Wine Chemistry and Biochemistry

(Steven Felgate) #1

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.

Free download pdf