Winemaking demands tight microbiological control, sound process decisions, and rigorous analytical monitoring. Within this framework, malolactic fermentation (MLF) is essential to achieve wines that are stable, balanced, and sensorially consistent. Below, we explain what MLF is, how it is carried out using a sequential post-alcoholic inoculation approach, which factors determine its duration, and what LEV2050 solutions help you execute it with precision.
What is malolactic fermentation?
MLF (malolactic fermentation) is the conversion of L-malic acid into L-lactic acid and CO₂, mediated by wine bacteria—primarily Oenococcus oeni as the target species. This transformation reduces the sharp, “green” acidity associated with malic acid, improves mouthfeel softness, and enhances microbiological stability in bottle.
MLF does not generate alcohol: it acts on acid balance and on specific aroma-related compounds (e.g., diacetyl and citrate-derived compounds), which must be managed according to the desired wine style.
Importance in modern winemaking
In modern winemakingIn modern winemaking, controlled fermentation is a fundamental process. It improves mouthfeel smoothness, balances the gustatory profile, and supports long-term stability. Sensory-wise, it can produce lactic/buttery notes that add complexity. It also enables acidity modulation based on the desired style, providing greater control during production.
MLF also has a key technological role: when completed correctly, it helps prevent refermentation or microbial deviations that could compromise final wine quality. That’s why more and more wineries choose to monitor and steer MLF precisely using selected strains and defined protocols
How is MLF performed using sequential post-alcoholic inoculation?
Sequential post-alcoholic inoculation means adding O. oeni after alcoholic fermentation (AF), once low residual sugars and stable process conditions have been confirmed. This approach supports scheduling, SOP standardization, and sensory profile control.
Typical operational steps:
- Confirm AF completion: sugars < 2 g/L (GLU + FRU) and stable density for 48 h.
- Condition the wine: target T = 16–20 °C; free SO₂ < 15 mg/L (adjusted to pH)
- Prepare the inoculum: culture/acclimation of O. oeni under oenological conditions.
- Inoculate: 10⁶–10⁷ CFU/mL depending on the matrix, with recirculation and minimal aeration.
- Monitor: L-malic/L-lactic acid, pH, and volatile acidity every 48 h.
- Close out: once L-malic acid < 0.15 g/L and the sensory profile meets the target, adjust protective SO₂.
Oenococcus oeni: the key player
This lactic acid bacterium is responsible for malolactic fermentation. Its action improves stability and the aromatic profile while softening the wine’s palate—making it an essential ally in modern oenology.
- Wine adaptation: tolerates moderate-to-high ethanol, low pH, and limited nutrient availability.
- Wine adaptation: tolerates moderate-to-high ethanol, low pH, and limited nutrient availability.
- Requirements: peptides and amino acids, B-group vitamins, and cofactors; yeast autolysis on fine lees can contribute nutrients and survival factors.
Lactic acid bacteria in wine
In this process, the real protagonists are lactic acid bacteria (LAB). Key species include Oenococcus oeni, Lactobacillus, and Pediococcus.. Each brings different traits, but in practice, O. oeni is the most widely used in winemaking due to its ability to withstand typical wine conditions (higher alcohol, low nutrient availability, and low pH).
Role in the fermentation
LAB transform malic acid into lactic acid, leading to direct consequences:
- The sharper, more aggressive malic acid is reduced.
- The softer, rounder lactic acid improves balance.
- Secondary compounds are produced that enrich aroma and flavor.
This role not only improves the sensory profile, but also helps ensure bottle stability.. Without LAB activity, undesired fermentations could occur months after bottling, altering the product..
Duration of malolactic fermentation
One of the most relevant questions for wineries is how long MLF takes. There is no single fixed timeline: it can vary widely depending on wine conditions and technical choices by the winemaker.
In general, the process may last from a few weeks to several months.
Factors that influence duration and success
- Temperature: operational optimum 16–20 °C (adjust to wine style and strain).
- Free SO₂: keep < 10 mg/L at inoculation; consider molecular SO₂ fraction as a function of pH.
- pH: the lower it is (≈ 3.1–3.3), the higher the stress; may require higher inoculation density and acclimation.
- Alcohol: higher ethanol increases lag time; prior culture acclimation is decisive.
- Nutrients: peptide and vitamin availability; well-managed fine lees can help.
- Polyphenols: tannic matrices can exert a bacteriostatic effect; consider bâtonnage or a concentrated pied de cuve (starter).
- Dissolved CO₂: gentle degassing improves enzymatic activity.
- Residual sugars: keeping them low reduces risks of increased volatile acidity from hexose consumption and/or potential refermentation.
Analytical monitoring and control
- L-malic / L-lactic acid (HPLC or enzymatic kits) every 24–48 h.
- pH and volatile acidity: confirm stability and absence of deviations.
Differences between lactic fermentation and malolactic fermentation
Lactic fermentation in wine
This is a biological process in which LAB (such as Lactobacillus or Leuconostoc) convert sugars (glucose, fructose) into lactic acid, increasing acidity and potentially producing sour or vinegar-like notes.
Therefore, in wine it is generally undesirable; it can occur in spoiled/altered wines due to bacterial contamination or poor winery hygiene.
Malolactic fermentation (MLF)
As noted, this is a secondary, controlled fermentation also carried out by LAB (mainly Oenococcus oeni), but it does not convert sugars. Instead, it converts malic acid into lactic acid and CO₂.
This process softens wine acidity and improves microbiological stability. The outcome:
- Acidity decreases (malic acid has two protons; lactic acid has one).
- A rounder, creamier mouthfeel is achieved.
- Secondary aromas are generated (butter, cream, nuts).
LEV2050 solutions to execute sequential MLF with precision
At LEV2050, we develop specific tools so that post-alcoholic MLF becomes predictable, efficient, and traceable within an industrial microbiology framework.
LACTILEV OENI — Culture medium for Oenococcus oeni
- Objective: growth, multiplication, and acclimation of O. oeni under oenological conditions (pH and ethanol).
- Operational results: highly viable, robust inocula for wine addition, reducing lag phase and improving process continuity
BR-LEV-LC/CV® — Bioreactors for O. oeni cultivation and scale-up
- Practical advantages: consistent pied de cuve preparation, fast starts, and rapid implantation in wine
- Economic advantages: 70–80% lower use of lactic bacteria.
In short, sequential post-alcoholic malolactic fermentation driven by Oenococcus oeni requires well-acclimated inocula, stable process parameters, and rigorous analytical monitoring. With LACTILEV OENI and BR-LEV-LC/CV® bioreactors, LEV2050 enables a robust, traceable, and highly cost-efficient technical implementation aligned with each winery’s sensory and stability goals.
Shall we talk? Our technical team can size the culture, define the inoculation SOP, and design the analytical plan for your wine and working conditions.