Abstract
Vineyards and grape musts harbor complex locally specific microbial communities, among which yeast species can be responsible of spontaneous alcoholic fermentation. Although relying on indigenous yeast can be a risk for winemaking, local yeast diversity is associated with complexity and stronger identity of the wine produced, compared to inoculated alcoholic fermentation with commercial yeast strains. In this context, the main yeast species present on grapes, leaves and soils of Tempranillo and Cabernet Sauvignon vineyards in the hot semi-arid climate of the Texas High Plains area were investigated, as well as the presence and dynamics of yeast species during spontaneous fermentations of Tempranillo grapes from the same vineyards. Molecular characterization of yeast species was performed using culture-dependent 5.8S-ITS restriction fragment length polymorphism method and sequencing. Yeast species recovered from grapes, leaves, and soils were mainly dominated by Aureobasidium pullulans, Cryptococcus species, Filobasidium species and Naganishia species, typical members of the vineyard environment. One isolate of potential enological interest, Lachancea thermotolerans, a fermenting yeast with potential in must acidification, was recovered from the vineyard environment. However, spontaneous alcoholic fermentations revealed the presence of fermenting yeast species, including Saccharomyces cerevisiae, Lachancea thermotolerans and Hanseniaspora species. The presence of the three aforementioned species is of extreme interest for winemaking in the Texas High Plains area. Indeed, Saccharomyces cerevisiae is the model for alcoholic fermentation, Hanseniaspora species have been shown to improve palatability of wines, and Lachancea thermotolerans has become of increasing interest due to its potential to acidify musts and palatability. One of the main characteristics of grapes grown in the Texas High Plains area being the lack of acidity, focusing on these three yeast species could promote the development of locally oriented started cultures for the production of wines with a stronger local identity.
Highlights
Wine is an alcoholic beverage made from fermented grape juice, and requires microorganisms to convert grape sugars into alcohol and carbon dioxide
In the present study we evaluated yeast diversity in the vineyard environment of the hot semiarid climate of the Texas High Plains, and the presence and dynamics of potential enological indigenous yeast populations during the spontaneous fermentation of grapes from their original vineyards
Yeast diversity in the vineyard environment was found to be higher in soil samples than in leaf or berry samples, and the soil population was differentiable from the two other types of samples (Fig 1)
Summary
Wine is an alcoholic beverage made from fermented grape juice, and requires microorganisms to convert grape sugars into alcohol and carbon dioxide. Winemakers perform inoculated fermentations by adding commercial active dry yeast (ADY) preparations to the must, or alternatively rely on the indigenous yeast populations present in the vineyard or the winery environment to perform spontaneous fermentations [1]. Inoculated fermentation of grape juice with S. cerevisiae strains can result in a decreased wine complexity in comparison to spontaneous fermentations [4, 5], and has been associated with a decreased environmental biodiversity [6]. It is recognized that the use of the same commercial strains in wineries all over the world could decrease the diversity of wines and lead to a globalization of wine sensory properties, due to the specific aromatic compounds released during fermentation by yeast strains [7]
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