Charles Sturt University
Charles Sturt University

Grape and Wine Quality

Grape and Wine Quality

Shiraz berry shrinkage

Project AimShiraz berry shrinkage

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 AimTranspiration

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
Ascorbic acid and white wine oxidation

Project Coordinator- Professor Geoffrey Scollary

Copper(II) oxidation of white wine

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