Important progress using stable isotope-based analytical techniques to determine wine authenticity and provenance has recently been made.
The research is exciting, because being able to demonstrate the authenticity and provenance of wine is important in the international wine market, both to ensure brand integrity and to protect consumers from fake products.
“Wine fraud is not new, nor is it something that is easy to define,” said lead author, Dr Eric Wilkes from the Australian Wine Research Institute (AWRI). “Fraud can include fake wine products (Is it wine? Has it been adulterated? Has it had glycerol, methanol, colour or sweeteners added?); misrepresentation (is this the wine they say it is?); counterfeiting or refill.”
“And it’s also important to remember that all wines are differentiated by just 2 per cent of their total components, as the rest is water and alcohol. So, many wines appear to be very similar when you look at just one component.”
Internationally, wine compositional analysis to detect fraud has included standard wine analysis, FTIR (Fourier transform infrared) spectroscopy, NMR (nuclear magnetic resonance) spectroscopy, trace DNA analysis, isotope ratios, trace metals or fluorescence.
In the authenticity project funded by Wine Australia, Dr Eric Wilkes and Dr Martin Day investigated the use of the stable isotope ratios of strontium, boron, lithium, lead and oxygen together with trace metals concentrations as a means of identifying a wine’s origin. The different elements analysed are known to come from a range of sources during the growth of the grapes, including the air, water, soil and geology. Importantly, the isotope ratios of strontium, boron and lithium are not affected by the process of converting grapes into wine. This allows the development of robust models for assessing provenance, avoiding a weakness identified in a number of other techniques.
The team tested a wide range of wines including Pinot Noir, Chardonnay, Cabernet Sauvignon, Shiraz, Merlot and Riesling. In total, 292 wines were from a broad selection of Australian wine regions, and 94 wines were from other countries including New Zealand, France, Spain, Italy, the US, Chile and Argentina.
The study demonstrated high classification rates using the technique, with 97.3 per cent of Australian wine samples and 77.7 per cent of international samples correctly classified. The overall classification rate was 92.5 cent.
However, the team found pinning down the region of origin for the Australian wines was a little more challenging.
“In terms of what state the wine came from, there was a fair bit of overlap. That’s probably not surprising when you consider that some regions overlap into different states,” Dr Wilkes said.
Overall, the classification success rate of region of origin for Australian wines was around 60 per cent.
“Investigating the impacts of vintage and variety on the use of these isotopic ratios showed they did not have a significant negative effect on the classification of whether a wine was of Australian origin; and that trace metals alone did not provide a clear differentiation of wine origin.”
Dr Eric Wilkes