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Understanding Malolactic Fermentation Knowing the what, when and how of this winemaking tool helps make balanced wines By Chris Stamp I f Winemaking 101 is about alcoholic fermentation, then Winemaking 201 should be about the fermentation of malic acid. This important bacterial fermentation has nowhere near the same name recognition as its yeast-induced cousin, yet the fermentation of malic acid to lactic acid (a.k.a. malolactic fermentation, or simply "MLF") plays a very important role in the production of many high-quality wines. In the northeastern United States, with many of our high acid varieties, it is an irreplaceable winemaking tool because the most pronounced chemical effect of MLF is the reduction of acid. But as we'll see, its impact on a wine can be far more complex than simply taking a bunch of hydrogens off the table. In its simplest representation, MLF is the bacterial degradation of malic acid into lactic acid by lactic acid bacteria (LAB). In this fermentation, bacteria cleave a carboxyl group off of malic acid, yielding lactic acid and CO2 : C4H6 C3 malic acid lactic acid + carbon dioxide O5 H6 O3 + CO2 Wine east hIGhLIGhTS: • • • The author explains the chemical process of malolactic fermen- tation, how to induce and monitor it and why it's so important. The acid-reduction effect of malolactic fermentation is especially important in the northeastern United states. Direct-inoculation lactic acid bacteria products have trans- formed cellar practices for many winemakers. Malic acid is a dicarboxylic acid, meaning it has two carboxyl groups. Lactic acid is a monocarboxylic acid with, as you might've guessed, a single carboxyl group. These carboxyl groups are what allow these acids to hold their hydrogen atoms more loosely. Since it is the degree to which hydrogen atoms get loose in a solution that determines the strength of an acid, the conversion of the dicarboxyl malic acid to the monocarboxyl lactic acid yields a net loss in acid- ity and a rise in pH. WineEast Wines & Vines JUne 2012 59