Getting to the heart of smoke taint’s impact

How and why smoke taint affects wine remains one of the unknowns of winemaking.

What is known is that bushfires can be a major problem for wine regions in Australia, the US and South Africa in particular. It is estimated that smoke taint from the 2007 fires in north-eastern Victoria cost the wine sector more than $300 million.

Research under way at the University of Adelaide is seeking to understand the chemical processes that occur in smoke-affected grapes, with a view to identifying what, if anything, can be done to reduce the impact of smoke taint.

PhD candidate Lieke van der Hulst is working with the Australian Wine Research Institute (AWRI) and the Australian Genome Research Facility on the project, with funding support through an AGWA scholarship.

The first step was to decide which of the many directions to take and the answer was to go back to first principles.

'We know so little about how this works in the grape that until we know what the specific triggers are we can’t go back and work out how to respond in any situation', Lieke said.

Trained in biotechnology and biochemistry in The Netherlands, Lieke was working as a cellar hand for Primo Estate and Wirra Wirra until last year, when the opportunity arose to apply her academic background to an industry and an issue she found fascinating.

'I really wanted to work on smoke taint because I’m not from Australia and I’m intrigued by the weather extremes here', she said.

'At Primo, I spent a lot of time in the vineyard and it was interesting to see what temperature differences and weather influences do to the grapes.

'I started reading up on smoke taint. It’s a bit of an enigma for grape growers because you don’t pick anything different when you taste the grapes; only as you start making wine and fermenting and breaking down the sugars do you notice the impact.

'That just drew me in. I’m really interested in seeing how that works.'

Previous research has shown that smoke-derived volatile phenols accumulate in the leaves and fruit of grapevines by binding to sugars. Some of these sugars are broken down during fermentation, which releases the smoke taint. Some are not broken down until later, however, which results in the gradual emergence of taint over time.

What is not clear is how the length of smoke exposure, the density of the smoke, the source material or the time of the year affects this process.

Before Lieke can try to answer those questions, she needs to try to understand exactly what happens in the grape when it is exposed to smoke. That answer may make the others irrelevant if it throws up options for intercepting or intervening in the process.

Previous research has shown that specific enzymes (glycosyl transferases) are part of the process. Lieke’s suspicion is that a stress response guides these enzymes.

'I am applying my knowledge in molecular genetics to see if this suspicion is correct – no work has been done on this yet.'