Butter cultures normally contain two distinct types of bacteria, (a) a typical lactic acid forming type (Streptococcus lactis) and (b) a type which is important from the standpoint of the production of satisfactory flavor and aroma and includes Streptococcus citrovorus and Streptococcus paracitrovorus.
Proceedings of the Iowa Academy of Science
©1935 Iowa Academy of Science, Inc.
Stahly, G. L.; Hammer, B. W.; Michaelian, M. B.; and Werkman, C. H.
"The Fate of Acetylmethylcarbinol and Diacetyl in Dairy Products,"
Proceedings of the Iowa Academy of Science, 42(1), 73-76.
Available at: https://scholarworks.uni.edu/pias/vol42/iss1/14