8D Yeasts and Wine Flavour 359
ethyl hexanoate, 3-methylbutyl acetate and hexyl acetate, to produce a clear clus-
ter by principal component analysis, whereas the indigenous yeast wines showed
no clear associations with volatile metabolites of yeast origin. Similar observations
have been reported by others (Garde-Cerd ́an and Anc ́ın-Azpilicueta 2006).
A consensus of the principal sensory attributes of indigenous yeast wines is
not possible since almost no controlled studies have been published. Based on
comments and articles by winemakers,wines made with ‘wild yeasts’ can be
summarised by terms such as complex, diverse, funky, mineral, creamy texture,
greater palate weight and flavour persistence (for example Bellon et al. 2008; Gold-
farb 1994; Ramey 1996; Ross 1997). Unlike inoculated yeast wines, which tend to
have well defined fruity aromas, indigenous yeast wines tend to show a broader,
less well defined fruity to savoury aroma profile. In one of several reports, Riesling
wines made by uninoculated fermentation, for example, had higher sensory scores
for ‘spice’, ‘apple’, ‘melon’, ‘pear’, ‘diacetyl’ and ‘H 2 S’ compared to ‘paper’,
‘oxidised’, ‘sweat’, ‘acetic’ and ‘overall fruit’ for wine made by inoculation (Egli
et al. 1998; Henick-Kling et al. 1998).
8D.6.2 Monocultures ofSaccharomycesSpecies
The speciesSaccharomyces cerevisiae, being highly adapted to fermenting grape
must in monoculture, has become the preferred species for global wine production
(Henschke 1997; Pretorius 2000). The number of strains developed commercially
has grown dramatically over the past five decades. This growth is, in part, due to
the progressive understanding of the numerous roles that yeast play in fermenta-
tion, and in the evolution and modulation of many key wine sensory character-
istics. Furthermore, growth in the selection of autochthonous strains, which are
intended to enhance regional attributes inwines, has greatly expanded the choice of
strains (Clemente-Jimenez et al. 2004; Dumont and Dulau 1997; Henschke 1997;
Lambrechts and Pretorius 2000; Pretorius 2000; Pretorius et al. 2006; Swiegers
et al. 2005; Swiegers and Pretorius 2007; Romano et al. 2003a,b). The extent to
which the commercialized strains can engender chemical differences in wine is
generally well shown (Table 8D.6) (Dubourdieu et al. 2006; Heard 1999; Lam-
brechts and Pretorius 2000; Kunkee and Vilos, 1994; Reynolds et al. 2001; Swiegers
et al. 2008c); however strain impact on sensory attributes is largely unknown since
there is almost a complete absence of well-designed, systematic studies published
(reviewed by Thorngate 1998; Dumont and Dulau 1997; Egli et al. 1998; Est ́evez
et al. 2004; Henick-Kling et al. 1998; Jane et al. 1996; Reynolds et al. 2001;
Reynolds et al. 2007; Swiegers et al. 2008a,c). Many of the grape and yeast
compounds with well documented sensory properties that vary according to yeast
species and strain have been discussed in Sects. 8D.3, 8D.4 and 8D.5.
In addition toSaccharomyces cerevisiae, other species of theSaccharomyces
sensu stricto group have recently become ofinterest to research and winemaking, in
part because of their different capacities to modulate wine composition, and flavour