PhD Précis: Peggy Tsai

Peggy is now based at Lincoln University’s Department of Wine, Food and Molecular Biosciences, where she’s investigating the efficacy of SO2 alternatives in preserving key sensory characteristics of the top three most produced varietals in New Zealand.

What role does sulphur dioxide play in wine?

Sulphur dioxide (SO2) has been used as the main antioxidant in wine production. During winemaking, the grape musts and wine inevitably contact oxygen in any oenological techniques involving air. Too much oxygen exposure causes oxidative loss of both grape-derived and fermentationderived aroma compounds, the development of undesirable oxidative odours, and the acceleration of colour browning. Its ability to enhance fruity notes, reduce oxidative characteristics, and limit the browning of the wine from crushing through to bottling has been affirmed.

Why do winemakers want possible alternatives?

The excessive use of SO2 can have negative impacts on wine quality. For example, not only does SO2 bind with acetaldehydes and other aldehydes with oxidative aromas, it can also bind with aroma-active carbonyl compounds, such as β‐damascenone, leading to the loss of fruitiness. Moreover, SO2 poses concerns with potential side effects, such as hives, swelling, headaches, stomach pain, and diarrhea, for some people sensitive to sulfites. Based on this, the maximum permitted level of total SO2 in wine is regulated and its use requires labelling in most winemaking. Therefore, the trend is oriented toward finding alternatives to reduce the usage of SO2.

What are some of the alternatives you have explored?

My research aims to investigate the efficacy of different SO2 alternatives, including glutathione, glutathione-enriched inactivated dry yeast (GSH-IDY), and chitosan in preserving key sensory characteristics of the top three most produced varietals in New Zealand, Sauvignon Blanc, Pinot Noir and Chardonnay. Most of these alternatives have combined effects when used together with SO2, while some of them need to be used complementary with SO2. Various combinations of these antioxidants have been researched in order to find the most effective and efficient way to protect the wines while keeping the SO2 addition to a minimum level.

How will you test their efficacy over time?

All the experimental wines treated with either SO2 or SO2 alternatives, or a lower dose of SO2 combined with alternatives, will undergo one year of bottle-ageing and will be analysed for their sensory characteristics, including chemical analysis of both nonvolatile and volatile compounds, mostly related to oxidation and sensory evaluation which investigates the varietal characteristics in regard to different wine varieties.

What drew you to Lincoln University and wine science?

I come from Taiwan, where I received my bachelor’s degree in horticulture. I started to grow an interest in wine when one of my undergraduate courses introduced all the deciduous fruits, including a small chapter on wine grapes, and we went on a field trip to one of the very few wineries in Taiwan. Since there wasn’t any related degree for me to undertake in Taiwan, I sought overseas options and decided to apply for the Taught Master of Wine and Viticulture from Lincoln University. After completing my Taught Master’s degree, while gaining knowledge from other aspects, I found myself indulged in this ‘winederland’ and therefore, started to do a Research Master’s degree, which was upgraded to a PhD earlier this year.

Who has helped you with this PhD?

been for a supportive supervisor team guiding me from the beginning. I would like to express my gratitude to my supervisors, Dr Bin Tian and Dr Leandro Dias Araujo, for sharpening my way of thinking and writing, and imparting wine knowledge through countless discussions. Also, I’m extremely grateful to Dr Eveline Bartowsky and Romina Meloni from Lallemand for giving me constructive advice and expressing great interest in this project.