PLAIN CONDENSED BULK MILK 129 



The purpose of incubation is to detect defective milk and de- 

 fective cans before they leave the factory. If the contents of 

 any of the cans have not been completely sterilized, or if any 

 cans have the minutest leak, the evaporated milk therein will 

 spoil within the time of incubation. Such milk either sours, 

 curdles or becomes solid, or it undergoes gaseous fermentation, 

 causing the appearance of "swell heads." The more nearly perfect 

 the process of sterilization and the better the construction and 

 seal of the cans, the fewer are the spoiled cans. This incubation 

 process is strictly a preventative measure. It is omitted in many 

 factories where the cans are labeled, packed and shipped to their 

 destination at once, or put in ordinary storage in the factory. 



CHAPTER XII. 

 PLAIN CONDENSED BULK MILK 



Definition. This is an unsweetened condensed milk made 

 from whole milk, or partly, or wholly skimmed milk, condensed 

 in vacuo at the ratio of about three or four parts of fluid milk to 

 one part of condensed milk. It is usually superheated to swell 

 and thicken it, and it has the consistency of rich cream. It is 

 sold in 10-gallon milk cans to ice cream factories and in milk 

 bottles to the direct consumer. Plain condensed bulk milk is 

 not sterile, nor is it preserved by sucrose. Its keeping quality 

 is similar to that of a high quality pasteurized milk. 



Quality of Fresh Milk. The sweeter and purer the fresh 

 milk or skim milk, the better will be the quality of this product. 

 Old milk, or skim milk in which the acid development has made 

 considerable headway, tends to form a lumpy, plain condensed 

 bulk milk. However, since this milk is not subjected to steriliz- 

 ing temperatures and is used up quickly after manufacture, the 

 quality of the fresh milk from which it is made, is not of such 

 magnitude as in the case of evaporated milk. 



Heating. In the manufacture of plain condensed bulk milk 

 the heating is accomplished much in the same manner as in the 

 case of sweetened condensed milk and evaporated milk. The 

 milk is usually heated by turning steam direct into it ; though 



