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.