1.4 The Lactic Acid Bacteria
The LAB involved in wine are comprised of acid and ethanol-tolerant strains
primarily from four genera Lactobacillus, Pediococcus, Leuconostoc, and
Oenococcus (formerly Lc. oeni) (Sponholz 1993; Lonvaud-Funel 1999; Osborne
and Edwards 2005). These microbes are commonly found on grapes and in the
winery environment. Newly fermented wines contain low populations of LAB,
usually less than 103 CFU per mL (Davis, et al. 1985), however, damage to the
grapes increases this number by several orders of magnitude. Three main factors
that dictate the extent of LAB growth in wine are pH, ethanol and antimicrobial
additions such as SO
2 or lysozyme. These latter additions purposely reduce LAB
concentrations to enable proper growth of S. cerevisiae and/or to microbially stabilize
the wine. Wine pH also strongly influences which LAB species will be present.
Higher pH wines (above pH 3.5) often harbor species of Lactobacillus and
Pediococcus, both during and after fermentation, while lower pH wines (< 3.5)
typically only contain O. oeni (Fleet 1998; Osborne and Edwards 2005).
Ethanol production from the dominant S. cerevisiae population also serves to
reduce all LAB populations in the first few weeks of the alcoholic fermentation.
However, as the wine is stored, the ability of ethanol-tolerant LAB to emerge
increases. Growth substrates can be available at this stage as a consequence of yeast
cell lysis and release of nutrients into the wine (Lonvaud-Funel 1999)