86 R. Peinado and J. Mauricio
population between wines from different cellars. However, more than 95% of the
film microbiota usually consists of film-formingSaccharomyces cerevisiaeraces
(Mart ́ınez et al. 1997a). The remainders are occasional microbes such as bacteria
and other, non-flor yeasts which are regarded as contaminants.
Presence and role of bacteria in the biological aging process have been not stud-
ied very much. These may be involved in the changes of different wine components
as organic acids (Su ́arez-Lepe and I ̃nigo-Leal 2004).
The other yeasts found in flor films include species of the generaDebaryomyces,
Zygosaccharomyces,Pichia,HansenulaandCandida(Ben ́ıtez and Cod ́on 2005;
Su ́arez-Lepe and I ̃nigo-Leal 2004). Guijo et al. (1986) also isolatedTorulaspora del-
brueckiiandZygosaccharomyces bailii, which were deemed contaminants, from flor
films in Montilla-Moriles wines. Some authors have additionally isolated species of
the generaDekkeraandBrettanomyces, which are believed to cause an abnormal
acidity increase in casks containing biologically aging wines (Ibeas et al. 1996).
Possibly, flor yeasts are present at very low concentrations during alcoholic fer-
mentation; once this completes and the wine contains 15–15.5 vol.% ethanol, their
presence increases as result of the disappearance of fermentation yeasts from the
medium (Esteve-Zarzoso et al. 2001). This is consistent with the results of Guijo
et al. (1986), who isolated flor yeasts during the fermentation of grape musts in the
Montilla-Moriles region. Flor yeastsconstitute a resident population incriaderaand
soleracasks that vary among cellars. On the other hand,sobretablaswine contains
a spontaneous population of yeasts that may come from the grapes.
Although flor yeasts possess good fermentation ability, they differ from typi-
cally fermentative yeasts in metabolic, physiological and genetic respects (Esteve-
Zarzoso et al. 2001, 2004; Budroni et al. 2005).
The restrictive conditions of the biological aging process of wine (namely low
pH, presence of sulphite, high ethanoland acetaldehyde concentrations, lack of
sugars and low oxygen concentration) are compatible with only a fewS. cerevisiae
races. Also, the presence of specific flor races has been correlated with the aging
stage of the wine and the sensory features of the end product (Mesa et al. 2000).
In Jerez, researchers have isolated fourS. cerevisiaeraces or varieties: two major
races (beticusandmontuliensis) and two minor ones (cheresiensisandrouxii). The
racebeticusis faster in forming a flor film; also, it is more abundant in the scales
holding the younger wines. On the other hand, the racemontuliensisprevails in the
scales containing the oldest wine by virtue of its increased tolerance and production
of acetaldehyde (Mart ́ınez et al. 1997a).
In Montilla-Moriles, Guijo et al. (1986) isolated five film-formingS. cerevisiae
races. Worthy of special note among them is one which forms a thick, rough film
and exhibits decreased production of acetaldehyde, and another which forms a thin
film and produces large amounts of this aldehyde (Mauricio et al. 1997).
Jura yellow wines have also been found to contain the racesbeticus(67%),mon-
tuliensis(26%) andcheresiensis(7%) (Charpentier et al. 2000).
Molecular techniques have enabled the identification of up to six types of flor
yeasts according to electrophoretic karyotype and mitochondrial DNA restriction
patterns (Ibeas et al. 1997). However, yeast types distribute in a non-uniform manner