The Microbial Diversity of Sherry Wines

Abstract

Abstract:The principal role of wine yeast is to transform efficiently the grape-berries' sugars to ethanol, carbon dioxide, and other metabolites, without the production of off-flavors. Wine yeast strains are able to ferment musts, while other commercial or laboratory strains fail to do so. The genetic differences that characterize wine yeast strains in contrast to the biological ageing of the veil-forming yeasts in Sherry wines are poorly understood. Saccharomyces cerevisiae strains frequently exhibit rather specific phenotypic features needed for adaptation to a special environment, like fortified wines with ethanol up to 15% (v/v), known as Sherry wines. Factors that affect the correct development of the veil of flor during ageing are also reviewed, along with the related aspects of wine composition, biofilm formation processes, and yeast autolysis. This review highlights the importance of yeast ecology and yeast metabolic reactions in determining Sherry wine quality and the wealth of untapped indigenous microorganisms co-existing with the veil-forming yeast strains. It covers the complexity of the veil forming wine yeasts' genetic features, and the genetic techniques often used in strain selection and monitoring during fermentation or biological ageing. Finally, the outlook for new insights to protect and to maintain the microbiota of the Sherry wines will be discussed.

Analytical and Chemometric Characterization of Fino and Amontillado Sherries during Aging in Criaderas y Solera System

“…During the first stages of biological aging of Sobretabla and 3rd Criadera of Fino, in addition to the biological activity of the flor yeasts, there is a slight malolactic fermentation carried out by the lactic bacteria [35] and even these same bacteria metabolize the existing gluconic acid [36]. This causes the generation of acetic acid [37] and, as a consequence, an increase in the volatile acidity, although sometimes this increase can be counteracted, in part, by the flor yeasts, which metabolize the acetic acid as it is produced. Table 2.…”

“…In the young fortified wine (vintage) there may remain traces of sugars, mostly fructose, from the alcoholic fermentation of the young Palomino wine of the year 11% vol. During the biological aging process in the Sobretabla, the flor yeasts use these residual sugars (1-2 g/L) as a source of carbon in their metabolism [37], which generates a decrease in the concentration of reducing substances in the wine, whose decreasing tendency is maintained in the Fino wines as they age. In the case of Amontillado wines, which are aged under oxidative aging, a change of trend is observed, which now becomes ascending over time.…”

“…The concentration of ethyl acetate increases in the Sobretabla with respect to the young fortified wine (vintage) due to the malolactic fermentation that takes place in the initial stage and is related to bacterial activity [34]. In the Fino wines, this compound decreases as the flor yeasts metabolize it [37,45,49], reaching its lowest concentration in the Fino of the Solera. In Amontillado wines aged under oxidative aging, a considerable increase of this compound is observed, due to the oxidative state in which it ages, which favors oxidation to acetic acid and subsequent esterification with alcohol.…”

“…to 16.5% vol. to replenish the last criadera of Amontillado, lysis of the residual yeast cells can occur and release these substances into the wine, as both these esters and their acids are present in the flor yeasts [37].…”

Microbiota of Fermented Beverages

“…Several studies have investigated specific and peculiar features of non-conventional yeasts in winemaking and their interactions with Saccharomyces cerevisiae, the main actor of fermentation [1][2][3][4][5]. Other reports focus on the microbiota of specific ecological niches, such as sherry wines [6], malting and brewing environments [7], and banana wastes [8]. Selected indigenous S. cerevisiae strains coming from Piceno DOC wines were also investigated by Agarbati et al [9], while Capece et al [10] reviewed recent developments on the use of conventional and non-conventional yeast in beer production.…”