Blackman said.
“Among these were three fatty acid ethyl esters, i.e. ethyl 2-methylbutanoate, ethyl 3-methylbutanoate and ethyl hexanoate, which have been shown by other scientific studies to be major contributors to fruity – especially red and blackberry – aromas in red wine.”
They were found to be generally present in higher concentrations in Hunter Valley and McLaren Vale wines.
“Aside from fatty acid ethyl esters, we also found that two related esters, ethyl cinnamate and ethyl dihydrocinnamate, were present at substantially higher concentration in Yarra Valley wines.”
While this correlated to a later harvest date, winemaking practices such as whole bunch inclusion were also acknowledged as being important.
In conclusion, the project has highlighted the distinctive profile of Shiraz wines from a range of ‘terroirs’ and attributed a molecular basis to that sense of place. Grapegrowers and winemakers can choose to make decisions about how to amplify or modify those attributes depending on their growing or winemaking practices.