The Coagulation Temperature of Milk as Affected by pH, Salts, Evaporation and Previous Heat Treatment

The stability of milk under various conditions has been studied from both a theoretical and practical standpoint. The milk has been subjected to temperatures ranging from room temperature to 150 C., and to the influence of salts and acids that are foreign as well as those normal to milk. Although valuable information has been added to our knowledge of milk, yet many theoretical and practical questions have not been answered which are significantly related to the stability of milk during pasteurization, boiling, preparation of various food-stuffs involving milk, and the manufacture of condensed and evaporated milks. The purpose of the work presented herein is to show the relationship between the pH and the coagulation temperature of milk ranging from about room temperature to the coagulation temperature of stable milk, and to show the effect of added salts, evaporation and previous heat treatment in displacing the '~coagulation curve." HISTORICAL It has been known for a long time that fresh milk would coagulate at elevated temperatures. Hammarsteu (10) in 1874 reported that the coagulation temperature varied from 130 to 150 C. Cazeneuve and Haddon (5) attributed the curdling of milk at 130 C. to the formation of acids, mainly formic, from lactose oxidation. Bardach (1) failed to confirm this conclusion. Milroy (20) showed that heating slightly increased the acidity of milk. More recently Whittier and Benton (43, Their results indicate that acid production may become an important factor with long holding periods at elevated temperatures. Holm, Deysher and Evans (11) concluded that the relationship between time and temperature of coagulation was of a logarithmic nature.