Agriculture Reference
In-Depth Information
it even occurs simultaneously with alcoholic fermentation and
you never notice.
Commercial wineries subject a large proportion of their red
wines and a lesser proportion of their white wines to
deliberate malolactic fermentation for a variety of reasons.
The most obvious reason is that malolactic fermentation
changes sharp malic acid to smooth lactic acid. It raises the
pH and reduces the acidity slightly. The formation of lactic
acid in the presence of ethanol also allows the creation of
ethyl lactate, an ester that gives wines a fruity character. In
addition, bacteria will produce diethyl succinate, another
fruity ester along with diacetyl and other flavor compounds.
Malolactic fermentation also serves to make wine more
self-preserving by consuming pentoses and hexoses
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not
used by yeast, as well as malic acid that would otherwise
serve as food for other bacteria. Malolactic bacteria secrete
bacteriocins that inhibit the growth of other bacteria, which
makes the wine more microbiologically stable. Finally, by
deliberately conducting a malolactic fermentation, you can be
certain that one won't occur spontaneously in the bottle.
There are a number of malolactic cultures available. Some are
single species (usually Oenococcus oenii) and others contain
a mix of species. Only Oenococcus oenii can work at pH
values lower than 3.5, so all cultures contain at least that one
bacteria.
Malolactic bacteria and wine yeast are often incompatible as
one will inhibit the other. Therefore, malolactic culture is best
introduced after the secondary alcoholic fermentation is
complete unless the wine has a final alcohol level exceeding
14%. Though different products will require slightly different
