Lactic Acid
A much milder acid than tartaric and malic, lactic acid is often associated with “milky” flavors in wine and is the primary acid of yogurt and sauerkraut. It is produced during winemaking by lactic acid bacteria (LAB), which includes three genera: Oenococcus, Pediococcus and Lactobacillus. These bacteria convert both sugar and malic acid into lactic acid, the latter through MLF. This process can be beneficial for some wines, adding complexity and softening the harshness of malic acidity, but it can generate off flavors and turbidity in others. Some strains of LAB can produce biogenic amines, such as histamine, tyramine and putrescine, which may be a cause of red wine headaches in some wine drinkers. Winemakers wishing to control or prevent MLF can use sulfur dioxide to stun the bacteria. Racking the wine quickly off its lees will also help control the bacteria, since lees are a vital food source for them. The winemakers must also be very careful of what wine barrels and winemaking equipment to which the wine is exposed, because of the bacteria's ability to deeply embed themselves within wood fibers. A wine barrel that has completed one successful malolactic fermentation will almost always induce MLF in every wine stored in it from then on.
Read more about this topic: Acids In Wine