Malolactic fermentation is a secondary fermentation process that almost every red wine and many white wines undergo, transforming the sharp acidity of malic acid into the softer acidity of lactic acid. This biological reaction, carried out by lactic acid bacteria rather than yeast, reduces the wine’s overall tartness and creates a smoother, more palate-friendly texture. Beyond acid adjustment, this process generates complex flavor compounds that contribute butter, cream, and subtle nutty notes, profoundly shaping the final character of the wine.
How Malolactic Fermentation Works at a Microscopic Level
The mechanism behind malolactic fermentation involves specific strains of lactic acid bacteria, most commonly Oenococcus oeni , thriving in the wine environment. These bacteria consume malic acid, the same tart compound found in green apples, and metabolize it to produce lactic acid and carbon dioxide. Lactic acid is notably gentler on the palate, meaning the wine loses its initial harshness while maintaining a balanced structure. This biological transformation usually occurs after the primary alcoholic fermentation has subsided, once the sugar has been converted to alcohol and the environment becomes more suitable for the bacteria.
Impact on Wine Flavor and Aroma
Beyond the fundamental shift in acidity, malolactic fermentation is a critical contributor to a wine’s aromatic profile. For rich, oaked Chardonnays, the process is often responsible for the signature "butter" and "creamy" textures, thanks to the production of diacetyl, a compound with a distinct buttery aroma. In red wines, it helps to integrate tannins and soften the edges, resulting in a rounder, fuller body. The suppression of undesirable volatile acidity and the creation of stable bacterial membranes also protect the wine from spoilage, ensuring a more consistent and complex bouquet over time.
Which Wines Undergo This Process
While nearly universal in red wine production, the application of malolactic fermentation varies significantly in the white wine world. Most red varietals, including Cabernet Sauvignon, Merlot, and Pinot Noir, almost always undergo this process to achieve their characteristic soft, velvety mouthfeel. For white wines, the decision is stylistic; it is a hallmark of fuller-bodied, oaked Chardonnays but is deliberately avoided in crisp, zesty wines like Sauvignon Blanc and most Rieslings. Winemakers carefully monitor the pH and acidity levels to determine if the process will enhance or detract from the intended style.
Controlling the Fermentation in the Winery Winemakers treat malolactic fermentation as a precise tool rather than a guaranteed inevitability. In cooler climates, where the process might occur too slowly or unpredictably, winemakers often inoculate the wine with selected bacterial strains to ensure a clean and timely conversion. Conversely, in warm regions or with specific grape varieties, they might inhibit the process by adding sulfur dioxide or maintaining lower temperatures to preserve the wine’s natural tartness. The vessel matters, too; stainless steel tanks minimize the flavor impact, while oak barrels encourage integration and the development of toasty, spicy nuances alongside the acid transformation. Common Descriptors and Sensory Experience
Winemakers treat malolactic fermentation as a precise tool rather than a guaranteed inevitability. In cooler climates, where the process might occur too slowly or unpredictably, winemakers often inoculate the wine with selected bacterial strains to ensure a clean and timely conversion. Conversely, in warm regions or with specific grape varieties, they might inhibit the process by adding sulfur dioxide or maintaining lower temperatures to preserve the wine’s natural tartness. The vessel matters, too; stainless steel tanks minimize the flavor impact, while oak barrels encourage integration and the development of toasty, spicy nuances alongside the acid transformation.
When you taste a wine that has completed this transformation, the effects are immediately noticeable on the palate. The wine tastes rounder and less angular, with a softer, silkier texture that feels almost velvety rather than mouth-puckering. Typical flavor descriptors range from the creamy profile of butter and yogurt to subtle hints of nuts, hay, or even a faint smokiness. This textural shift is particularly evident in the mid-palate, where the absence of harsh malic acid allows other flavors to open up and linger, creating a more cohesive and satisfying finish.
