Malolactic Fermentation



Fermentation is a chemical process. A process during which compounds are incompletely oxidized. And also, they undergo a change in their chemical structure in the absence of oxygen and become organic compounds.

The winemaking process consists of multiple steps: harvesting the grapes through the must, fermentation, distillation, decantation, and bottling production.

Fermentation is the key and most important process in winemaking. Due to the presence of a great variety of chemical compounds in grapes, there are different fermentation types. The type of fermentation in the production of wine will depend on which compounds react, which substance it transforms to, and what conditions need to be meet for its transformation; that’s where the name for each type of fermentation comes from.

This post will explain what malolactic fermentation is about, one of the most common fermentation types in the wine industry. Also, we will know its advantages, behavior, which wines benefit from this process, and what effects this fermentation has on the wine.

What is Malolactic Fermentation?

This fermentation is when malic acid is chemically transformed into lactic acid, using a bacteria of lactic origin such as Oenococcus oeni that exist naturally in the environment where the reaction occurs.

Malic acid is a component present in many fruits’ pulp, and its transformation occurs within it.

This fermentation type acts as a secondary fermentation for a short time after the primary fermentation (alcoholic fermentation). Although sometimes both fermentations can co-occur. Besides, this process is very common in producing red wines and other types of everyday wines. Among which Chardonnay stands out.

WikimediaOenococcus oeni

What Bacteria is Responsible for Malolactic Fermentation?

Malolactic fermentation occurs in bacteria belonging to the genus Leuconostoc, such as Oenococcus oeni, some Lactobacillus species, and Pediococcus.

Malic acid is one of the two primary acids in wine grapes. During this reaction, malic acid transforms into lactic acid. This happens through a decarboxylation reaction, which involves the release of carbon dioxide.

This type of reaction occurs under natural conditions. However, in commercial wine production, malolactic fermentation begins by the injection of bacteria, mainly O. oeni. This prevents another group of undesirable bacteria from acting on the wine, changing its flavor.

O. oeni works in warm environments (above 60.8 °F/16 ° C), which means that winemakers tend to wait until spring during aging for this fermentation to occur. However, currently, some cellars and tanks can be heated to start the malolactic fermentation as soon as they want it.

How to Control Malolactic Fermentation During Wine Production?

When malolactic fermentation is desirable in the production of wine, the temperature of the cellar is set at 64.4 °F (18 ° C), and the tanks are inoculated with selected freeze-dried O. oeni strains.

This fermentation process lasts between 4 and 6 weeks. By monitoring the acidity of the wine or by titrating samples you can control the process. After obtaining the desired acidity level in the wines, they are drained for the clarification process.

During the clarification process, the wine undergoes a filtration process. For this process winemaker uses diatomaceous earth, membrane filters, cartridge, or pad filters, to filter it later using cross-flow or centrifugation. This step aims to eliminate impurities and obtain a clear and natural wine (vins clairs).

What is the Importance of Malolactic Fermentation?

This process helps decrease the wines’ acidity, generally down to a pH of around 3.5.

The malolactic fermentation favors those wines that contain too much acidity. When this process occurs under controlled conditions, the quality of the wine produced increases, especially red wines. It provides a characteristic flavor that “fills the mouth”. Also giving body, density, and a persistent flavor to the wine to produce a sensation of smoothness, on the palate.

People apply this process widely in those wines whose grapes have grown in cold climates; these grapes’ acidity is much higher than those that have grown in hot climates. Also, wines that have undergone maceration in carbon dioxide atmospheres before being crushed (carbonic maceration) suffer an increase in flavor when subjected to this type of fermentation.

Malolactic fermentation gives the wine notes of brioche and butter to the wine due to the presence of diacetyl, a by-product of the reaction, and dairy notes such as milk, cheese, yogurt, and cream.

Does Malolactic Fermentation Benefit All Wines?

Not all. Malolactic fermentation is undesirable in some styles of wine. Particularly those that are aromatic or white with a high level of acidities like Riesling or Sauvignon Blanc. Winemakers can inhibit malolactic fermentation by adding sulfur dioxide to wines at the end of alcoholic fermentation or using enzymes such as lysozyme.

The wines highly favored by malolactic fermentation are generally red wines, where their acidity is a crucial factor. Chardonnay and Viognier wines are an exception to this process as their malic acid content gives them a smooth feel and more pronounced acidity.

As for white wines, some producers use malolactic fermentation to control acidity in wines from Semillon and Sauvignon Blanc grapes.

Are There Red Wines Where Winemakers Avoid This Process?

Malolactic fermentation in red wines helps to accentuate their fruity flavors and cherry notes and helps to remove some of their sour notes. Those red wines that have grown in warm climates and have low acidity do not benefit from the process as it makes them less balanced wines.

However, many red wines undergo malolactic fermentation in barrels. In these cases, in addition to reducing its acidity and giving fruity notes, malolactic fermentation in barrels provides the wine with smoky and spicy notes and reduces its vegetable notes.

Now you can get more knowledge about this process in wine production and how it involves your favorites’ white and red wines.

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