Using chemistry to assess quality

The Australian wine community is about a year away from having a much clearer idea of what chemistry can tell it – in a practical way – about the grapes it is growing and the wine that can be made from them.

An AGWA-funded project nearing completion at the AWRI is looking to determine which of the many measurable chemical compounds in grapes can be used, independently or in combination, to determine grape quality and even grape style.

Dr Paul Smith, the project leader, and colleagues Dr Keren Bindon and Dr Leigh Francis are consolidating, refining and building on two decades of work by a number of researchers with a view to identifying those measures that could become standard procedures for wineries.

‘Industry has always said, at a strategic level, that it wants objective measures of quality and it’s always been something that AGWA has supported and funded, so we in Australia are considered the leaders in creating and finding those measures’, Dr Smith said.

‘The next step is to make them available to industry in a way that they can use to benchmark their own fruit; that’s not really been taken up in a comprehensive way until this project’.

At the start of the project, the focus was on fruit measurement and getting a detailed dataset. The researchers collected 60 samples each of Shiraz, Cabernet and Chardonnay grapes from the Riverland region of SA and, in Dr Smith’s words, ‘hit them with everything we could analyse’.

Armed with this knowledge they then worked with Accolade to compare what chemistry told them about given parcels of fruit, with how the winemakers had assessed and graded them as part of their normal procedures.

‘So we had the grade information and we had the chemistry information and we wanted to see if there were any relationships that suggest that certain aspects of chemical composition could be used to predict grape quality’, Dr Smith said.

Dr Bindon has finished crunching the data for 2013 and is working on the 2014 results. In the meantime, they have switched their attention to a second phase of the project, which is to assess whether certain chemical measures can help determine what style of wine a given parcel of fruit will produce (for example a lean Chardonnay or a tropical one).

This time they asked Accolade to provide four different batches of fruit, each representative of a different style. After analysing the grapes they made them into wine and in the next few weeks will look for the same compounds in the wine – that is, those that have survived the winemaking process.

‘Our aim is to be able to say that while there are X compounds that are predictive of grade in fruit there are only Y of them that are predictive of the final wine values’, Dr Smith said. ‘So if you want to have a lean style of Chardonnay, for example, you want fruit with X and Y characteristics.

‘At the end of the day, when winemakers are making decisions about sourcing grapes, the style they will produce is probably often as important as their absolute quality. In other circumstances a winemaker may decide to produce a certain style that year because the grapes of that style are of such high quality’.

The research will continue to the end of this year, with the final report due by mid-2016.