Sometimes shortened as MLF, this is a bacterial fermentation which can occur after yeast fermentation winds down or finishes. The bacterium Bacillus gracile converts malic acid into lactic acid and carbon dioxide. Lactic_acid is much less harsh than malic and thereby softens and smooths the wine, but the wine also is endowed with a cleaner, fresher taste. In addition, diacetyl (or biacetyl) is produced as a byproduct, which resembles the smell of heated butter and adds complexity to wine. MLF is a positive event in some cases and has a downside in others - the fruitiness of wines undergoing MLF is diminished and sometimes off odors can result. To ensure MLF, the wine should not be heavily sulfited and it should be inoculated with an MLF culture.
The ideal time to inoculate wine with an M-L bacteria is early in the winemaking process, at the beginning of the sugar fermentation (if using Lalvin X-3 (MLC10) , and toward the end of fermentation or shortly after (if using CHML & 35ML). The addition of Bactiv-aid, a special organic nutrient for Malolactic Bacteria, will improve the growth conditions for the bacteria, and will encourage a faster, more successful malolactic fermentation. 375 gr. works for 660 gal. (2500 liter.)
The CHML & 35ML cultures will inoculate either 66 or 660 gallons and are easy to use, direct addition cultures, not requiring further culturing before adding to the wine.
Acidity is reduced as well throughout the conversion of v (a dicarboxylic acid) to the monocarboxylic lactic acid. Most red wines undergo MLF and have a detectable buttery aroma, while sourness is reduced. MLF is encouraged in Burgundian whites and Chardonnay wines made elsewhere in the world for stylistic reasons. Similarly, MLF is prevented in most aromatic white varieties. Diacetyl and 2,3-pentanedione are also formed in fermentation by yeast, and generally are considered to be a defect in beers.