Malolactic Fermentation (often abbreviated to MLF) is a technical wine word that refers to a winemaking technique routinely used in red winemaking and selectively in white. It's not actually a 'fermentation'; rather, it's a conversion process that occurs near the end, or just after, the alcoholic fermentation.
t is a process whereby the tart, naturally occurring malic acid (think unripe apple) in the wine/fermenting wine is converted into the softer, creamier lactic acid (think milk).
The most important reason that MLF is carried out is to adjust acidity. MLF reduces the acidity in a wine. It also works as a flavor and mouth feel enhancer and it can add complexity to a wine. Wines that have undergone MLF have a fuller, rounder mouthfeel, and in many cases a creamier, more buttery flavor.
Some grape varieties such as Chardonnay have a strong affinity with MLF. Others such as Sauvignon Blanc and Riesling eschew it in favor of making crisper, more refreshing, fruitier wines.
However, it is not an all or nothing scenario. Some producers blend cuvées of wines that have undergone MLF with cuvées that have not in order to achieve a reduction in acidity and enhance mouthfeel as well as retain freshness and fruit flavor. This is known as 'partial MLF'.
Naturally occurring MLF or induced
The MLF conversion is undertaken by bacteria (lactic acid bacteria). It can happen naturally in the wine or it can be induced using a desirable commercial strain of bacteria. Most winemakers inoculate to have greater control over the process and prevent naturally occurring undesirable strains from causing off-flavors in the wine.
Many white wines do not undergo MLF, particularly wine styles/varieties that want to retain a noted crisp acidity such as Sauvignon Blanc and Riesling, or styles/varieties that are relatively low in natural acidity. As MLF is a naturally occurring process, it has to be inhibited by keeping the new wine at a cool temperature, measuring appropriate additions of sulfur dioxide, and early racking and clarification of the wine.
Mary Gorman-McAdams, MW (Master of Wine), is a New York based wine educator, freelance writer and consultant.
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