Malolactic fermentation (MLF) is a process in winemaking and fermentation where Malic Acid (a tart acid found in fruits, especially in grapes) is converted into Lactic Acid (a softer, milder acid) by bacteria, primarily Lactic Acid Bacteria (such as Oenococcus oeni).

This secondary fermentation typically occurs after the primary fermentation (alcoholic fermentation) has finished, and it plays an important role in shaping the flavor, texture, and overall profile of the wine.

Key Points about MLF:

1. Acidity Reduction: MLF reduces the overall acidity of the wine, making it taste smoother and less tart.
2. Flavor Changes: It can also contribute to more complex flavors, such as buttery, creamy, or nutty notes, especially in white wines like Chardonnay.
3. Stability: MLF can help to stabilize the wine by reducing the malic acid content, which can prevent the wine from becoming overly acidic as it ages.
4. Occurrence: MLF is common in red wines, where the lower acidity and tannin structure help to facilitate the process, but it can also be induced in certain white wines (like Chardonnay) to achieve a fuller, rounder mouthfeel.
5. Controlled or Spontaneous: Winemakers can choose to induce MLF by adding specific bacteria to the wine, or they may allow it to occur naturally if conditions are favorable.