Malolactic fermentation

• Read the post in Catalan
• Read the post in Spanish

Let’s discover one of the best-kept secrets in the world of wine: malolactic fermentation, responsible for transforming wines with intense acidity into smooth and complex creations. The magic of this process not only improves the wine’s texture but also unveils unexpected aromas that will delight the most discerning palates.

MALOLACTIC FERMENTATION

Malolactic fermentation is an important biochemical process in winemaking, especially in red wines and some white wines. This fermentation occurs after alcoholic fermentation and involves the conversion of malic acid (which has a more acidic and harsh taste) into lactic acid (which is softer and more pleasant) thanks to the action of lactic acid bacteria, primarily Oenococcus oeni.

KEY POINTS OF MALOLACTIC FERMENTATION

Malolactic fermentation takes place after alcoholic fermentation, which, as we know, is the main process of converting grape sugars into alcohol through yeast.

• Starting Moment

It typically begins naturally, right after alcoholic fermentation, when the wine conditions (temperature, pH, and absence of free sulfur dioxide) are suitable for the growth of lactic acid bacteria. In some cases, wineries induce malolactic fermentation in a controlled manner by inoculating bacteria like Oenococcus oeni, to ensure the process develops properly under optimal conditions.

• Duration and Conditions

The process can last from a few weeks to several months, depending on conditions such as temperature, which is ideally kept between 18 and 22ºC, and sulfur dioxide levels. Excess sulfur dioxide can inhibit or delay the process.

• Time Control

In red wines, malolactic fermentation is almost always carried out because it improves texture and balances acidity. In this case, it naturally forms part of the wine aging process in barrels or tanks.

In white wines, winemakers decide whether or not to carry it out depending on the style of wine they want to produce. In some wines, like Chardonnay, a controlled malolactic fermentation is sought to add complexity and soften the acidic profile.

MANAGING THE MALOLACTIC FERMENTATION PROCESS

Controlling malolactic fermentation is a key process in winemaking, as it can influence the wine’s taste, stability, and final quality. Wineries use various techniques to ensure that malolactic fermentation occurs under the right conditions or, if it is not desired, to avoid it.

Below are the main factors that are controlled:

• Inoculation of Lactic Bacteria

Winemakers can directly add selected lactic bacteria, primarily Oenococcus oeni, to ensure that malolactic fermentation begins optimally and under the desired conditions. This allows for control over the timing and ensures a uniform fermentation.

In other cases, malolactic fermentation is allowed to occur naturally, depending on the presence of lactic bacteria in the wine, although this method is less predictable.

• Temperature Control

Temperature is a key factor in regulating fermentation. It is usually carried out at temperatures between 18 and 22ºC, which are optimal conditions for the growth of lactic bacteria. If the temperature is too low, the process may stop or slow down. If it is too high, there may be a risk of microbial imbalance.

Wineries use refrigeration or heating systems to maintain the temperature at the appropriate levels.

• Sulfur Dioxide (SO₂) Levels

Sulfur dioxide (SO₂) is a preservative used to control microbial activity in wine. Excessive levels of this compound can inhibit malolactic fermentation by slowing down the development of lactic bacteria. For this reason, winemakers adjust the levels of sulfur dioxide before malolactic fermentation to ensure that it can occur.

Once malolactic fermentation is complete, SO₂ is often added to stabilize the wine and prevent possible bacterial contamination.

• pH and Acidity

The pH of the wine also influences malolactic fermentation. A pH that is too low (very acidic) can inhibit the process. For this reason, the acidity of the wine is controlled and adjusted when necessary.

The ideal pH for malolactic fermentation is typically around 3.3 to 3.5.

• Oxygenation

Lactic bacteria may require small amounts of oxygen for their development. For this reason, some winemakers opt to introduce oxygen in a controlled manner or carry out racking (moving wine between containers) during the malolactic fermentation process.

• Analytical Monitoring

Regular wine analyses are carried out during malolactic fermentation to monitor the levels of malic acid and lactic acid and ensure that the conversion is proceeding correctly.

The activity of the bacteria and the composition of the wine can also be measured using techniques such as chromatography, which helps determine when fermentation has finished.

• Decision to Stop or Avoid Malolactic Fermentation

If the winemaker wants to avoid malolactic fermentation, especially in white wines where freshness and acidity are to be preserved, they may increase the levels of SO₂ or maintain the wine at lower temperatures (below 15ºC).

