Acetic acid bacteria are Gram-negative, rod-shaped, and acido-tolerant to acidophilic organisms with a strictly aerobic type of metabolism. These fastidious organisms thrive in complex, nutrient-rich environments of high osmolarity such as honey bees, on the surface of fruits, in nectar, plant saps, fruit juices, cider, must, wine, sake, beer or other sweet or alcoholic beverages (Lambert et al. 1981; De Ley et al. 1984; Gupta et al. 2001). Some genera can grow in highly concentrated sugar solutions of up to 30% (w/v) glucose and at pH values as low as 2.5. The most prominent physiologic feature of acetic acid bacteria is that they derive their energy from incomplete oxidations of a multitude of substrates, mainly alcohols, sugars and other polyols. The most important of these oxidations with respect to oenology are the oxidation of ethanol to acetate and that of glucose to gluconic acid. As most of their oxidation products are acids, and as acetic acid bacteria rapidly convert large amounts of substrate, they quickly acidify their environment during growth. This inhibits growth of many other bacteria and gives them a selective advantage as they can tolerate low pH values. Another oenologically important aspect is their tendency to form biofilms. A remarkable example of these biofilms is the Mother of Vinegar. This is a massive gelatinous or leathery layer that develops on the surface of nutrient rich, unstirred alcoholic solutions such as wine during prolonged aerobic incubation that transforms wine to vinegar by oxidizing ethanol to acetic acid. The matrix of this biofilm consists of cellulose fibrilli that are synthesized by Gluconacetobacter xylinum (Wong et al. 1990; Ross et al. 1991). Besides cellulose fibrillae, a number of other exopolysaccharides are formed by acetic acid bacteria, such as levans or acidic polysaccharide acetan. Some strains of Gluconobacter show viscous growth in beer due to formation of dextrans.