200 SWEETENED CONDENSED MILK DEFECTS 



milk. The thickening of the sweetened condensed milk in early 

 summer, therefore, very probably is the result of a slow curdling 

 of its casein, caused by enzymes which are produced by bacteria. 

 It has further been demonstrated that condensed skim milk 

 thickens more readily than condensed whole milk, which may be 

 explained by the fact that condensed milk without butter fat 

 represents a more favorable medium for bacterial growth. Fur- 

 thermore, it has been conclusively demonstrated by the writer 

 and others that the addition of cane sugar to condensed milk, in 

 excess of that present in normal condensed milk, greatly retards 

 thickening. This fact suggests that the higher per cent, of 

 sucrose has an inhibiting effect on the enzyme-producing bac- 

 teria, and perhaps, on the action of the enzyme itself. This 

 condensed milk defect can be prevented entirely by using, during 

 the summer months, eighteen pounds of sucrose per one hundred 

 pounds of fresh milk, so that the condensed milk contains about 

 45 per cent, sucrose. 



Effect of Finishing in Pan With High Steam Pressure on 

 Thickening. Abnormally thick condensed milk is also the result 

 of overheating the condensed milk in the vacuum pan toward 

 the close of the process. The batch should be finished with low 

 steam pressure in the jacket and coils, not to exceed five pounds 

 of pressure, and the milk should be drawn from the pan at once 

 after condensation is completed. The superheating to which 

 the condensed milk is subjected in the pan, when finishing with 

 a high steam pressure in jacket and coils, or when the milk is 

 not drawn from the pan promptly when the vacuum pump is 

 stopped, or when an effort is made to condense to a very high 

 degree of concentration, is almost sure to cause the finished 

 product to spontaneously thicken with age and this tendency 

 is especially pronounced in the spring and early summer. 



Effect of Age on Thickening. Finally, all sweetened con- 

 densed milk has a tendency to thicken with age. Kxposure to 

 high storage temperature (summer heat) hastens this action. 

 The rapidity of thickening in storage increases with the increase 

 in temperature. This tendency is very much reduced, therefore, 

 by protecting the goods from high temperatures and by storing 

 them below 60 degrees F. (See Chapter on "Storage," page 152.) 



