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Malolactic fermentation, also known as MLF, is a secondary fermentation process that occurs in wine production. It is the conversion of malic acid to lactic acid by lactic acid bacteria, resulting in a smoother and less acidic wine. While this process is desirable for some styles of wine, there are instances where winemakers may want to prevent malolactic fermentation. Here are some methods to achieve this:
1. Temperature Control:
Malolactic fermentation is sensitive to temperature. By maintaining the wine at a lower temperature, usually below 55°F (13°C), the growth of lactic acid bacteria is inhibited, preventing MLF. Temperature control is most effective during the initial stages of winemaking, such as fermentation and aging in stainless steel tanks.
2. Sulfur Dioxide:
Sulfur dioxide (SO₂) is commonly used in winemaking as a preservative and antioxidant. In its free form, SO₂ inhibits microbial growth, including lactic acid bacteria. By adding sulfur dioxide to the wine, MLF can be prevented. However, it is crucial to measure and control the sulfur dioxide levels to avoid complications.
3. Filtration:
Filtration is an effective method to remove yeast and bacteria from wine, including lactic acid bacteria responsible for MLF. Filtration works by passing the wine through a membrane or pad, capturing unwanted microorganisms. There are several types of filters, including depth filters and sterile membrane filters. Winemakers can choose the appropriate filter depending on their specific needs.
4. Chilling and Fining Agents:
Chilling the wine to near-freezing temperatures can suppress the activity of lactic acid bacteria and prevent MLF. By keeping the wine at low temperatures, around 35-40°F (2-4°C), the bacteria’s growth is inhibited. Additionally, fining agents, such as bentonite or gelatin, can be added to clarify the wine. These fining agents can also remove any remaining lactic acid bacteria, further preventing MLF.
5. Early Sulfiting:
Another preventive strategy is sulfiting the wine early in the winemaking process. By adding a calculated amount of sulfur dioxide during or shortly after the initial fermentation, the growth of lactic acid bacteria can be suppressed. However, it is essential to monitor and adjust the sulfur dioxide levels as needed to ensure wine stability without exceeding limits.
6. Inhibiting Bacteria Growth:
Promoting the growth of other microorganisms, such as yeast or bacteria strains that do not perform MLF, can help prevent MLF. These non-lactic acid bacteria present in the wine can outcompete lactic acid bacteria and limit their growth. Utilizing selected yeast strains or conducting specific fermentation practices can help encourage the desired microbial activity.
7. Acid Adjustments:
Malic acid is the precursor for lactic acid fermentation. By reducing the malic acid content in the wine, the chances of malolactic fermentation occurring are minimized. Acid adjustments can be made by various methods like blending with low acid wines, adding tartaric acid, or conducting partial deacidification.
It is important to note that preventing MLF should not be done haphazardly, as MLF can contribute positively to the sensory characteristics of certain wines. Winemakers should carefully consider the desired wine style and balance to determine whether or not to prevent MLF.
In conclusion, preventing malolactic fermentation in wine involves a combination of temperature control, the use of sulfur dioxide, filtration, chilling, fining agents, early sulfiting, inhibiting bacteria growth, and acid adjustments. These techniques allow winemakers to have greater control over the final characteristics and style of their wines.
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