The identification and characterization of indigenous yeast in a Chardonnay fermentation of an Ohio winery /

Abstract

The identification and characterization of indigenous yeast populations during the initial eight days of spontaneous fermentation of an Ohio Chardonnay must were examined and compared to a controlled inoculated fermentation in two consecutive harvest seasons, 2000 and 2001. Identification of the indigenous yeasts were determined by physiological tests, whereas strain succession was partly assessed by electrophoretic karyotyping. It was hypothesized that there is a difference in the yeast species present based on the type of fermentation. Based on the results of the physiological tests, three yeast species were identified in the spontaneous fermentation during consecutive harvest seasons. During both 2000 and 2001 seasons, Hanseniaspora uvarum was the predominant yeast species with few Pichia membranaefaciens present as well, in fermentation days one through five. As expected, with an increase in alcohol content, the indigenous yeasts did not survive, instead the more alcohol tolerant yeast, Saccharomyces, dominated and completed the fermentation process. Colony Forming Units (CFUs) were determined for both harvest seasons by performing serial dilutions and plating in triplicate on Sabouraud agar plates. Significant differences existed in yeast populations between the 2000 and 2001 fermentations regardless of type (p=O.OOOI, Multiple Regression Analysis). The yeast populations in the 2000 inoculated fermentation ranged from 106 to 108 per ml in the initial week followed by a decline in numbers to 103 per ml by the end of weeks two and three. By comparison, the 2001 inoculated fermentation ranged from 104 to 108 per ml in week one, followed by a gradual decrease to 103 per ml upon completion of fermentation. The spontaneous 2000 fermentation indicates an increase from 106 to 108 CFU per ml in the first week and remained in that range through the second followed by a gradual decline to approximately 106 CFU per ml upon completion of fermentation. In contrast, yeast populations during the 2001 spontaneous fermentation increased from 104 to 108 CFU per ml in the first week. A subsequent decrease in numbers occurred through weeks two through four with a final CFU number ofapproximately 105 CFU per ml. Electrophoretic karyotyping of select samples of both harvest season indicates variability within the fermentation types and year to year. Although the same three yeasts were present in the spontaneous fermentation of both harvest seasons, these data suggest there is year-to-year variability in both spontaneous and inoculated fermentation.