What bacteria causes milk to spoil?
Lactobacillus is the major part of the lactic acid bacteria group, named as such because most of its members convert lactose and other sugars to lactic acid. Bacterial Growth in Milk In both pasteurized and raw milk, various microorganisms succeed one another as the chemical environment of the milk changes. The microbes themselves bring about these changes. The stages of microbial growth are Streptococcus, then Lactobacillus, then yeasts and molds, and finally Bacillus. Streptococci convert the milk sugar (lactose) to lactic acid. The acidity of the milk increases to the point where further streptococci growth is inhibited. Lactobacilli then begin to grow and convert the remaining lactose into lactic acid. Acidity increases further until Lactobacilli growth is suppressed. The lactic acid sours the milk and curdles (coagulates) the milk protein. Yeasts and molds grow well in this acid environment, and they convert acid into non-acid products. Finally, bacilli multiply in the environment
