Which bacteria is commonly involved in malolactic fermentation?

Malolactic fermentation is a critical process in winemaking that involves the conversion of malic acid into lactic acid and carbon dioxide. This transformation softens the wine's acidity and contributes to its overall flavor profile. Leuconostoc is the bacterium most commonly associated with this fermentation process.

Leuconostoc species are lactic acid bacteria that are capable of metabolizing malic acid, making them well-suited for this specific stage in winemaking. They help in not just acid reduction but also in the development of complex flavors and aromas through their metabolic byproducts.

In contrast, while Lactobacillus also plays a role in lactic acid fermentation, it is not as directly involved in malolactic fermentation as Leuconostoc. Streptococcus, another lactic acid bacterium, is more commonly related to fermentation processes in dairy rather than wine. Acetobacter is a type of bacteria responsible for acetic acid production, leading to vinegar formation, which is not desirable in most winemaking contexts. Therefore, Leuconostoc's specific ability to facilitate malolactic fermentation is what makes it the correct answer in this scenario.