Propionic acid bacteria were found in various cheeses, including Iowa swiss-type, domestic swiss and cheddar. Swiss-type cheese with a desirable sweet flavor generally contained relatively large numbers of propionic acid bacteria, and cheese with a poor flavor generally contained few or none (in 0.1 gram). All the domestic swiss cheese contained rather large numbers of propionic acid bacteria. About 85 percent of the cheddar cheese, of both good and poor quality, contained propionic acid bacteria; there was no correlation between the numbers of the organisms and the quality. A canned cheddar cheese which had eyes similar to those in swiss cheese contained a considerable number of propionic acid bacteria.

Eighteen strains of propionic acid organisms were used in the manufacture of swiss-type cheese from pasteurized milk. Several of the cultures were rather consistent in the type of flavor produced, while others were variable. Results indicated that certain cultures rather regularly produced cheese having either an excellent or good flavor. The addition of propionic acid organisms was not beneficial from the standpoint of eye formation, since none of the cultures were consistent in producing good eyes. In several instances, the four cheese in a series showed the same type of eye formation, even though one of the cheese was a control, while the other three were made with propionic acid cultures. Cheese in which no propionic acid bacteria could be detected in 0.1 gram sometimes developed satisfactory eyes.