Wine Chemistry and Biochemistry

(Steven Felgate) #1

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

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