366 M. Ugliano and P.A. Henschke
than could be achieved by blending wines made by monoculture fermentation
(Swiegers et al. 2008a). Alchemy I and II mixed yeast cultures for enhancing white
wine aroma have been commercialized by Anchor Yeast, South Africa.
8D.6.4 Non-SaccharomycesSpecies and Cofermentation
Grapes and associated processing equipment contain a variety of yeasts that accu-
mulate in the must or juice. Whether or not the must or juice is inoculated with a
starter culture, some species and strains will grow according to their adaptability
to the must/juice composition and fermentation conditions, and metabolise grape-
derived compounds, to produce a variety of volatile and non-volatile metabolites and
carry out transformation reactions. Depending on the vigour of theSaccharomyces
starter culture and the growth and metabolic activity of the non-Saccharomyces
yeasts during fermentation, wine composition will to various degrees reflect the
metabolic activities of all yeasts present. Fermentations in which non-Saccharomyces
species produce significant populations will have greater metabolic impact on wine
composition and flavour.
Many of the persistent and numerically dominant non-Saccharomycesspecies,
observed in fermentations made with indigenous yeasts, have been isolated and
characterised, and in some cases experimental wines have been made to evaluate
their potential sensory contribution (Bisson and Kunkee 1993; Ciani and Mac-
carelli 1998; Clemente-Jimenez et al. 2004; Fleet 2003; Fleet and Heard 1993;
Heard 1999; Henschke et al. 2002; Hern ́andez-Orte et al. 2008; Jolly et al. 2003,
2006; Moreno et al. 1991; Moreira et al. 2002; Mateo et al. 1991; Plata et al. 2003;
Romano et al. 2003b; Rojas et al. 2001; Soden et al. 1999; Zeeman et al. 1982).
Table 8D.9 records some of the aroma descriptors associated with wines made with
several species of non-Saccharomycesyeasts. Despite considerable genetic distance
between non-SaccharomycesandSaccharomycesyeasts, they share some aroma
attributes but in addition non-Saccharomycesyeasts produce a diversity of novel
aromas, some of which can be perceived as positive whereas other are distinctly
negative. Clearly, strain selection, as it is forSaccharomycesspecies, is important.
The nature of these aroma attributes suggests that these yeasts could be useful in
wine production by providing extensive wine blending options in order to increase
aroma diversity, such that the aroma notes do not become dominant and impart
a monodimensional character. For example, the production of phenyl ethanol and
its acetate by someSaccharomyces bayanusstrains can mask more delicate aroma
attributes (Dubourdieu et al. 2006).
A practical problem with non-Saccharomycesyeasts is that few strains are capa-
ble of completing fermentation, and in many cases only a small proportion of grape
sugar will be fermented. Two strategies have evolved to enable complete fermen-
tation; these are cofermentation with a robustSaccharomycesstrain and sequen-
tial fermentation, in which the non-Saccharomycesyeast andSaccharomycesstrain
are inoculated successively, in order to complete fermentation. Several studies have