Malolactic Fermentation vs No Malolactic
Creamy, complex, and softened versus bright, vivid, and unapologetically tart: one winemaking decision that changes everything in the glass.
Malolactic fermentation (MLF) is one of the most consequential decisions a winemaker makes after harvest. It determines whether a wine presents as round and textured or crisp and electric. The choice hinges on grape variety, regional climate, and the intended style: nearly all red wines undergo MLF to soften tannins and integrate structure, while the world's most aromatic and high-acid whites actively block it to preserve freshness and varietal character.
MLF is a bacterial conversion, not a true fermentation, in which lactic acid bacteria (primarily Oenococcus oeni, with support from Lactobacillus and Pediococcus species) decarboxylate L-malic acid into L-lactic acid and CO2. The reaction reduces titratable acidity by 1 to 3 g/L and raises pH by approximately 0.3 units. It typically occurs after alcoholic fermentation but can run concurrently.
Blocking MLF means the original malic acid profile of the grape is preserved intact in the finished wine. Winemakers suppress lactic acid bacteria through early addition of sulfur dioxide post-fermentation, sterile filtration to remove bacteria, tight temperature control below 16 degrees Celsius (61 degrees Fahrenheit), and in some cases the use of lysozyme enzyme. Maintaining low pH (below 3.1) also creates an inhospitable environment for LAB activity.
MLF replaces the sharp, green-apple snap of malic acid with the softer, milk-like character of lactic acid. The key aromatic byproduct is diacetyl, which delivers notes of cream, butter, almond, and hazelnut in white wines at higher concentrations, and more subtle complexity in reds. Red wines going through MLF may also develop enhanced spicy, toasty, and cocoa notes, while fruitiness can decrease slightly.
Without MLF, wines retain their primary fruit energy. In whites, this means vivid citrus, green apple, stone fruit, and floral aromatics remain front and center with no dairy or nutty overlay. In reds that deliberately skip it, vibrant berry fruit and tangy acidity dominate. The malic acid contributes a distinctive tartness and crispness that many winemakers in warm climates prize for maintaining freshness when natural grape acidity is already lower.
MLF creates a rounder, fuller, and creamier mouthfeel. The increased pH softens the perception of sourness, and the production of compounds such as ethyl lactate (which can reach 110 mg/L post-MLF) and sugar alcohols including glycerol and erythritol contribute to palate weight and texture. In red wines, it also smooths harsh tannin edges, making the wine feel more approachable earlier in its life.
Wines blocked from MLF retain higher perceived acidity and a leaner, more taut texture on the palate. The mouthfeel is crisper and more linear, with less mid-palate weight. This structure can be ideal for high-acid varieties where the goal is a refreshing, cleansing finish. The absence of softening also means the wine feels more vibrant and energetic rather than plush or generous.
MLF is standard practice for virtually all red wine production globally, including Cabernet Sauvignon, Pinot Noir, Merlot, Syrah, and Nebbiolo. Among whites, Chardonnay is the prime example, particularly in Burgundy, Champagne, and California. Viognier also commonly undergoes MLF. Cool-climate regions such as Burgundy and Champagne rely on MLF most heavily because their grapes accumulate the highest levels of malic acid before harvest.
Riesling, Sauvignon Blanc, Gewurztraminer, Pinot Gris, Muscat, Torrontes, and Vermentino are the varieties most commonly protected from MLF. Key regions include the Loire Valley (Sancerre, Pouilly-Fume), Alsace, Germany, Austria, New Zealand's Marlborough, and the Mosel. Muscadet is another classic non-MLF white. In warmer climates such as California and Australia, winemakers with naturally low-acid fruit across many varieties also block MLF to preserve whatever freshness the grapes retained.
Completing MLF before bottling is one of the most effective stability tools available. Once all the malic acid is consumed, lactic acid bacteria have no remaining substrate to re-activate in the bottle. This eliminates the risk of spontaneous re-fermentation in bottle, which causes cloudiness, slight effervescence, and off-aromas. Wines that have finished MLF are therefore considered microbiologically stable from a LAB perspective.
Wines that have not undergone MLF retain residual malic acid, which can serve as a carbon source for lactic acid bacteria if they are ever introduced or reactivated. This creates a risk of unwanted spontaneous MLF post-bottling, requiring careful management through sterile filtration, adequate free SO2 levels, and cold storage. The higher natural acidity of these wines does provide its own protective antimicrobial effect, as bacteria struggle to thrive at lower pH values.
