National Wine and Grape Industry Centre
Grape and Wine Quality
- Shiraz berry shrinkage
- Water economy of the grape berry
- Ascorbic acid and white wine oxidation
- Copper(II) oxidation of white wine
Shiraz berry shrinkage
Project Aim
Determine the physiological causes for pre-harvest weight loss in Shiraz berries
Outcomes
- Weight loss can begin at 80 to 95 days after flowering and varies from 10 to 25%
- Degree of shrinkage is related to canopy architecture
- Irrigation has an effect on the time of onset and degree of weight loss
Project Co-ordinator- Dr. Suzy Rogiers
The water economy of the grape berry
Project Aim
To characterise the physiological factors that impact on the water budget of the berry - in particular, xylem and phloem flow into the berry, backflow from berry to the vine, and berry transpiration rates
Outcomes
- The relative contribution by the xylem and phloem appears to change curing development
- Xylem flow is variable and highly dependent on environmental conditions
- Berry transpiration fluctuates diurnally
Project Co-ordinator- Dr. Suzy Rogiers
Ascorbic acid and white wine oxidation
Project Aims
- To establish the critical role of ascorbic acid in wine oxidation
- To determine the wine components most susceptible to oxidative browning in the presence of ascorbic acid
- To study the influence of sulfur dioxide on the role of ascorbic acid as either a pro- or anti-oxidant
Project Outcomes
- Recognition that the reactivity of ascorbic acid in wine is not as simple as has been assumed
- Dehydroascorbic acid and hydrogen peroxide are only first reaction products; that is, the "classical" equation as shown does not represent the true chemistry of ascorbic acid
- Ascorbic acid, in an oxidative environment, leads to rapid browning of catechin
- The presence of sulfur dioxide leads only to a delay in the ascorbic acid mediated browning of catechin
- The rate of decay of sulfur dioxide is enhanced in the presence of ascorbic acid
- Sulfur dioxide alone is a better inhibitor of catechin browning than ascorbic acid
Project Coordinator- Professor Geoffrey Scollary
Copper(II) oxidation of white wine
Project Aims
- Development of a measurement technique that describes the relationship between copper speciation and enhancement of oxidative browning
- Identify the products generated during accelerated oxidative browning trials using model white wine
- Propose a mechanism for the role played by copper(II) in mediating oxidative browning in white wine
Project Outcomes
- Knowledge of copper speciation in wine and its possible link with copper-mediated oxidative browning
- Identification of xanthylium salts as brown products generated as a consequence of oxidative browning
- Production of hydrogen peroxide and glyoxylic acid in solutions of tartaric acid exposed to sunlight
Project Coordinator- Dr. Andrew Clark