Metabolic characteristics of wine strains during spontaneous and inoculated fermentation

The spontaneous alcoholic fermentation is characterized by the contribution of different Saccharomyces cerevisiae strains, which grow in succession or in combination throughout the fermentation process and exhibit different metabolic patterns. The formation of secondary compounds is a strain-specific characteristic and the strains are distinguishable in phenotypes through the production of different amounts of by-products. Natural fermentation is a source of indigenous Sacch. cerevisiae strains, which seem more suitable to be used as starter cultures for that particular wine because they were isolated from the original region and, consequently better adapted to the particular vinification conditions of that enological area. Among the indigenous strains, the cultures for must fermentation should be chosen on the basis of aroma and flavour determinants typical of the wine under study. Successively, the selected cultures should be tested for the genetic segregation of traits tinder consideration in order to identify strains completely homozygous for the metabolic characteristics. Only a small proportion of natural wine strains is completely homozygous, the majority being heterozygous for one or more traits. In addition, a significant proportion of natural wine strains can sporulate on rich media, such as grape must, and, as a consequence, the progeny of such strains can exhibit differences in the levels of by-products, thereby affecting the organoleptic properties of the final product. Determination of the degree of strain stability overcomes this problem and allows the choice of the most suitable selected culture to be used in inoculated fermentation. The feature, "stability of metabolic phenotype in industrial strains", represents a selective index, which ensures that the final product is always consistent with the own properties of each wine.