Introduction to Fungi, Third Edition

276 HEMIASCOMYCETES
is extracted rapidly from the white or red grapes,
respectively. Once the must has been obtained
and filtered, subsequent treatment is similar
for red, rosé and white wines. The must is either
fermented directly, relying on the natural yeast
flora of the grapes (‘spontaneous fermentation’),
or a pure yeast starter culture is added at such
high concentrations that this strain suppresses
the wild yeasts. Spontaneous fermentations still
account for 80% of the worldwide wine production,
and up to 100 000 wild yeast cells mostly
not belonging to S. cerevisiae may be found on
the surface of one berry or in 1 ml must (Dittrich,
1995). The diversity of yeasts changes rapidly
during the initial stages of the wine fermentation,
with S. cerevisiae displacing the obligately
aerobic species as oxygen becomes depleted. The
total fructose and glucose content of musts may
be as high as 150 g l 1 . In principle, fermentation
is completed when no further release of CO 2
occurs, either due to exhaustion of sugars or due
to ethanol poisoning of the yeast, but in practice
fermentations are often terminated artificially
by addition of sulphite, especially if a sweet wine
is desired.
Fermentation may carry on for up to 1 year
with white wine; red wine develops faster but
is often stored in barrels for prolonged periods to
permit maturation. If red wine is stored in oak
wood, it is called ‘barrique’ wine and it acquires
a characteristic additional flavour. Good concise
accounts of the processes and microbiology of
wine making are those of Dittrich (1995)
and Hartmeier and Reiss (2002).
10.2.11 Production of sake¤
Saké production (for a review, see Oliver, 1991)
involves the conversion of rice starch into monosaccharides
which are then fermented into
ethanol. Saké is thus technically a beer rather
than a wine. It has been produced for several
thousand years in China, but its current production
principles based on the synergistic action
of two fungi date back to the fifth century AD.
Saké production relies on the degradation of
starch in cleaned and boiled rice by a filamentous
fungus, Aspergillus oryzae, which produces
several different amylases as well as proteases
and other enzymes (see p. 302). Koji, a solid
culture of A. oryzae on steamed rice, is used as
a starter for starch hydrolysis.
Fermentation (moromi) is carried out in
a large volume of water to which successive
quantities of boiled rice, koji and the S. cerevisiae
starter culture (moto) are added. Stepwise addition
and a highly ethanol-tolerant yeast strain
ensure that saké is the most strongly alcoholic
beverage produced by fermentation without
distillation, containing up to 20% (v/v) ethanol.
Fermentation takes about 25 days and is followed
by storage, maturation and filtration. In order
to avoid contamination by lactic acid bacteria,
saké is pasteurized. It is interesting to note that
this practice was introduced in the sixteenth
century, 300 years before Pasteur.
10.3 Candida (anamorphic
Saccharomycetales)
Candida is a very large genus of anamorphic
Saccharomycetales, currently comprising some
165 accepted species (Meyer et al., 1998; Kirk et al.,
2001), with new ones being described at a high
frequency. The genus is polyphyletic (Kurtzman
& Robnett, 1998). By far the best-known species
is C. albicans, which is associated with human
disease, and on which we will focus here. A very
similar species, and possibly one which has
been misdiagnosed as C. albicans in the past, is
C. dubliniensis (Martinez et al., 2002). Other species
(C. glabrata, C. inconspicua, C. krusei) may also cause
opportunistic infections of man. In contrast,
Candida utilis (now called Pichia jadinii; see
p. 281) has been used for food and fodder
production for over 80 years, and other Candida
spp. are also suitable for this purpose (Boze et al.,
1995; Scrimshaw & Murray, 1995).
Candida spp. are cosmopolitan and can be
found in many ecological situations (Meyer et al.,
1998), e.g. the surface of fruits and other plant
organs, rotting wood, the soil, sea water, or
associations with mammals and insects (especially
bees). Candida spp. can contaminate grape
musts during the early stages of wine making