Wine fermentation is an important step in the winemaking process. Fermentation happens in various stages and the primary fermentation happens naturally with the yeast present in the grape skin converting the sugars in the grapes into ethanol and carbon dioxide. This is also known as Alcoholic Fermentation. Next comes secondary fermentation, also known as Malolactic fermentation. Some winemakers prefer to use the term Malolactic conversion as this process converts the malic acid present in the wine to lactic acid. Since carbon dioxide gets released this process has come under fermentation.
What is Malolactic Fermentation?
Malolactic fermentation has bought a new style to the wine, the buttery style. The malolactic fermentation happens with the malolactic bacteria present in the grapes. Just like the natural yeast on the skins of the grape, there is a little number of malolactic bacteria present in the grapes which make the malolactic fermentation happen naturally.
Malolactic bacteria converts the malic acid to lactic acid. Malic acid is found in fruits like peaches, plums, blackberries, blueberries, and apples. Malic acid is responsible for the sourness in the grapes which causes a tingling sensation in the mouth, Along with the tartaric acid, malic acid is present naturally in the grapes. In general, we find the malic acid and tartaric acid present in different ratios in the grapes, like one-third of malic acid and two-third of tartaric acid.
The ratio of malic acid to tartaric acid differs with many factors like the climate in which the grapes are grown, their ripeness level, etc. Overripe grapes have very little malic acid present in them, as the grapes use the malic acid for their ripeness, and wines made from these grapes have a different malolactic fermentation from the wines made from the less ripe grapes.
In general,the wines made from the thick juice of the grapes have high amounts of malic acid.Hence they undergo good malolactic fermentation.
Malolactic fermentation process
Malolactic fermentation gives the buttery aroma to the wine.The process is also known as decarboxylation.
Malic Acid->Lactic acid +carbon dioxide
When we look into the malolactic conversion happening in the fermentation, the carboxyl group present in the malic acid is replaced with a hydrogen atom and carbon dioxide. Diacetyl is the by-product of malolactic fermentation.
Malolactic fermentation can happen naturally with the little number of malolactic bacteria present in the grapes. Many winemakers prefer to inoculate the malolactic bacteria culture to the wine to get the desired buttery wine style. There are different strains of the bacteria giving different results. Again the decision is left with the winemaker.
When does the malolactic fermentation start?
Malolactic fermentation can either happen simultaneously with the primary fermentation or it can happen sequentially after the primary fermentation. In general malolactic fermentation is preferred to happen after the primary fermentation because the yeast breaks down the buttery components when it happens simultaneously. To avoid this, Malolactic bacteria are added after the primary fermentation and pressing of the wine is done. Hence this fermentation is also known as secondary fermentation.
For the malolactic fermentation to happen the wine must be warm. Make sure that the wine is racked and the temperature of the wine is around 65 degrees to 75 degrees F to get that desired buttery smooth finish.
What wines undergo Malolactic fermentation?
Medium to full bodied dry red wines undergo Malolactic fermentation. Most red wines with moderate acidity are improved by the Malolactic Conversion.
Grapes from cooler regions have high acidity and the wines produced from them are the best benefited by the malolactic conversion, as they become less acidic and balanced after the malolactic fermentation.
Full-bodied dry whites undergo Malolactic fermentation. But when you look at Pinot Griogo or Reisiling that is light-bodied and are crisp rather than savory, the malolactic conversion is not needed for them. Chardonnay is the best-known buttery white wine.
There are many sparkling wines that undergo Malolactic fermentation as well.
What happens to the wine after Malolactic fermentation?
Malolactic fermentation makes the wine stable.It deacidifies the wine.It reduces the effect of tastaric acid by 1-3 grams/l.The PH of the wine gets raised,suppose if the Ph of the wine before Malolactic fermentation is 3.4,it gets raised to 3.65.The PH raises by 0.3 units.
Lactic acid is generally found in dairy products. Lactic acid is less sour than malic acid and it results in a softness mouthfeel in the wine. Hence the wine after malolactic fermentation becomes smooth and soft. The softness is the result of the reduced acidity. Wine profile becomes smoother, rounder and mouthfeel.
Some winemakers try to reacidify the wine if the acidity is reduced too much after the malolactic fermentation.
The sensory quality of the wine gets changed,Malolactic fermentation effects the flaovr and aroma of the wine.
Both red and white wines get a buttery,roasted nutty aromas with creamy texture.
How to stop Malolactic fermentation?
When the malolactic bacteria converts the malic acid to lactic acid,it shifts to the remaining acid in the grape,the tartaric acid or citric acid.
It also converts citric acid to acetic acid and pyruvic acid. The Pyruvic acid then gets converted to diacetyl. The result of this conversion is the more buttery taste in the wine than required. Often the acetic acid gives the unpleasant sour milk characteristics to the winemaking the wine undrinkable.
So, there is always a need to stop the malolactic bacteria from resulting in these side effects. The presence of malolactic fermentation is observed through a spectrophotometer. To arrest the malolactic fermentation the winemakers often follow these techniques.
1.The growth or reproduction of the malolactic bacteria can be arrested or controlled by keeping the wine at low temperatures, Chill the wine and make sure that the temperature is very low.
2.Anti microbial actions like sulfur dioxide are added to the wine to stop the malolactic fermentation.In general Lysozyme can be used to control the Malolactic fermentation.
3.Sterile filtering the malolactic bacteria from the wine to arrest the malolactic fermentation.