2019 ASHS Annual Conference

Daytime temperatures in the San Joaquin Valley can reach well over 37°C during harvest. Biological and chemical reaction processes are increased as the temperature increases. Thus wine grapes are commonly harvested in early morning hours to prevent heat from affecting chemical and biological reaction rates, i.e., spoilage of grapes by microorganisms. With growers and processing facilities being spread out over large distances, longer transport times or waiting in line to be processed at a winery’s test stand, processing the grapes might take longer and the gondola will be subjected to warmer parts of the day. Three truck loads of gondolas from three different vineyards were sampled every two hours, from 6:00 a.m. to 2:00 p.m. for FT-MIR analysis and temperature tracking. Analytical attributes tracked over the course of this study included brix, titratable acidity, ethanol, volatile acidity, tartaric acid, malic acid, gluconic acid, glucose, and fructose. Volatile acidity and gluconic acid were more closely looked at as they are seen as rot indicators. Higher rates of gluconic acid can be formed through fungal metabolism, as it is a metabolite of Penicillium, allowing the first carbon of glucose to become oxidized. The goal was to test the FT-MIR based calibration model to determine beginning levels of microbial spoilage in gondolas and find if temperature has an effect on the growth of the microbial contaminants in gondolas. Results of the three truck loads of gondolas show a significant linear increase of temperature of juice, gluconic acid, volatile acid, and FT-MIR rot predicted values based on time.