Group of bacteria (MSB), which are one of the few that can survive in an acidic solution. They do not require oxygen. They are therefore anaerobic bacteria for which oxygen is poison, so to speak. They are found in milk and are involved in the production of cheese, yoghurt or sour milk. Their growth or multiplication in grapes takes place only to a small extent. During alcoholic fermentation they are almost inactive and can hardly reproduce. With regard to carbohydrate metabolism, a distinction is made between homofermentative and heterofermentative MSB. Homofermentative MSB such as Lactobacillus plantarum form exclusively lactic acid.
Heterofermentative MSBs such as Oenococcus oeni, on the other hand, also form ethanol (alcohol), acetic acid, carbon dioxide and other partly undesirable by-products. In malolactic fermentation (BSA), the two above-mentioned genera of lactic acid bacteria are preferably optionally used as so-called starter cultures to convert the "pungent" malic acid into the "milder" lactic acid. Undesirable by-products can cause the wine defects bitter clay, geranium clay, linden clay, mannitic sting and lactic acid sting. The MSB are sensitive to sulphur dioxide and cold and therefore easier to control than Acetobacter (acetic acid bacteria).