Malolactic fermentation is a secondary fermentation that occurs in nearly all red wines and many white wines, transforming sharp malic acid into softer lactic acid. This biological process, carried out by lactic acid bacteria, reduces the wine’s overall acidity and introduces a layer of creamy texture and complex flavor compounds. For winemakers and enthusiasts, understanding malolactic fermentation is essential for predicting a wine’s structure, aging potential, and sensory profile.
How Malolactic Fermentation Works
Unlike primary fermentation, which converts sugar into alcohol, malolactic fermentation is a bacterial process that follows the initial yeast-driven stage. The primary agents are lactic acid bacteria, notably species of Oenococcus oeni , which thrive in the wine environment once sugar levels drop and alcohol rises. These bacteria metabolize malic acid, naturally present in grapes, and convert it into lactic acid and carbon dioxide. The result is a decrease in total acidity, often by 10 to 30 percent, and a shift in the acid balance from tart malic acid to rounder lactic acid.
The Role of Lactic Acid Bacteria
The success of malolactic fermentation hinges on the presence and activity of specific bacterial strains. Oenococcus oeni is the most reliable species for winemaking due to its predictable behavior and ability to survive in wine. Other bacteria, such as Lactobacillus and Pediococcus , can also perform the conversion but are often associated with spoilage if not carefully managed. Winemakers may introduce these bacteria via cultured inoculants or rely on native strains present in the vineyard, cellar, and barrels.
Impact on Wine Flavor and Texture
The biochemical change during malolactic fermentation does more than alter acidity; it reshapes the wine’s aromatic and tactile profile. The production of diacetyl, a byproduct of the fermentation, imparts buttery, creamy notes that are characteristic of many Chardonnays. Additionally, the process can reduce harsh green flavors in cooler-climate wines, smoothing out aromas of green apple or gooseberry. The softened acid structure allows the fruit and oak characteristics to integrate more harmoniously, creating a rounder, more supple mouthfeel.
Common Flavor Descriptors
Butter
Cream
Cheese rind
Hazelnut
Savory complexity
Which Wines Undergo Malolactic Fermentation
While nearly all red wines experience malolactic fermentation, either naturally or induced, the choice with white wines is more deliberate. Full-bodied whites such as Chardonnay are frequently processed to enhance richness and stability. In contrast, light whites like Sauvignon Blanc or Riesling often skip this step to preserve their crisp, acidic character. Sparkling wines also benefit from malolactic fermentation, as the resulting lactic acid provides a smoother backdrop for the mousse and balances the autolytic flavors from yeast lees aging.
