Malolactic fermentation softens the wine and changes its acidity.
According to winemaker Joel Burt of Las Jaras Wines, this fermentation converts malic acid into lactic acid and rounds out the mouthfeel of the wine.
Some winemaking terms, such as "whole clusters," "carbonic maceration," and "barrel aging," offer clues about a wine's flavor profile even before it's opened. Among these, few elicit as much reaction from professionals and enthusiasts as malolactic fermentation.
"Malolactic fermentation (MLF) is a bacterial fermentation that converts malic acid into lactic acid, which provides a smoother mouthfeel," explains Joel Burt, Californian winemaker at Las Jaras Wines.
According to Burt, winemakers can choose to subject their wines to this process or block it, either partially or completely, "depending on the style of wine they want to achieve." In addition to a smoother texture, fermentation raises the wine's pH and reduces its overall acidity, so the wine can feel creamier or velvetier on the palate. In some wines, it imparts buttery flavors, depending on the strain and other factors: a pure strain of lactic acid bacteria that produces large amounts of diacetyl, the compound responsible for that flavor in dairy products, popcorn, and wine, could be used for a powerful, buttery Chardonnay.
In red wines, winemakers seek this fermentation because it reduces astringency, according to Burt. In white wines, it can contribute stability and a creamier texture.
Some wines are preferred without malolactic fermentation. "Avoiding it can make the wine more angular and bright, which is preferred in some wines, such as Sauvignon Blanc and Riesling," says Burt. Since it's a natural process, if it's not desired, it must be stopped, for example with filtration, large doses of sulfur dioxide, or the enzyme lysozyme.
When conditions are less than ideal, such as in cool cellars with high alcohol levels, low pH, high sulfur content, or high volatile acidity, some winemakers add a bacterial strain to stimulate fermentation. This fermentation also allows many wines to be bottled without sterile filtration, thanks to the increased microbial stability it provides. This is an advantage for producers who prefer natural winemaking, with minimal intervention or low sulfur content.
"At Las Jaras Wines we do not interrupt malolactic fermentation, as we do not normally filter our wines and prefer a less prudent use of sulfur," says Burt.