Wine:30 – Malolactic Fermentation

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Malolactic fermentation or malolactic conversion in winemaking is the process in which malic acid is transformed into lactic acid. This is a standard process for most red wines and is common for some white wines such as Chardonnay.

It is often a secondary fermentation which happens shortly after the end of the primary fermentation, but can sometimes run concurrently with the primary. This fermentation will soften the wine. Malic acid implies tart characteristics in wine and when converted to lactic acid, the wine’s tart flavors will mellow. This is typically desired in most red wines and is seen in some white wines as well.

In Chardonnay, the process is sometimes used to give a rounder more mellow component to the varietal. With the lactic acid, diacetyl (used in flavoring movie popcorn) is also produced, which will provide the wine with a buttery flavor.

The malolactic fermentation process can naturally occur in wines, but now is typically started by wine makers at desired times in the winemaking process or prevented in wines where it is not wanted, such as in the making of Rieslings or Gewürztraminers.

Malolactic fermentation is as old as wine making but the scientific understanding of the process is relatively recent in history. For centuries, winemakers would notice wines going through some type of transformation of the wines that were stored in barrels during the warm months of spring, after the fall harvest. Like the primary fermentation, this process would release carbon dioxide and have a profound change on the wine that was not always welcomed. Described as a second fermentation by German enologist Freiherr Von Babo in 1837, he encouraged wine makers to rack the wine into a new barrel and add sulfur dioxide and then repeat the racking a second time to help stabilize the wine.

In 1866, Louis Pasteur isolated the first bacteria from wine and determined that all bacteria that were found in wines were a cause for wine spoilage. Even though he noticed a reduction in the acid in wine, he did not link this reduction to the process of bacteria consuming malic acid and changing it into lactic acid.

Then in 1891, Swiss enologist Hermann Müller theorized that bacteria may be the cause of the acid reduction. He then explained his theory of this biological acid reduction in 1913 to be caused by wine Bacterium gracile. In the 1930s, French enologist Jean Ribéreau-Gavon published papers that promoted the benefits of this process in wine making. By the 1950s, advances in enzymatic analysis allowed enologists to better understand malolactic fermentation and soon, cultured stock of beneficial lactic acid bacteria to make it available for winemakers to use at desired times.

Karl Bradley is the wine sales representative for General Beverage Wines for the Door County area. He has worked in fine dining and wine sales for more than 25 years and has a sommelier certificate from the Court of the Master Sommeliers.