CHEESE 359 



strong solutions which are much less sensitive than dilute 

 extracts. 



Certain antiseptics, especially borax and formalin, 

 damage its curdling power, but chloroform, thymol (. I per 

 cent.), or carbolic acid (. 5 to i per cent.) have little effect 

 upon it, although they check the activity of bacteria. 



In the stomachs of the young animals, from which 

 home-made rennet extracts are sometimes prepared, 

 several different species of bacteria are often found. 

 According to Thoni such bacterial flora consists of 



(i) A group of organisms, such as Bs. subtilis, Bs. 

 vulgatus, species of Sarcina and Streptothrix, 

 which have little effect on the quality of the 

 extract and soon disappear ; 

 (ii) Some of the useful lactic acid organisms ; 

 (iii) Bs. colt and Bact. lactis aerogenes, which may 

 multiply and ultimately contaminate the curd ; 

 this group is the most to be feared by the 

 cheesemaker. 



Ex. 158. Repeat Exs. 113, 114. 



Ex. 159. Make a bacteriological analysis of home-made and 

 commercial rennet extracts on the lines indicated in Exs. 125, 

 147, 155- 



2. Cheese, (i) Composition and ripening. When 

 rennet is added to milk which has been allowed to 

 become slightly sour, a solid curd or coagulum is 

 thrown down, and a greenish yellow liquid, the whey, 

 is separated. This curd is the raw material from which 

 various kinds of cheese are made. It consists chiefly of 

 a protein substance termed casein (sometimes paracasein, 

 see p. 237), along with a considerable proportion of the 

 fat, sugar, and mineral matter originally present in the 



