Vineyard Management to Meet Grape Quality Specifications
The aim of this program is to develop vineyard management systems that will be used to grow grapes with specified quality attributes for each sector of Australia's viticultural industries.
The research in this program will lead to the development of analytical methods to measure critical grape components such as flavour and vineyard management strategies for the production of grapes to these specifications. Defining grape quality attribute specifications will be of great benefit to the grape industries.
Program Manager
Dr Elizabeth Waters
Dr Elizabeth Waters is the Principal Research Biochemist with The Australian Wine Research Institute. Liz has been involved for 14 years in research on protein, polysaccharide and tannin chemistry and the influence of viticultural practices on the levels of these polymeric compounds. Her work has also established the oxidation of wines. Since obtaining her PhD in 1992 she has published more than 20 publications.
program update (19/12/2005)
The development of fast and reliable analytical methods continues to measure critical grape components related to wine flavour and colour continues to be a major aim of this research program. Such methods will help growers to grow their grapes to meet specifications and give winemakers an improved ability to create different wine styles for various markets and price points.
While we can reliably measure pH, total acidity, colour, sugar and tannins in grapes, the challenge exists for us to also measure agrochemical residues, fungal contaminants, flavour compounds and precursors and other precursors for colour and mouthfeel.
Not only do we need to have the ability to measure these characteristics, we also have to understand how viticultural and winemaking processes modify wine quality.
We have several projects directed at the winemaking process. One of these has given us a greater understanding about how beta-damascenone is lost in bottled wine. This compound is found in all young wines and provides wines with fruity, stewed apple and quince aroma notes, but the levels decrease as aging continues. We have found that the principal cause for the loss is reaction of damascenone with sulphur dioxide.
Another of our “winemaking” projects is focussed on the sulphur containing volatiles that are important for providing Sauvignon Blanc and other wines with their tropical nature. In addition to characterising these compounds we have gained knowledge about how they break down during fermentation. By collaborating with the Bioscience team at The Australian Wine Research Institute, we have discovered that the strain of yeast used is critical in retaining the right level of this compound in the finished wine (the right amount gives a pleasant tropical character, but too much causes an unpleasant aroma of cat urine).
In another project focused on the impact of winemaking practices, we looked at the impact of cold soaking and maceration on colour and tannin in the finished product. In Pinot Noir, maceration treatments had no affect on the total amount of anthocyanins, but did affect pigmented polymer concentrations, with the three week extended maceration treatment having the lowest colour content at 176 days post crushing. We found that a three-day soak with or without plunging gave the highest colour concentration. However, when the experimental wines were tested by a sensory panel, no differences where detected in the overall astringency or bitterness of the wines.
Back in the vineyard, the application of precision viticulture techniques continues to be a major aim. In particular, we have been trying to identify experimental designs and methods of data analysis for our new ‘whole-of-block’ approach to experimentation.
Trial design is important because trials are often used to make important management decisions and growers need to be confident that the design of the trial is conducive to providing accurate data that can help, rather than hinder, management decisions. Of particular concern here is that the trial is done at a scale that is appropriate to the management decisions that it is intended to inform.
Whole-of-block experiments are operating in Clare and Coonawarra, assessing vineyard floor management strategies for improved vine nutrition and different pruning options for improving wine quality. Yield maps, target vine data, EM38 soil surveys and elevation data have been collected and are being analysed.
Our research into the management of Aspergillus carbonarius in vineyards has indicated that soil amendments and the use of cover crops may substantially reduce the survival of this problem fungus. In particular, the use of lucerne hay or oat straw reduced the incidence of A.carbonarius in moist soils.
Our work into the development of rapid methods have produced some great outcomes for industry. In the coming months we will see the launch of a benchtop Vis-NIR to measure colour (total anthocyanins), pH and sugar. Now at the commercial stage of the project, our team has been working with Sydney company Integrated Spectronics to develop and test the product.
Integrated Spectronics has expertise in building the hardware – the physical machine – that will test the grape samples, while we have been able to develop the software needed for the machine to provide an accurate result. NIR is based on predictive calculation and a calibration that compares the sample to others in order to provide a result is needed. Our years of work in sampling thousands of grapes from around Australia have allowed this machine to be developed.
We have also developed a tannin assay to measure total tannin concentration in grape and wine samples. The assay will not only be used by researchers but also for wineries to aid grape streaming decisions, the type of winestyle and determine processing options.
