To be precise, malolactic fermentation is not a true fermentation. Chemically, it is a decarboxylation reaction, meaning the transformation of an acid group (-COOH) from the malic acid molecule into water and carbon dioxide (H2O and CO2) by the lactic acid bacteria oenococcus oeni and lactococcus lacti, while malic acid is converted into lactic acid.
Malolactic fermentation usually follows alcoholic fermentation and thus occurs during the aging/maturation of wine, affecting both white and red winemaking. For malolactic fermentation to begin, the following conditions are necessary:
- Wine pH not excessively low, meaning wines that are not excessively acidic;
- low sulfur dioxide concentration;
- ethyl alcohol below 15%;
- temperature between 18° and 20° C.
During malolactic fermentation in wine, the more astringent malic acid is converted into lactic acid, which is weaker than malic acid and perceived as milder and less tart. To prevent malolactic fermentation, high doses of sulfur dioxide or sterile filtration can be used, both of which negatively impact the wine's organoleptic profile. To induce malolactic fermentation, as with alcoholic fermentation, one can rely on bacteria naturally present in the must and reactivated by changes in environmental conditions, or use selected bacterial strains (belonging to the genera Oenococcus or Lactobacillus).
The main impact of malolactic fermentation from an organoleptic point of view on any type of wine is to reduce its acidity, as lactic acid is a weaker acid than malic acid. Malolactic fermentation gives the wine greater balance, persistence, body, and finer aromas. Grassy notes become less pronounced, and nuances of walnut, vanilla, spices, leather, and toastiness are enhanced. It is more commonly used in red wines but has recently been introduced in more important white wines. It is not performed in younger, fresher white wines, which are expected to have higher acidity. Let's look in detail at the organoleptic effects of malolactic fermentation on various types of wine.
Malolactic Fermentation in Red Wines
Red wines produced in cool climate regions tend to have relatively high acidity levels. The reduction of acidity in these cases can positively influence the wine's taste, making it more pleasant, round, and complex. Lactic acid bacteria also produce various aromatic compounds as byproducts that can enrich the wine's organoleptic profile. Most of these wines are therefore improved by malolactic fermentation.
Malolactic Fermentation in White Wines
Malolactic fermentation is less common in white wines than in reds, as white wines derive their strength from primary aromas, savoriness, and a pronounced acidic profile, all characteristics that are partially obscured by malolactic fermentation. Furthermore, since white wines are produced with reduced skin contact, malolactic fermentation has less tendency to occur spontaneously. For white wines produced in cool climate regions, malolactic fermentation is generally sought to be prevented to maintain the wine's pronounced acidic profile, and for white wines produced in warmer climate regions, and thus inherently less acidic to begin with, malolactic fermentation is not beneficial because it would further reduce the wine's acid backbone.
Malolactic Fermentation in Rosé and Orange Wines
Orange wines are white grape wines fermented with long skin contact, essentially a true red wine vinification process. Orange wines, being similar to red wines in terms of organoleptic profile and certain characteristics such as the presence of tannins, can often benefit from malolactic fermentation, gaining in complexity and stability.
