Date of Award:


Document Type:


Degree Name:

Master of Science (MS)


Animal, Dairy, and Veterinary Sciences

Committee Chair(s)

A. J. Morris


A. J. Morris


Paul Larsen


Lewis Jones


Problem and its importance:

Starter is the "heart" of the cheese making industry. only by proper handling of starter can good quality cheese be made. The economic loss from contaminated starter may prove disastrous to a cheese plant if proper corrective measures are not taken.

Milk usually contains a variety of bacteria. Under plant conditions some of these bacteria get into the mother starter or bulk starter unless extreme caution is used. Comparatively little is known about how one organism influences another when grown in milk. This problem is important in the cheese industry.


The purpose of this research project is to determin the effect of some common contaminants on cheese starters. Some of the off flavors and slow acid production found in cheese making may be due to the results of contaminant organisms growing with the starter organisms. If this be true, more information on this subject will prove valuable.

Some organisms have detrimental effects on milk. The question arises: What will two different organisms do when grown together in milk? Streptococcus lactis is important in the cheese industry because it satisfactorily produces the acid necessary in cheese making. If some organism inhibits or stimulates this acid production when grown with Streptococcus lactis, it is important that the cheesemaker know this.


Only those contaminants commonly found in dairy products are considered in this project. Simulated plant conditions are used; that is, the starter being tested is contaminated one evening and the results checked and read the next day. Commercial lactic acid cheese starter from the Hansen's Laboratories and milk from the Utah State Agricultural College Creamery are used to propagate the starter. Different percentages of the contaminant are added to the starter to determine the effects of varying numbers of the contaminant on the starter organisms. A control starter is incubated and tested along with the contaminated starter. After the starters have been incubated at 70°F. Overnight, the following tests are run on each one: activity, acidity, pH, creatine, odor and appearance, and microscopic count.

Starter vitality may be determined by the above tests; however, these do not indicate how the contaminant organisms affect cheese when carried on into the cheese making process. Therefore, this project is limited to the effects of contaminants on the starter and not on cheese. This latter problem is reserved for future investigators.



Included in

Dairy Science Commons