Oenococcus oeni

Oenococcus oeni

Oenococcus oeni under a microscope

Oenococcus oeni is a species of lactic acid bacteria that plays a crucial role in the winemaking process, particularly during malolactic fermentation. This bacterium is known for its ability to convert malic acid into lactic acid and carbon dioxide, a transformation that softens the taste of wine and enhances its stability and flavor profile.

Taxonomy and Classification

Oenococcus oeni belongs to the family Lactobacillaceae within the order Lactobacillales. It is a Gram-positive bacterium, characterized by its spherical to ovoid shape. O. oeni is the only species within the genus Oenococcus that is commonly associated with wine.

Role in Winemaking

The primary function of Oenococcus oeni in winemaking is to conduct malolactic fermentation (MLF), a secondary fermentation process that follows the primary alcoholic fermentation. During MLF, O. oeni converts the sharper malic acid present in wine into the softer lactic acid, thereby reducing the wine's acidity and contributing to a smoother mouthfeel.

This process not only enhances the sensory qualities of wine but also increases its microbial stability by reducing the amount of malic acid, which can be a substrate for spoilage organisms. The activity of O. oeni can also lead to the production of desirable flavor compounds, such as diacetyl, which imparts a buttery aroma to the wine.

Chemical structure of diacetyl, a compound produced by Oenococcus oeni

Environmental Conditions

Oenococcus oeni is well-adapted to the harsh conditions of wine, which include low pH, high alcohol content, and limited nutrients. It thrives in environments where other bacteria might struggle, making it an ideal candidate for conducting MLF in winemaking.

The optimal growth conditions for O. oeni include a temperature range of 18-22°C and a pH of 3.2-3.5. It is also tolerant of alcohol concentrations up to 14% by volume, which is typical in many wines.

Commercial Use

Winemakers often inoculate their wines with commercial strains of Oenococcus oeni to ensure a reliable and controlled malolactic fermentation. These strains are selected for their ability to perform well under specific winemaking conditions and for their contribution to the desired flavor profile of the wine.

Challenges and Considerations

While Oenococcus oeni is beneficial for wine production, its activity must be carefully managed. Excessive production of diacetyl can lead to undesirable buttery flavors, and incomplete malolactic fermentation can result in spoilage. Winemakers must monitor the progress of MLF and adjust conditions as necessary to achieve the desired outcome.

Related Pages

• Lactic acid bacteria
• Malolactic fermentation
• Winemaking
• Diacetyl