Molecular and Phenotypic Diversity of Indigenous Oenological Strains of Saccharomyces cerevisiae Isolated in Greece

During 3 years, we explored the biodiversity of the indigenous yeast flora in five Greek wine regions by collecting five varietal grape samples, conventionally and biologically cultured. Spontaneous wine fermentations were carried out by the native microbiota of the grape juice, without the inoculation of selected industrially produced yeast. The indigenous yeast flora, isolated at three phases of these fermentations, was purified and characterized using different oenological and technological criteria. The pre-selected Saccharomyces cerevisiae strains, with the most promising oenological characteristics, were evaluated in microvinifications of Malagousia must and the quality of the produced wines was subjected to a sensorial descriptive analysis.

Survey of Inoculated Commercial Saccharomyces cerevisiae in Winery-Based Trials

Wine production has developed from spontaneous to controlled fermentations using commercial active dry yeasts (ADY). In this study, S. cerevisiae commercial ADY were tested, and yeast community dynamics were monitored at different fermentation stages in three winery-based trials with volumes ranging from 60 L to 250 hL. The differentiation of S. cerevisiae strains was achieved using microsatellite markers. In Experiment 1, results showed that both ADY strains revealed similar profiles, despite being described by the producer as having different properties. In Experiment 2, higher genetic diversity was detected when co-inoculation was tested, while in sequential inoculation, the initial ADY seemed to dominate throughout all fermentation. Pilot-scale red wine fermentations were performed in Experiment 3, where one single ADY strain was tested along with different oenological additives. Surprisingly, these trials showed an increase in distinct profiles towards the end of fermentation, indicating that the dominance of the ADY was lower than in the blank modality. The use of ADY is envisaged to promote a controlled and efficient alcoholic fermentation, and their purchase represents an important cost for wineries. Therefore, it is most relevant to survey commercial ADY during wine fermentation to understand if their use is effective.

A simple coloring method to distinguish colonies of the yeasts Lachancea thermotolerans and Saccharomyces cerevisiae on agar media

The yeast Lachancea thermotolerans converts consumed sugar partly to lactic acid instead of ethanol and is therefore used together with Saccharomyces cerevisiae to produce wines with a lower alcohol content. Being able to distinguish these yeasts is important for quality control and quantitative assessment of the contributions of both yeasts to wine fermentations. Commonly used methods to routinely distinguish these organisms are indirect or rely on commercial products of undisclosed composition. Here we describe that adding bromocresol purple to agar media induces Lachancea colonies to develop a brown color, whereas Saccharomyces colonies remain white.

Co-Inocula Assays of Yeasts with “Killer” Pheno-Type and Sensitive Strains of Saccharomyces cere-visiae with Defects in Mannoprotein Synthesis

Yeast mannoproteins have been thoroughly studied in recent years due to their contribution to different properties of wines. Our working group has the aim to establish the possible relationship between the structure of the mannoprotein (size and charge) and its effect on wines. For this, we have different non-transgenic mutants that synthesize mannoproteins with altered but known structures (mnn mutants). We have constructed double mutants with each of the available single mutants, thus obtaining a very diverse collection of mannoproteins that differ in size and charge. Since the mutants are unable to complete wine fermentations satisfactorily, an alternative is to grow mutants in the laboratory, purify their mannoproteins and add them later to wines. Another option would be to use co-inocula of the mentioned mutants, together with “killer” wine yeast strains capable of killing the mutants. In this work, experiments were carried out to determine the behavior of different “killer” wine strains with each one of the defective mutants in mannoprotein synthesis. The yeast Torulaspora delbrueckii Killer (Kbarr1) has been proved to be especially suitable for making this type of co-inoculum.

The Genus Metschnikowia in Enology

Over the last decade, several non-Saccharomyces species have been used as an alternative yeast for producing wines with sensorial properties that are distinctive in comparison to those produced using only Saccharomyces cerevisiae as the classical inoculum. Among the non-Saccharomyces wine yeasts, Metschnikowia is one of the most investigated genera due to its widespread occurrence and its impact in winemaking, and it has been found in grapevine phyllospheres, fruit flies, grapes, and wine fermentations as being part of the resident microbiota of wineries and wine-making equipment. The versatility that allows some Metschnikowia species to be used for winemaking relies on an ability to grow in combination with other yeast species, such as S. cerevisiae, during the first stages of wine fermentation, thereby modulating the synthesis of secondary metabolites during fermentation in order to improve the sensory profile of the wine. Metschnikowia exerts a moderate fermentation power, some interesting enzymatic activities involving aromatic and color precursors, and potential antimicrobial activity against spoilage yeasts and fungi, resulting in this yeast being considered an interesting tool for use in the improvement of wine quality. The abovementioned properties have mostly been determined from studies on Metschnikowia pulcherrima wine strains. However, M. fructicola and M. viticola have also recently been studied for winemaking purposes.