Dynamics of Yeast Populations during the Early Stages of Natural Fermentations for the Production of Brunello di Montalcino Wines

Lisa Granchi, Donatella Ganucci, Anna Messini, Daniele Rosellini, C. P. Berrie, Massimo Vincenzini

Dipartimento di Scienze e Tecnologie Alimentari e Microbiologiche, Universitá degli Studi di Firenze, Piazzale delle Cascine 27, 50144 Firenze, Italy

Article history:
Received September 9, 1997
Accepted November 11, 1998

Key words:
wine microbiology, non-Saccharornyces yeasts, natural wine fermentation

Summary:
The growth behaviour of the individual yeast species dominating the early stages of natural fermentations of grape musts for the production of quality Brunello di Montalcino wines in the course of three consecutive vintages was quantitatively determined, under commercial conditions in two different cellars, and following the time course of fermentation parameters. Freshly extracted grape juices, sulfured to initial concentrations between 40 and 100 mg of total SO_² per liter, contained 10³ to 10⁶ yeast cells per mL, depending on the vintage. Kloeckera apiculata, Metschnikowia pulcherrima and, occasionally, Candida stellata and Candida valida zoere the dominant species. Saccharomyces cerevisiae zvas present in much lower numbers than the non-Saccharomyces species. Independently from the initial SO_² concentration, a significant growth of non-Saccharomyces yeasts was generally observed before the onset of the vigorous fermentation phase. The kinetic characteristics of this growth were found to vary with the fermentation as well as with the yeast species. K. apiculata remained the species with the highest specific growth rate and yield, reaching maximum density of about 10⁸ cells per mL. After growing to maximum density, the non-Saccharomyces yeasts rapidly lost their viability. The decline phase of K. apiculata started once Sacch. cerevisiae became the dominant yeast, rather than once ethanol and temperature reached values known to inhibit growth of apiculate yeasts. Sacch. cerevisiae showed only slight differences in its growth behaviour, with maximum specific growth rates quite similar to those of K. apiculata. The rate of ethanol production during the vigorous fermentation phase seemed to be affected by the extent to which the density of non-Saccharomyces yeasts grew.