2019 ASHS Annual Conference

Higher levels of fungal infections on wine grapes can negatively impact fermentation behavior and the flavor profile of the finished wine. The most common molds that were shown to have an impact on grape quality are Botrytis, Penicilium, and Aspergillus. The objective of this study was to evaluate the effects of different levels of bunch rot on fermentation kinetics. Clean and infected grapes were crushed separately to prevent contamination. Four lots of Chardonnay were crushed into six separate twelve gallon fermentations and divided into two clean controls, 5%, 10%, 15%, and 20% rot by volume to volume. One lot of Petite Sirah was crushed and divided into two two clean controls, 10%, and 20% rot weight by weight. Samples were taken daily for FT-MIR analysis. Analytical attributes tracked over the course of fermentation were changes in brix, titratable acidity, ethanol, volatile acidity, tartaric acid, malic acid, gluconic acid, glucose, and fructose. The goal was to develop an FT-MIR based calibration model to determine the level or concentration of rot that affects the final wine in white and red varieties. The wines were also subjected to difference and preference testing by a trained sensory panel to determine differences between control wines and wines made from infected grapes. Sugar levels were higher in the initial juice containing 20% rot compared to the control, however all wines were fermented to dry. Infected grapes consistently recorded higher levels of titratable acidity, volatile acidity, fermentable sugars, and ethanol. Preliminary sensory studies based on preference showed minimal differences in 5%, 10% and 15%, furthermore 20% wines indicated distinct differences in sensory from controls. Vineyards suffer quality loss due to fungal contamination, currently visual inspections of fungal contamination is the standard practice to quantify rot quality. The analytical testing of the quantification of rot percentage levels, based on the FT-MIR rot indicator matrix, assists in creating a new industry standard for fungal identification pre and post harvest, and understand sensory differences in fungal infected wines.