Initial Saccharomyces cerevisiae concentration in single or composite cultures dictates bioprocess kinetics

The growth dynamics of three non-Saccharomyces strains in combination with Saccharomyces cerevisiae during fermentation of a sterile grape juice have been studied. The influence of the initial concentrations of S. cerevisiae on the whole yeast community was the main purpose of this research. The progression of S. cerevisiae within the first 5 days of fermentation was monitored by enumeration on selective and non-selective media. The population of each species was evaluated by morphological criteria. After 24 h, Hanseniaspora uvarum represented more than 50% of the whole yeast community, including ferments with the highest initial concentration of S. cerevisiae. As the population of S. cerevisiae increased, H. uvarum decreased. Metchnikowia pulcherrima was more inhibited by S. cerevisiae than H. uvarum, whereas the growth of Candida stellata was less inhibited. After thirty days, irrespective of the initial concentration of S. cerevisiae, only S. cerevisiae was detected in all ferments. Conversion of sugars to ethanol correlated with the initial population of S. cerevisiae. Glucose was almost completely exhausted in all cases, independent of the initial S. cerevisiae concentration used. Grape juices inoculated with composite inocula of non-S. cerevisiae and S. cerevisiae, with its initial concentration lower than 5 cfu/ml did not produce wines according to wine regulations. The concentration of ethanol in the wines did not reach the minimum amount of 9 vol%. Samples of wines fermented with a composite inoculum the concentration of S. cerevisiae represented 50 cfu/ml of grape juice, were judged to have the best sensorial properties.