8D Yeasts and Wine Flavour 371
The potential for non-Saccharomycesyeasts to enhance wine aroma intensity
and flavour complexity is considerable. Few strains are capable of completing fer-
mentation in monoculture and therefore are used in cofermentation, usually with
Saccharomyces cerevisiae. The extent of flavour enhancement can be modulated
by using different inoculation strategies. In practice, it is difficult to obtain balanced
wines by cofermentation withSaccharomyces cerevisiae; however, wines made with
high non-Saccharomycesyeast character, although normally very unbalanced, make
useful blending options. The pace of research on this topic is now considerable and
new yeasts with better properties are to be expected. Sensory evaluations, which are
strongly lacking in current research, will be essential for successful industry adop-
tion. Although the isolates studied are normally obtained from grape must, health
and safety aspects should be observed when producing high cell density cultures.
A significant technical problem has been the successful development of active dried
yeast preparations.
8D.7 Future Directions
The past decade has witnessed a remarkable expansion in knowledge of the roles
that yeasts play in the development of wine sensory properties. Until recently, yeasts
were assumed to provide a generic vinous character upon which the highly dis-
tinctive secondary compounds, derived from the grape or formed through purely
chemical processes, definedthe varietal and regional characteristics of the wine.
With the recent discovery that yeastsare responsible for unlocking from non-
volatile precursors several aroma compounds involved in wine varietal attributes,
such as monoterpenes, norisoprenoids, and long-chain polyfuntional thiols, we are
learning that yeasts play a much more complex role in determining wine varietal
character. These important finding have enabled a more detailed understanding of
yeast transformation reactions and mechanisms involved in the development of sev-
eral key varietal odorants (Dubourdieu et al. 2006; Loscos et al. 2007; Swiegers and
Pretorius 2007; Ugliano and Moio 2008).
Progress in this field has been driven, at least in part, by advances in analytical
techniques. The use of simple analyticalstrategies, based on HPLC and GC, has
provided an important but limited understanding of wine volatile composition and
of the importance of individual components to the overall flavour composition of
wine. Advances in GC-Olfactometry and GC-MS are now allowing identification
and characterization of many new wine components. Compounds that are consid-
ered of primary importance in wine flavour are only now being discovered, as
in the case of rotundone, responsible for the peppery character in wine, and the
esters cyclohexanoate and 2-, 3-, and 4-methylpentanoate, considered to contribute
to the berry fruit character of wine (Campo et al. 2007; Escudero et al. 2007; Wood
et al. 2008). Nevertheless, the effect of yeast and fermentation on these compounds
is still to be established. In addition, the role of some volatile compounds, origi-
nally considered spoilage off-flavours, such as volatile sulfur compounds, is being
reassessed (Fedrizzi et al. 2007).