Purpose: The main objective was to determine the effect of incubation time of yeast, the main spoilage microorganisms in fruit juices and wine, on inactivation in order to define the most promising process step in wine manufacturing for the application of the technology.
Methods: Saccharomyces cerevisiae was incubated at 23°C in red grape juice for 0, 1, 2, 6 or 9 days. The fermented grape juice was treated in a pressure chamber at 500 bar with nitrogen at different temperatures (10, 25, 40°C) in triplicate, respectively. The viable count before and after decompression was determined by plating on wort agar and incubation at 30°C for 3 - 5 days.
Results: The resistance of yeast decreased for all process temperatures until an incubation time of two days (end of exponential growing phase). Afterwards in the stationary phase the resistance increased significantly. For an incubation time of 2 days the highest viable count reduction was found at 25°C (-1.0 ± 0.1 log) while at 10°C and 40°C the reduction was slightly lower (-0.8 ± 0.2 log and -0.7 ± 0.1 log, respectively) indicating that the process temperature had a minor effect.
Significance: The pressure change technology is a valuable tool for reducing spoilage microorganisms in wine and fruit juice while retaining the aroma and flavor. Most promising is the application for the inactivation of yeast in the transition from exponential to stationary growing phase to stop the fermentation in the wine making process without adding sulfur dioxide.