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

Abstract

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.