Butter cultures sometimes fail to develop acid at a normal rate, and such slow growth has probably been encountered wherever butter cultures are used.

One characteristic of certain types of abnormally slow growth in butter cultures is the sudden manner in which the defect often occurs. A culture may appear satisfactory at the time it is used for inoculation and then fail to bring about the desired changes in the product being manufactured. Such an occurrence greatly interferes with general plant routine. If additional time is allowed for the formation of acid, a defective product may result. Sometimes acid development is so slow and the defects in the product being manufactured so serious that the finished material is unsalable.

There are various causes of slow acid production by butter cultures. Some of these are easily determined by investigation of the methods used in propagation or by direct microscopic examination of the cultures. In other cases such methods fail to disclose the cause or causes of the abnormally slow growth, and the rather unusual aspects of such cases have motivated the work herein reported.