However, several different kinds of ML bacteria exist, and different types of bacteria produce different byproducts in wine. This is sage advice because most types of lactic bacteria can and will ferment sugar. When lactic bacteria attack grape sugars, the glucose is converted into lactic acid and acetic acid, and the fructose can be converted into a nasty material called mannitol. When lactic bacteria ferment sugar, the volatile acidity of the infected wine can increase rapidly, and the wine often takes on a characteristic sweet-sour taste. This type of bacterial spoilage occurs most often when wines have an excessively high pH. Lactic souring and vinegar formation are quite different.
Lactic bacteria produce acetic acid by fermenting the sugar.
Unlike acetobacter, lactic bacteria produce little ethyl acetate and large amounts of air are not required. Sometimes this type of spoilage is difficult to diagnose because the wine often has a good bouquet and the flavor may be good. However, a hot, burning characteristic is always present in the aftertaste. A lingering hotness in a wine always suggests excessive acetic acid, and sweet-sour tastes sometimes occur when considerable sugar remains in the wine. Lactic bacteria are probably the culprits rather than acetobacter when wine contains excessive acetic acid and little ethyl acetate.