Bacterial Fermentation Products

While yeast is necessary for alcoholic fermentation during wine production, several types of bacteria may also affect wine composition. Those with the best established role in wine production are lactic acid bacteria (LAB) and two members of the acetic acid bacteria (AAB) family: Acetobacter and Gluconobacter. The changes imparted by these microflora can be desirable (and encouraged) in some circumstances, as is frequently the case for Oenococcus oeni (an LAB) in conducting malolactic fermentation (MLF). Semi-aerobic conditions will favor the accumulation of diacetyl through its non-enzymatic formation. Metabolism of citric acid will also yield lactate, ethanol, ethyl lactate (from esterification of lactate), and at least one molar equivalent of acetic acid; hence volatile acidity (VA) typically increases during MLF. Bacterial spoilage is defined as the unintended growth of bacteria and the subsequent production of compounds that negatively impact on wine quality due to undesirable organoleptic and/or health effects.