Malolactic Fermentation.

05 Aug 2024

Malolactic fermentation (MLF) is a secondary fermentation (referring to it as a fermentation is debatable) process in winemaking that significantly influences the flavour, texture, and stability of wine. Unlike primary fermentation, where yeast converts sugars into alcohol, MLF involves the conversion of malic acid to lactic acid by lactic acid bacteria, primarily Oenococcus oeni. This process reduces the wine's overall acidity, resulting in a smoother, rounder mouthfeel and complex flavours.

Monitoring and Control; Throughout MLF, winemakers closely monitor the wine's temperature, pH, and microbial activity. The optimal temperature for MLF is generally between 18°C and 22°C. Maintaining a stable environment ensures the bacteria thrive and complete the fermentation effectively. Winemakers may also add nutrients to support bacterial activity and avoid undesirable by-products.

Conversion of Acids: Malic acid, which is sharp and green-apple-like in taste, is converted into softer, creamier lactic acid. This conversion involves the decarboxylation of malic acid, where the bacteria remove a carbon dioxide molecule, transforming it into lactic acid. This reduces the wine’s total acidity and can lead to a smoother, more balanced profile.

Flavour and Aroma: MLF imparts distinct flavours and aromas to wine. The conversion of malic to lactic acid often results in buttery, creamy notes, particularly in white wines like Chardonnay. Additionally, MLF can enhance fruit flavours and introduce subtle nuances of nuts, spice, and earthiness.

Texture and Mouthfeel: The reduction in acidity leads to a smoother, rounder mouthfeel. This textural change is particularly desirable in red wines, such as Pinot Noir and Merlot, where MLF contributes to a fuller, more velvety palate.

Initiation: MLF typically begins after the completion of primary fermentation, though it can sometimes occur simultaneously. Winemakers may introduce lactic acid bacteria cultures to the wine or rely on naturally occurring bacteria present in the winery environment. The choice to induce MLF depends on the desired wine style and the conditions of the vintage.

While MLF offers numerous benefits, it also presents challenges. If not carefully managed, it can produce off-flavours or unwanted spoilage. Winemakers must decide whether to induce MLF based on the wine style and desired characteristics. For instance, high-acid wines like Riesling may skip MLF to retain their crispness, whereas full-bodied reds and certain whites often benefit from the process.