Yeast communities before and after spontaneous fermentation of wine grapes: a case study from Nova Scotia

Wine fermentations are generally completed by the domestic yeast Saccharomyces cerevisiae, but many indigenous vineyard yeasts also influence wine flavour and aroma. Despite the flourishing wine industry in Nova Scotia, there has yet to be any systematic evaluation of these yeasts in Atlantic Canada. The yeast communities of pressed L'Acadie blanc grapes sampled from an organic vineyard in the Annapolis Valley in 2018 and 2019 were characterized before and after spontaneous fermentation by both Illumina and PacBio sequencing, to address and compare potential platform biases. Chemical and sensory evaluations were also conducted. Basidiomycete yeasts, including Vishniacozyma carnescens, Filobasidium globisporum, and Curvibasidium cygneicollum, dominated pre-fermentation diversity. Species of Saccharomyces made up ∼0.04% of sequences prior to fermentation, but 85%-100% after fermentation, with some replicates dominated by S. cerevisiae and some by S. uvarum. PacBio sequencing detected high proportions of Hanseniaspora uvarum, while Illumina sequencing did not. A better understanding of Nova Scotia vineyard yeast communities will allow local wine makers to make better use of non-traditional yeasts and spontaneous fermentations to produce high-quality wines unique to the region.

Sensorial and Volatile Analysis of Wines Made from Partially Dehydrated Grapes: An Ontario Case Study

Winemaking in cool climate viticultural areas can pose challenges due to difficulties in achieving optimal ripeness from climatic conditions that tend to vary vintage-to-vintage. To stabilize quality, the use of partially dehydrated grapes has been indicated as beneficial to the production of high-quality wine (“appassimento” style) despite climatic variation. Postharvest wine grape dehydration is a complex process that involves the concentration or formation of sugars, aromas, and flavours. One of the quality challenges facing appassimento style winemaking is elevated levels of undesirable oxidation compounds. The aim of this study was to characterize wines made from a local yeast isolate, Saccharomyces uvarum CN1, which demonstrates limited osmotolerance and may have application to this wine style, as it is a known lower producer of such compounds. Wines made with CN1 were compared to wines made with the accepted commercial standard, S. cerevisiae, EC1118. Fermentations (n = 24) were established at three target starting sugar concentrations from dehydrated Cabernet franc grapes (24.5, 26.0, and 27.5°Brix) and a control (21.5°Brix) and were assessed for volatile organic compound (VOC) composition via gas chromatography-mass spectrometry (GC-MS). Wines also underwent quantitative descriptive analysis to identify and quantify sensory attributes by a trained panel (n = 11). Results show that the wines fermented with the yeast isolate contain significant differences in the concentrations of VOCs in the wines. Sensorially, the wines differed in intensity for a number of attributes, including red fruit aroma, black fruit flavour, and length of finish both within Brix treatments and amongst yeast strains. The most important differentiating factor amongst these wines was the combination of yeast strain at the highest starting sugar concentration (27.5°Brix). These findings may assist winemakers by informing the yeast strain choice for optimizing appassimento style wine quality in cool climates.

Genomic Adaptation of Saccharomyces Species to Industrial Environments

The budding yeast has been extensively studied for its physiological performance in fermentative environments and, due to its remarkable plasticity, is used in numerous industrial applications like in brewing, baking and wine fermentations. Furthermore, thanks to its small and relatively simple eukaryotic genome, the molecular mechanisms behind its evolution and domestication are more easily explored. Considerable work has been directed into examining the industrial adaptation processes that shaped the genotypes of species and hybrids belonging to the Saccharomyces group, specifically in relation to beverage fermentation performances. A variety of genetic mechanisms are responsible for the yeast response to stress conditions, such as genome duplication, chromosomal re-arrangements, hybridization and horizontal gene transfer, and these genetic alterations are also contributing to the diversity in the Saccharomyces industrial strains. Here, we review the recent genetic and evolutionary studies exploring domestication and biodiversity of yeast strains.

Saccharomyces bayanus Enhances Volatile Profile of Apple Brandies

Qualitative and quantitative profiles of volatiles in alcoholic beverages depend mainly on the quality of raw materials, yeasts used for fermentation, and processing technique. Saccharomyces bayanus is a yeast species which is not commonly used for the production of alcoholic beverages, but it is able to produce volatiles that add desirable aroma. Since there is little information regarding the application of that microorganism for the production of apple brandies and how it affects volatile profile of finished products, we decided to address that issue. The aim of the study was to determine the impact of S. bayanus on the profile of volatile compounds and sensory properties of apple spirits obtained from three apple cultivars (Topaz, Rubin, and Elise) in comparison to spirits obtained from fermentation carried out spontaneously or with Saccharomyces cerevisiae. Obtained brandies were analysed using gas chromatography-flame ionization detector (GC-FID), solid phase microextraction-gas chromatography-mass spectrometry (SPME-GC-MS) and sensorially. In our study, brandies produced from musts fermented by S. bayanus demonstrated the highest concentration of ethyl esters and increased concentrations of isoamyl acetate, 2-phenylethyl acetate, ethyl palmitate and hexanol. Moreover, our results support the hypothesis that non-Saccharomyces yeasts which are present during spontaneous fermentation and demonstrate higher β-glucosidase activities enhance aroma of alcoholic beverages through releasing aroma compounds from glycosidic forms, e.g., α-phellandrene, (E)-β-fanesene, (Z,E)-α-farnesene, α-farnesene, and farnesol. Considering results obtained in sensory analysis, we proved that S. bayanus is suitable for the production of apple brandies, improving their flavour. Brandies obtained from musts fermented by S. bayanus obtained the highest average range for "overall note" parameter in sensory analysis.

Wine Fermentation

Currently wineries are facing new challenges due to actual market demands for creation of products exhibiting more individual flavors[...]