Chapter 7

Malolactic Fermentation in Wine

Spontaneous Malolactic Fermentation

Spontaneous malolactic fermentation in wine, which is conducted by indigenous lactic acid bacteria originates from the vines and grape skins and found on winery equipment. Typically, spontaneous MLF occurs in wines above pH 3.4, as low pH will strongly inhibit the growth of most Lactobacillus and Pediococcus species (Bartowsky et al., 2005). In regions where malolactic fermentation is systematically practiced, its initiation does not pose any particular problems, since strains of lactic acid bacteria found on grapes and the winery equipment (notably the barrels) contains an abundant bacterial inoculum and malolactic fermentation is difficult to avoid. It's still the prevalent way in France and Italy.

Risks Associated with Spontaneous Fermentation

There are risks associated with spontaneous malolactic fermentation. During naturally occurring fermentation by indigenous Lactobacillus and Pediococcus strains, excessive volatile acidity or diacetyl can be formed. These compounds are not only likely to mask the primary fruit flavors of the wine, they can also contribute undesirable characters to the bouquet. For example, volatile acidity is irritating to the nose and causes a sour taste. Diacetyl can contribute a nutty flavor or characteristics that can resemble caramel, yeast and even wet animal fur.

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