EFFECT OF HIGH HEATING ON PROPERTIES OF MILK 41 



in most of our up-to-date creameries to-day is to pasteurize 

 the cream, under the vat or holding system, to 170 F. or above, 

 or, under the flash system, to at least 180 F. 



The reason why this cooked flavor is found in milk when 

 heated is not well understood. It is supposed to be due to 

 the effect which heat has upon the nitrogeneous constituents 

 and the sugar. 



5. Precipitates Albuminoid and Ash Constituents. When 

 milk is heated, there is a tendency for the soluble salts and a 

 portion of the albuminoids to be thrown down, or changed into 

 an insoluble form. 



The higher the milk is heated, the greater is this tendency. 

 If a sample of milk in a flask is subjected to intense heat, and 

 then allowed to stand, a fine white sediment will be deposited on 

 the bottom. This is believed to consist of minerals precipitated 

 from the milk. 



When milk has been heated to about 170 F., and cooled, 

 rennet is unable to precipitate the curd in a normal way. The 

 curd resulting from adding rennet to pasteurized milk is flocculent 

 in nature. It does not assume that smooth and even texture 

 that curd from raw milk has when precipitated with rennet. 

 The behavior of pasteurized milk towards rennet can be ren- 

 dered normal by adding a small quantity of calcium chloride 

 (CaCl). Whether this would affect the quality of cheese mate- 

 rially has not yet been determined definitely. According to G. 

 Fascetti, 1 if pasteurized milk is used for cheese-making, the 

 cheese ripens more slowly than when made from raw milk. The 

 same investigator also claims that a larger quantity of cheese 

 is obtained per 100 parts of milk when pasteurized milk is 

 used. 



6. Destroys Properties of Enzymes. As was mentioned in 

 the chapter on the composition of milk, there is a substance nor- 

 mal to milk named galactase. This is an enzyme. By heating 

 milk to about 175 F. the properties of the enzyme are destroyed. 

 Owing to this it is easy to determine whether a certain sample of 

 milk has been pasteurized or not. Galactase is present in milk in 



1 Exp. Sta. Record, Vol. 15, No. 10, 1904. 



