The biological transformation of the strict malic acid (lat. 'malum': 'apple') into the milder lactic acid (lat. 'lac': milk) is called 'malolactic fermentation' (common abbreviation: 'MLF' = 'malo-lactic fermentation'; 'ML' = 'malo-lactic').
This process, which occurs in winemaking, is also known as 'biological acid degradation' ('BSA'). It is actively promoted in many red as well as white wines. In the past, malolactic fermentation was also erroneously referred to as 'second fermentation'. Cellar masters note that although 'malolactic fermentation' is a common term in wine production, it does not represent fermentation in the true sense.
Fermentation' in wine represents the conversion of sugar to alcohol (mainly ethanol) by the metabolic activity of added yeast, releasing carbon dioxide (CO2). However, yeast is not important in 'malolactic fermentation'. Instead, it is tiny bacteria that are responsible for converting apflesic acid into lactic acid. In terms of scale, these bacteria to yeasts are more like ants compared to elephants. The only commonality of the usual with malolactic fermentation is to find the release of CO2 by conversion of the acid. However, the amount of CO2 emitted is many times greater in common fermentation. However, let's just leave it at the common name, 'malolactic fermentation', and turn to more details:
A certain Dr. Wenzel Seifert (1862-1942) from Austria first identified an acid-resistant and acid-degrading bacterium as responsible for the degradation of malic acid to lactic acid with the release of CO2. These 'lactic' bacteria (or Lactobacillus) are species such as Leuconostoc and Pediococcus. Similar to yeasts, different species of bacteria influence the aromas and thus the taste of the wine.
Malolactic fermentation or acid degradation can occur as a natural process due to bacteria transferred from the grapes (e.g. on the grape skin, on stems, leaves or even on the tool and in barrels previously used for fermentation) or can also be actively promoted by the cellar master himself.
Malolactic fermentation can occur already in the must, but also later during winemaking or even in the bottled wine. Likewise, it can occur completely or only partially. It can also be avoided by the cellar master, if he so desires. The successful work of these bacteria depends on the temperature and on certain nutrients. The pH values in the must or wine must be neither too high nor too low. In addition, these bacteria are very sensitive to sulfur dioxide. A high level of alcohol (ethanol) in the wine can also kill the bacteria completely. They feel most comfortable at temperatures above 20°C. At temperatures below 15°C, on the other hand, they find it too cold for malolactic fermentation. In those days when modern air conditioning did not exist in the production of wines, malolactic fermentation often developed spontaneously on its own during the summer months.
Cellar masters 'inoculate' their wines with these bacteria generally after alcoholic fermentation by yeast. The residues of the dying yeast provide nutrients for the bacilli. Many other factors also influence the success of malolactic fermentation, such as the presence of oxygen, tannin, certain types of yeast, barrel aging and filtering of the wines.
A cellar master may consciously decide for or against malolactic fermentation in the production of a wine for several reasons. One main reason for malolactic fermentation is often that the type of wine used might seem atypical or too tart for the connoisseur without the breakdown of the severe malic acid. Another reason in favor of malolactic fermentation is the desired aromatic change (sometimes also aromatic refinement) in the wine, which naturally accompanies malolactic fermentation. Some wines gain additional pleasant 'creamy' or 'buttery' aroma and flavor nuances through malolactic fermentation.
In turn, another cellar master might distance himself from malolactic fermentation because his wine is purposefully composed so that the natural malic acid adds a special dimension of freshness and fruitiness to the wine. In addition, natural fruit acids contribute to the better storability of wines.
Das eher kühle Klima der Champagne bedingt oft verhältnismäßig hohen Säuregehalt in den geernteten Reben. Dies bietet sich wiederum für die maloloktische Gärung an. Somit wird die malolaktische Gärung von vielen Häusern in der Champagne bewusst gefördert. Es gibt jedoch auch einige wenige Champagner-Häuser (wie z.B. Gosset), die auf die malolaktische Gärung streng verzichten und ihre Cuvées mit der natürlichen Apfelsäure der Reben komponieren. Dadurch werden oft aussergewöhnlich frisch und fruchtig anmutende Champagner geschaffen, welche sich nicht selten durch bemerkenswerte Lagerungsfähigkeit und zunehmender Geschmeidigkeit auszeichnen.