8D Yeasts and Wine Flavour 357
yeasts is a relatively unreliable fermentation strategy, a growing proportion of
wines in the New World are being produced in this way. The basis of mod-
ern winemaking has been the so-called ‘pure culture inoculation technology’ that
commenced with isolation of yeasts by M ̈uller-Thurgau (1896), but in winemak-
ing this practice only became widely established in the second half of the twen-
tieth century (Rankine 1953). This biotechnological process involves minimiz-
ing the presence of indigenous yeasts by chemical and/or physical processes and
adding a starter culture of a selected strain ofSaccharomyces cerevisiae.The
advent of active dried yeast has revolutionised the availability of yeast selections
with some 200 strains used globally, mostlySaccharomyces cerevisiae(Fernandez-
Espinar et al. 2001; Henschke 2007). SeveralSaccharomycessensu stricto species,
includinguvarum, bayanusand theircerevisiaehybrids,paradoxus, and hybrids
ofcariocanusandkudriavzeviiwithcerevisiae,have also been recently produced.
A few selections of non-Saccharomycesspecies,Candida stellata,Torulaspora
delbrueckiiandKluyveromyces thermotolerans, mainly in mixtures withSaccha-
romyces cerevisiae, have also recently become available for commercial wine pro-
duction (Antonelli et al. 1999; Bellon et al. 2008; Henschke 2007; see also the web-
sites of yeast producers, such as http://www.chr-hansen.com; http://www.lallemandwine.com;
http://www.maurivinyeast.com)..)
8D.6.1 Indigenous Yeasts
The simplest form of fermentation, in which no intervention is needed except for
preparation of the must, is to rely on the indigenous strains of yeasts that are asso-
ciated with the grapes, and harvest, must processing and fermentation equipment.
The diversity of populations of yeast species and strains in the must or juice at
the beginning of fermentation is remarkably variable. The dynamics of growth and
decline of each yeast species and strains is likewise highly variable (Fleet 2003;
Fleet and Heard, 1993; Fleet et al. 2002), Therefore, in general terms, the ecology of
fermentation can be summarised as: the highly oxidative (non-fermentative) species
undergo little or no growth and decline earlyin fermentation, the weakly fermenta-
tive species, which are usually present in greater initial numbers, grow to a greater
extent but eventually become superseded by the physiologically better adapted and
most strongly fermentative yeastsSaccharomycesspecies.Saccharomyces cere-
visiaeis the most commonly encountered species whereas in cool climate wine-
making regionsSaccharomyces bayanus (var.uvarum)can occur more frequently,
due to its cryotolerant properties (Le Jeune et al. 2007; Naumov et al. 2000).Saccha-
romyces paradoxusis commonly found in Croatian musts (Redzepovic et al. 2002).
Because of the high variability of yeast species and their population sizes, and
the difficulty in microbial profiling of fermentation, few studies have reported on
wine chemical composition (Beh et al. 2006). General characteristics are recorded
in Table 8D.5. These data suggest that the diminished role ofSaccharomyces
allows some of the non-Saccharomycescharacteristics to be more evident and to