Oenococcus oeni is a type of facultative anaerobic bacterium often found in various fermented foods and beverages, including fruit mashes. In winemaking, it is known for its ability to thrive in challenging environments, such as low pH and high alcohol levels.
The Role of Oenococcus Oeni in Winemaking
Oenococcus oeni plays a significant role in winemaking by facilitating malolactic fermentation (MLF), a secondary fermentation process. This process converts malic acid, naturally present in grapes, into lactic acid. This conversion reduces the wine’s overall acidity, contributing to a smoother and less harsh taste. MLF also contributes to the microbiological stability of the wine. By consuming malic acid, Oenococcus oeni helps prevent spoilage by other microbes that might later metabolize residual malic acid, potentially causing faults in the bottled wine.
How Oenococcus Oeni Transforms Wine
The activity of Oenococcus oeni during malolactic fermentation significantly impacts the sensory profile and structural characteristics of wine. The conversion of malic acid to lactic acid softens the wine’s acidity, replacing the sharp, green apple notes of malic acid with the milder, creamier sensation of lactic acid. This reduction in tartness contributes to a more balanced and approachable taste.
Oenococcus oeni also influences the wine’s mouthfeel, often leading to a smoother, rounder, or creamier texture. The bacteria contribute to the wine’s flavor and aroma profile by producing compounds like diacetyl, which imparts buttery or butterscotch notes. Other flavor contributions can include nutty or caramel notes. Certain strains of Oenococcus oeni can also enhance fruity, floral, and spicy notes, and contribute to the longevity of these aromas during aging.
Controlling Oenococcus Oeni in Winemaking
Winemakers actively manage Oenococcus oeni to achieve specific wine styles. To encourage MLF, winemakers may inoculate the wine with selected strains of Oenococcus oeni after the primary alcoholic fermentation by yeast has completed. Maintaining the wine temperature within an optimal range, typically between 17-25°C (63-77°F), and ensuring a pH above 3.1 promotes bacterial activity. Providing adequate nutrients can further support a successful MLF.
Conversely, winemakers may prevent MLF to preserve a wine’s crisp acidity, particularly in certain white and rosé wines. Methods to inhibit Oenococcus oeni include keeping the wine at low temperatures, generally below 15°C (59°F), and adding sulfur dioxide (SO2), which acts as an antimicrobial agent. Sterile filtration, which physically removes bacteria, is another method to prevent MLF. Early racking and clarification can also help by reducing bacterial populations and available nutrients.