Influence of temperature and pH on Saccharomyces bayanus var. uvarum growth; impact of a wine yeast interspecific hybridization on these parameters.

The species Saccharomyces bayanus var. uvarum possesses interesting enological characteristics but produces high concentration of volatile fermentative compounds not desirable in Sauvignon blanc wines. Interspecific hybrids between Saccharomyces cerevisiae and S. bayanus var. uvarum were made in order to join the main parental advantages. Two hybrids were selected on the basis of their fermentation characteristics and their karyotypes, i.e. they have a different mitochondrial DNA. In order to produce these hybrids as active dry yeast to be used as starter in wine-making, their optimal environmental conditions for growth, i.e. temperature and pH, were determined as the objective of our work. Using a two-level factorial design it was found that the two parental strains have different optimal temperature but for the two strains, pH does not have a significant influence on growth. The influence of temperature on biomass productivity for hybrid strains were strictly identical, so we suppose that the main genes coding for temperature sensitivity were not contained in mitochondrial DNA, but in nuclear DNA. Moreover the reactions of hybrid strains to the temperature variations were similar to the one of S. bayanus var. uvarum. This latter strain could have a majority of genes responsible of temperature sensitivity dominant in comparison with those of the strain S. cerevisiae.