What is malolactic fermentation?
In wine terminology, it's called "malolactic fermentation." But to be precise—and precision matters in the cellar—it's not a true fermentation. Instead, it's a decarboxylation reaction: a chemical transformation in which malic acid converts into lactic acid, water, and carbon dioxide.
This work is carried out by lactic acid bacteria—mainly Oenococcus oeni and Lactococcus lactis—which intervene after alcoholic fermentation, during the aging or maturation phase of the wine.
The result? A softer, more balanced, and more complex wine. But not always—and understanding when malolactic fermentation is beneficial and when it should be avoided is one of the winemaker's most delicate tasks.
Necessary Conditions for Malolactic Fermentation
Malolactic fermentation does not spontaneously occur under all conditions. For lactic acid bacteria to become active, the wine must be in a precise balance:
- pH not excessively low — overly acidic wines inhibit bacteria
- Low sulfur dioxide concentration — sulfites are the main natural inhibitors
- Ethyl alcohol below 15% — higher concentrations block bacterial activity
- Temperature between 18° and 20°C — the optimal thermal window for lactic acid bacteria
As with alcoholic fermentation, here too the winemaker can choose: rely on bacteria naturally present in the must, or use selected strains of Oenococcus or Lactobacillus for a more controlled process.
What Changes in Wine: Sensory Effects
The most immediate impact of malolactic fermentation is a single one: acidity reduction. Malic acid—the kind you taste in a bite of a green apple, tart and sharp—transforms into lactic acid, which is more delicate, softer, and perceived as less acrid on the palate.
But it's not just about acidity. Malolactic fermentation also affects the wine's aromatic profile:
- Herbaceous tones are softened
- Shades of nut, vanilla, spices, leather, and toast are accentuated
- The wine gains greater body, balance, and persistence
- Aromas become finer and more integrated
A profound change that transforms the wine's character—for the better, when the conditions are right.
Malolactic Fermentation in Red Wines: Almost Always an Advantage
In red wines, malolactic fermentation is a common practice, and almost always beneficial. Reds produced in cool climates—with naturally high acidity—gain roundness and pleasantness. Lactic acid bacteria also produce secondary aromatic compounds that further enrich the wine's profile.
The result is a more round, complex, and long-lived wine—ready to face years in the bottle with elegance.
Malolactic Fermentation in White Wines: A Choice, Not an Automatic Process
For white wines, the situation is more nuanced. White wines' strength lies in their primary aromas, savoriness, and acidity—characteristics that malolactic fermentation tends to diminish. For this reason, in fresh, young white wines, malolactic fermentation is often avoided.
In white wines produced in cold climates, where acidity is already high, malolactic fermentation can be a useful tool to soften the structure. In white wines from warm climates—like those from Sardinia—where acidity is already naturally low, malolactic fermentation risks further flattening the wine's freshness: an effect that is almost always undesirable.
Malolactic Fermentation in Orange Wines: Complexity and Stability
Orange wines—wines made from white grapes fermented with long skin contact, similar to red wine vinification—behave similarly to reds concerning malolactic fermentation.
The presence of tannins and their more complex structure make them suitable to benefit from malolactic fermentation: the wine gains complexity, stability over time, and a more enveloping texture.
This is the case with our Zankitai, our orange wine refermented in the bottle with sur lies aging: a wine that embodies the Mediterranean scrub of Villasimius, the granite, the wind—and an aromatic complexity that arises precisely from the interplay of white wine vinification, prolonged skin contact, and skilled management of malolactic fermentation.
Malolactic Fermentation: A Balance, Not a Rule
Like every significant choice in the cellar, malolactic fermentation is neither always right nor always wrong. It is a powerful, delicate tool that requires knowledge and intention to use.
At Colline del Vento, we evaluate it wine by wine, vintage by vintage, always striving for the same goal: that every bottle tells the most honest story possible of the land it comes from.
Because the best wine isn't the most technical one. It's the truest one.
