ECOLOGY OF YEAST-STRAIN SACCHAROMYCES-CEREVISIAE DURING SPONTANEOUS FERMENTATION IN A BORDEAUX WINERY

The pulsed field gel electrophoresis of chromosomes by its simplicity and discriminating power, constitute an ideal technique for the differentiation of Saccharomyces cerevisiae strains. Analyses of karyotypes have been applied for the study of ecology of wild yeast strains involved in the spontaneous fermentation in red wine making in Bordeaux. The aims of this work were to establish whether spontaneous fermentation is carried out by a small number of wild strains of Saccharomyces cerevisiae and if there is a stability of yeast strains in the winery studied from one year to another. Analyses of karyotypes were performed on Saccharomyces cerevisiae strains isolated at different stages of the fermentation in several vats of the same winery over a period of two years. A small number of strains of Saccharomyces cerevisiae were found to be capable of dominating the alcoholic fermentation in all vats of the same winery, independently of the grapevine cultivar and the time of the harvest. Similarly, stability among the dominant yeast karyotypes was observed. Mitochondrial DNA analysis of certain isolates of the dominant yeast karyotype gave identical restriction profiles. Taking into account the criteria for distinguishing strains of Saccharomyces cerevisiae, it is hypothesized that, over the timer period studied, there existed in one winery a wild strain that was dominant and stable during vinification.