In some cases, malolactic fermentation can be completely avoided by filtering the bacteria before the process begins.

IMPACT OF MALOLACTIC FERMENTATION ON WINES

Malolactic fermentation has a significant impact on the sensory and structural characteristics of wines. The following are the main effects it has on the wine:

• Reduction of Acidity

Malolactic fermentation converts malic acid, which is more acidic and harsh on the palate, into lactic acid, which is smoother and creamier. This change reduces the overall acidity of the wine, making it less sharp and rounder.

This is especially noticeable in wines with initially high acidity, such as those from colder regions or those made from very acidic grapes.

• Change in Texture

The transformation of malic acid into lactic acid results in a wine with a softer, creamier texture. This effect is particularly desirable in certain white wines, where malolactic fermentation provides a fuller and more velvety mouthfeel.

In red wines, this process can soften tannins, making the wine more balanced and approachable on the palate.

• Secondary Aromas and Flavors

Malolactic fermentation can generate secondary aromas that add complexity to the wine. Often, lactic or buttery notes such as butter, cream, or yogurt emerge. Nutty or toasted bread notes can also appear.

In wines aged in oak, this process can accentuate aromas of oak, spices, vanilla, or caramel.

• Microbiological Stabilization

Once malolactic fermentation is complete, the wine becomes more microbiologically stable because the lactic bacteria have consumed the malic acid, which is a potential food source for other harmful bacteria. This reduces the risk of re-fermentation or microbiological contamination during aging or storage.

• Change in Wine Balance

The reduction of acidity and the addition of new flavors and aromas result in a different balance in the wine. In some cases, this makes the wine more harmonious, smooth, and pleasant on the palate. This is especially important in red wines, where it helps better integrate tannins and other structural components.

• Increased Aging Potential

Malolactic fermentation, when combined with other winemaking processes, can improve the aging potential of wines, particularly reds. The reduction in acidity and microbiological stability help maintain the wine in good condition for longer periods.

• Influence on Wine Style

In many whites (such as Chardonnay), malolactic fermentation is used to add complexity and softness. However, in other whites (such as Riesling or Sauvignon Blanc), this process is often avoided to preserve lively acidity and fruity flavors.

In reds, malolactic fermentation is almost always carried out, as it softens the tannins and improves the overall balance of the wine.

WINES THAT INCLUDE MALOLACTIC FERMENTATION

Malolactic fermentation is mainly carried out in certain types of wines, depending on the desired style by the winemakers and the characteristics of the grape. Below are the types of wines in which malolactic fermentation is commonly practiced or avoided:

• Red Wines

In red wines, as mentioned, malolactic fermentation is almost universal, as it adds smoothness and reduces acidity, making the wine more approachable and better integrating the tannins. Most red wines, especially those that are aged or reserved, undergo this process.

Some examples of red wines where malolactic fermentation takes place include Cabernet Sauvignon, Merlot, Syrah, Tempranillo, Pinot Noir, among others.

• White Wines

Malolactic fermentation in white wines depends on the style that is desired:

– In some white wines, such as Chardonnay, malolactic fermentation is common because it adds a creamier texture and lactic notes (butter, cream) that are appreciated in these richer, more structured styles.

– In other white wines, malolactic fermentation is avoided to maintain freshness, lively acidity, and the fruity flavors characteristic of the wine. This is common in varieties such as Riesling, Sauvignon Blanc, Albariño, or Pinot Grigio. In these cases, the pronounced acidity is a desired feature, and malolactic fermentation is blocked through the use of sulfur dioxide or temperature control.

• Sparkling Wines

In sparkling wines, such as Cava or Champagne, malolactic fermentation may or may not occur, depending on the style. In some sparkling wines, especially those with long aging, it is allowed to soften the base wine and provide a rounder mouthfeel. In others, especially fresh and vibrant sparkling wines, it is blocked to maintain acidity.

• Rosé Wines

In general, malolactic fermentation is not common in rosé wines, as the goal is to preserve freshness and liveliness, with high acidity and fruity flavors. However, some more complex and structured rosés may undergo this process to gain texture and soften acidity.

When a process influences various aspects of the wine by reducing its acidity, providing a smoother texture, enriching it with more complex aromas and flavors, and contributing to its final character and long-term stability, it is clear that it is a beneficial process for the wine and, consequently, for us who enjoy it.

Goodbye for now, and see you soon.