342 CREAM AND CREAM RIPENING 



wanted, some of this soured milk may be added daily to a 

 further amount of pasteurized milk. However pure they 

 are at first, cultures kept going from day to day sooner 

 or later become valueless ; the organisms degenerate or 

 slowly lose their vitality and ripening power, or the starter, 

 in spite of careful precautions, becomes contaminated with 

 objectionable organisms. This usually occurs in a week 

 or two, after which time it is necessary to begin again 

 with pure commercial or laboratory cultures. 



Ex. 155. Make a bacteriological analysis of any commercial 

 starter you can obtain. If a powder, dissolve or distribute in 

 sterile distilled water and plate out on litmus lactose gelatine 

 and agar. Isolate and make pure cultures of each kind found. 

 Examine and stain specimens and try the action of each on milk 

 and other media. How many are liquefiers ? Are any coliform 

 organisms present ? (Ex. 147). Are moulds abundant? 



The chief object of the addition of a starter to cream 

 is to immediately increase the number of organisms of a 

 desirable kind to such an extent that they may suppress 

 or overcome the activity of any bacteria of a deleterious, 

 nature, which may have found their way into the cream. 

 Usually from 8 to 10 volumes of starter are added to 

 every I oo volumes of cream to be ripened. 



Starters may be added 



(1) to cream raised by gravitation, which is neces- 



sarily several hours old and therefore contains 

 considerable numbers of bacteria. 



(2) to freshly separated cream, in which also a 



certain number of different kinds of bacteria 

 are present, and 



(3) to cream which has been subjected to the 



pasteurization process to get rid of all 

 organisms in a growing state. 



