Attack of the bacteria
All red wines undergo a second fermentation after alcoholic fermentation is complete. It is called lactic acid fermentation or simply „malo“. Malo comes from the Latin word malum: the apple. There is an acidity in the wine that tastes as tart as an unripe apple. This is what malolactic fermentation is all about.
Red wines from all temperate growing regions have a more or less large surplus of malic acid. Even in warm temperatures and late harvests, it is not completely degraded. The raw, sometimes astringent-tasting malic acid can still be found in fermented wine – to a particularly high degree in cool years. This malic acid is eventually attacked by the lactic acid bacteria. They break down the malic acid molecules and convert them into the milder lactic acid. This reduces the acidity in the wine, making it taste softer and fuller.
Natural process
Malolactic fermentation is therefore not set in motion by yeasts, but by bacteria. It is a natural process. It is also often referred to as malolactic fermentation. It takes place spontaneously in spring in many growing regions. The only cellar-technical measure required for this is to open the windows so that the spring warmth flows into the cellar. When the temperatures rise and the cellar warms up, the fermented wine becomes active again. It begins to tingle, later to bubble – a sure sign that something is going on inside it. What exactly happened to him was unclear for a long time. It was only before the Second World War that the exact chemical reaction was researched at the Institut Œnologique of the University of Bordeaux. Bacteria were found under the microscope that also multiply in an acidic environment and do not need sugar.
Only stable after the malo
On closer inspection, there are three lactic acid bacteria: Pediococcus, Leuconostoc and Lactobacillus. They can already be found mixed in with the yeasts in the vineyard, but also in the cellar and in the fermentation barrels (an empty barrel contains around five liters of liquid mixed with yeasts and bacteria stored in the wood). However, they are sluggish. They only become active at temperatures above 20° C – i.e. normally only when it gets warm. Pediococcus and Leuconostoc in particular only attack malic acid, but leave glycerol and tartaric acid untouched. As the wine is not stable until malolactic fermentation is complete, in modern wineries the cellar is heated after alcoholic fermentation to stimulate the malo. It takes about two or three weeks. After this, the wine no longer contains malic acid.
„Inoculated“ with bacteria
In many growing regions of the New World, especially in California, South Africa and Australia, there are often not enough bacteria in the cellars, and sometimes none at all. In order to carry out malolactic fermentation, the wine must be „inoculated“ with selected, cultivated lactic acid bacteria. This approach is also occasionally used in some European regions. The only important thing is that the wine is bottled without malic acid. Otherwise there is a risk that it will continue to ferment in the bottle. Typical indication: The cork rises under the pressure of the escaping carbon dioxide.
Malo for white wines
White wines also contain malic acid – those from cool growing regions more, those from warm growing regions very little. However, most white wine winemakers reject malolactic fermentation. They are happy about every gram of acidity in their wine. Acidity makes white wines lively, refreshing and fine. Acidity is indispensable, especially for young white wines. In addition to the fruity tartaric acid, which makes up the largest proportion, a few grams of malic acid are perfectly tolerable. Even Alsace, German and Austrian Riesling, which have high acidity levels despite late ripening, are practically never subjected to malolactic fermentation. For other white wines, it is the rule. Originally, it was white Burgundy wines made from Chardonnay grapes and white Bordeaux wines made from Sémillon and Sauvignon that led the way. Today, almost all Chardonnay wines are fermented in small wooden barrels, regardless of whether they come from Italy, Australia, California or Chile. Sometimes only half of the wine undergoes malolactic fermentation and the other half does not, so that the acidity does not drop too low.
