364 M. Ugliano and P.A. Henschke
their hybrids withSaccharomyces cerevisiae, have improved ability to hydrolyse
S-cysteinylated conjugates to increase the concentration of the tropical fruity long-
chain polyfunctional thiols (Dubourdieu et al. 2006), and mask the green/vegetative
aromas, possibly due to methoxypyrazines (Bellon et al. 2008; Eglinton and Hen-
schke, unpublished). Consequently, selected strains ofSaccharomyces bayanus/
uvarumand hybrids are becoming useful for improving the flavour of Sauvignon
Blanc, Semillon, Chardonnay, Cabernet Sauvignon and Merlot wines.
Little information is yet available on otherSaccharomycessensu stricto species.
Saccharomyces paradoxuswines are augmented in ‘floral’ and ‘citrus’ attributes,
and contain lower concentrations of ethyl acetate, 3-methylbutanol, total volatile
esters, higher concentrations of total higher alcohols and variable formation of
volatile fatty acids, when compared to the reference strain ofSaccharomyces cere-
visiae(Orlic et al. 2007). No aroma descriptions have been published forSac-
charomyces kudriavzeviiwines but the one strain tested in a red and white juice
produced less total esters and more higher alcohols than the reference strain of
Saccharomyces cerevisiae(Gonz ́alez et al. 2007). TwoSaccharomyces kudriavzevii
xSaccharomyces cerevisiaehybrids (Lallemand W27 and W46) tended to show a
more moderate behaviour although with slightly higher amounts of higher alco-
hols than the reference yeast. Another hybrid (Maurivin AWRI 1503) has been
reported to produce ‘estery’, ‘floral’, ‘tropical’, ‘citrus’, ‘nutty’ and ‘waxy’ aromas
in Chardonnay wines, whereas aSaccharomyces cariocanusxSaccharomyces cere-
visiaehybrid (Maurivin AWRI 1502) gave a different profile described as ‘peach’,
‘pear’, ‘nectarine’, ‘violets’, ‘lemon fruit/zest’, ‘creamy’, ‘mineral’ and ‘match-
stick’; the non-Saccharomycesparents of these hybrids failed to ferment grape must
(Bellon et al. 2008; Henschke 2007).
8D.6.3 Mixed Cultures ofSaccharomyces
Winemakers have been combining strains ofSaccharomyces cerevisiaefor several
decades on the basis of observations that mixed-cultures produce more flavour diver-
sity and balanced wines, by introducing a greater range of flavour notes and moder-
ating the intensity of distinctive estery/fruity notes, such as pineapple and banana in
Chardonnay wines. Little research has, however, been conducted into the effects on
yeast growth, wine composition and flavour profiles resulting from fermentations
made with mixed cultures ofSaccharomycesstrains (Cheraiti et al. 2005; Favale
et al. 2007; Fleet 2003; Grossmann et al. 1996; Howell et al. 2004a, 2006). The
differences in yeast growth patterns of genetically distinct strains, that are observed
when they are cultivated individually and in mixtures, suggest that metabolic inter-
actions can occur between different yeasts, and that they can be antagonistic, neutral
or stimulatory.
Diffusable metabolites, such as acetaldehyde, are likely candidate effector
molecules. Acetaldehyde can, for example, be produced/utilised at different rates by
different strains, and can affect the redox status of each yeast, as has been observed