Malolactic Fermentation

Malolactic fermentation is the process by which bacteria convert malic acid into lactic acid and carbon dioxide, giving wine (red and white) a richer, creamier mouthfeel.

Malic acid is that which contributes to the sour taste of fruits (green apples are highest in malic acid). This process of converting malic acid to lactic acid and carbon dioxide typically takes place during yeast fermentation (the primary fermentation) - which is why it’s typically referred to as a secondary fermentation.

However, MLF isn’t technically a fermentation because it does not use yeast. A bacteria, Oenococcus oeni and a few other Lactobacillus strains eat the malic acid in wine and excrete lactic acid.

Think of a creamy, buttery, rich Chardonnay. What results is a creamy, oil-like texture on your tongue. The wine gets that butteriness from the process by muting/mellowing out those tart, fruity flavors. This also allows the wine to have a full, smooth, mouthfeel. Other reasons a winemaker might facilitate malolactic fermentation would be to reduce the total acidity or to increase the stability of a wine.

Most red wines undergo malolactic fermentation, while about one-fifth of white wines undergo the process. The acid in chardonnay and cabernet sauvignon grapes lend themselves better to malolactic fermentation. In addition to grape type, some colder regions, like Burgundy and Champagne are proponents of malolactic fermentation since low temperatures usually yield more acidic grapes.