218 UNSWEETENED CONDENSED MILK 



exposure of the milk to the process. It consists largely of the 

 mineral matter of milk, rendered insoluble and precipitated by 

 heat. The use of lower sterilizing temperatures or the shorten- 

 ing of the period of sterilization will help to avoid this defect. 

 Evaporated milk in the condensation of which the "Continu- 

 ous Concentrator" was used, has a tendency to show slight grainy 

 condition, though this is barely perceptible. 



Separated and Churned Evaporated Milk 



General Description. This is a very common defect. A 

 portion of the butter fat of the contents of the hermetically 

 sealed cans, has separated and appears in the form of lumps of 

 cream or of churned butter, on top of the evaporated milk. While 

 this separated evaporated milk is normal in quality and whole- 

 someness, its appearance condemns it. 



Causes and Prevention. As explained in Chapter IX on 

 "Homogenizing," p. 110, the fundamental cause of separated and 

 churned evaporated milk lies in the difference of the specific 

 gravity between the butter fat and the rest of the milk constitu- 

 ents. The fat globules, being lighter than the serum, tend to 

 rise to the surface, forming a layer of thick cream. When this 

 separated evaporated milk is subjected to agitation, as is the 

 case in transportation, this 'cream churns into lumps of butter. 

 This tendency of the fat to separate in storage and churn in 

 transportation, increases with the increase of the size of the fat 

 globules, because the larger the globules, the larger is their cubic 

 content in proportion to their surface. This fact is based on the 

 well known physical law, that the surfaces of two spheres are 

 to each other as the squares of their diameters, and the cubic 

 contents of two spheres are to each other as the cubes of their 

 diameters. The cubic contents determine the gravity force, or 

 .buoyancy, while the surfaces control the resistance force. There- 

 fore, the larger the fat globules the greater is their buoyancy 

 and the weaker is the relative resistance w r hich they must over- 

 come in their upward passage. 



Effect of Locality and Season. Since the predominating 

 size of fat globules in milk, varies with breed and period of 

 lactation of the cows, the ease with which evaporated milk 

 separates and the difficulty of overcoming this defect, differ 



