# **Malolactic fermentation** In this post, we'll take a look at the secondary fermentation process known as Malolactic Fermentation (MLF). It follows other winemaking posts about **[Alcoholic Fermentation](https://modernwineclub.com/blogs/news/alcoholic-fermentation)** and **[Fining](https://modernwineclub.com/blogs/news/fining-other-wine-adjustments)**. While alcoholic fermentation is essential to wine production, MLF is an optional step in winemaking used for stylistic and stability purposes. **Malolactic Fermentation** Malolactic fermentation is the conversion of malic acid in wine to lactic acid plus carbon dioxide. It is the work of lactic acid bacteria (LAB). There are many different strains of LAB that are capable of MLF. The preferred strain for winemaking is Oenococcus oeni as it ferments quickly without producing the off-flavors associated with other strains such as Lactobacillus and Pediococcus. Compared to alcoholic fermentation, this is a much more gentle fermentation, with slower growth of the microorganisms involved and less production of carbon dioxide. This makes it a lot less obvious that MLF is happening compared to alcoholic fermentation.  **When Is MLF Complete?** MLF is generally considered completed when the level of malic acid in the wine is less than 0.25 grams per liter measured through analytical chemistry lab analysis or when there are no malic acid spots present on an inexpensive paper chromatogram like the **[below](https://candlewineproject.wordpress.com/2010/12/01/testing-for-mlf/)**. Paper chromatography works in a similar way to a standard Litmus test in that it indicates the presence of acids. Wine is put onto the chromatogram and after a while, the user looks for the presence or absence of dots in positions associated with different acids. In the case below, the paper chromatogram has been tuned to detect the presence of lactic acid (L), malic acid (M) and tartaric acid (T). **Effect of MLF** The principal effect of MLF is deacidification of the wine making it less tart. This happens as the dicarboxylic acid (malic acid) loses a proton to get converted to a monocarboxylic acid (lactic acid). In plain language this means that lactic acid is a lot less tart than malic acid. There is typically a reduction in the level of Titratable Acidity of 0.1 to 0.3 g/L and a corresponding increase in the pH of the wine by 0.1 to 0.3 units. This makes MLF unsuitable in some situations such as wines from warm growing conditions that may be lacking in acidity. A side effect of MLF is the production of diacetyl which is a compound with a buttery aroma. This is the explanation why white wines (e.g. Chardonnay) often get a buttery aroma after MLF. In addition, MLF reduces fruity aromas in wines. So in cases where a fresh and fruity white wine is the desired style, it makes sense to block MLF to avoid the reduction in fruitiness and the development of buttery aromas. Another effect of MLF is that it improves wine stability. Wines that have not completed MLF run the risk of a spontaneous MLF happening during barrel aging or even after the wine has been bottled if not sterile filtered and treated to prevent the growth of microorganisms. Having completed MLF prevents this from happening as the malic acid will already have been consumed by the LAB. Another reason why stability is improved is because tartaric acid reacts with potassium in wine to form potassium bitartrate also known as cream of tartar. These are glass-looking crystals that precipitate out of the wine to form sediment at the bottom of the bottles. While completely harmless, many wine drinkers have mistaken such crystals for broken glass and avoided the wine brand going forward or written negative online reviews about the wines. **Which Wines Benefit?** White wines that are tart and not dependent on fruity characteristics generally have a lot to gain from MLF. This has often made MLF a weapon of choice for Chardonnay and especially for Chardonnay fermented or matured in oak given that the buttery aromas marry well with the oak. On the other hand, white wines with crispy acidity and floral characteristics often do not gain from MLF. Examples of such varietals include Sauvignon Blanc, Pinot Gris, Muscat, Riesling and Gewürztraminer. Such wines often have a little residual sugar left and are typically sterile filtered prior to bottling to prevent alcoholic fermentation from happening again in the bottles as well as to inhibit the growth of spoilage microorganisms. For red wines, MLF is often more about stability than about a sensory impact. The benefits include not having to worry about spontaneous MLF while the wine is matured in oak barrels or after it has been bottled. Once complete, MLF will not happen a second time given that the malic acid has been consumed. This makes it less risky to bottle such wines without sterile filtering or adding agents that prevent the growth of microorganisms. **How and When to Initiate MLF** The most straightforward way to initiate MLF is to inoculate the wine with a commercially sourced culture of LAB. This comes at the cost of purchasing the LAB culture but it lowers the downside risk of something going wrong. Alternatives include blending wine that is in the middle of MLF with another wine to transfer LAB that way or to reuse wooden barrels from previous MLF as LAB survives on wooden surfaces unless sterilized.  Chances of a successful MLF is higher if it is started relatively early in the winemaking process. Many winemakers prefer to start MLF immediately upon completion of the alcoholic fermentation. And others prefer to start even earlier by inoculating the juice with LAB already in the middle of alcoholic fermentation. **Conditions for Successful MLF** Lallemand and Scott Laboratories have collaborated to create the below useful MLF scorecard showing the conditions that improve the likelihood of success of MLF. Lower points in the scorecard mean more favorable conditions for completion of MLF. We learn from the scorecard above that a lower alcohol level is beneficial as is a higher starting pH level of the wine. Sulfur dioxide (SO₂) inhibits LAB so it is best avoided during MLF. Temperature and the level of malic acid should ideally be in the middle. Too high or too values for either makes MLF more difficult. Overall, the scorecard points to favorable conditions for MLF being present when the total points come to less than 13. **Selecting a LAB Strain** Key things to consider when selection an appropriate LAB strain is the alcohol tolerance (especially when making bold red wines), impact on fruity characteristics (especially for aromatic white wines), and the production of compounds with sensory properties such as diacetyl (buttery aromas) or volatile acidity (sharp vinegar aromas including from acetic acid). Below is an example of a LAB strain from Laffort called **[LACTOENOS 450 PreAc®](https://laffort.com/en/products/lactoenos-450-preac/)**. As the above shows, this is a strain selected for high alcohol tolerance so it is suitable also for powerful red wines. It is aromatically neutral so it does not remove the fruit characteristics important to many white wines. And it has low production of diacetyl and volatile acids. So if you are selecting a LAB strain to produce buttery aromas in your Chardonnay, this one may not be optimal for that purpose. **Blocking MLF** As noted above, MLF is not always desirable for wines. To prevent it from happening, e.g. in a fruity Sauvignon Blanc, there are several steps that winemakers can take. First, all winery equipment, including barrels should be kept immaculately clean so that LAB don't remain on surfaces. Second, sulfur dioxide (SO₂) can be added to the wine as it inhibits MLF in addition to being an anti-oxidant. Third, the pH level should be monitored and acidity adjusted as necessary to reduce the pH and create an unfavorable environment for LAB. Fourth, the wine could be sterile filtered at bottling, and fifth, fumaric acid can be added to inhibit LAB growth.  That was all for this time. If you haven't read them already, we recommend that you take a look at our other blog posts about winemaking including **[Alcoholic Fermentation](https://modernwineclub.com/blogs/news/alcoholic-fermentation)** and **[Fining](https://modernwineclub.com/blogs/news/fining-other-wine-adjustments)**. **Cheers!** Andreas