Practical tools for reliable fermentation control
By: Andreea Botezatu, Ph.D., Associate Professor and Extension Enology Specialist, Texas A&M AgriLife Extension
Malolactic fermentation plays a central role in winemaking and can be either beneficial or detrimental depending on wine style and chemistry. In some wines it contributes complexity and softness, while in others it reduces freshness or creates instability. The challenge is not deciding whether MLF is good or bad, but ensuring that it happens only when it fits the intended wine profile. This challenge has become more pressing in warm growing regions, where fruit often arrives with unusually high pH values that make spontaneous MLF more likely and more difficult to control.
Traditional approaches include temperature control, sulfur dioxide management, and sanitation, but these methods alone are often insufficient for modern high pH wines. Additional tools such as lysozyme, chitosan based products, DMDC, nisin and fumaric acid now play important roles in suppressing or delaying malolactic activity. The following sections describe how these inhibitors work and how to use them effectively in commercial winemaking.
Winemakers often inhibit MLF to preserve the crisp aromatics of delicate whites such as Riesling, Muscat, Sauvignon Blanc, Trebbiano, and Blanc du Bois. These wines rely on bright acidity and fragile aroma compounds that can be dulled by malolactic activity. Off dry and sweet wines are also at risk because residual sugar provides a nutrient source for lactic acid bacteria, increasing the likelihood of haze, volatile acidity, and off odors. Sparkling wine bases require microbial stability before tirage, because unwanted MLF in bottle can cause turbidity or pressure issues.
Warm climate fruit presents unique challenges. Grapes may arrive with pH values above 4.0, and sometimes even above 4.2. Tartaric acid additions may not fully correct such elevated pH, and alcoholic fermentation can increase the pH further. Once pH rises above 3.8 or 4.0, sulfur dioxide loses much of its antimicrobial power, allowing lactic acid bacteria to grow quickly. Excessive tartaric acid additions can result in a sharp, unbalanced palate, so winemakers must sometimes suppress MLF even in red wines where full conversion is traditional.
Sulfur dioxide remains the most widely used tool for inhibiting MLF. The active antimicrobial form is molecular sulfur dioxide, and its effectiveness depends strongly on pH. At pH around 3.1 to 3.3, relatively small free sulfur dioxide additions can suppress Oenococcus oeni. At pH 3.6 or higher, the required free sulfur dioxide concentration becomes very high and may cause sensory defects. Binding reactions further reduce the available molecular sulfur dioxide. Although sulfur dioxide is essential, it becomes unreliable as the sole inhibitor in high pH wines.
Lysozyme provides targeted inhibition of Gram positive bacteria. Derived from egg white, it breaks down the cell walls of Oenococcus oeni, Pediococcus species, and Lactobacillus species, while leaving yeast unaffected. Lysozyme can delay MLF until alcoholic fermentation finishes, suppress early spontaneous activity, or prevent MLF entirely in wines where freshness is a priority. Its limitations include allergen labeling requirements, potential protein instability, and the need for bentonite fining before bottling. It is effective but less reliable at very high pH.
Chitosan derived from fungal sources provides another microbial control option. It disrupts bacterial cell membranes and promotes flocculation and settling. Chitosan reduces populations of lactic acid bacteria and Brettanomyces and can be used in both tank and barrel applications. It functions primarily as a population reducer rather than a permanent inhibitor. When paired with sulfur dioxide, chitosan can significantly improve microbial stability, particularly in moderately high pH wines.
DMDC, also known as Velcorin, is a strong antimicrobial agent typically used at bottling. It inactivates essential microbial enzymes and kills yeasts and bacteria quickly. DMDC breaks down into carbon dioxide and methanol within hours, leaving no sensory trace. Because it is toxic in concentrated form, DMDC must be applied with certified dosing equipment. It is particularly useful for sweet wines, low sulfur wines, and high pH wines, providing strong protection at packaging even when other inhibitors have limitations.
Fumaric acid has become a valuable tool because it serves two roles simultaneously. It is both a potent acidifier and an effective inhibitor of malolactic activity. Fumaric acid is significantly stronger than tartaric acid, so small additions can produce meaningful reductions in pH. This is especially useful in warm climate wines where starting pH values are high and tartaric acid alone cannot achieve the desired acidity. Fumaric acid also suppresses Oenococcus oeni, and additions of 300 to 600 mg per liter can delay or prevent MLF. Its dual action makes it one of the most efficient tools for improving stability and sensory balance in high pH wines.
Nisin is an antimicrobial peptide produced by Lactococcus lactis and is gaining attention as a possible MLF inhibitor. It targets Gram positive bacteria including Oenococcus oeni, Pediococcus species, and certain Lactobacillus species by disrupting their cell membranes. Nisin is approved for food use in many applications, but approval for wine varies by region and must be verified before use. When permitted, it can be effective at low concentrations and does not affect yeast. Its effectiveness can be influenced by binding reactions in wine, but it remains a promising option for warm climate winemakers working with high pH grapes.
Environmental factors remain central to MLF control. Cooler temperatures slow lactic acid bacteria considerably, and storing wine at 8 to 10 degrees Celsius can halt or delay MLF. Alcohol concentration can inhibit bacteria, although the effect varies among strains. pH is the single most influential natural control factor. Wines at pH 3.2 or lower resist MLF naturally, while wines above pH 3.6 encourage rapid bacterial growth. Wines above pH 4.0 are extremely challenging to stabilize without a multifaceted inhibition strategy.
Effective inhibition strategies typically involve combining several tools. A well managed sulfur dioxide program and cold storage provide the base layer. Lysozyme offers targeted control of Oenococcus oeni. Chitosan reduces microbial populations and strengthens sulfur dioxide activity. Fumaric acid increases acidity while inhibiting malolactic metabolism. DMDC at bottling provides a strong final safeguard for wines at high microbial risk. Used together, these tools create a robust defense system that protects wine quality and stability.
If MLF begins unexpectedly, prompt intervention is essential. Corrective measures may include increasing sulfur dioxide to achieve molecular targets, cooling the wine, adding lysozyme if allowed, applying chitosan to reduce bacterial populations, racking off lees, sterile filtration, and applying DMDC at bottling. Unintended MLF often signals deeper problems such as inadequate sanitation, poor sulfur dioxide control, or inconsistent temperature management. Addressing these issues reduces long term risk.
As climate patterns shift and more wineries pursue fresher, lower sulfur styles, reliable MLF inhibition becomes increasingly important. Modern inhibitors provide flexibility across diverse wine styles and chemistry conditions. A careful combination of chemical, biological, and environmental strategies remains the most effective path to producing stable, expressive, high quality wines.
For more information please contact…
Andreea Botezatu, Ph.D.
Assistant Professor of Enology and Extension Specialist.
Texas AgriLife Extension, Department of Horticultural Sciences.
E-Mail: abotezatu@tamu.edu
Phone: 979-845-8563
