The citric acid which is normally present in milk and cream can be fermented by a number of organisms commonly present in· dairy products. Some of these, such as the citric acid positive colon-aerogenes organisms, are always objectionable in milk and its derivatives, while others, Streptococcus citrovorus and S. paracitrovorus, which are frequently associated with S. lactis, are important in the development of flavor and aroma in starter and in butter, and undoubtedly in other materials.