356 M. Ugliano and P.A. Henschke
8D.6 Yeast Modulation of Wine Flavour
From the proceeding discussion on yeast metabolism in this chapter, it is clear that
the scope for yeast to modulate the non-volatile and volatile composition of wine
is considerable. And while the impact of many compounds on their own may not
be detectable, some chemically-alike compounds act together, such as esters, to
make a significant sensory impact (Francis and Newton 2005; Ferreira et al. 2008;
Guth 1997; Van der Merwe and van Wyk 1981). Many of the metabolic com-
pounds produced during sugar metabolism contribute to the appearance, aroma,
flavour and mouth-feel properties of wine. Furthermore, the profile of sensorially
important metabolites can vary considerably with the fermentation conditions under
which the yeast is subjected, that is, thephysicochemical and nutrition parameters.
Finally, the release of a wide range of grape secondary metabolites present in grape
must as non-volatile flavour precursors, principally glycosides andS-cyteinyl and
related conjugates, depends on the strain of yeast (Dubourdieu et al. 2006; Ferreira
et al. 2008; Jolly et al. 2006; Lambrechts and Pretorius 2000; Swiegers et al. 2005).
In addition to the choice of yeast strain, the method of inoculation can be used
to modulate wine flavour in ways not readily achievable with conventional yeasts,
which are typically used in monoculture. A combination of alternative yeast species
and inoculation strategies can lead to wines with very different chemical and flavour
profiles, such as greater complexity and diversity of flavours, and enhanced mouth-
feel and persistence of flavour (Table 8D.4).
Allowing musts to ferment with indigenous yeasts can potentially produce a high
diversity of flavours but the flavour profile is dependent on the yeast species and
numbers present in the must, as well as the physico-chemical and nutrient com-
position. Although, from a microbiological perspective, depending on indigenous
Ta b l e 8 D. 4Types of yeasts and starter cultures used in winemaking
Starter culture Yeast species Wine characteristicsIndigenous yeast Multiple species and Complexity and
strains of non- diversity of flavours,
Saccharomyces enhanced mouth-feel
andSaccharomyces
Selected strains of Predominantly Intensity and diversity
Saccharomyces Saccharomyces of fruity flavours or
cerevisiae cerevisiaeselected enhancement of varietal
strain attributes
Saccharomyces Predominantly strain Increased diversity of
sensu stricto species of selected non- flavours, especially
Saccharomyces mouth-feel properties
cerevisiaespecies
Non-Saccharomyces Predominantly non- More controlled
species Saccharomycesspecies complexity and diversity
and indigenous or added of flavours, and
Saccharomyces enhanced mouth-feel
cerevisiae