MLF raises the wine's pH, which can slightly reduce aging potential by making the wine more susceptible to oxidation and microbial spoilage if SO2 is not carefully managed. However, in the context of red wines with tannin structure, MLF is part of a broader matrix of factors that enable long aging. The stability gained from eliminating malic acid as a spoilage substrate partially offsets the acidity loss. Re-acidification with tartaric acid is a common corrective step post-MLF.
Preserving malic acidity keeps pH lower, and lower pH wines demonstrably age more gracefully, as acidity acts as a natural preservative against premature oxidation. The world's longest-lived white wines, including great German Rieslings and top-tier Chablis, typically retain high acidity, whether through blocked MLF or naturally low malic acid levels. Acidity maintains color, freshness, and aromatic persistence across decades. The trade-off is that these wines can feel austere young and require time for primary fruit to integrate.
MLF wines, with their rounder texture and richer weight, pair naturally with richer dishes. Full MLF Chardonnay is the classic companion for lobster bisque, cream-based pasta, roast chicken, and dishes with butter sauces. Red wines that have undergone MLF offer softened tannins ideal for matching with red meat, lamb, aged cheeses, and mushroom-rich preparations. The texture complements rather than cuts through food.
Non-MLF wines are prized for their food versatility and palate-cleansing acidity. Crisp Sauvignon Blanc and Riesling without MLF excel alongside raw oysters, sushi, delicate seafood, fresh salads, goat cheese, and dishes with citrus or herb-based sauces. Their vivid acidity cuts through fat and lifts flavors rather than matching weight with weight. Non-MLF reds, with their tangy brightness, pair well with poultry, charcuterie, and lighter meat dishes.
Choosing MLF is typically a statement of texture and complexity over freshness. Winemakers use it to build palate weight, integrate oak, and create wines that feel generous and approachable. In reds, it is rarely a stylistic choice since it occurs almost universally. In whites, opting for full or partial MLF signals a deliberate move toward richness, such as barrel-fermented Burgundy or a New World Chardonnay built for weight. Partial MLF, where only a fraction of the blend goes through conversion, allows nuanced tuning of texture versus vibrancy.
Blocking MLF is an act of preservation and precision. The winemaker is committing to the grape's inherent aromatic fingerprint and structural architecture. It requires more active cellar intervention, including careful SO2 management, temperature control, and sometimes sterile filtration, making it technically demanding. It is the dominant philosophy for high-acid aromatic white wines globally and represents a growing counter-trend in warm climates where retaining freshness is increasingly difficult due to rising temperatures and earlier harvest dates.
Reach for an MLF wine when you want generosity: a creamy, textured Chardonnay with dinner, or a red with polished tannins and immediate approachability. Choose a non-MLF wine when precision and lift are the priority: crisp Riesling with fish, vibrant Sauvignon Blanc with a salad, or any occasion calling for a wine that refreshes rather than envelops. Neither approach is superior; they serve fundamentally different purposes, and the most skilled winemakers know exactly which tool fits which grape, climate, and table.
- MLF is technically a bacterial conversion, not a true fermentation, carried out by Oenococcus oeni and related lactic acid bacteria (LAB). It reduces titratable acidity by 1 to 3 g/L and raises pH by approximately 0.3 units by converting diprotic malic acid into monoprotic lactic acid.
- Diacetyl is the key aromatic byproduct of MLF and is responsible for buttery and creamy notes in white wines; at low concentrations it is subtle and nutty, while at concentrations above 5 mg/L it becomes strongly buttery. Extended lees contact after MLF reduces diacetyl as residual yeast break it down into acetoin and 2,3-butanediol.
- Blocking MLF requires active cellar management: SO2 additions post-alcoholic fermentation, keeping wine below 16 degrees Celsius, early racking, maintaining pH below 3.1, sterile filtration, or use of lysozyme. Failure to block it completely risks spontaneous MLF in bottle, causing cloudiness and unwanted effervescence.
- The classic exam distinction: virtually all red wines undergo MLF; only about 20 percent of white wines worldwide do. Riesling, Gewurztraminer, Sauvignon Blanc, Muscat, and Pinot Gris are the canonical non-MLF whites. Chardonnay and Viognier are the principal MLF white exceptions.
- The relationship between MLF and aging potential is nuanced: MLF boosts microbial stability by eliminating malic acid as a LAB substrate but can reduce longevity by raising pH and making the wine more vulnerable to oxidation. Conversely, non-MLF wines retain lower pH and higher acidity, which acts as a preservative, helping the world's longest-lived whites such as German Riesling age for decades.