Yeast Biodiversity In Wineries 21 Yeast Species Diversity During Vinification

All the investigations carried out on grape surfaces by direct isolation (without enrichment) have constantly shown that Hanseniaspora uvarum (anamorph: Kloeckera apiculata) is always the predominant inhabitant of the grape surface (75% of the cells); this numerical supremacy may explain its initial domination in natural fermentations. Metschnikowia pulcherrima is often present, followed by a group of film-forming yeasts (Pichia anomala) or pigmented species (Rhodotorula sp.). In a general study of yeasts isolated from grapes, however, it was noticed that the profile of yeast species may also vary from region to region (Martini and Vaughan-Martini 1990). Numerous factors affect the total yeast population and the relative proportions of individual species on the grapes. These factors include climatological conditions, the grape variety and the degree of maturity at harvest, the use of fungicides and the physical damage of the grapes (Fleet and Heard 1992). The yeast diversity found in wine-producing regions is strongly related to the quality and organoleptic characteristics of the wine produced from one year to another. However, the most significant finding was that S. cerevisiae is practically absent from grapes and vineyard soils (Martini and Vaughan-Martini 1990). The presence or absence of S. cerevisiae on grapes is the subject of some debate. Some authors propose that this species is a "natural" organism present in plant fruits (Mortimer and Polsinelli 1999; Sniegowski et al. 2002). Others argue that it is an artificial species that originated from the hybridization of other Saccharomyces species, and which then evolved over several centuries to become fully adapted to man-made environments such as wineries (Martini 1993). Finally, some other authors postulate that S. cerevisiae is a domesticated species that originated from its closest relative, S. paradoxus, a wild species found all around the world that is associated with insects, tree exudates, and fermenting plant extracts (Naumov 1996).

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