In unsalted butter made from sweet cream with butter culture there was commonly a striking production of acetylmethylcarbinol plus diacetyl when the butter was held at a temperature permitting activity of the butter culture organisms. Under these conditions also the pH of the butter markedly decreased. The production of the carbinol plus diacetyl varied widely with different lots of butter held under the same conditions. The largest production occurred at the higher holding temperatures and in samples which developed the lowest pH values. Occasionally the amount of the carbinol plus diacetyl decreased during the first few days of holding; this decrease was sometimes followed by an increase. A striking production of the carbinol plus diacetyl was sometimes followed by a decrease.
In salted butter no conspicuous production of acetylmethylcarbinol plus diacetyl occurred even when but little salt was added, and significant changes in the pH did not take place.
The production of acetylmethylcarbinol plus diacetyl in unsalted butter was usually greater with a large addition of butter culture to the cream than with a small addition, and, in some cases, it was conspicuously increased by adding citric acid-fermenting streptococci along with the usual butter culture.
Slatter, W. L. and Hammer, B. W.
"Changes in the Acetylmethylcarbinol plus Diacetyl content of butter,"
Research Bulletin (Iowa Agriculture and Home Economics Experiment Station): Vol. 19
, Article 1.
Available at: https://lib.dr.iastate.edu/researchbulletin/vol19/iss211/1