Adding science to the grape grading process
Determining winegrape quality has always had an element of subjectivity. Most people do it simply through taste, smell, vineyard observations and a knowledge of history, often combined with some basic chemical analyses.
The Australian Wine Research Institute (AWRI) can now provide some additional scientific objectivity to the process, with potential for winemakers to stream fruit based on its chemical makeup.
It’s not a new subject; objective measurement of wine and winegrape quality has been a topic of discussion around the world for decades. And it’s not the first attempt to get some clarity. But it’s by far the most comprehensive.
‘In the past, studies have generally focused on just one or two chemical measures; for example, grape colour or glycosyl-glucose as a marker for aroma molecules’, said Dr Paul Smith, who led the recently completed project. ‘What sets this work apart is that we sought to bring together the majority of proposed measures in one big suite of analyses and then apply it to two vintages of fruit in the Australian situation.’
Working with Accolade Wines, which provided Shiraz, Chardonnay and Cabernet Sauvignon grapes of varying grades from its vineyards across Australia, Dr Smith and AWRI colleague Dr Keren Bindon demonstrated clearly that the chemical composition of winegrapes can be used to differentiate between grape grades.
This gives individual wineries the potential to make grading decisions quickly and with confidence if they have, or can access, a little scientific expertise to measure the right things and build appropriate models.
‘We’ve seen that certain chemical compounds are consistently important for grape quality, with some being variety-specific’
The second stage of the project, which developed after discussions with the sector, has just as much potential. Studies with Shiraz and Chardonnay showed that chemical compounds in grapes can help determine to what style of wine a specific batch of fruit is best suited – and thus will enable the fruit to be used most effectively.
‘And that applies whatever the grade of fruit’, Dr Smith said. ‘We can tell, for example, whether a particular batch of Grade B Chardonnay grapes would best suit a really lean kind of wine or a peachy, tropical style or one or two other styles in between.
‘We’re confident about the types of compounds that should be measured for grape grading and wine style streaming. However, the specific relationships between fruit composition, grape grade and wine style need to be established by each winery on an individual basis because they will be a function of the fruit that they receive and their specific wine production processes.
‘This case study has shown that objective measures of this type are valuable, and we encourage the grape and wine community to consider how they could be implemented.’
In a new project that builds on this work, Dr Bindon is working with Pernod Ricard Winemakers on Shiraz grapes in the Barossa Valley.