Comparative Evaluation of the Dynamics of Alcohol Production of Wine Yeast Strains Isolated in Tokaj Region
The dynamics of ethanol production of wine yeasts were examined in model experiments as well as in the winery. The ethanol concentration in young wines fermented by local strains of Saccharomyces cerevisiae, S. uvarum or Starmerella bacillaris (21, 2 and 2, respectively) did not vary considerably (c.v. 1.9 %). All of them produced significantly higher amount of ethanol than the type strain [ATCC 26108] of S. cerevisiae. However, their performance during the fermentation process diverged significantly. Thus the lag phase varied between 33 and 123 hours, while the time requested to produce half of the final ethanol concentration varied between 67 and 294 hours. The dynamics of ethanol production differed at high degree between S. cerevisiae strains isolated of several vintages of local wines (c.v. 25 %), where the intensity of specific ethanol production (ISEP) varied between 0.81-4.56 % ethanol per day. Reverse relationship was revealed between the Lag phase and the ISEP (r2=0.858, p>0.01), and the circumstances of fermentation did affect this trend. Based on their properties, S. uvarum and St. bacillaris strains applied nowadays in wine making have been positioned in the ranges of S. cerevisiae strains. Baule-Mitherlich, Gompertz, hyperbolic, logistic, logarithmic, polynomial, and probit functions were applied to analyze the dynamics of fermentation. All functions fitted well to experimentally measured values at the range of 2 to 9 % of ethanol, that means, the half time could be approached by any of them at p<0.05 level. However, the predictive power of these functions differed significantly; both Lag phase and End point of fermentation could be calculated with requested precision (p<0.001) only with a polynomial function. The constant and secondary coefficients of this function counteracted to the primary one strictly in strain dependent manner, and the role of these three factors groups also varied in strain-dependent manners during the vinification process.
