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A Note on the Acidity of Fresh Milk

Department of Dairy Industry, Cornell University, Ithaca, New York

ABSTRACT

When milk is first drawn from the cow's udder it gives what is known as an amphoteric reaction, that is it turns red litmus paper blue and blue litmus paper red. In spite of this fact fresh milk is rarely alkaline and is always acid toward phenolphthalein as an indicator.

Dairy chemists mention two kinds of acidity in milk; apparent acidity and real acidity. The real acidity of milk is due to lactic acid. This is never found in milk when it is first drawn from the udder. It is produced by the action of the lactic acid organisms on the milk sugar.

The so-called apparent acidity of milk is what gives fresh milk its acid reaction. It is now generally believed to be due to the presence of the carbon dioxide, acid phosphates and casein, all of which are found in fresh milk and which have an acid.

About a year ago the writer tested two samples of milk that were brought to this department.