Malolactic Fermentation: Creamy Wine Process
Learn what malolactic fermentation (MLF) is, how it transforms wine's texture and flavor, and why it makes some Chardonnays taste buttery and smooth.
Malolactic fermentation is a process where bacteria convert tart malic acid into smoother lactic acid, giving wines a softer, creamier texture. It is standard in red wines and buttery-style Chardonnays.
If you have ever wondered why some Chardonnays taste rich and buttery while others taste crisp and mineral, the answer often comes down to a process called malolactic fermentation. Despite its technical name, understanding malolactic fermentation unlocks a key piece of the puzzle in how winemakers shape the wines we drink.
What Is Malolactic Fermentation?
Malolactic fermentation, commonly abbreviated as MLF or simply “malo,” is a secondary fermentation that occurs after the primary alcoholic fermentation. Unlike primary fermentation, where yeast converts grape sugar into alcohol, MLF involves bacteria, specifically Oenococcus oeni, converting malic acid into lactic acid and carbon dioxide.
Malic acid is the sharp, green-apple-like acid naturally present in grapes. Lactic acid is the softer, creamier acid found in dairy products like yogurt and milk. When malic acid is converted to lactic acid, the wine’s total acidity decreases and its texture becomes noticeably smoother and rounder. This transformation also produces diacetyl, the compound responsible for the buttery flavor associated with certain wine styles.
Why Malolactic Fermentation Matters
MLF is one of the most important tools winemakers have for controlling the style and texture of their wines. By choosing whether to encourage or prevent malolactic fermentation, a winemaker can steer the same grape variety toward dramatically different styles.
For Chardonnay, this choice is particularly significant. Chardonnay that undergoes full malolactic fermentation, combined with oak aging, develops the rich, buttery, creamy profile associated with many California and Australian styles. Chardonnay where MLF is blocked retains its crisp malic acidity and delivers the lean, mineral, razor-sharp profile associated with Chablis and other cool-climate examples.
Beyond Chardonnay, MLF is standard practice for virtually all red wines. Red wine grapes are typically higher in malic acid, and the conversion to lactic acid is essential for creating a smooth, palatable wine. A red wine that retained all its malic acid would taste aggressively sharp and unbalanced. This is why you rarely hear MLF discussed in the context of red wine: it is simply assumed to happen.
MLF also contributes to microbial stability. Once malic acid has been converted, it is no longer available as a food source for unwanted bacteria that could cause spoilage in the bottle. Completing MLF before bottling gives winemakers confidence that the wine will remain stable during storage and aging.
Malolactic Fermentation in Practice
Winemakers manage MLF through temperature control and the use of sulfur dioxide. Lactic acid bacteria are most active at temperatures between 18 and 22 degrees Celsius. To encourage MLF, winemakers keep the wine warm after primary fermentation and may even inoculate with a specific bacterial culture to ensure a clean, controlled conversion.
To prevent MLF, winemakers can chill the wine to inhibit bacterial activity, add sulfur dioxide to kill the bacteria, or sterile-filter the wine to remove the bacteria entirely. Many white wine producers who want to preserve bright, fresh acidity in varieties like Riesling, Sauvignon Blanc, and Pinot Grigio actively prevent MLF from taking place.
Some winemakers take a middle path, allowing partial malolactic fermentation. They might convert a portion of the wine through MLF and keep the rest crisp, then blend the two together. This technique creates a wine with both richness and freshness, a balance that many modern consumers prefer over the fully buttery or fully austere extremes.
The diacetyl produced during MLF is responsible for the buttery aroma that many people associate with oaked Chardonnay. In small amounts, it adds complexity and richness. In excessive amounts, it can make a wine taste overwhelmingly like movie theater popcorn, which is why careful winemakers monitor the process closely and use batonnage, the stirring of lees, to help integrate the diacetyl into the wine.
Explore with Sommo
Understanding winemaking processes like malolactic fermentation helps you decode what you taste in the glass. With Sommo’s WSET study tools and structured tasting notes, you can learn to identify the signs of MLF in wine, from buttery aromas to creamy textures, and understand how winemaking choices shape every bottle you open.
