Fermentation is the process which is carried by anaerobic respiration of microorganism which leads to the production of lactic acid or alcohol with the release of carbon dioxide. Lactobacillus is a genus of bacteria, which can convert sugars into lactic acid by means of fermentation. Milk contains a sugar called as lactose, a disaccharide (compound sugar) made by the glycosidic bonding between glucose and galactose (monosaccharides). The bacteria convert the lactose into lactic acid, which imparts the sour taste to curd. Raw milk naturally contains Lactobacillus.