Wine Chemistry and Biochemistry

354 M. Ugliano and P.A. Henschke

vinyl phenol

polysaccharide–

polyphenolic

complex

acetaldehyde

ketoacids

vinyl phenols

HSO 3 –

exogenous

HSO 3 –

β-glucosidase

β-glucanase

(Exg1p)

anthocyanin X pyranoanthocyanin

anthocyanin

flavanol

ethyl-bridge

linked dimer

Hydroxy-

cinnamicacid

acetaldehyde

glu

glu

glu

glu

anthocyanidin glu

COOH

OH

OH

phenylacrylicacid

decarboxylase

Pad1p

Fig. 8D.11Modifications of grape phenolic compounds bySaccharomyces
Anthocyanins react with several yeast metabolites (e.g.acetaldehyde, ketoacids, vinyl phe-
nols) to form stable pyranoanthocyanin pigments; bisulfite can inhibit these reactions by forming
adducts with anthocyanins and carbonyls. Acetaldehyde can condense anthocyanins and flavanols
to form stable ethyl-bridge linked polymeric pigments. Anthocyanins can bind to yeast cell walls,
complex with yeast polysaccharides (mannoproteins), and form unstable anthocyanidin aglycones
after hydrolysis by -glucosidase or -glucanase (Exg1p). Hydroxycinnamic acids can be decar-
boxylated to volatile vinyl phenols by phenylacrylic acid decarboxylase (Pad1p)

The chemical basis for these apparent changes is unknown but is likely to involve
yeast mediated changes to tannin structure.

8D.5.3.3 Modulating Factors

The depth of colour and hue of red wine is largely dependent on grape variety, viti-

cultural factors and choice of winemaking conditions. Nevertheless, the choice of

fermentation yeast has a larger impact on red wine colour and mouth-feel properties

than previously believed (Bartowsky et al. 2004; Caridi et al. 2004; Castino 1982;

Eglinton et al. 2005; Medina et al. 2005). A survey of 17Saccharomyces cerevisiae

wine fermentation yeast showed that the colour density of 4–6 week old red wines

varied by 38% (6.8–11.0 AU); however, the colour stability of aged wines was not

necessarily maintained according to yeast strain, suggesting that colour stability is

a complex phenomenon. Relative colour properties of yeast strains were, however,

maintained for grapes of different phenolics composition, such as from different

viticultural regions.Saccharomyces bayanusstrains compared to speciescerevisiae