PhD Précis: Gillean Miller

Please describe your PhD topic

My research looks at gamma-nonalactone, a volatile compound associated with stone fruit and coconut aroma in wines. Although this compound has been quantified in both white and red wines, and its contribution to wine aroma has been demonstrated, little is known about how it is produced during winemaking. Does it come from the grapes, yeast metabolism, malolactic fermentation, or oak during fermentation or ageing?

How have you progressed?

We addressed the above questions in three steps. First, we developed a sensitive analytical chemistry method for the quantification of gamma-nonalactone in wine, which was necessary as gammanonalactone is generally present in very low concentrations in wine and therefore difficult to measure accurately. We used this method to quantify gamma-nonalactone in New Zealand wines for the first time, focusing on Pinot Noir, as well as white wines with and without noble rot (which in wines from other countries has been shown to increase the amount to gammanonalactone present). Those two steps have been completed, and I have published a paper on method development and analysis of New Zealand Pinot Noir wines, with a paper on white wines currently in the works. The third step is to investigate the biogenesis of gamma-nonalactone during alcoholic fermentation, using different yeast strains, oak, and spiking juice with different precursors prior to fermentation. The resulting wines will be analysed using the method we developed.

What did you present at the New Zealand Wine Centre Scientific Research Conference?

I focused on the third stage of my research, because I’ve had some interesting results here. I’ve identified a few chemical compounds from which gammanonalactone can be produced, although the mechanisms of these processes are not yet clear. I am currently investigating the impact of using different yeast strains and strains with certain genes ‘deleted’ to get a better idea of what might be going on.

What's most challenging about this research?

The multidisciplinary nature of my project is both the best and most challenging part. I’m lucky enough that I’ve been able to develop a range of skills, including organic synthesis, analytical chemistry, and microbiology/ biochemistry – but this means I need to be constantly researching the techniques I’m using, and figuring out new ideas for experiments. It’s definitely not boring though!

What drew you to Auckland University and wine science?

University of Auckland (UoA) has excellent schools of chemical and biological sciences, which originally drew me to this university. I completed my BSc in these subjects and was keen to undertake research involving both organic chemistry and microbiology. It just so happened that my current supervisors, Drs Rebecca Deed, David Barker, and Lisa Pilkington, had the perfect project, which was in the wine science field. This was also quite fortunate as I do enjoy the occasional glass of wine!

Who has helped you with this PhD?

I couldn’t ask for a better supervisory team – any time I need advice or just to discuss something, they are always happy to help. I work with a great bunch of people in the lab, who are always keen to bounce ideas off each other. Of course, I wouldn’t have made it this far without the support of my family or partner, and the financial support of the UoA Doctoral Scholarship.

What's next for you?

I’m in the final year of my PhD now, so I’m writing my thesis while I finish my last few experiments in the lab. I’m excited to see my research collated in a cohesive way, then see what opportunities may lie ahead in my career.