Malolactic fermentation (MLF) is a secondary fermentation process that occurs in winemaking after the primary fermentation, which converts malic acid into lactic acid. It is primarily used in winemaking to modify and enhance the flavor and stability of wines.
During malolactic fermentation, bacteria of the species Oenococcus oeni (formerly known as Leuconostoc oenos) or other lactic acid bacteria convert the harsher-tasting malic acid, found in grape must, into the softer-tasting lactic acid. Malic acid is often associated with green apple or tart flavors, while lactic acid contributes to a creamier and smoother mouthfeel.
Winemakers have the option to either allow MLF to occur naturally or to inoculate the wine with a selected strain of lactic acid bacteria. Natural MLF can occur spontaneously if the wine contains viable malolactic bacteria, which are often present in the vineyard or winery environment. However, relying on natural MLF can be risky, as the process might not complete or can result in undesirable off-flavors. Therefore, many winemakers choose to control the MLF process by adding a specific bacterial culture.
The decision to use malolactic fermentation depends on several factors, including the style of wine desired and the grape variety. Here are some common situations where winemakers may choose to employ MLF:
Red Wines – MLF is commonly employed in the production of red wines. It helps to soften the wine’s acidity and can contribute to a smoother, more rounded mouthfeel. MLF can also promote the development of desirable flavors and aromas, such as buttery or nutty notes.
Full-Bodied Whites – Certain white wines, particularly those with higher acidity and fuller body, can benefit from MLF. Chardonnay is a classic example where MLF is often utilized to create a rich, creamy texture and add complexity to the flavor profile.
Acidic Wines – MLF can be used to reduce the overall acidity in a wine. By converting malic acid (which is sharper) into lactic acid (which is milder), MLF can help balance the wine and make it more approachable.
Malic Acid Presence – If the grape must or juice contains high levels of malic acid, such as in cool-climate regions or underripe fruit, MLF can be employed to mitigate the perceived tartness and improve the wine’s flavor balance.
Stability – Malolactic fermentation can contribute to the long-term stability of wines by reducing the likelihood of certain microbial spoilage, such as malolactic bacteria outcompeting harmful bacteria or yeast.
It’s important to note that MLF is not suitable for all wines. Some styles, such as crisp, light-bodied whites, sparkling wines, or wines meant to be consumed young and fresh, may intentionally avoid or inhibit MLF to preserve the wine’s acidity and freshness.
Ultimately, the decision to use malolactic fermentation depends on the winemaker’s stylistic goals, grape characteristics, and desired flavor profile for the wine.