362 M. Ugliano and P.A. Henschke
the warmer viticultural regions but recent data suggest that the high conversion effi-
ciency trait is highly conserved inSaccharomyces cerevisiae(Palacios et al. 2007).
Saccharomyces bayanus/uvarumstrains, however, show a small reduction in ethanol
production efficiency but this is probably of limited commercial significance. Polyol
production varies widely amongstSaccharomycesstrains, and is notably higher in
bayanus, uvarum, paradoxusandkudriavzeviispecies, and partially accounts for the
lower ethanol yield (Antonelli et al. 1999; Castellari et al. 1994; Eglinton et al. 2000;
Feuillat et al. 1997; Giudici et al. 1995; Gonz ́alez et al. 2007; Nieuwoudt et al. 2002;
Orlic et al. 2007; Radler and Sch ̈utz 1982; Rankine and Bridson 1971).
Although non-volatile acids are important towine flavour balance, strain vari-
ability in acid metabolism bySaccharomyces cerevisiaeis generally limited, though
with several important exceptions. SeveralSaccharomyces cerevisiaeandparadoxus
strains can degrade a higher proportion ofL-malic acid, thereby lowering wine acid-
ity, whereas other strains of these species, including cryotolerantSaccharomyces
bayanus/uvarumstrains, produce elevated amounts of succinic acid, and sometimes
malic acid. While increased acid production also partially contributes towards lower
ethanol yield, it is beneficial in improving acidity in low acid musts. This property,
however, appears to be erratic inSaccharomyces cerevisiae, that is, acid production
depends on poorly understood must factors, and therefore causes difficulties in man-
aging wine acidity in commercial scale volumes. Acetic acid production is lower in
non-Saccharomyces cerevisiaespecies, especiallybayanus/uvarum. This character-
istic is of practical importance in wines subjected to malolactic fermentation and
wood aging, and in the production of sweet wines, during which volatile acidity
tends to increase (Antonelli et al. 1999; Castellari et al. 1994; Eglinton et al. 2000;
Feuillat et al. 1997; Giudici et al. 1995;Holgate 1997; Muratore et al. 2007;
Redzepovic et al. 2003).
The impact of yeasts on the phenolics compounds of wine has long been rec-
ognized (Castino 1982; Wenzel 1989) but with little specific information until
suitable analytical methods had been developed.Saccharomyces cerevisiaestrains
affect anthocyanin, polymeric pigments and tannin profiles of red wines (see for
example Bartowsky et al. 2004; Caridi et al. 2004; Medina et al. 2005; Morata
et al. 2006). The complex interactions between yeast and wine phenolics has been
discussed in Sect. 8D.5.3. Colour density of Shiraz red wines was reported to
vary by 38% in a study of 17 strains, showing considerable scope for strain selec-
tion. A survey of non-Saccharomycesyeasts generally revealed greater colour loss
than bySaccharomyces cerevisiaestrains (Gockowiak and Henschke, unpublished
data). However,Saccharomyces bayanu/uvarumsand hybrid strains can increase
the polymeric pigments fraction, which is associated with chemically more stable
pigments (Bellon et al. 2008; Caridi et al. 2002; Eglinton et al. 2005; Hayasaka
et al. 2007). Increased production of carbonyls, such as acetaldehyde, is associated
with stable pigment formation. Changes to the tannins fraction and the mouth-
feel properties of red wine, texture and astringency, are also affected by yeast
species and strains; the mechanisms are likely to involve similar reactions shown for
anthocyanins.