The Role of Lactic Acid in Wine and the Winemaking Process
Maintaining the acid content in wine is critical to establish a well balanced wine. If a wine doesn’t have enough acid, it will taste dull or flat. If a wine has too much acid, it will taste sour or tart. Luckily for winemakers, it is not hard to control wine acidity.
Malic acid is one of the principle components of acid that can be controlled by the winemaker. Largely, it is the Malic acid that contributes to the sour, tart taste of wines that have too much acid. This is where Lactic Acid comes into play in the form of Malo-Lactic Fermentation.
Lactic Acid in Wine
Lactic Acid is an organic acid that contributes to the overall acidity of wine. The reason why it is so attractive to winemakers is because its much softer on the palate than malic acid, the principle acid component in wine. For this reason, many wine will undergo Malo-Lactic Fermentation.
The primary source of lactic acid in wine is from the metabolic activity of bacteria. Many know this process as malo-lactic fermentation, where malic acid is decarboxylated into lactic acid. However, as small amount of lactic acid is produced during fermentation.
Lactic acid is the predominant acid in milk, and is much “softer” than malic acid. For this reason, it is a highly desirable component in some wines. This process happens naturally in most red wines, but is encouraged in some whites to achieve a certain taste and feel.
There are two stereoisomers of lactic acid; L-lactic acid and D-lactic acid. The distinction between the two lies in the special arrangement of their substituents. Although this seems trivial, they are different and can be used to determine if a wine has gone through malo-lactic fermentation.
L-lactic acid is the isomer produced through malo-lactic fermentation. The other isomer is not produced. However, during fermentation, both L and D isomers are produced in equal quantities.
Malo-Lactic Fermentation (MLF)
Malo-Lactic Fermentation is the process by which Malic Acid is converted to Lactic Acid and Carbon Dioxide. Usually, white wines will be sent into MLF, while red wine undergoes this process naturally. On the palate, wines that have undergone MLF are round and fuller-bodied.
While MLF is a beneficial process, there are downsides. An increase in Lactic Acid concentration in a wine will make it suseptable to Lactic Acid Bacteria, These bacteria use the Lactic Acid as energy and can create a problem for winemakers if not carefully monitored.
Many winemakers take sterilization measures to ensure that these bacteria are not introduced into the winery. Once they have been used in a winery, they will induce malolactic fermentation the next year as well unless stringent sterilization measures are taken.
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