THE CONDUCT OF SOME SELECTED YEASTS STRAINS UNDER THE INFLUENCE OF SOME EXOGENOUS FACTORS

Abstract

SUMMARY It is already known the fact that in the spontaneou s fermentation that is produced in the sowing absence with the selection yeasts, the indig ene micro flora assures the fermentation process (2). Although the Saccharomyces cerevisiae species with her grate variety is not dominated on the grape surface, when it grows the a lcohol contain of the fermentation must, the yeasts indigene of Saccharomyces type become predominant and ensures the fermentation ending. In the present study, after th e selection of the present yeast strains in the spontaneous micro flora, the identification and the systematic integration of the isolated (1), we have passed to the second level: the conduct che ck of the strains in different environmental conditions (temperature, sugar concentration, and the SO 2 doses). All the tests have been made in comparison with natural fermentation of grape must, separated for each strain. The strains that belong to the Saccharomyces ellipsoideus strain from the spontaneous micro flora show o good fermentation activity when the fermentation temperature is between 18 and 25°C and the maximum sugar concentration from the environment is under 250g/l. The natural concentration that was made in the same environmental conditions show a higher prefermentation and fermentation period and a lower maximum of sugar metabolic process in comparison with the fermentation inducted in the se lection strains. When the grapes were sulfated as a result of a crop that was stroked wit h mould the natural fermentation is developing very slow, so it is required a use of th e selection yeasts, that prove to be very useful in those conditions.