Effects of powdery mildew on the sensory properties and composition of Chardonnay juice and wine when grape sugar ripeness is standardised

Copyright © 2008 Australian Society of Viticulture and Oenology Inc.Chardonnay juice from grape batches with increasing severity of powdery mildew (0-100%) was assessed over three seasons (2001-2002, 2002-2003 and 2003-2004). In each season, grapes across infection categories were harvested at a target total soluble solids (TSS) value. In 2001-2002, wine was made under replicated conditions. In each year there was an increase in titratable acidity (TA), total phenolics, hydroxycinnamates and flavonoids in grapes and wine, corresponding with increasing severity of infection. Grape bunches with the most severe disease accumulated TSS earlier. Also, there was a trend for mean bunch and berry weights to decrease with increase in powdery mildew severity. The total microbial population was larger on powdery mildew-affected grapes than on healthy grapes. Sensory descriptive analysis of Chardonnay wines from the 2002 vintage showed that wines made from grapes with powdery mildew, even the least affected, were perceived as having more pronounced viscosity/oiliness mouth-feel than wines made from disease-free grapes. This attribute was correlated with the phenolic composition of the wines. In addition, samples from powdery mildew-affected grapes were more pronounced in fungal, earthy and cooked tomato aroma attributes (wine) and dusty and mushroom aroma (juice) than healthy controls. This study demonstrated that compositional and sensory changes were detected in juice and wines made from grape batches with as little as 1-5% of bunches affected by powdery mildew.Belinda E. Stummer, I. Leigh Francis, Timothy Zanker, Kate A. Lattey and Eileen S. Scot

Quantification of condensed tannins by precipitation with methyl cellulose: development and validation of an optimised tool for grape an wine analysis

A precipitation assay is presented that enables tannin measurement in matrices of red wine, 50% ethanol grape extract and aqueous tannin solutions. By exploiting the polysaccharide polymer methyl cellulose to precipitate tannins, the absorbance of phenolics at 280 nm before and after tannin precipitation (subtractive approach) can be obtained, thus enabling selective measurement of tannin only. This methyl cellulose precipitable (MCP) tannin assay allows complete precipitation of tannin from red wine and from grape homogenate extracts. The subtractive assay is both simple and robust, selective for condensed tannins and does not suffer interference from other 280 nm-absorbing phenolics such as anthocyanins or catechins. Matrix effects have only minimal impact on the assay performance and validation parameters indicate a robust performance. There was good correlation between tannin measured by reverse-phase HPLC and the MCP tannin assay for 121 Australian red wines (r = 0.74) and also 54 grape extracts (r = 0.79). We envisage that the technical simplicity of this tannin assay will enable widespread research and field applications. In addition, an alternative format that requires re-solubilisation of the tannin-polymer pellet in acetonitrile is reported, which is particularly suitable for measurement of smaller tannin concentrations. Notwithstanding that option, technical requirements of the re-solubilisation step lead us to suggest that the subtractive format would be simple for adoption by wine industry practitioners.Sarneckis, C. J. ; Dambergs, R. G. ; Jones, P. ; Mercurio, M. ; Herderich, M. J. ; Smith, P. A

Uptake and metabolism of a systemic fungicide (triadimenol) by pre-veraison grapes

Triadimenol (1-(4-chlorophenoxy)-3,3-dimethyl-1-(1H-1,2,4,-triazol-1-yl)butan-2-ol, formulated as Bayfidan® 250 EC), is one of the most frequently used systemic fungicides in viticulture. However, little is known about the behaviour of this compound once applied to Vitis vinifera sp. and hence strategies to use this fungicide are hard to optimise in an informed manner. Accordingly, uptake and metabolism of triadimenol applied to berries of Vitis vinifera cultivars Chardonnay, Cabernet Sauvignon and Riesling was investigated. Triadimenol rapidly became resistant to removal by washing with aqueous solutions in all cultivars studied, indicating that this fungicide is unlikely to succumb to rain wash erosion after spraying. Metabolism of triadimenol by grapevines was also investigated using 14C-triadimenol by thin layer chromatography/autoradiography. Direct conversion of a minor proportion of triadimenol into polar conjugates, and into conjugates of its oxidation product, was evident. Although similar patterns of triadimenol metabolism were observed with all three cultivars, the proportion of triadimenol metabolised differed, possibly due to minor differences in berry maturity. Metabolism of triadimenol in grapes does not involve breakdown of the fungicide into simpler and smaller compounds, but rather, does result in formation of bigger, conjugates with the original fungicide structure largely conserved

The effect of powdery mildew infection of grape berries on juice and wine composition and on sensory properties of Chardonnay wines

The composition of juice and wine made from Chardonnay, Shiraz and Cabernet Sauvignon grapes with increasing levels of powdery mildew infection was assessed over two vintages (2000 and 2001). Chardonnay juice and wine made from grape lots with 0 %, 1-5 %, 10-30 % and 31-100 % of bunches visually infected with powdery mildew showed an increase in titratable acidity, total phenolics, hydroxycinnamates and flavonoids with increasing level of infection. In vintage 2001, Chardonnay bunches with greater than 30% powdery mildew infection had lower total soluble solids (TSS) than lower infection categories and healthy grapes. Powdery mildew infection of Cabernet Sauvignon bunches (1-20%) also resulted in lower TSS, and in lower wine phenolic concentration and spectral colour values compared with healthy grapes. The total microbial population was higher on powdery mildew affected Chardonnay, Shiraz and Cabernet Sauvignon grapes than on healthy grapes. Sensory descriptive analysis of Chardonnay wines from the 2001 vintage showed that wines made from grapes with powdery mildew infection were rated higher in 'oily' and 'viscosity' attributes than wines made from disease-free grapes. Other sensory attribute differences were also apparent, but these were likely to be related to differences in fermentation rate or secondary compositional effects of the powdery mildew infection, notably differing TSS and acidity in the juice. No mouldy or 'off aromas' were associated with wine made from infected grapes. Nevertheless, the study indicated that even very low levels of infection appear to be detrimental to wine sensory characteristics.Belinda E. Stummer, I. Leigh Francis, Andrew J. Markides and Eileen S. Scot

The impact of closures, including screw cap with three different headspace volumes, on the composition, colour and sensory properties of a Cabernet Sauvignon wine during two years' storage

Mariola J. Kwiatkowski, George K. Skouroumounis, Kate A. Lattey and Elizabeth J. Water