Can a thermal shock produce stuck or sluggish fermentation in oenological conditions?

LERENA M.C.; VARGAS A.S.; ESTEVE-ZARZOSO B.; MERCADO L. A.; MAS A.; QUEROL A.; COMBINA M.

Bariloche

Simposio; 34th International Specialized Simposium on Yeast (34 ISSY).; 2018

CONICET

Problematic fermentations are one of the main problems affecting winemaking industry leading in many cases to important economic losses in part due to a decrease in the quality of the wine. Several factors have been described to be the reason for stuck and sluggish fermentations, being exposure to extreme temperatures among them. During early fermentation stages, high metabolic activity of yeast usually leads to an increase in musts temperature. This increase can be favored by the nutrition of the musts with nitrogenous sources, which is a widely used oenological practice. On the other hand, sudden drops in temperature may occur during the first days of autumn influencing fermentation development. The objective of this study was to identify thermal conditions leading to problematic fermentations, focusing on the impact of abrupt increase/decrease of temperature on fermentation kinetics and yeast viability. Saccharomyces cerevisiae strains used in this study were: T73 and PDM (commercial yeasts) and SBB11 (isolated from Mendoza). Fermentations were conducted at 25°C using synthetic must. The impact of heat shock at 36°C and 40°C was assessed increasing must temperature during 16 hours on the third day of fermentation, together with must nutrition with diammonium phosphate. In contrast, cold shock was assessed by decreasing must temperatures (1.5°C, 8°C and 10°C) during 16 hours on days 2, 6, 10 and 14 of alcoholic fermentation. Fermentation kinetic was monitored through density measurements whereas cell viability/vitality was evaluated with flow cytometry. Heat shock affected fermentation kinetics with different intensity depending on the temperature or yeast strain evaluated. None of the conditions evaluated leaded to a stuck fermentation, although sluggish fermentation was observed for heat shock assays. Native strain SBB11 showed to be the most sensitive to heat shock. Moreover, no effect of cold shock on alcoholic fermentation performance was observed for all the conditions assessed.