malolaktische

Malolactic fermentation, commonly referred to in German as malolaktische Gärung, is a secondary process in winemaking where lactic acid bacteria convert malic acid into lactic acid and carbon dioxide. This transformation reduces sharp acidity and helps stabilize the wine microbiologically.

The main organism responsible is Oenococcus oeni, though other lactic acid bacteria such as Lactobacillus and Leuconostoc species can participate under certain conditions. MLF can occur spontaneously in tanks or barrels or be initiated by inoculating a commercial malolactic starter culture. It is typically allowed to proceed after the primary alcoholic fermentation, often in a controlled temperature range around 18–22°C and at pH levels that favor bacterial activity.

The effect of malolactic fermentation is to soften acidity and broaden mouthfeel by converting the sharper malic acid into the milder lactic acid. It can also lead to changes in aroma and flavor, most notably the production of diacetyl, which can impart buttery or creamy characteristics in some wines, especially certain Chardonnays. Beyond texture and aroma, MLF can enhance microbial stability and reduce the risk of lingering malic acid fermentation.

Winemakers manage MLF through inoculation decisions, monitoring of pH and acidity, and sensory evaluation. Potential drawbacks include a stuck or incomplete fermentation, development of unwanted flavors, or the formation of off-flavors if inappropriate bacteria dominate. Overall, malolactic fermentation is a widely used tool to modulate acidity, flavor, and stability in many wine styles.