Malolactic fermentation
Malolactic fermentation is a secondary fermentation process in winemaking that involves the conversion of malic acid into lactic acid by specific lactic acid bacteria, most notably *Oenococcus oeni*.[1] While not a true fermentation in the alcoholic sense, it plays a crucial role in softening the acidity of wine and contributing to flavour development. The process occurs after or near the completion of alcoholic fermentation and is especially common in red wines and some white wines such as Chardonnay. It is considered a natural but controllable microbiological transformation that can significantly affect a wine’s sensory profile, microbiological stability, and ageing potential.[2]
Definition and Process
Malolactic fermentation (commonly abbreviated to MLF) is a biological conversion in which sharp-tasting malic acid is transformed into the softer lactic acid through the action of lactic acid bacteria, primarily *Oenococcus oeni* but also species such as *Lactobacillus* and *Pediococcus* under certain conditions.[3] This process reduces total acidity and contributes to the microbial stability of the finished wine.
MLF typically occurs after alcoholic fermentation, though it may overlap in spontaneous fermentations. It can be initiated either naturally—by relying on ambient bacteria—or through inoculation with selected bacterial cultures.[4] Winemakers may choose to encourage or suppress MLF depending on stylistic goals.
In practical terms, the process is monitored by tracking malic acid concentrations or the presence of diacetyl, a byproduct associated with buttery aromas.[5] Once completed, MLF is often followed by sulphur dioxide additions to prevent further microbial activity.
Relevance in Wine
Malolactic fermentation plays a critical role in defining wine style, particularly in red wines and certain fuller-bodied whites such as Chardonnay. In reds, MLF is almost universally employed to soften acidity, enhance microbial stability, and integrate flavours.[6] In white wines, it is a stylistic decision: it can add complexity, mouthfeel, and buttery or creamy notes due to compounds such as diacetyl, though it may also reduce freshness and varietal purity.
Wines that have undergone MLF tend to exhibit a smoother texture, reduced perception of tartness, and increased roundness on the palate.[7] These effects can be desirable or detrimental depending on the grape variety, intended wine style, and market expectations.
Some winemakers may choose to block MLF entirely—especially in aromatic whites such as Riesling or Sauvignon Blanc—to preserve high acidity and crispness.[8] In such cases, strict hygiene and the use of sulphur dioxide are essential to prevent spontaneous fermentation.
Geography and Use
Malolactic fermentation is employed in nearly all major wine-producing regions, though its use and management vary significantly depending on tradition, climate, and wine style. In cool-climate areas such as Burgundy and Champagne, MLF is a routine part of red wine vinification and is also frequently applied to white wines to temper high acidity.[9]
In New World regions like California and Australia, where grapes can be harvested with lower natural acidity, winemakers often consider whether MLF is necessary or desirable on a case-by-case basis. For fuller-bodied white wines such as barrel-aged Chardonnay, MLF is widely used to enhance texture and aromatic profile.[10]
In sparkling wine production, particularly in the Champagne region, MLF is typically encouraged to reduce sharp malic acidity and create a more harmonious base wine. However, some producers may inhibit MLF deliberately to preserve tension and precision in the final cuvée.[11]
MLF is almost universal in red wine production worldwide, with very few exceptions. Even in traditionally high-acid wines such as Barolo or Rioja, the process is considered essential for balance, ageing potential, and microbial stability.
See also
Fermentation Malic acid Lactic acid Wine microbiology Chardonnay Barolo
References
- ↑ Robinson (ed.), *The Oxford Companion to Wine*, Oxford University Press, 2015, p. 443.
- ↑ Goode, *The Science of Wine: From Vine to Glass*, University of California Press, 2014, pp. 89–91.
- ↑ Jackson, *Wine Science: Principles and Applications*, Academic Press, 5th ed., 2020, pp. 441–443.
- ↑ Goode, *The Science of Wine: From Vine to Glass*, University of California Press, 2014, p. 90.
- ↑ UC Davis, “Malolactic Fermentation in Wine”, wineserver.ucdavis.edu.
- ↑ Robinson (ed.), *The Oxford Companion to Wine*, Oxford University Press, 2015, p. 431.
- ↑ Lonvaud-Funel, “Lactic acid bacteria in the quality improvement and depreciation of wine”, *FEMS Microbiology Reviews*, Vol. 19, No. 4, 1997.
- ↑ Goode, *The Science of Wine: From Vine to Glass*, University of California Press, 2014, p. 91.
- ↑ Robinson (ed.), *The Oxford Companion to Wine*, Oxford University Press, 2015, p. 431.
- ↑ Goode, *The Science of Wine: From Vine to Glass*, University of California Press, 2014, p. 91.
- ↑ Comité Champagne, “Malolactic Fermentation in Wine”, wineserver.ucdavis.edu