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Research Bulletin (Iowa Agriculture and Home Economics Experiment Station)

Article Title

Slimy and ropy milk

Abstract

A study of slimy and ropy milk sent for examination to the dairy bacteriological laboratories of Iowa State College has shown the following:

1. Cultures of organisms secured from slimy starters, apparently typical Streptococcus lacticus forms, sometimes showed marked capacity to produce ropiness when inoculated into sterile milk. This slime producing power is evidently a variable characteristic, appearing and disappearing without apparent cause.

2. Associative action of organisms in some cases is responsible for ropiness. Two organisms, neither of which alone can cause ropiness, may, when grown together, cause the medium to become slimy.

3. Bacterium (lactis) viscosum is one common cause of slimy milk.

4. Certain peptonizing bacteria, as Bact. peptogenes, produce a very slimy residuum after digestion of the casein.

5. Bacterium bulgaricum and certain related high acid organisms frequently produce marked viscosity in milk.

Sliminess in milk is apparently due to different causes with different organisms:

1. Gum and gum-like capsular materials partially soluble, or at least swelling in water, al'e frequently the same.

2. In many cases there seems to be a direct relationship between chain formation of streptococcus and the development of ropiness, likewise between the numbers of bacteria and ropiness.

3. Associative action between two distinct organisms resulting in great increases in number of each is not uncommon as a cause of ropiness.

Methods of control and prevention of slimy milk are discussed.

Keys to the organisms that have been described as responsible for slimy production in milk are presented. An attempt has been made to clear up synonymy. Descriptions of thirty-three species of bacteria that have been found associated with milk are given, and the literature reviewed.

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