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Testing for Extraneous Matter in Cheese^*

University of Wisconsin, Madison

ABSTRACT

The test for sediment in cheese detects unsatisfactory conditions of milk and cheese production except when the milk supply is filtered efficiently. The results of the test may be graded by macroscopic appearance but should also be examined microscopically for critical material.

The two practical tests use solutions of either sodium citrate or orthophosphoric acid. Commonly eight ounces of cheese is used with the citrate test while 50 grams of cheese is used with the acid solvent. The larger sample must be filtered through a reversed, milk-sediment disc while the smaller sample is most effective when a filter of Irish poplin is used over a milk sediment disc. The smooth surface of poplin can be examined more easily with a microscope since it retains all particles in view; the milk-sediment disc tends to hide all small particles of sediment.

There is not much to choose between the solvents although the acid seems to work faster on young cheese. Neither solvent, under the conditions used in making the tests, destroys enough of the common types of extraneous material to prevent identification although both attack, such material more or less. The acid tends to reduce the size and increase the number of sediment particles.

The distribution of extraneous material seems to be fairly uniform within a single cheese but from cheese to cheese from a single lot the distribution is not uniform. Such irregularity makes it desirable to take plugs from several cheese in each lot and essential to test the cheese from a given outlet regularly and as frequently as possible.

The identification of extraneous material by microscopic examination of test pads may provide a useful method of determining sources of contamination. Photographs of common types of extraneous matter which are available for distribution from this laboratory may prove helpful in this respect although they cannot replace microscopic study of the actual material from local sources.

^* This study was made possible by an industrial fellowship granted by the National Cheese Institute.