® 
SWEETENED CONDENSED M1LnK—HEATING 61 
of the milk to stick to the heating surface is a permanent obstacle 
and efforts to overcome this frequently result in sacrificing thor- 
oughness of heating. 
A variety of methods and numerous different types of ma- 
chines are used for this purpose in the different milk condensing 
factories. Some use large copper kettles in which the milk is 
heated by turning steam direct into the milk. Others use jacketed 
copper kettles equipped with a revolving agitator. The milk is 
heated by turning steam under 
pressure into the jacket and the 
burning of the milk is prevented by 
Keeping the milk in constant motion. 
In this case the milk is usually 
heated to about 170 degrees F. by 
the jacket and from there on the 
temperature 1s raised to that desired. 
by turning steam direct into the hot 
milk. Still others are heating the 
milk by means of large continuous 
pasteurizers in which case hot water 
or steam serves as the heating medi- 
um. ‘The milk passes in a thin laver 
The hot well or forewarmer 
between two water-heated surfaces, 
eae re ert rie revolving. In some 
factories the milk is forced through a series of pipes inclosed in 
a hot water or steam jacket. 
Finally, in some condenserics a combination of the con- 
tinuous pasteurizer and the piain or jacketed kettle is used. The 
milk is heated to nearly the desired temperature in the pasteur- 
izer. From there it flows into the kettie, where the heating is 
completed. This method insures efficient heating and, at the 
same time, if operated properly. it prevents scorching of the 
milk on the heating surface. 
Advantages and Disadvantages of Different Methods of 
Heating.—In most factories in this country the first named 
method is used. Steam is turned direct into the milk until it 
boils up. This is the oldest and most primitive method. \While 
very simple in operation, this method has some objections. At 
